A genetic analysis of VSX2 function in the mouse eye

Vsx2 is a homeodomain-containing transcription factor essential for maintenance of neuroretinal identity and neurogenesis. Vsx2 is believed to function via mechanisms that are strictly cell-intrinsic. However, recent research reveals evidence for involvement of Vsx2-mediated cell non-autonomous mechanisms. This leads to the hypothesis that Vsx2 regulates cell non-autonomous pathways that play a role in maintaining neuroretinal identity and neurogenesis. To test this hypothesis, genetic chimeras were generated by morula aggregations of transgenic ActB:EYFP transgenic mice homozygous for wild type alleles of Vsx2 [Tg(EYFP/EYFP);Vsx2] and mice that are homozygous for null alleles of Vsx2 (Vsx2orj/orj). Maintenance of neuroretinal identity is assessed by immunostaining for the expression of MITF, a retinal pigmented epithelium (RPE) gene that regulates many pigmentation pathway genes. Neurogenesis is assessed through analysis of cell differentiation using immunostaining for several cell-type specific markers. Analysis of the retinas of tg(EYFP/EYFP);Vsx2 ↔ Vsx2orj/orj chimeras reveals the presence of MITF expression in Vsx2orJ/orJ cells but not Vsx2+/+ cells indicating that neighboring Vsx2+/+ cells are unable to rescue Vsx2orJ/orJ cells from loss of neuroretinal identity. Analysis also reveals that Vsx2orJ/orJ cell differentiation remains delayed indicating that neighboring Vsx2+/+ cells are unable to rescue Vsx2orJ/orJ cells from delayed neurogenesis. These findings suggest that Vsx2 regulates neuroretinal identity and neurogenesis by cell-autonomous mechanisms.