S–crystallin mRNA and protein expression increase in dark–adapted octopus retinas.

Abstract

Abstract: : Purpose: S–crystallin is expressed in the octopus retina and the protein is 2–fold more abundant in the dark than in the light. S–crystallin also binds to F–actin. We suspect that increased expression is due to an increased synthesis of S–crystallin mRNA in the dark that is subsequently translated into protein. We are also curious to know how long it takes to visualize the increased amount of S–crystallin protein in the dark compared to the amount present in the light. We have examined the time course for S–crystallin expression and the relative expression of S–crystallin mRNA in light– and dark–adapted (LA/DA) octopus retinas. Methods: Octopuses were LA or DA for up to 120 minutes and animals sacrificed at 15 minute intervals. The retinas were homogenized, proteins separated by SDS–PAGE and relative protein concentrations determined. S–crystallin mRNA amounts in LA/DA animals were determined by quantitative RT–PCR. Results: S–crystallin protein expression in LA animals remained low during the course of the experiment. In the dark, S–crystallin expression appeared cyclical with an increased amount of S–crystallin noticeable by 30–45 minutes after the beginning of dark adaptation. Expression decreased at 60 minutes and then rose again at 75 minutes followed by a decrease at 90 minutes. Quantitative RT–PCR results showed that S–crystallin mRNA levels in the light are 5–fold higher than they are in the dark. Conclusions: S–crystallin protein expression in LA retinas is depressed while in DA retinas S–crystallin expression may be cyclical. The amount of S–crystallin mRNA is greater in the light than in retinas maintained in the dark. Further studies will show if S–crystallin mRNA expression is also cyclical.

Keywords: crystallins • photoreceptors • protein structure/function