Consumer Market for Personal DNA Sequencing: Part 4
Reporter: Aviva Lev-Ari, PhD RN

Word Cloud by Daniel Menzin
This Part 4 of the series on Present and Future Frontier of Research in Genomics has been
UPDATED on 12/6/2013
23andMe Suspends Health Interpretations
Direct-to-consumer genetic testing company 23andMe hasstopped offering its health-related test to new customers, bringing it in line with a request from the US Food and Drug Administration.
In letter sent on Nov. 22, FDA said that 23andMe had not adequately responded to its concerns regarding the validity of their Personal Genome Service. The letter instructed 23andMe to “immediately discontinue marketing” the service until it receives authorization from the agency.
According to a post at the company’s blog from CEO Anne Wojcicki, 23andMe customers who purchased their kits on or after Nov. 22 “will not have access to health-related results.” They will, though, have access to ancestry information and their raw genetic data. Wojcicki notes that the customers may have access to the health interpretations in the future depending on FDA marketing authorization. Those customers are also being offered a refund.
Customers who purchased their kits before Nov. 22 will have access to all reports.
“We remain firmly committed to fulfilling our long-term mission to help people everywhere have access to their own genetic data and have the ability to use that information to improve their lives,” a notice at the 23andMe site says.
In a letter appearing in the Wall Street Journal earlier this week, FDA Commissioner Margaret Hamburg wrote that the agency “supports the development of innovative tests.” As an example, she pointed to its recent clearance of sequencing-based testsfrom Illumina.
She added that the agency also understands that some consumers do want to know more about their genomes and their genetic risk of disease, and that a DTC model would let consumers take an active role in their health.
“The agency’s desire to review these particular tests is solely to ensure that they are safe, do what they claim to do and that the results are communicated in a way that a consumer can understand,” Hamburg said.
In a statement, 23andMe’s Wojcicki says that the company remains committed to its ethos of allowing people access to their genetic information. “Our goal is to work cooperatively with the FDA to provide that opportunity in a way that clearly demonstrates the benefit to people and the validity of the science that underlies the test,” Wojcicki adds.
UPDATED on 11/27/2013
FDA Tells Google-Backed 23andMe to Halt DNA Test Service
VIEW VIDEO
FDA Letter to 23andME
|
Public Health Service Food and Drug Administration |
10903 New Hampshire Avenue
Silver Spring, MD 20993
|
Nov 22, 2013
SOURCE
http://www.fda.gov/ICECI/EnforcementActions/WarningLetters/2013/ucm376296.htm
Cancer Diagnostics by Genomic Sequencing: ‘No’ to Sequencing Patient’s DNA, ‘No’ to Sequencing Patient’s Tumor, ‘Yes’ to focus on Gene Mutation Aberration & Analysis of Gene Abnormalities
Symposia
http://aaas.confex.com/aaas/2013/webprogram/start.html
Personal Genetics: An Intersection Between Science, Society, and Policy
Saturday, February 16, 2013: 8:30 AM-11:30 AM
Room 203 (Hynes Convention Center)
On 26 June 2000, scientists announced the completion of a rough draft of the human genome, the result of the $3 billion publicly funded Human Genome Project. In the decade since, the cost of genome sequencing has plummeted, coinciding with the development of deep sequencing technologies and allowing, for the first time, personalized genetic medicine. The advent of personal genetics has profound implications for society that are only beginning to be discussed, even as the technologies are rapidly maturing and entering the market. This symposium will focus on how the genomic revolution may affect our society in coming years and how best to reach out to the general public on these important issues. How has the promise of genomics, as stated early in the last decade, matched the reality we observe today? What are the new promises — and pitfalls — of genomics and personal genetics as of 2013? What are the ethical implications of easy and inexpensive human genome sequencing, particularly with regard to ownership and control of genomic datasets, and what stakeholder interests must be addressed? How can the scientific community engage with the public at large to improve understanding of the science behind these powerful new technologies? The symposium will comprise three 15-minute talks from representatives of relevant sectors (academia/education, journalism, and industry), followed by a 45-minute panel discussion with the speakers.
Organizer:
Peter Yang, Harvard University
Co-organizers:
Brenna Krieger, Harvard University
and Kevin Bonham, Harvard University
Discussant:
James Thornton, Harvard University
Speakers:
Ting Wu, Harvard University
Personal Genetics and Education
Mary Carmichael, Boston Globe
The Media and the Personal Genetics Revolution
Brian Naughton, 23andMe Inc.
Commercialization of Personal Genomics: Promise and Potential Pitfalls
Mira Irons, Children’s Hospital Boston
Personal Genomic Medicine: How Physicians Can Adapt to a Genomic World
Sheila Jasanoff, Harvard University
Citizenship and the Personal Genomics
Jonathan Gitlin, National Human Genome Research Institute
Personal Genomics and Science Policy
THIS IS A SERIES OF FOUR POINTS OF VIEW IN SUPPORT OF the Paradigm Shift in Human Genomics
How to Tailor Cancer Therapy to the particular Genetics of a patient’s Cancer
‘No’ to Sequencing Patient’s DNA, ‘No’ to Sequencing Patient’s Tumor, ‘Yes’ to focus on Gene Mutation Aberration & Analysis of Gene Abnormalities PRESENTED in the following FOUR PARTS. Recommended to be read in its entirety for completeness and arrival to the End Point of Present and Future Frontier of Research in Genomics
Part 1:
Research Paradigm Shift in Human Genomics – Predictive Biomarkers and Personalized Medicine
Part 2:
LEADERS in the Competitive Space of Genome Sequencing of Genetic Mutations for Therapeutic Drug Selection in Cancer Personalized Treatment
Part 3:
Personalized Medicine: An Institute Profile – Coriell Institute for Medical Research
Part 4:
The Consumer Market for Personal DNA Sequencing
Part 4:
The Consumer Market for Personal DNA Sequencing
How does 23andMe genotype my DNA?
Technology and Standards
23andMe is a DNA analysis service providing information and tools for individuals to learn about and explore their DNA. We use the Illumina OmniExpress Plus Genotyping BeadChip (shown here). In addition to the variants already included on the chip by Illumina, we’ve included our own, customized set of variants relating to conditions and traits that are interesting. Technical information on the performance of the chip can be found on Illumina’s website.
All of the laboratory testing for 23andMe is done in a CLIA-certified laboratory.
Once our lab receives your sample, DNA is extracted from cheek cells preserved in your saliva. The lab then copies the DNA many times — a process called “amplification” — growing the tiny amount extracted from your saliva until there is enough to be genotyped.
In order to be genotyped, the amplified DNA is “cut” into smaller pieces, which are then applied to our DNA chip, a small glass slide with millions of microscopic “beads” on its surface (read more about this technology). Each bead is attached to a “probe”, a bit of DNA that matches one of the approximately one million genetic variants that we test. The cut pieces of your DNA stick to the matching DNA probes. A fluorescent signal on each probe provides information that can tell us which version of that genetic variant your DNA corresponds to.
Although the human genome is estimated to contain about 10-30 million genetic variants, many of them are correlated due to their proximity to each other. Thus, one genetic variant is often representative of many nearby variants, and the approximately one million variants on our genotyping chip provide very good coverage of common variation across the entire genome.
Our research team has also hand-picked tens of thousands of additional genetic variants linked to various conditions and traits in the scientific literature to analyze on our genotyping chip. As a result we can provide you with personal genetic information available only through 23andMe.
Genetics service 23andMe announced some new cash in the bank today with a $50 million raise from Yuri Milner, 23andMe CEO Anne Wojcicki, Google’s Sergey Brin (who also happens to be Wojcicki’s husband), New Enterprise Associates, MPM Capital, and Google Ventures.
With today’s new funding also comes the reduction of the price of its genome analysis service to $99. This isn’t special holiday pricing (as 23andMe has run repeatedly in the past) the company tells me, but rather what its normal pricing will be from now on.
This move is overdue, at least as far as 23andMe’s business model is concerned. Just yesterday TechCrunch Conference Chair Susan Hobbs told me she was waiting for another $99 pricing deal to buy the Personal Genome Analysis product. Sure 23andMe has experimented with various pricing models, including subscription, since its founding in 2007, but had been at an official and prohibitive $299 price point until today. It’s also apparently been rigorously beta-testing various price points in the past couple of weeks, at some point experimenting with some lower than $99.
For comparison, the company’s original pricing began at $999 and offered subscribers just 14 health and trait reports versus today’s 244 reports, as well as genetic ancestry information. Natera, Counsyl and Pathway Genomics are also in the genomics space, but they work by offering their services through doctors rather than direct to consumer.
Since the company’s launch five years ago, it’s had 180K civilians profile their DNA, and representative Catherine Afarian tells us that, post-price drop and funding, its goal is to reach a million customers in 2013. This is a supremely ambitious goal considering it wants to turn an average user acquisition rate of 36K per year into one of 820K in one year alone.
But Afarian isn’t fazed and brings up how the company once sold out 20k in $99 account inventory on something called “DNA Day.” “Once we can offer the service at $99 it means the average American will buy in,” she said.
That $299 was too pricey, according to Hobbs, but $99 might be just right. She said the $99 price point, which yes, is less than an iPhone, was the main factor in her decision to buy in. “23andMe is more ‘nice-to-know’ information rather than ‘need-to-know’ information. It’s nice to know your ancestry. It’s more of a need to know that you are predisposed genetically for a type of cancer, so that you may take precautionary measures,” she said, implying that the data given by 23andMe isn’t necessarily vital medical information, or actionable when it is. While 23andMe can give you indicators about certain disease risks, it doesn’t close the loop, as in tell you what to do to prevent these diseases.
“Its [utility] depends on your genetic data,” said Afarian when I asked her about the usefulness of the product. “If you’ve got a Factor 5 that puts you at risk for clotting, you might want to invest in anti-clotting socks. [And] there’s always something about themselves that people didn’t know.”
Hobbs said eventually that she wouldn’t buy it, but only because she was looking into more exact lineage information for her little girl, and you need a Y chromosome in all DNA tests to show paternal lineage. Afarian also countered this hesitation, saying that what makes 23andMe unique is that it’s not only looking at just your Y or your mitochondrial DNA, but also your autosomal DNA, which does show some patrilineal information for females who lack that precious Y.
While still sort of a novelty, the potential for 23andMe goes beyond lineage and hopefully that extra $50 million will go further than keeping the price low and into research. The company hopes that a million users will result in a giant database of 23andWe genetic info that can be used to spot trends, like which genes mean a higher risk of diabetes/cancer, etc. Which is great if it happens but for now remains a pipe dream for 23andMe/We.
http://techcrunch.com/2012/12/11/23andnotme/
12/13/2012 @ 5:23PM |6,471 views
What Is 23andMe Really Selling: The Moral Quandary At The Center Of The Personalized Genomics Revolution
This week, 23andme, the personalized genomics company founded by Anne Wojcicki, wife of Google co-founder Sergey Brin, got an influx of investment cash ($50 million). According to their press release, they are using the money to bring the cost of their genetic test down to $99 (it was previously $299) which, they hope, will inspire the masses to get tested.
So should the masses indulge?
I prefer a quantified self approach to this question. At the heart of the quantified self-movement lies a very simple idea: metrics make us better. For devotees, this means “self-tracking,” using everything from the Nike fuel band to the Narcissism Personality Index to gather large quantities of personal data and—the bigger idea—use that data to improve performance.
If you consider that performance suffers when health suffers then a genetic test can been seen as a kind of metric used to improve performance. This strikes me as the best way to evaluate this idea and leads us to ask the same question about personalized genomics that the quantified self movement asks about every other metric: will it improve performance.
Arguments rage all over the place on this one, but the short answer is that SNP tests—which is the kind of DNA scan 23andme relies upon— don’t tell us all that much (yet). They analyze a million genes out of three billion total and the impact those million play in long term-health outcomes is still in dispute. For example, the nature/nurture split is normally viewed at 30/70—meaning environmental factors play a far more significant role in long-term health outcomes than genetics.
Moreover, all of the performance metrics used by the quantified self movement are used to for behavior modification—to drive self-improvement. Personalized genomics isn’t there yet. As Stanford University’s Nobel Prize-winning RNA researcher Andy Fire once told me, “if someone off the street is looking for pointers on how to live a healthier life, there’s nothing these tests will tell you besides basic physician advice like ‘eat right, don’t smoke and get plenty of exercise.’”
And even with more well-regarded SNP tests, like the ones that examine the BRCA 1 and 2 markers for breast cancer—which . NYU Langone Medical Center bioethicist Arthur Caplan explains it like this, “Say you test positive for a breast cancer disposition—then what are you going to do? The only preventative step you can take is to chop off your breasts.”
So if prevention is not available the only thing left is fear and anxiety. Unfortunately, in the past few decades, there have been hundreds of studies linking stress to everything from immunological disorders to heart disease to periodonitic troubles. So while finding out you may be at risk for Parkinson’s may make you feel informed, that knowledge isn’t going to stop you from developing the disease—but the resulting stress may contribute to a host of other complications.
This brings up a different question: if personalized genomics can’t yet help us much and could possibly hurt us—where’s the upside?
Turns out there’s a big upside: Citizen science. SNP tests are not yet viable because we need more info. 23andme talks about the “power of one million people,” meaning, if one million take these tests then the resulting genetic database could lead to big research breakthroughs and these could lead to all sorts of health/performance improvements.
This is what 23andme is really selling for $99 bucks a pop—a crowdsourced shot at unraveling a few more DNA mysteries.
And this also means that the question at the heart of the personalized genomics industry is not about metrics at all—it’s about morals: Should I risk my health for the greater good?
You can browse your data for all of the variants we test using the Browse Raw Data feature, or download your data here.
What unexpected things might I learn?
How does 23andMe genotype my DNA?
Can I use the saliva collection kit for infants and toddlers?
When and how do I get my data?
How do I collect saliva samples?
How long will it take for my sample to reach the lab?
account/profile settings (20) »
Which Ancestry setting in My Profile should I choose?
What do the options under the “Account” link in the upper right-hand corner control?
What is the average percent DNA shared for different types of cousins?
How does Relative Finder estimate the Predicted Relationship?
What do I get in return for taking surveys?
https://customercare.23andme.com/categories/20021003-faqs
https://customercare.23andme.com/home
REFERENCES
http://www.foundationmedicine.com/diagnostics-publications.php
PUT IT IN CONTEXT OF CANCER CELL MOVEMENT
The contraction of skeletal muscle is triggered by nerve impulses, which stimulate the release of Ca2+ from the sarcoplasmic reticuluma specialized network of internal membranes, similar to the endoplasmic reticulum, that stores high concentrations of Ca2+ ions. The release of Ca2+ from the sarcoplasmic reticulum increases the concentration of Ca2+ in the cytosol from approximately 10-7 to 10-5 M. The increased Ca2+ concentration signals muscle contraction via the action of two accessory proteins bound to the actin filaments: tropomyosin and troponin (Figure 11.25). Tropomyosin is a fibrous protein that binds lengthwise along the groove of actin filaments. In striated muscle, each tropomyosin molecule is bound to troponin, which is a complex of three polypeptides: troponin C (Ca2+-binding), troponin I (inhibitory), and troponin T (tropomyosin-binding). When the concentration of Ca2+ is low, the complex of the troponins with tropomyosin blocks the interaction of actin and myosin, so the muscle does not contract. At high concentrations, Ca2+ binding to troponin C shifts the position of the complex, relieving this inhibition and allowing contraction to proceed.
Figure 11.25
Association of tropomyosin and troponins with actin filaments. (A) Tropomyosin binds lengthwise along actin filaments and, in striated muscle, is associated with a complex of three troponins: troponin I (TnI), troponin C (TnC), and troponin T (TnT). In (more ) Contractile Assemblies of Actin and Myosin in Nonmuscle Cells
Contractile assemblies of actin and myosin, resembling small-scale versions of muscle fibers, are present also in nonmuscle cells. As in muscle, the actin filaments in these contractile assemblies are interdigitated with bipolar filaments of myosin II, consisting of 15 to 20 myosin II molecules, which produce contraction by sliding the actin filaments relative to one another (Figure 11.26). The actin filaments in contractile bundles in nonmuscle cells are also associated with tropomyosin, which facilitates their interaction with myosin II, probably by competing with filamin for binding sites on actin.
Figure 11.26
Contractile assemblies in nonmuscle cells. Bipolar filaments of myosin II produce contraction by sliding actin filaments in opposite directions. Two examples of contractile assemblies in nonmuscle cells, stress fibers and adhesion belts, were discussed earlier with respect to attachment of the actin cytoskeleton to regions of cell-substrate and cell-cell contacts (see Figures 11.13 and 11.14). The contraction of stress fibers produces tension across the cell, allowing the cell to pull on a substrate (e.g., the extracellular matrix) to which it is anchored. The contraction of adhesion belts alters the shape of epithelial cell sheets: a process that is particularly important during embryonic development, when sheets of epithelial cells fold into structures such as tubes.
The most dramatic example of actin-myosin contraction in nonmuscle cells, however, is provided by cytokinesisthe division of a cell into two following mitosis (Figure 11.27). Toward the end of mitosis in animal cells, a contractile ring consisting of actin filaments and myosin II assembles just underneath the plasma membrane. Its contraction pulls the plasma membrane progressively inward, constricting the center of the cell and pinching it in two. Interestingly, the thickness of the contractile ring remains constant as it contracts, implying that actin filaments disassemble as contraction proceeds. The ring then disperses completely following cell division.
Figure 11.27
Cytokinesis. Following completion of mitosis (nuclear division), a contractile ring consisting of actin filaments and myosin II divides the cell in two.
http://www.ncbi.nlm.nih.gov/books/NBK9961/
This is good. I don’t recall seeing it in the original comment. I am very aware of the actin myosin troponin connection in heart and in skeletal muscle, and I did know about the nonmuscle work. I won’t deal with it now, and I have been working with Aviral now online for 2 hours.
I have had a considerable background from way back in atomic orbital theory, physical chemistry, organic chemistry, and the equilibrium necessary for cations and anions. Despite the calcium role in contraction, I would not discount hypomagnesemia in having a disease role because of the intracellular-extracellular connection. The description you pasted reminds me also of a lecture given a few years ago by the Nobel Laureate that year on the mechanism of cell division.
PUT IT IN CONTEXT OF CANCER CELL MOVEMENT
The contraction of skeletal muscle is triggered by nerve impulses, which stimulate the release of Ca2+ from the sarcoplasmic reticuluma specialized network of internal membranes, similar to the endoplasmic reticulum, that stores high concentrations of Ca2+ ions. The release of Ca2+ from the sarcoplasmic reticulum increases the concentration of Ca2+ in the cytosol from approximately 10-7 to 10-5 M. The increased Ca2+ concentration signals muscle contraction via the action of two accessory proteins bound to the actin filaments: tropomyosin and troponin (Figure 11.25). Tropomyosin is a fibrous protein that binds lengthwise along the groove of actin filaments. In striated muscle, each tropomyosin molecule is bound to troponin, which is a complex of three polypeptides: troponin C (Ca2+-binding), troponin I (inhibitory), and troponin T (tropomyosin-binding). When the concentration of Ca2+ is low, the complex of the troponins with tropomyosin blocks the interaction of actin and myosin, so the muscle does not contract. At high concentrations, Ca2+ binding to troponin C shifts the position of the complex, relieving this inhibition and allowing contraction to proceed.
Figure 11.25
Association of tropomyosin and troponins with actin filaments. (A) Tropomyosin binds lengthwise along actin filaments and, in striated muscle, is associated with a complex of three troponins: troponin I (TnI), troponin C (TnC), and troponin T (TnT). In (more ) Contractile Assemblies of Actin and Myosin in Nonmuscle Cells
Contractile assemblies of actin and myosin, resembling small-scale versions of muscle fibers, are present also in nonmuscle cells. As in muscle, the actin filaments in these contractile assemblies are interdigitated with bipolar filaments of myosin II, consisting of 15 to 20 myosin II molecules, which produce contraction by sliding the actin filaments relative to one another (Figure 11.26). The actin filaments in contractile bundles in nonmuscle cells are also associated with tropomyosin, which facilitates their interaction with myosin II, probably by competing with filamin for binding sites on actin.
Figure 11.26
Contractile assemblies in nonmuscle cells. Bipolar filaments of myosin II produce contraction by sliding actin filaments in opposite directions. Two examples of contractile assemblies in nonmuscle cells, stress fibers and adhesion belts, were discussed earlier with respect to attachment of the actin cytoskeleton to regions of cell-substrate and cell-cell contacts (see Figures 11.13 and 11.14). The contraction of stress fibers produces tension across the cell, allowing the cell to pull on a substrate (e.g., the extracellular matrix) to which it is anchored. The contraction of adhesion belts alters the shape of epithelial cell sheets: a process that is particularly important during embryonic development, when sheets of epithelial cells fold into structures such as tubes.
The most dramatic example of actin-myosin contraction in nonmuscle cells, however, is provided by cytokinesisthe division of a cell into two following mitosis (Figure 11.27). Toward the end of mitosis in animal cells, a contractile ring consisting of actin filaments and myosin II assembles just underneath the plasma membrane. Its contraction pulls the plasma membrane progressively inward, constricting the center of the cell and pinching it in two. Interestingly, the thickness of the contractile ring remains constant as it contracts, implying that actin filaments disassemble as contraction proceeds. The ring then disperses completely following cell division.
Figure 11.27
Cytokinesis. Following completion of mitosis (nuclear division), a contractile ring consisting of actin filaments and myosin II divides the cell in two.
http://www.ncbi.nlm.nih.gov/books/NBK9961/
This is good. I don’t recall seeing it in the original comment. I am very aware of the actin myosin troponin connection in heart and in skeletal muscle, and I did know about the nonmuscle work. I won’t deal with it now, and I have been working with Aviral now online for 2 hours.
I have had a considerable background from way back in atomic orbital theory, physical chemistry, organic chemistry, and the equilibrium necessary for cations and anions. Despite the calcium role in contraction, I would not discount hypomagnesemia in having a disease role because of the intracellular-extracellular connection. The description you pasted reminds me also of a lecture given a few years ago by the Nobel Laureate that year on the mechanism of cell division.
PUT IT IN CONTEXT OF CANCER CELL MOVEMENT
The contraction of skeletal muscle is triggered by nerve impulses, which stimulate the release of Ca2+ from the sarcoplasmic reticuluma specialized network of internal membranes, similar to the endoplasmic reticulum, that stores high concentrations of Ca2+ ions. The release of Ca2+ from the sarcoplasmic reticulum increases the concentration of Ca2+ in the cytosol from approximately 10-7 to 10-5 M. The increased Ca2+ concentration signals muscle contraction via the action of two accessory proteins bound to the actin filaments: tropomyosin and troponin (Figure 11.25). Tropomyosin is a fibrous protein that binds lengthwise along the groove of actin filaments. In striated muscle, each tropomyosin molecule is bound to troponin, which is a complex of three polypeptides: troponin C (Ca2+-binding), troponin I (inhibitory), and troponin T (tropomyosin-binding). When the concentration of Ca2+ is low, the complex of the troponins with tropomyosin blocks the interaction of actin and myosin, so the muscle does not contract. At high concentrations, Ca2+ binding to troponin C shifts the position of the complex, relieving this inhibition and allowing contraction to proceed.
Figure 11.25
Association of tropomyosin and troponins with actin filaments. (A) Tropomyosin binds lengthwise along actin filaments and, in striated muscle, is associated with a complex of three troponins: troponin I (TnI), troponin C (TnC), and troponin T (TnT). In (more ) Contractile Assemblies of Actin and Myosin in Nonmuscle Cells
Contractile assemblies of actin and myosin, resembling small-scale versions of muscle fibers, are present also in nonmuscle cells. As in muscle, the actin filaments in these contractile assemblies are interdigitated with bipolar filaments of myosin II, consisting of 15 to 20 myosin II molecules, which produce contraction by sliding the actin filaments relative to one another (Figure 11.26). The actin filaments in contractile bundles in nonmuscle cells are also associated with tropomyosin, which facilitates their interaction with myosin II, probably by competing with filamin for binding sites on actin.
Figure 11.26
Contractile assemblies in nonmuscle cells. Bipolar filaments of myosin II produce contraction by sliding actin filaments in opposite directions. Two examples of contractile assemblies in nonmuscle cells, stress fibers and adhesion belts, were discussed earlier with respect to attachment of the actin cytoskeleton to regions of cell-substrate and cell-cell contacts (see Figures 11.13 and 11.14). The contraction of stress fibers produces tension across the cell, allowing the cell to pull on a substrate (e.g., the extracellular matrix) to which it is anchored. The contraction of adhesion belts alters the shape of epithelial cell sheets: a process that is particularly important during embryonic development, when sheets of epithelial cells fold into structures such as tubes.
The most dramatic example of actin-myosin contraction in nonmuscle cells, however, is provided by cytokinesisthe division of a cell into two following mitosis (Figure 11.27). Toward the end of mitosis in animal cells, a contractile ring consisting of actin filaments and myosin II assembles just underneath the plasma membrane. Its contraction pulls the plasma membrane progressively inward, constricting the center of the cell and pinching it in two. Interestingly, the thickness of the contractile ring remains constant as it contracts, implying that actin filaments disassemble as contraction proceeds. The ring then disperses completely following cell division.
Figure 11.27
Cytokinesis. Following completion of mitosis (nuclear division), a contractile ring consisting of actin filaments and myosin II divides the cell in two.
http://www.ncbi.nlm.nih.gov/books/NBK9961/
This is good. I don’t recall seeing it in the original comment. I am very aware of the actin myosin troponin connection in heart and in skeletal muscle, and I did know about the nonmuscle work. I won’t deal with it now, and I have been working with Aviral now online for 2 hours.
I have had a considerable background from way back in atomic orbital theory, physical chemistry, organic chemistry, and the equilibrium necessary for cations and anions. Despite the calcium role in contraction, I would not discount hypomagnesemia in having a disease role because of the intracellular-extracellular connection. The description you pasted reminds me also of a lecture given a few years ago by the Nobel Laureate that year on the mechanism of cell division.
PUT IT IN CONTEXT OF CANCER CELL MOVEMENT
The contraction of skeletal muscle is triggered by nerve impulses, which stimulate the release of Ca2+ from the sarcoplasmic reticuluma specialized network of internal membranes, similar to the endoplasmic reticulum, that stores high concentrations of Ca2+ ions. The release of Ca2+ from the sarcoplasmic reticulum increases the concentration of Ca2+ in the cytosol from approximately 10-7 to 10-5 M. The increased Ca2+ concentration signals muscle contraction via the action of two accessory proteins bound to the actin filaments: tropomyosin and troponin (Figure 11.25). Tropomyosin is a fibrous protein that binds lengthwise along the groove of actin filaments. In striated muscle, each tropomyosin molecule is bound to troponin, which is a complex of three polypeptides: troponin C (Ca2+-binding), troponin I (inhibitory), and troponin T (tropomyosin-binding). When the concentration of Ca2+ is low, the complex of the troponins with tropomyosin blocks the interaction of actin and myosin, so the muscle does not contract. At high concentrations, Ca2+ binding to troponin C shifts the position of the complex, relieving this inhibition and allowing contraction to proceed.
Figure 11.25
Association of tropomyosin and troponins with actin filaments. (A) Tropomyosin binds lengthwise along actin filaments and, in striated muscle, is associated with a complex of three troponins: troponin I (TnI), troponin C (TnC), and troponin T (TnT). In (more ) Contractile Assemblies of Actin and Myosin in Nonmuscle Cells
Contractile assemblies of actin and myosin, resembling small-scale versions of muscle fibers, are present also in nonmuscle cells. As in muscle, the actin filaments in these contractile assemblies are interdigitated with bipolar filaments of myosin II, consisting of 15 to 20 myosin II molecules, which produce contraction by sliding the actin filaments relative to one another (Figure 11.26). The actin filaments in contractile bundles in nonmuscle cells are also associated with tropomyosin, which facilitates their interaction with myosin II, probably by competing with filamin for binding sites on actin.
Figure 11.26
Contractile assemblies in nonmuscle cells. Bipolar filaments of myosin II produce contraction by sliding actin filaments in opposite directions. Two examples of contractile assemblies in nonmuscle cells, stress fibers and adhesion belts, were discussed earlier with respect to attachment of the actin cytoskeleton to regions of cell-substrate and cell-cell contacts (see Figures 11.13 and 11.14). The contraction of stress fibers produces tension across the cell, allowing the cell to pull on a substrate (e.g., the extracellular matrix) to which it is anchored. The contraction of adhesion belts alters the shape of epithelial cell sheets: a process that is particularly important during embryonic development, when sheets of epithelial cells fold into structures such as tubes.
The most dramatic example of actin-myosin contraction in nonmuscle cells, however, is provided by cytokinesisthe division of a cell into two following mitosis (Figure 11.27). Toward the end of mitosis in animal cells, a contractile ring consisting of actin filaments and myosin II assembles just underneath the plasma membrane. Its contraction pulls the plasma membrane progressively inward, constricting the center of the cell and pinching it in two. Interestingly, the thickness of the contractile ring remains constant as it contracts, implying that actin filaments disassemble as contraction proceeds. The ring then disperses completely following cell division.
Figure 11.27
Cytokinesis. Following completion of mitosis (nuclear division), a contractile ring consisting of actin filaments and myosin II divides the cell in two.
http://www.ncbi.nlm.nih.gov/books/NBK9961/
This is good. I don’t recall seeing it in the original comment. I am very aware of the actin myosin troponin connection in heart and in skeletal muscle, and I did know about the nonmuscle work. I won’t deal with it now, and I have been working with Aviral now online for 2 hours.
I have had a considerable background from way back in atomic orbital theory, physical chemistry, organic chemistry, and the equilibrium necessary for cations and anions. Despite the calcium role in contraction, I would not discount hypomagnesemia in having a disease role because of the intracellular-extracellular connection. The description you pasted reminds me also of a lecture given a few years ago by the Nobel Laureate that year on the mechanism of cell division.
PUT IT IN CONTEXT OF CANCER CELL MOVEMENT
The contraction of skeletal muscle is triggered by nerve impulses, which stimulate the release of Ca2+ from the sarcoplasmic reticuluma specialized network of internal membranes, similar to the endoplasmic reticulum, that stores high concentrations of Ca2+ ions. The release of Ca2+ from the sarcoplasmic reticulum increases the concentration of Ca2+ in the cytosol from approximately 10-7 to 10-5 M. The increased Ca2+ concentration signals muscle contraction via the action of two accessory proteins bound to the actin filaments: tropomyosin and troponin (Figure 11.25). Tropomyosin is a fibrous protein that binds lengthwise along the groove of actin filaments. In striated muscle, each tropomyosin molecule is bound to troponin, which is a complex of three polypeptides: troponin C (Ca2+-binding), troponin I (inhibitory), and troponin T (tropomyosin-binding). When the concentration of Ca2+ is low, the complex of the troponins with tropomyosin blocks the interaction of actin and myosin, so the muscle does not contract. At high concentrations, Ca2+ binding to troponin C shifts the position of the complex, relieving this inhibition and allowing contraction to proceed.
Figure 11.25
Association of tropomyosin and troponins with actin filaments. (A) Tropomyosin binds lengthwise along actin filaments and, in striated muscle, is associated with a complex of three troponins: troponin I (TnI), troponin C (TnC), and troponin T (TnT). In (more ) Contractile Assemblies of Actin and Myosin in Nonmuscle Cells
Contractile assemblies of actin and myosin, resembling small-scale versions of muscle fibers, are present also in nonmuscle cells. As in muscle, the actin filaments in these contractile assemblies are interdigitated with bipolar filaments of myosin II, consisting of 15 to 20 myosin II molecules, which produce contraction by sliding the actin filaments relative to one another (Figure 11.26). The actin filaments in contractile bundles in nonmuscle cells are also associated with tropomyosin, which facilitates their interaction with myosin II, probably by competing with filamin for binding sites on actin.
Figure 11.26
Contractile assemblies in nonmuscle cells. Bipolar filaments of myosin II produce contraction by sliding actin filaments in opposite directions. Two examples of contractile assemblies in nonmuscle cells, stress fibers and adhesion belts, were discussed earlier with respect to attachment of the actin cytoskeleton to regions of cell-substrate and cell-cell contacts (see Figures 11.13 and 11.14). The contraction of stress fibers produces tension across the cell, allowing the cell to pull on a substrate (e.g., the extracellular matrix) to which it is anchored. The contraction of adhesion belts alters the shape of epithelial cell sheets: a process that is particularly important during embryonic development, when sheets of epithelial cells fold into structures such as tubes.
The most dramatic example of actin-myosin contraction in nonmuscle cells, however, is provided by cytokinesisthe division of a cell into two following mitosis (Figure 11.27). Toward the end of mitosis in animal cells, a contractile ring consisting of actin filaments and myosin II assembles just underneath the plasma membrane. Its contraction pulls the plasma membrane progressively inward, constricting the center of the cell and pinching it in two. Interestingly, the thickness of the contractile ring remains constant as it contracts, implying that actin filaments disassemble as contraction proceeds. The ring then disperses completely following cell division.
Figure 11.27
Cytokinesis. Following completion of mitosis (nuclear division), a contractile ring consisting of actin filaments and myosin II divides the cell in two.
http://www.ncbi.nlm.nih.gov/books/NBK9961/
This is good. I don’t recall seeing it in the original comment. I am very aware of the actin myosin troponin connection in heart and in skeletal muscle, and I did know about the nonmuscle work. I won’t deal with it now, and I have been working with Aviral now online for 2 hours.
I have had a considerable background from way back in atomic orbital theory, physical chemistry, organic chemistry, and the equilibrium necessary for cations and anions. Despite the calcium role in contraction, I would not discount hypomagnesemia in having a disease role because of the intracellular-extracellular connection. The description you pasted reminds me also of a lecture given a few years ago by the Nobel Laureate that year on the mechanism of cell division.
PUT IT IN CONTEXT OF CANCER CELL MOVEMENT
The contraction of skeletal muscle is triggered by nerve impulses, which stimulate the release of Ca2+ from the sarcoplasmic reticuluma specialized network of internal membranes, similar to the endoplasmic reticulum, that stores high concentrations of Ca2+ ions. The release of Ca2+ from the sarcoplasmic reticulum increases the concentration of Ca2+ in the cytosol from approximately 10-7 to 10-5 M. The increased Ca2+ concentration signals muscle contraction via the action of two accessory proteins bound to the actin filaments: tropomyosin and troponin (Figure 11.25). Tropomyosin is a fibrous protein that binds lengthwise along the groove of actin filaments. In striated muscle, each tropomyosin molecule is bound to troponin, which is a complex of three polypeptides: troponin C (Ca2+-binding), troponin I (inhibitory), and troponin T (tropomyosin-binding). When the concentration of Ca2+ is low, the complex of the troponins with tropomyosin blocks the interaction of actin and myosin, so the muscle does not contract. At high concentrations, Ca2+ binding to troponin C shifts the position of the complex, relieving this inhibition and allowing contraction to proceed.
Figure 11.25
Association of tropomyosin and troponins with actin filaments. (A) Tropomyosin binds lengthwise along actin filaments and, in striated muscle, is associated with a complex of three troponins: troponin I (TnI), troponin C (TnC), and troponin T (TnT). In (more ) Contractile Assemblies of Actin and Myosin in Nonmuscle Cells
Contractile assemblies of actin and myosin, resembling small-scale versions of muscle fibers, are present also in nonmuscle cells. As in muscle, the actin filaments in these contractile assemblies are interdigitated with bipolar filaments of myosin II, consisting of 15 to 20 myosin II molecules, which produce contraction by sliding the actin filaments relative to one another (Figure 11.26). The actin filaments in contractile bundles in nonmuscle cells are also associated with tropomyosin, which facilitates their interaction with myosin II, probably by competing with filamin for binding sites on actin.
Figure 11.26
Contractile assemblies in nonmuscle cells. Bipolar filaments of myosin II produce contraction by sliding actin filaments in opposite directions. Two examples of contractile assemblies in nonmuscle cells, stress fibers and adhesion belts, were discussed earlier with respect to attachment of the actin cytoskeleton to regions of cell-substrate and cell-cell contacts (see Figures 11.13 and 11.14). The contraction of stress fibers produces tension across the cell, allowing the cell to pull on a substrate (e.g., the extracellular matrix) to which it is anchored. The contraction of adhesion belts alters the shape of epithelial cell sheets: a process that is particularly important during embryonic development, when sheets of epithelial cells fold into structures such as tubes.
The most dramatic example of actin-myosin contraction in nonmuscle cells, however, is provided by cytokinesisthe division of a cell into two following mitosis (Figure 11.27). Toward the end of mitosis in animal cells, a contractile ring consisting of actin filaments and myosin II assembles just underneath the plasma membrane. Its contraction pulls the plasma membrane progressively inward, constricting the center of the cell and pinching it in two. Interestingly, the thickness of the contractile ring remains constant as it contracts, implying that actin filaments disassemble as contraction proceeds. The ring then disperses completely following cell division.
Figure 11.27
Cytokinesis. Following completion of mitosis (nuclear division), a contractile ring consisting of actin filaments and myosin II divides the cell in two.
http://www.ncbi.nlm.nih.gov/books/NBK9961/
This is good. I don’t recall seeing it in the original comment. I am very aware of the actin myosin troponin connection in heart and in skeletal muscle, and I did know about the nonmuscle work. I won’t deal with it now, and I have been working with Aviral now online for 2 hours.
I have had a considerable background from way back in atomic orbital theory, physical chemistry, organic chemistry, and the equilibrium necessary for cations and anions. Despite the calcium role in contraction, I would not discount hypomagnesemia in having a disease role because of the intracellular-extracellular connection. The description you pasted reminds me also of a lecture given a few years ago by the Nobel Laureate that year on the mechanism of cell division.
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Open Journals vs. Subscription-based « Pharmaceutical Intelligenceâ, very compelling plus the blog post ended up being a good read.
Many thanks,Annette
I actually consider this amazing blog , âSAME SCIENTIFIC IMPACT: Scientific Publishing –
Open Journals vs. Subscription-based « Pharmaceutical Intelligenceâ, very compelling plus the blog post ended up being a good read.
Many thanks,Annette
I actually consider this amazing blog , âSAME SCIENTIFIC IMPACT: Scientific Publishing –
Open Journals vs. Subscription-based « Pharmaceutical Intelligenceâ, very compelling plus the blog post ended up being a good read.
Many thanks,Annette