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CRISPR-Cas9 and the Power of Butterfly Gene Editing

Reporter: Madison Davis

Genome editing is a relatively new branch of genetic engineering that utilizes modern technologies in altering, inserting, or deleting selective DNA sequences within cells.  CRISPR-Cas9, otherwise known as “Clustered Regularly Interspaced Short Palindromic Repeat”, is a groundbreaking genome editing technique for scientists, as it is more efficient and allows for more precise genome changes at less of a cost in comparison to other editing methods.  The CRISPR-Cas9 procedure chiefly involves two biological molecules: an enzyme known as “Cas9” whose role is to cut the DNA during transcription, and a guide RNA molecule located within the Cas9 enzyme.  

The process of extracting and editing certain segments of DNA begins with identifying the respective segment of DNA to edit, typically around twenty nucleotides in length but can vary depending on the goal of the scientists.  This selection process can be based on prior knowledge of gene mapping sequences or random experimentation.  Upon identifying the segment, scientists will manually formulate a guide RNA molecule that matches the sequence of nucleotides found in the DNA sequence.  This gRNA molecule will then be placed in empty Cas9 enzymes.  Through the process of transcription, Cas9 enzymes will find and cut out the designated DNA sequence, where scientists are then able to insert, delete, or modify certain sequences by hand under high-definition microscopes.  

The usage of CRISPR can range from identifying tumor suppressor genes to gene mapping for species.  In recent years, it has been used more specifically to understand the evolutionary genetics behind butterfly wing patterns.  Butterfly wings are constructed from two separate layers that contain thousands of individual scales made of a hard protein called chitin.  Each individual scale contains embedded structures and pigments that reflect or absorb certain colors of light depending on their wavelengths.  Their unique structures allows certain butterfly species to exhibit wide ranges of color variation.  All together, these scales can act as identification, insulation, and camouflage. 

Through selective processing, scientists were able to identify how a loss in a certain genetic sequence labeled WntA results in a reduction in CSS (Central Symmetry Systems) and pattern boundaries, resulting in more abstract wing patterns.  A research expedition led by Anyi Mazo-Vargas experimented on two species, Heliconius erato demophoon and Heliconius sara sara.  Each butterfly wing pair composed of mainly black pigment with two main stripe patterns consisting of red and yellow and blue and white for each species, respectively.  When the WntA gene was removed in offspring, there was an increase in color pigment in areas that were previously black scales.   For instance, in Heliconius erato demophoon, there appeared to be more blurred red and yellow pigment rather than distinct colored stripe patterns.  The WntA gene was also experimented in monarch butterflies, where an absence in WnTA genes caused the initially black tipped-scales of the monarch wings to become a whiter, “bleached” pigment.

While efficient in scale, CRISPR-Cas9 editing system is often riddled with mosaic mutations, which can be a challenge in making valid conclusions in gene editing.  Mosaicism is a process of gene editing that results in an individual having multiple cells with different DNA sequences.  Not all cells of a singular individual contain the same genetic code.  When editing genetic sequences during the larva stage, not all subsequent cells are affected by such a change, and thus changes in butterfly wings can only be partially identified.  As CRISPR and other gene editing technologies continue to evolve, scientists should try to increase the accuracy of their experiments, such as editing genes in earlier germline cells or varying their experiments on more subspecies for more data analysis. 

 

SOURCES

“What Are Genome Editing and CRISPR-Cas9? – Genetics Home Reference – NIH.” U.S. National Library of Medicine, National Institutes of Health, 17 Aug. 2020, ghr.nlm.nih.gov/primer/genomicresearch/genomeediting.

Pak, Ekaterina. “CRISPR: A Game-Changing Genetic Engineering Technique.” Science in the News, 31 July 2014, sitn.hms.harvard.edu/flash/2014/crispr-a-game-changing-genetic-engineering-technique/.

Mazo-Vargas, A., Concha, C., Livraghi, L., Massardo, D., Wallbank, R., Zhang, L., Papador, J., Martinez-Najera, D., Jiggins, C., Kronforst, M., Breuker, C., Reed, R., Patel, N., McMillan, W. and Martin, A., 2020. Macroevolutionary Shifts Of Wnta Function Potentiate Butterfly Wing-Pattern Diversity. [online] PNAS. Available at: https://www.pnas.org/content/114/40/10701 [Accessed 20 August 2020].

Mehravar, Maryam, et al. “Mosaicism in CRISPR/Cas9-Mediated Genome Editing.” Developmental Biology, Academic Press, 22 Oct. 2018, www.sciencedirect.com/science/article/pii/S0012160618302513.

https://pharmaceuticalintelligence.com/2020/08/29/prime-editing-as-a-new-crispr-tool-to-enhance-precision-and-versatility/

 

 

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