Abstract
Purpose: :
Previous work from our lab and others have shown that Vsx1, a paired-like homeodomain transcription factor, is essential for the terminal differentiation of Type 2 OFF bipolar cells and OFF visual signaling. Vsx1 is also expressed in putative Type 7 ON cone bipolar cells, however, due to the lack of specific markers, we have been unable to address Vsx1’s role in this cell type. The purpose of this work is to utilize the alpha-gustducin:GFP transgenic reporter, known to label Type 7 bipolar cells, to further investigate the function of Vsx1 in bipolar cell development.
Methods: :
Alpha-gustducin:GFP reporter mice were crossed to mice carrying the mGluR6:LacZ reporter gene or the Vsx1-tau-LacZ knock-in null allele. Immunostaining on frozen retinal sections was used to examine the expression of alpha-gustducin GFP as well as the expression of other cell markers.
Results: :
In the wild type retina, a subset of Vsx1-positive cells colocalized with all strongly expressing alpha-gustducin:GFP Type 7 bipolar cells. In mice containing both the alpha-gustducin:GFP reporter and the mGluR6:LacZ reporter gene (which labels all ON bipolar cell types), not all Vsx1-ON type bipolar cells were co-labeled with the alpha-gustducin:GFP reporter. Alpha-gustducin:GFP expression was still present in Vsx1-null mice and colocalized with Vsx1 knock-in LacZ gene expression. CaB5 immunostaining, which is normally restricted to Types 3, 5 and rod bipolar cells, was upregulated in GFP-positive Type 7 ON bipolar cells in Vsx1-null mice.
Keywords: retinal development • bipolar cells • transcription factors