Induction of myopia in tilapia (Oreochromis niloticus ): Initial molecular characterization

Gene expression patterns in the retina and choroid associated with the induction of myopia by form deprivation and negative imposed defocus were characterized in tilapia (Oreochromis niloticus). Two main studies were completed. Study 1 involved form deprivation and Study 2, imposed defocus. Translucent (form deprivation) or lens compensation (imposed defocus) goggles were directly sutured over the one eye, while the other eye served as an untreated contralateral control. In addition to those above, sham-surgery and sham-untreated contralateral controls (Study 1 and 2), as well as, "treated" and "contralateral" controls from a within tank untreated group (Study 2 only) were included. Targeted gene expression analysis was carried out using Real-time PCR on separated retinal and choroidal tissue after 14 days of form deprivation (Study 1) and 1, 4 and 14 days of imposed defocus (Study 2). The targeted genes were cloned from tilapia retinal/choroidal tissue and were selected based upon two distinct approaches. The first (Objective 1), involved a new myopia candidate (ANXA5) discovered via a proteomics screening study performed on form deprived tilapia and the second (Objective 2), was a comparative approach using myopia candidate genes discovered previously in chicks studies (LWS, SWS-2A, RARalpha and TGFbeta2). ANXA5 mRNA abundance was significantly lower in the retina of form deprived eyes relative to the matched contralateral eyes (P = 0.041). No significant differences in ANXA5 mRNA abundance were observed in the choroid following 14 days of form deprivation or in either tissue type (retina and choroid) after 1, 4 and 14 days of imposed defocus. ANXA5 mRNA abundance levels were on average 350 fold higher in the choroid relative to the retina. Tilapia ANXA5 may play a role in the induction of myopia by form deprivation, but not negative imposed defocus. In addition, the expression patterns of LWS, SWS-2A, RARalpha and TGFbeta2 reported in chicks were not conserved in tilapia suggesting that these specific genes are not important in the emmetropization process of all animals and/or that an alternate molecular pathway or time course for emmetropization may exist in lower vertebrates.