When neurons exit the cell cycle after division at the apical surface of the proliferating neuroepithelium, they sever their attachments to the apical surface while migrating to their correct laminar positions. Although apical retraction is an essential step in neuronal differentiation, its underlying molecular mechanisms remain unknown. The accessibility of the retina, together with the ease of genetic manipulation and <i>in vivo </i>imaging capabilities of the vertebrate zebrafish, make zebrafish retinal ganglion cells (RGCs) an ideal model system to study the molecular basis of apical retraction in the CNS. I was able to show that the axonal guidance molecule, Slit1b, is necessary for apical retraction. <i>Slit1b </i>mRNA is expressed during RGC differentiation. Time-lapse imaging in <i>slit1b </i>morphants revealed a delayed retraction of apical processes in RGCs. Other developmental events, such as axon extension, progresses normally, thus ruling out a general developmental delay. Transcripts of the Slit receptors, <i>robo2 </i>and <i>robo3</i>, were detected in the retina during RGC differentiation. Morpholino knockdown experiments revealed that <i>robo3</i>, but not <i>robo2</i>, was required for normal apical retraction of RGCs. In addition, expression of dominant-negative N-cadherin caused RGCs to lose apical attachments prematurely. Finally, dominant-negative N-cadherin expression in <i>slit1b </i>morphants resulted in early retraction even in <i>slit1b </i>morphants, suggesting that N-cadherin functions downstream of Slit/Robo signalling during apical retraction. This study helped shed light on molecular events underlying apical retraction in RGCs. It now needs to be shown if these mechanisms are more general during neuronal differentiation throughout the CNS.
| Identifer | oai:union.ndltd.org:bl.uk/oai:ethos.bl.uk:603741 |
| Date | January 2011 |
| Creators | Harris, W. |
| Publisher | University of Cambridge |
| Source Sets | Ethos UK |
| Detected Language | English |
| Type | Electronic Thesis or Dissertation |
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