Abstract
Abstract: :
Purpose. In chickens, the immediate early gene ZENK (the avian Egr–1 homologue) is regulated according to the sign of imposed defocus, and the levels of TGF–ß (Transforming Growth Factor), VIP (Vasoactive Intestinal Polypeptide) and Shh (Sonic hedgehog) are changed when myopia is induced by diffusers. Little is known about the role of these molecules in visual control of eye growth in mice. Methods. C57BL/6 mice, 29–32 day old, were kept in darkness overnight and then exposed to light either for 30 or 120 min with (a) the eyes uncovered or (b) with a diffuser over one eye and a neutral density filter (NDF, of the same attenuation of 0.3 log) over the other eye. Additionally, one group of control animals was not exposed to light. After extraction of retinal mRNA, the relative expression levels of TGF–ß, Egr–1, VIP and Shh were determined by semi–quantitative real–time RT–PCR. The number of amacrine and ganglion cells expressing Egr–1 protein was quantified by immunohistochemistry. Results. (1) Egr–1 mRNA levels were regulated in a light dependent manner. They were 19–fold higher after 30 min light exposure, compared to the control in the dark, but increased less if the eyes wore NDF, and even less if they wore diffusers (p<0.05). This latter difference disappeared after 120 min. (2) More cells were stained for Egr–1 protein in eyes that were exposed to light than to darkness, and also in eyes with normal spatial vision with NDFs, compared to diffusers. (3) VIP mRNA levels were lower in eyes exposed to light through NDFs than in darkness after 30 min, but higher after 120 min, both with occlusion and NDF–treatment. (4) Shh mRNA was significantly down–regulated by 120 min of light exposure in control animals while mRNA levels in NDF and diffuser treated eyes remained at the level of the control group in the dark. (5) TGF–ß mRNA was not affected by the different treatments. Conclusion. Both Egr–1 mRNA and protein in mouse retina are increased by light, but there is additional input from retinal image quality. VIP and Shh are up–regulated by both NDF and diffuser treatment after 120 min. As in other species, the expression of several genes in the mouse retina is changed by light and spatial properties of the image; some of these might play a role in myopia development.
Keywords: myopia • retina • gene/expression