Advertisements
Feeds:
Posts
Comments

Posts Tagged ‘Cilium’


Cilia and the Oviduct

Author: Aashir Awan, PhD

In a previous article, there was a discussion on the role of primary cilia in ovarian cancers with specific context to the hedgehog signal transduction system.  The article helped to highlight not only the role that this organelle plays in ovarian cancer tumorigenesis but also hints at perhaps a mechanistic explanation at the molecular level (Egeberg et al., 2012).  In this review, we focus on primary cilia and some of the signal transduction pathways it helps to coordinate within the oviduct.  Motile cilia are probably better known in their roles  aiding in the movement of the oocyte.  But, in the last few years, research has been undertaken to study the sensory role of the cilium in the female reproductive system.  As such, Drs. Christensen and Stefan Teilmann (University of Copenhagen) undertook a few studies to show the importance of three different signal transduction systems that are being coordinated by the cilium in this particular tissue.

Fig2Their first paper demonstrated that progesterone receptor was localized to the cilia on the epithelial layer of cells surrounding the oviduct and specifically to the lower half of the ciliary length which can be seen in the immunofluorescence analysis of the progesterone receptor profile in the left hand-side figure (Teilmann et al., 2006).  Furthermore, the expression of this receptor is markedly increased upon exposure to gonadotrophin hormones indicating that there is a feedback loop that is sensitive to hormonal regulation.  Previously, it had been shown that progesterone regulates the activity of the outer dynein arms of the cilium through specific effector molecules (Fliegauf et al., 2005).  Thus, the progesterone released upon ovulation would be thought to directly affect the ciliated epiethlium in order to help facilitate the movement of the oocyte through the oviduct thereby highlighting the important role of the cilium (and the signal transduction pathway) to the overall physiology of the female reproductive system.  This work has recently been reproduced by Dr. Larrson’s group in Sweden (Bylander et al., 2013).

Fig1

The Christensen group continued further studies by localizing the angipoeiten receptors, Tie-1 and Tie-2, to the primary cilia of the ovarian surface epithelial as well as the oviduct as seen in the figure on right showing an immunoflourescent micrograph of the infundibulum (Teilmann and Christensen 2005).  Since the expression of their agonist, Ang1, increases during ovulation (Hazzard et al., 1999), both these receptors are thought to play a role in vascularization of the tissue surrounding the developing follicles.  Also, using this  reasoning, the paper argues that the Ang/Tie signaling axis plays an important and general role by serving as an anti-apoptotic system to maintain a dedifferentiated phenotype of both endothelial cells.

Fig3

Finally, Dr. Christensen’s group also demonstrated a unique localization of polycystins 1 and 2 to the primary cilia of ovarian granulose cells (Teilmann et al., 2005).  These calcium cation channels have been shown to sense the flow of urine in the kidney in monitoring general homeostasis and whose mutations have been shown to cause polycystic kidney disesase (Pazour et al.,2002; Yoder et al., 2002).  As with the progesterone receptor, there is a marked effect on polycystins concentration upon gonadrotrophin stimulation as clearly seen on the left-hand side figure (the arrow show ciliary localization of the polycystin 2 receptor; also, note the dramatic increase in polycystin 2 immunofluorescence in the infundibulum).  Further, the Ca2+ permeable cation channel, TRP vaniloid 4 (TRPV4) was found to be localized to the motile cilia in specific subpopulation of epithelial cells within the ampulla and isthmus.  Thus, the localization of these receptors  indicates that the primary cilia would again be involved in a sensory role perhaps by affecting the differentiation and maturation of the emerging oocyte and in relaying physiological information upon ovulatation to the epithelial cells of the surrounding oviduct.

One can imagine that these are probably only a partial list of the important receptor molecules localized thus far to the  cilia that exist within the female reproductive system.  Since more and more receptor molecules are being found within the relatively small confines of this organelle, one can hypothesize that perhaps the signal transduction mechanism between different receptor molecules is ocurring within the cilium itself perhaps even independent of what may be occurring in the cell body. Since reproductive and fertility issues remain a problem in the medical field, it behooves us to continue research into the overall contributions of  this organelle within the female reproductive system.

REFERENCES

Bylander ALind KGoksör MBillig HLarsson DJ. 2013 The classical progesterone receptor mediates the rapid reduction of fallopian tube ciliary beat frequency by progesterone. Reprod Biol Endocrinol. 11:33.

Egeberg DLLethan MManguso RSchneider LAwan AJørgensen TSByskov AGPedersen LBChristensen ST. 2012 Primary cilia and aberrant cell signaling in epithelial ovarian cancer. Cilia. 1:15.

Fliegauf MOlbrich HHorvath JWildhaber JHZariwala MAKennedy MKnowles MROmran H. 2005 Mislocalization of DNAH5 and DNAH9 in respiratory cells from patients with primary ciliary dyskinesia. Am J Respir Crit Care Med. 171:1343-1349.

Hazzard TMMolskness TAChaffin CLStouffer RL. 1999 Vascular endothelial growth factor (VEGF) and angiopoietin regulation by gonadotrophin and steroids in macaque granulosa cells during the peri-ovulatory interval. Mol Hum Reprod. 5:1115-1121.

Pazour GJ, San Agustin JT, Follit JA, Rosenbaum JL, Witman GB.20002 Polycystin-2 localizes to kidney cilia and the ciliary level is elevated in orpk mice with polycystic kidney disease. Curr Biol. 12:R378-R380.

Teilmann SC, Christensen ST. 2005 Localization of the angiopoietin receptors Tie-1 and Tie-2 on the primary cilia in the femalereproductive organs. Cell Biol Int.29:340-346.

Teilmann SCByskov AGPedersen PAWheatley DNPazour GJChristensen ST. 2005 Localization of transient receptor potential ion channels in primary and motile cilia of the female murine reproductive organs. Mol Reprod Dev. 71:444-452.

Teilmann SCClement CAThorup JByskov AGChristensen ST. 2006 Expression and localization of the progesterone receptor in mouse and human reproductive organs. J Endocrinol. 191:525-535.

Yoder BKHou XGuay-Woodford LM. 2002 The polycystic kidney disease proteins, polycystin-1, polycystin-2, polaris, and cystin, are co-localized in renal cilia. J Am Soc Nephrol. 13:2508-2516.

 

Advertisements

Read Full Post »


Author: Aashir Awan, PhD

The primary cilium is organelle that has garnered much attention in the field of cell biology during the last 15 years. It is a slender, solitary hair-like organelle that extends 5-10 uM from each mammalian cell (in the G0 cell cycle state) that is microtubule-based (9 outer doublets arranged in a circular fashion) and dependent on a process called Intraflagellar Transport (IFT). IFT is the bidirectional movement of motors (kinesin-2 in the anterograde and dynein-2 in the retrograde direction) responsible for the assembly and maintenance of the cilium (Pedersen et al., 2006).

Until this time, it had been labeled a ‘vestigial’ organelle not worthy of research. Yet, a breakthrough into the sensory role of the primary cilium came in 2000 based on Dr. Rosenbaum’s research on Chlamydomonas and the motile cilium or flagella. Along with Dr. George Whitman’s group, they were able to show the importance of Tg737 (IFT88) protein to the pathology of polycystic kidney disease in mouse (Pazour et al., 2000). Since then, research into the primary cilium has exploded and has been linked to diverse pathologies (collectively known as ciliopathies) such as

  • retinitis pigmentosa,
  • hydrocephaly,
  • situs inversus,
  • ovarian and pancreatic cancers among others (Nielsen et al., 2008; Edberg et al., 2012). Also, various
  • signal transduction pathways have been found to be coordinated by the primary cilia such as hedgehog, wnt, PDGF among others (Veland et al., 2008).

Thus, in 2006, the Christensen lab at the University of Copenhagen (Denmark) with the collaboration of Dr. Peter Satir’s group at Albert Einstein College of Medicine (Bronx, NY) began to investigate whether the human embryonic stem cells (hESCs) possess primary cilium and then to begin preliminary molecular dissections of the role that this organelle could play in the proliferation and differentiation profiles of these pluripotent cells. The Albert Einstein group, due to NIH restrictions, had to work with two federally-sanctioned cell lines. Working with the Laboratory of Reproductive Biology at RigsHospital, the Danish side had access to in-house derived stem cell lines from discarded blastocysts. The advantage for the Danish side was obvious since these newer cell lines hadn’t undergone as many passages as the NIH cell lines and were thus more robust. To begin preliminary characterizations of these lines, some basic hallmarks of hESCs (Bernhardt et al., 2012) had to be localized to the nucleus such as the transcription factor (TF) Oct4 (Fig. 1).

In addition, a single primary cilium can be seen denoted by the acetylated tubulin staining emanating from each cell in the micrographs. Also, the base of the cilium is marked by the presence of pericentrin and centrin which demarcate the centriole.

Fig1 Fig. 1 Primary cilia stained with anti-acetylated tubulin (tb, red) are indicated by arrows and undifferentiated stem cells are identified by nuclear colocalization of OCT-4 (green) and DAPI (dark blue) in the merged image (light blue). A primary cilium (tb, red, arrow) in undifferentiated hESCs emerges from one of the centrioles (asterisks) marked with anti-centrin (centrin, green). Inset shows anti-pericentrin localization to base of cilia (Pctn, green).

Together, the three labs were the first to discover primary cilia in stem cells while other groups have since then confirmed these findings (Kiprilov et  al. 2008; Han et al. 2008). Attention was then to characterize different signal transduction pathways in the stem cell cilium. Since the hedgehog pathway has been shown to be important for differentiation and proliferation (Cerdan and Bhatia, 2012), the groups characterized this signal pathway in these cells using immunofluorescence, electron microscopy and qPCR techniques. One particularly interesting experiment to show that the hedgehog pathway was functional in these cells was to add the hedgehog agonist, SAG (Smoothened agonist), and then to isolate the cells for immunofluorescence at different times.

Gradually, one can see the appearance of the smoothened protein into the cilium as indicated by increasing intensity of the immunofluorescence staining. Conversely, patched levels in the cilium, decreased. This is a hallmark of hedgehog activation (Fig. 2).
Fig. 2 copiaFig. 2 Immunofluorescence micrographs of hESC showing smoothened (green), acetylated tubulin (red) and DAPI (blue). The micrographs from left to right represents SAG treatments at t = 0, 1 and 4 hours.

However, an additional interesting observation was made concerning these stem cells. An important characteristic for stem cells is the presence of certain transcription factors which render these cells in the pluripotent or undifferentiated state. These include Oct4, Sox2, and Nanog whose localization had been observed in the nucleus as expected for other TFs.

However, the Danish groups curiously found a subpopulation of stem cells where these TFs were additionally localized to the primary cilium (Fig. 3). This had never been observed or investigated before.  Additionally, proper negative controls were  carried out to exclude this phenomenon from being an artifact (e.g. bleed through).
Fig. 3 copia Fig. 3 Stem cell markers (Sox2, Nanog, and Oct4) localizing to the nucleus and the primary cilia (arrows) of hESC line LRB003. This and the previous figure show shifted overlay images whereby the green and red channels have been slightly shifted so that the red channel doesn’t swamp out the intensity of the green channels.

Thus, it raises an intriguing possibility that perhaps the primary cilia plays a previously uncharacterized role in the differentiation/proliferation state of the hESCs via possible modifications of these TFs perhaps analogous to the processing of the Gli transcription factors (Hui and Angers, 2011). Another curious observation is that the subpopulation of cells whose primary cilia are positive for these TFs always occur in clusters which might hint at its mechanistic explanation.  In conclusion, since stem cells are now being more routinely used for regenerative medicine such as repair of severed spinal cord (Lu et al. 2012), it behooves us to better learn the molecular mechanisms that keeps these invaluable cells in an undifferentiated state so that we can harness their full therapeutic potential.

REFERENCES

Awan A, Oliveri RS, Jensen PL, Christensen ST, Andersen CY. 2010 Immunoflourescence and mRNA analysis of human embryonic stem cells (hESCs) grown under feeder-free conditions. Methods Mol Biol. 584:195-210.

Bernhardt M, Galach M, Novak D, Utikal J. 2012 Mediators of induced pluripotency and their role in cancer cells – current scientific knowledge and future perspectives. Biotechnol J. 7:810-821.

Cerdan C, Bhatia M. 2010 Novel roles for Notch, Wnt and Hedgehog in hematopoesis derived from human pluripotent stem cells. Int J Dev Biol. 54:955-963.

Han YG, Spassky N, Romaguera-Ros M, Garcia-Verdugo JM, Aguilar A, Schneider-Maunoury S, Alvarez-Buylla A. 2008 Hedgehog signaling and primary cilia are required for the formation of adult neural stem cells.Nat Neurosci. 11:277-284.

Hui CC, Angers S. 2011 Gli proteins in development and disease. Annu Rev Cell Dev Biol. 27:513-537.

Kiprilov EN, Awan A, Desprat R, Velho M, Clement CA, Byskov AG, Andersen CY, Satir P, Bouhassira EE, Christensen ST, Hirsch RE 2008 Human embryonic stem cells in culture possess primary cilia with hedgehog signaling machinery. J Cell Biol. 2008 180:897-904.

Lu P, Wang Y, Graham L, McHale K, Gao M, Wu D, Brock J, Blesch A, Rosenzweig ES, Havton LA, Zheng B, Conner JM, Marsala M, Tuszynski MH. 2012 Long-distance growth and connectivity of neural stem cells after severe spinal cord injury. Cell 150:1264-73.

Nielsen SK, Møllgård K, Clement CA, Veland IR, Awan A, Yoder BK, Novak I, Christensen ST. 2008 Characterization of primary cilia and Hedgehog signaling during development of the human pancreas and in human pancreatic duct cancer cell lines. Dev Dyn. 237:2039-52.

Pazour GJ, Dickert BL, Vucica Y, Seeley ES, Rosenbaum JL, Witman GB, Cole DG. 2000 Chlamydomonas IFT88 and its mouse homologue, polycystic kidney disease gene tg737, are required for assembly of cilia and flagella. J Cell Biol 151: 709-18.

Pedersen LB, Veland IR, Schrøder JM, Christensen ST. 2008 Assembly of primary cilia. Dev Dyn. 237:1993-2006.

Veland IR, Awan A, Pedersen LB, Yoder BK, Christensen ST. 2009 Primary cilia and signaling pathways in mammalian development, health and disease. Nephron Physiol. 111: 39-53.

Read Full Post »