Temporal changes of novel transcripts in the chicken retina following imposed defocus

Changes in retinal gene expression are one of the first steps in the signaling pathway underlying the visual control of eye growth. We tried to identify novel, yet unknown, genes, that alter their expression pattern following imposed defocus, wearing of diffusers, or during recovery from myopia. Sequences found earlier by differential display studies were applied to 5'-RACE and identified as 15 kDa selenoprotein P and prolidase. Moreover, we obtained more sequence information for a yet unidentified gene. We have studied the time course of expressions of these genes following lens or diffuser treatment.

Ten to 14 day old white leghorn chickens (4-7) were treated with a monocular +7 D or -7 D lenses for 2, 4, 6, or 24 h, or treated with monocular or binocular diffusers for 2, 4, or 6 h. Chickens of another group were allowed to recover from 4 days of diffuser wear for 4 h. Untreated chicks served as a control for contralateral eye effects. Following the extraction of retinal RNA, the relative expression of the three genes was determined by semi-quantitative real time PCR.

We found a significant up regulation of selenoprotein P expression after 24 h of treatment with positive (+380%) or negative lenses (+387%) which was even more prominent in the contralateral untreated eyes (positive: +542%; negative: +786%). A rapid change in selenoprotein mRNA levels was induced by binocular diffuser wear for 2 h (+425%), whereas defocus blur in one eye led to an increase only after 6 h (+261%). There was a significant upregulation of prolidase mRNA after 24 h of treatment with positive (+75%) but not with negative lenses. Moreover, blur induced by diffusers resulted in a highly significant rise of prolidase mRNA levels after 4 h, both with monocular (142%) and binocular (106%) treatment. This is similar to what was found in the previous differential display (DD) screening of monocularly treated eyes. In contrast to the findings of the DD screening, the mRNA expression of the unknown gene remained unchanged both after hyperopic and myopic defocus. Again, blur induced by diffusers evoked the most prominent change after 6 h of binocular treatment. There were no significant alterations in the mRNA levels of the three investigated genes after 4 h of recovery from myopia that was induced by a 4 day period of diffuser treatment.

The mRNA expression of selenoprotein P, prolidase, and of the not yet identified gene (sequence 3) is clearly altered by retinal image degradation imposed by diffuser wearing and, in part, by defocus imposed by spectacle lenses. However, none of the candidates are regulated by the sign of imposed defocus, suggesting a role in retinal contrast processing.