RNA-binding proteins in early eye development.

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Project Summary The eye developmental disorders microphthalmia (small eye) and anophthalmia (no eye) result due to defects in early eye development and affect 2-6 in 50,000 live human births. Microphthalmia often presents with other ocular defects such as cataract and coloboma. The etiology of these genetically heterogeneous disorders is still not clearly understood; for example, thus far 24 genes are linked to anophthalmia in humans, and even here, the pathways involved in the regulation of these genes in eye development are not well established. We have developed a novel bioinformatics approach, iSyTE (integrated Systems Tool for Eye gene discovery, http://research.bioinformatics.udel.edu/iSyTE) to predict new genes that are associated with eye developmental defects. Based on iSyTE, our recent findings – namely, that deficiency of the RNA-binding proteins (RBPs) Celf1 and Tdrd7 cause congenital cataract – have demonstrated that RBP-based post-transcriptional regulatory mechanisms are essential for lens fiber cell differentiation. However, whether RBPs are involved in critically controlling other key aspects of ocular morphogenesis, especially in the early stages of optic vesicle and lens ectoderm/placode development, is unknown. Here, we used iSyTE to identify a new RBP, the RNA-binding motif protein Rbm24, that mediates distinct gene regulatory control in both optic vesicle and lens ectoderm in early eye development. We developed a new Rbm24-targeted conditional knockout (KO) mouse model and find that both constitutive and optic vesicle-specific Rbm24-KO mice exhibit fully penetrant eye defects namely, microphthalmia and/or anophthalmia. In this proposal, we will test the overarching hypothesis that Rbm24 mediates post-transcriptional control of key genes in optic vesicle and lens ectoderm /placode in early eye development. Specifically, we will address the following goals. (Aim 1) Characterize the pathogenesis of eye defects in Rbm24 KO mice (germline KO, and conditional KOs in optic vesicle and lens) and gain insights into the molecular underpinnings of the ocular defects by analysis of the Rbm24 cKO optic vesicle and lens placode transcriptome and proteome. (Aim 2) Elucidate the direct RNA targets of Rbm24 by RNA-immunoprecipitation (RIP) and cross-linked IP (CLIP) followed by RNA-Sequencing (RNA-seq). Further, test the mechanism of Rbm24-mediated control of key regulatory genes that function in early eye development and are linked to anophthalmia/microphthalmia. Specifically, we will investigate the molecular basis of Rbm24 function in: (1) control of Sox2 in the optic vesicle and the lens, (2) control of Lhx2 in the optic vesicle, and (3) control of Pax6 in the lens. (Aim 3) Integrate and analyze these Rbm24 data within the larger context of existing eye data to derive Rbm24 downstream gene regulatory networks (GRNs) in the optic vesicle and lens. The expected overall impact of this innovative proposal is that it will fundamentally advance our mechanistic understanding of post- transcriptional control of gene expression in optic vesicle and lens ectoderm/placode and lead to identification of new targets associated with the eye disorders microphthalmia and anophthalmia.