Clonal expansion and cell dispersion in the developing mouse retina

The present study has used two different approaches for labelling progenito r cells at the optic vesicle stage in order to examine patterns of clonal e xpansion and cellular dispersion within the developing retina. X-inactivati on transgenic mice and chimeric mice expressing the lacZ reporter transgene were examined during development and in adulthood to study the radial and tangential dispersion of proliferating neuroepithelial cells and postmitoti c retinal cells of known identities. Chimeric retinas were used to measure tangential dispersion distances, while transgenic retinas were used to asse ss the frequency of tangential dispersion for individual populations of ret inal neurons. Tangential dispersion is shown to be a universal feature of p articular retinal cell types, being contrasted with the strictly radial dis persion of other cells. Tangential dispersion is a relatively short-distanc e phenomenon, with distinct dispersion distances characteristic for cone, h orizontal, amacrine and ganglion cells. Embryonic and postnatal retinas sho w that tangential dispersion occurs at different times for these distinct c ell types, associated with their times of differentiation rather than their neurogenetic periods. These developmental results rule out the possibility that tangential dispersion is due to a passive displacement produced by th e proliferation of later-born cells, or to the lateral dispersion of a divi ding sibling; rather, they are consistent with the hypothesis that tangenti al dispersion plays a role in the establishment of the orderly spatial dist ribution of retinal mosaics.