Synthesis and stability of retinal photoreceptor mRNAs are coordinately regulated during bovine fetal development

Steady state photoreceptor specific mRNA levels in bovine retina were studied during fetal maturation for five gene transcripts, including rhodopsin, arrestin (S-antigen), rod alpha-subunit of transducin, interphotoreceptor retinoid-binding protein (IRBP) and rod alpha-subunit of cGMP phosphodiesterase in order to understand mechanisms of gene regulation during photoreceptor development. A 10-15-fold increase in each transcript level begins between 5.5 and 6 months of gestation for each gene, suggesting a single coordinate induction event at this time. Quantitative analysis of transcriptional rates for each gene by nuclear run-on also reveals a coordinate increase at approximately the same time, demonstrating that induction is achieved by transcriptional activation. Interestingly, however, gene specific transcription rates in the pre-induction retina do not appear to parallel mRNA steady state levels. During fetal development neither the transcript level of each gene relative to the others nor relative mRNA turnover rates change substantially after the induction event at 5.5-6.0 months. However, at earlier times all genes exhibit higher mRNA turnover, implying that differential mRNA stability may also play an important role in determining steady-state levels.