RADIAL AND TANGENTIAL DISPERSION PATTERNS IN THE MOUSE RETINA ARE CELL-CLASS SPECIFIC

The retina is derived from a pseudostratified germinal zone in which t he relative position of a progenitor cell is believed to determine the position of the progeny aligned in the radial axis. Such a developmen tal mechanism would ensure that radial arrays of cells which comprise functional units in the mature central nervous system are also clonall y related. The present study has tested this hypothesis by using X chr omosome-inactivation transgenic mosaic mice. We report that the retina shows a conspicuous distinction for clonally related neuroblasts of d ifferent laminar and functional fates: the rod photoreceptor. Muller, and bipolar cells are aligned in the radial axis, whereas the cone pho toreceptor, horizontal, amacrine, and ganglion cells are tangentially displaced with respect to them. These results indicate that the disper sion of cell classes across the retinal surface is differentially cons trained. Some classes of retinal neuroblast exhibit a significant tang ential, as well as radial, component in their dispersion from the germ inal zone, whereas others disperse only in the radial dimension, Conse quently, the majority of radial columns within the mature retina must be derived from multiple progenitors, Because the cone photoreceptor, horizontal, amacrine, and ganglion cells establish nonrandom matrices in their cellular distributions within the respective retinal layers, tangential dispersion may be the means by which these matrices are con structed.