Pax6 Regulates Gene Expression in the Vertebrate Lens through miR-204

Abstract

During development, tissue-specific transcription factors regulate both protein-coding and non-coding genes to control differentiation. Recent studies have established a dual role for the transcription factor Pax6 as both an activator and repressor of gene expression in the eye, central nervous system, and pancreas. However, the molecular mechanism underlying the inhibitory activity of Pax6 is not fully understood. Here, we reveal that Trpm3 and the intronic microRNA gene miR-204 are co-regulated by Pax6 during eye development. miR-204 is probably the best known microRNA to function as a negative modulator of gene expression during eye development in vertebrates. Analysis of genes altered in mouse Pax6 mutants during lens development revealed significant over-representation of miR-204 targets among the genes up-regulated in the Pax6 mutant lens. A number of new targets of miR-204 were revealed, among them Sox11, a member of the SoxC family of pro-neuronal transcription factors, and an important regulator of eye development. Expression of Trpm/miR-204 and a few of its targets are also Pax6-dependent in medaka fish eyes. Collectively, this study identifies a novel evolutionarily conserved mechanism by which Pax6 controls the down-regulation of multiple genes through direct up-regulation of miR-204.

microRNAs and inherited retinal dystrophies

“…Mutation in miR-204 as the cause of the disease is consistent with the observation that miR-204 is preferentially expressed in multiple ocular tissues, including the retina, RPE, ciliary body, and lens (11)(12)(13). In addition, previous in vitro and in vivo studies in medaka fish suggested its important roles in the development and function of the retina (13,14), lens (13)(14)(15), and RPE (12). Knockdown of miR-204 in fish resulted in microphthalmia, abnormal lens formation, altered dorso-ventral (D-V) patterning of the retina, and coloboma (13).…”

MiR-204 is responsible for inherited retinal dystrophy associated with ocular coloboma

“…Despite its pervasive role in many aspects of ocular differentiation, miR-204 has not previously been reported to be significantly expressed in photoreceptor cells (3,11,25,26,28) or to have an effect on photoreceptor function. Here, we provide for the first time to our knowledge RNA ISH data for miR-204 in the human retina, which also reveals its expression in photoreceptors (Fig.…”

“…MiR-204 has discrete and dynamic expression domains in the eye throughout development, being expressed in the RPE, neural retina, lens, and ciliary body in fish, mouse, and human (3,4,10,11,(26)(27)(28). This miRNA has a closely related paralog in mammals; namely, miR-211, with which it shares the same seed sequence and very likely a similar set of targets and tissue expression pattern, although, in the latter respect, precise information is still lacking.…”

“…S5) supports the hypothesis that miR-204 could exert its role on photoreceptor function through a cell autonomous mechanism. However, a contribution to a noncell autonomous action mediated by the strong expression of miR-204 in the RPE is also likely (3,11,28). There are many examples of RPE-specific genes that play essential roles in photoreceptor function and whose mutations have a pathogenic role in inherited retinal dystrophies (32,33).…”

“…The n.37C > T mutation identified in the microRNA MIR204 (reference sequence NR_029621) was an excellent candidate for further study. MiR-204 is preferentially expressed in the eye, and several studies have determined its role in eye development (3,(9)(10)(11). Evidence of the critical function of miR-204 in eye development strongly suggests a pathogenic role for the mutation identified in this family.…”