Overexpression of FGF-2 alters cell fate specification in the developing retina of Xenopus laevis

The developing vertebrate retina produces appropriate ratios of seven pheno typically and functionally distinct cell types. Retinal progenitors remain multipotent up until the last cell division, favoring the idea that extrins ic cues direct cell fate. We demonstrated previously that fibroblast growth factor (FGF) receptors are necessary for transduction of signals in the de veloping Xenopus retina that bias cell fate decisions (S. McFarlane et al., 1998, Development 125, 3967-3975). However, the precise identity of the si gnal remains unknown. To test whether an FGF signal is sufficient to influe nce cell fate choices in the developing retina, FGF-2 was overexpressed in Xenopus retinal precursors by injecting, at the embryonic 16-cell stage, a cDNA plasmid encoding FGF-2 into cells fated to form the retina. We found t hat FGF-2 overexpression in retinal precursors altered the relative numbers of transgene-expressing retinal ganglion cells (RGC) and Muller glia; RGCs were increased by 35% and Muller glia decreased by 50%. In contrast, the p roportion of retinal precursors that became photoreceptors was unchanged. W ithin the photoreceptor population, however, we found a twofold increase in rod photoreceptors at the expense of cone photoreceptors. These data are c onsistent with an endogenous FGF signal influencing cell fate decisions in the developing vertebrate retina. (C) 2000 Academic Press.