Involvement of Bcl-2-associated transcription factor 1 in the differentiation of early-born retinal cells.

Retinal progenitor proliferation and differentiation are tightly controlled by extrinsic cues and distinctive combinations of transcription factors leading to the generation of retinal cell type diversity. In this context, we have characterized Bcl-2-associated transcription factor (Bclaf1) during rodent retinogenesis. Bclaf1 expression is restricted to early-born cell types, such as ganglion, amacrine, and horizontal cells. Analysis of developing retinas in Bclaf1-deficient mice revealed a reduction in the numbers of retinal ganglion cells, amacrine cells and horizontal cells and an increase in the numbers of cone photoreceptor precursors. Silencing of Bclaf1expression by in vitro electroporation of shRNA in embryonic retina confirmed that Bclaf1 serves to promote amacrine and horizontal cell differentiation. Misexpression of Bclaf1 in late retinal progenitors was not sufficient to directly induce the generation of amacrine and horizontal cells. Domain deletion analysis indicated that the N-terminal domain of Bclaf1 containing an arginine-serine-rich and a bZip domain is required for its effects on retinal cell differentiation. In addition, analysis revealed that Bclaf1 function occurs independently of its interaction with endogenous Bcl-2-related proteins. Altogether, our data demonstrates that Bclaf1expression in postmitotic early-born cells facilitates the differentiation of early retinal precursors into retinal ganglion cells, amacrine cells, and horizontal cells rather than into cone photoreceptors.