Overexpression of Msx2 caused a delay in retinal cell differentiation and resulted in retinal ganglion cell deficiency

Abstract

Abstract: : Purpose: Msx2, a homeodomain transcriptional factor belonging to the msh gene family, has been shown to be expressed in the developing optic vesicle. The aim of this study was to investigate possible function of Msx2 in controlling retinal ganglion cell (RGC) development. Methods: For this investigation, we utilized transgenic animals that overexpress Msx2. Msx2 transgenic embryos or adult and nontransgenic littermates were examined histopathologically. To follow RGC development, the expression of RGC–specific markers was assessed by performing in situ hybridization or immunohistochemical staining. Results: Forced expression of the Msx2 gene resulted in RGC deficiency. At E12.5, differentiation of RGC has occurred in the nontransgenic neural retina as RGCs sent axonal projections medially though the optic stack. However, in the Msx2 transgenic retina, RGC differentiation did not occur at the same developmental stage. At E12.5, the expression of Math5 and Brn3b, two RGC early differentiation markers, didn’t appear in the transgenic mice retina while they were expressed in the retina of the wild littermate. However, at E15, Math5 and Brn3b were expressed in the transgenic mice retina, though the expression domain in the developing retina was, to some extent, different from that in the wild littermate. In the adult transgenic retina, neural retina survived but a large reduction in cell number of RGC layer was evident. The number of RGCs labeled by anti–Pax6 antibody was reduced remarkably in the RGC layer of the transgenic retina. Conclusions: These results indicated that forced expression of the Msx2 gene delayed differentiation of RGCs and resulted in RGC deficiency.

Keywords: ganglion cells • retinal development • in situ hybridization