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Donald Zack, Anitha Yerrabelli, Xiaodong Zhang, Elizabeth Conner, Snorri Thorgeirsson, Anand Swaroop, Shiming Chen, Tomohiro Masuda; GTF2IRD1 is a Dual-FunctionTranscription Factor that Promotes M Opsin Gene Expression and Suppresses S Opsin Gene Expression in M Cones. Invest. Ophthalmol. Vis. Sci. 2013;54(15):2613.
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© ARVO (1962-2015); The Authors (2016-present)
The mechanisms controlling cone photoreceptor-specific gene expression are not fully understood. Our aim was to identify transcription factors (TFs) that regulate cone opsin gene expression.
Yeast one hybrid (YOH) screening of a retinal library was performed to identify TFs that interact with the locus control region (LCR) of the mouse M opsin gene. Histological studies were applied to examine the expression pattern of identified TFs in the developing mouse retina. Interaction of the identified TF with the upstream regions of opsin genes was examined by ChIP. Transcriptional activity was characterized by siRNA-mediated gene knockdown in primary murine retinal cells, and transient co-transfection assay in HEK 293 cells with a reporter containing opsin gene upstream regions. Finally, we analyzed the retina of a Gtf2ird1-null mouse using molecular, histological, and electrophysiological approaches.
YOH screening identified several TFs that bind to the LCR. Among those was Gtf2ird1, whose role in the retina has not been studied. Gtf2ird1 expression in M cones is first detectable at P10 and is maintained through adulthood. ChIP assays showed that Gtf2ird1 interacts with the LCR and promoter regions of the M and S opsin genes. siRNA-mediated Gtf2ird1 knockdown suppressed M opsin expression; transient co-transfection assays showed that Gtf2ird1 synergistically enhanced L opsin promoter activity in the presence of CRX. On the other hand, Gtf2ird1 abolished S opsin promoter activity enhanced by CRX with RORα or RORβ. Consistent with these results, M opsin gene expression in the Gtf2ird1-null mouse retina was significantly suppressed, while S opsin gene expression was significantly increased. Histological studies of Gtf2ird1-null mouse retina showed that S opsin immuno-positive cells were increased in the dorsal retina, where S cones are normally scarce. Interestingly, most of them were also M opsin immuno-positive. On the other hand, there was no significant change between Gtf2ird1-null and wild-type mouse retinas in both the number of cells and the dorsal-ventral distribution pattern of M opsin immuno-positive cells. ERGs reflected these cone changes.
Our results indicate that Gtf2ird1 is a dual-function transcription factor that maintains M cone function by promoting M opsin expression and suppressing S opsin expression in M cones.
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