Changes in retinal crystallin gene expression have been implicated in the development of myopia in animal models. We therefore investigated the expression of αB-crystallin (cryab) in the chicken retina during periods of increased ocular growth induced by form-deprivation and negative lens-wear, and during periods of decreased ocular growth induced by diffuser removal from previously form-deprived eyes, and plus lens-wear. Cryab RNA transcript levels in the chicken retina were measured using semi-quantitative real-time RT-PCR, at times between 1 h and 10 days after the fitting of diffusers or negative lenses, and at times between 1 h and 3 days following the removal of diffusers from previously form-deprived eyes, or the addition of plus lenses. Changes in expression for each condition at each time-point are analysed relative to expression in retinas from age-matched untreated control birds. No change in relative expression of cryab RNA transcript was detected 1 h after fitting diffusers to induce form-deprivation myopia. A transient increase in cryab RNA transcript expression was detected around 1 day later (p = 0.02), but expression returned to control levels after three days. After 7 (p = 0.005) and 10 (p = 0.001) days, retinal cryab RNA transcript expression progressively increased relative to controls. After removal of the diffusers, to initiate recovery, cryab RNA transcript expression remained elevated, with only a slight return to control levels. During the development of lens-induced myopia, no changes in cryab RNA transcript expression relative to controls were seen on day 1, but increases were seen at 10 days (p = 0.004). No significant changes in retinal cryab RNA transcript expression were seen in response to plus lenses compared to either contralateral control values (MANOVA; F = 0.60, p = 0.48) or age-matched untreated values (MANOVA; F = 4.10, p = 0.08). Changes in retinal cryab RNA transcript expression were not systematically related to changes in the rate of eye growth. The role of the transient increase in cryab expression observed after 1 day of form-deprivation, which was not seen after fitting negative lenses, is unclear. The later increases in relative cryab expression seen during the development of form-deprivation and lens-induced myopia occur too late to have a major role in the differential regulation of eye growth between experimental and control eyes. Given that cryab is a member of the small heat shock protein family, the later increases may reflect the emergence of cell damage related to high myopic pathology in the experimentally enlarged eyes and retina.
- Eye growth