Figure 10.

Schematic summary of horizontal cell development. (A): Schematic figure of the generation and migration of Lim1+ and Isl1+ HCs. S and M denote stages of the cell cycle. Position of M-phase cells is according to the classical view, however see also Godinho et al [56]. (B): Proposed model for the effects of follistatin on RPCs during retinogenesis. During normal development, high follistatin levels stimulate the proliferation of RPCs by preventing e.g. activin (or related factors) to decrease or inhibit proliferation. As follistatin decreases over time, RPCs specialize to generate e.g. HC progenitors. Under the influence of exogenous follistatin, again preventing activin (or related factors) from controlling cell cycle withdrawal, proliferation in the HC generating progenitor pool is stimulated and therefore, more HCs than normal are eventually generated.