Deficiency of copper responsive gene stmn4 induces retinal developmental defects

As part of the central nervous system (CNS), the retina senses light and also conducts and processes visual impulses. The damaged development of the retina not only causes visual damage, but also leads to epilepsy, dementia and other brain diseases. Recently, we have reported that copper (Cu) overload induces retinal developmental defects and down-regulates microtubule (MT) genes during zebrafish embryogenesis, but whether the down-regulation of microtubule genes mediates Cu stress induced retinal developmental defects is still unknown. In this study, we found that microtubule gene stmn4 exhibited obviously reduced expression in the retina of Cu overload embryos. Furthermore, stmn4 deficiency (stmn4^-/-) resulted in retinal defects similar to those seen in Cu overload embryos, while overexpression of stmn4 effectively rescued retinal defects and cell apoptosis occurred in the Cu overload embryos and larvae. Meanwhile, stmn4 deficient embryos and larvae exhibited reduced mature retinal cells, the down-regulated expression of microtubules and cell cycle-related genes, and the mitotic cell cycle arrests of the retinal cells, which subsequently tended to apoptosis independent on p53. The results of this study demonstrate that Cu stress might lead to retinal developmental defects via down-regulating expression of microtubule gene stmn4, and stmn4 deficiency leads to impaired cell cycle and the accumulation of retinal progenitor cells (RPCs) and their subsequent apoptosis. The study provides a certain referee for copper overload in regulating the retinal development in fish.