Study of the role of miR-204 in photoreceptor development

Bhat, Rajeshwari Subray (2016). Study of the role of miR-204 in photoreceptor development. PhD thesis The Open University.

DOI: https://doi.org/10.21954/ou.ro.0000bc4f

Abstract

MicroRNAs (miRNAs), a class of small non-coding RNAs with a basic role in post-transcriptional regulation of gene expression, are emerging as key players in the control of fundamental biological processes during the differentiation of many tissues and organs. The goal of my thesis is to shed light on the role of specific miRNAs in regulating the retina development especially photoreceptors. In particular, I focused on miR-204, one of the miRNAs our laboratory is mostly focusing on, and whose role in multiple aspects of eye development has been elucidated in the past few years from our lab and other groups. I dissected the role of miR-204 in photoreceptor cell differentiation and maturation by means of in vivo (Oryzias latipes i.e. medaka fish) and in vitro (661W cell line) systems. I found that, the gain-of-function of miR-204 led to an earlier exit of photoreceptor precursors from cell cycle and to a concomitant earlier ‘fate determination’, which in turn resulted in earlier onset of photoreceptor cell formation. Interestingly, I found that the induction of photoreceptor differentiation in 661W cells was accompanied by an upregulation of miR-204 levels, supporting the hypothesis that miR-204 may play a role in cell cycle and/or cell fate determination. To better investigate on this aspect, I demonstrated that Cyclin D1 (Ccnd1) and Cd44 play a key role in miR-204-induced photoreceptor differentiation, as assessed by both in vivo and in vitro experiments. Moreover, I generated two medaka transgenic lines exclusively overexpressing miR-204 either in cone or in rod photoreceptors (TαC:GFP:miR-204 and Rho:TK:GFP:miR-204 respectively). Interestingly, I observed that cones and rods attained their maturation earlier respectively in the TαC:GFP:miR-204 and Rho:TK:GFP:miR-204 lines in comparison with controls. Overall this study strongly suggests a prominent role of miR-204 in photoreceptor differentiation and maturation and sheds further light on the contribution of this miRNA to ocular development and function.