TPLSM is the approach used to address how asymmetric cell divisions might take place in the retina. Asymmetric cell division is a mechanism thought to be involved in generating neuronal diversity from a homogeneous progenitor population, and may be mediated by the orientation of progenitor cell divisions. 3D reconstructions of the developing zebrafish retina were analysed for orientation of cell division. Contrary to currently proposed models for vertebrate asymmetric divisions, apico-basally oriented cell divisions, perpendicular to the ventricular surface, are not found to occur in the zebrafish retina during the formation of postmitotic neurons. However, a shift in the orientation of cell division from central-peripheral to circumferential orientations occurs within the plane of the ventricular surface at a time when neuronal cells are differentiating. The shift from central-peripheral to circumferential divisions is absent or delayed in the <i>sonic you (syu)</i> mutant, which lacks retinal ganglion cell neurons. This delay correlates with a delay in neuronal differentiation, suggesting that the circumferential orientations of division may represent asymmetric, neuron-generating cell divisions. <i>In vivo</i> imaging also shows that mitotic cells, found in the apical side of the neuroephithelium, retain a process connected to the opposite basal surface, and that this process can be inherited asymmetrically by one daughter cell. Although this may also a play a role in asymmetric cell division, it does not correlate with a specific orientation of division. It may be important for the radial migration of newborn neurons to the appropriate layer of the retina. After neuronal differentiation, tangential migration of cells and cell death may be required to maintain regularity in newly-formed neuronal cell mosaics. The <i>in vivo</i> behaviour of amacrine cells in early development was studied using TPLSM. Amacrine cell death, correlated with short distances between cells, is shown to occur in early retinal development, although evidence for tangential cell migration is not found. It is plausible that apoptosis, thought to be a rare event in the zebrafish retina, is in fact required for the formation of regular cell mosaics by the removal of incompatible cells from a mosaic by short-range interactions with other cells in the mosaic.
| Identifer | oai:union.ndltd.org:bl.uk/oai:ethos.bl.uk:598285 |
| Date | January 2003 |
| Creators | Das, Tilak |
| Publisher | University of Cambridge |
| Source Sets | Ethos UK |
| Detected Language | English |
| Type | Electronic Thesis or Dissertation |
| Source | https://www.repository.cam.ac.uk/handle/1810/275268 |
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