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Abstract
PURPOSE: Nuclear run-on analysis has documented three categories of opsin gene expression during bovine fetal retinal development: basal levels of transcription occurring before 6 months gestation; opsin-specific enhanced levels of fetal transcription at 7-7.5 months gestation; and a switch from fetal to adult transcription, where transcriptional activity acquires a sarkosyl sensitive component in the adult. To begin determining the mechanism of these multiple levels of gene regulation, DNA regulatory elements within 2.1 kb of the rod opsin upstream region were identified in fetal and adult bovine retinal extracts that represented the transcriptional activities characteristic of each stage of opsin gene expression. METHODS: DNAse I footprint experiments were performed on fetal and adult bovine retinal extracts from each of the developmental stages of opsin expression. RESULTS: Ten regions of protection were mapped and the level of protection was quantitated as a function of the developmental stage. CONCLUSIONS: The 10 DNA elements identified fell into three categories of developmental protection: those elements that were protected similarly at each developmental stage; those elements that were more highly protected when opsin transcription was at basal levels (i.e., less than 6 months gestation); and those elements that were more highly protected in fetal ages as compared to the adult animal. These elements are likely to be important in the developmental regulation of rod opsin gene expression.