Purpose: To investigate the expression pattern of the homeobox transcription factor Rinx (also referred to as Vsx1) during postnatal eye development of the mouse.
Methods: We cloned the mouse Rinx gene, inferred the sequence of the encoded protein, and prepared polyclonal antibodies against it. Immunohistochemical analysis (IHC) and in situ hybridization were employed to localize Rinx in postnatal and adult mouse eyes. Double-labeled IHC either with anti-protein kinase C (PKC, a marker of rod bipolar cells) or anti-vimentin (a marker of Muller glial cells) antibodies was performed in the adult retina. Rinx mRNA was also analyzed by reverse transcription-polymerase chain reaction in the lens.
Results: At P0 and P4 (postnatal days), Rinx-immunoreactive cells included retinal ganglion cells (RGC), cells of the innermost nuclear layer (INL) and of presumptive INL, differentiating lens fiber cells, and a few cells of the presumptive outer nuclear layer (ONL). At P8, both Rinx protein and mRNA were detected in the middle of the INL, and in RGC, but not in the lens. When the mice were 8 weeks of age, only a subset of nuclei in the outer half of the INL expressed both Rinx protein and mRNA. Double-labeling IHC indicated that Rinx- and either PKC- or vimentin-labeled cells were not colocalized. Therefore, Rinx is most likely expressed in adult cone bipolar cells and possibly in horizontal cells.
Conclusions: Rinx may play important roles in the differentiation and maintenance of cone bipolar cells. Rinx is unique among members of this family of homeodomain proteins in that it may also be involved in differentiation of RGC and lens fiber cells.