Identification of an RNA binding protein Celf1 (Cugbp1) associated with lens defects and cataract

Abstract

Purpose: We recently reported mutations in the RNA granule component gene Tdrd7 to cause juvenile cataracts in human and mouse, suggesting that post-transcriptional regulators play a critical function in lens development. Here, we report the identification of a conserved lens-enriched RNA binding protein Celf1 (CUGBP, Elav-like family member 1) deficiency of which disrupts gene expression in lens development and causes severe nuclear cataracts.

Methods: iSyTE identified Celf1 as a post-transcriptional regulatory protein highly expressed in the lens. To test its ocular functions, we generated and characterized Celf1 conditional knockout (cKO) mice by performing histological analyses, scanning electron microscopy (SEM), immunofluorescence and expression microarrays. RNA immunoprecipitation (RIP) and RNA Cross-linked immunoprecipitation (CLIP)-qPCR analyses were performed to identify transcripts that directly associate with Celf1.

Results: Celf1 is expressed early in mouse lens development, from E10.5, and is progressively enriched in fiber cells. Celf1 cKO mutants exhibit severe lens defects including cataract at birth. Celf1 cKO lens initially exhibits delayed fiber cell elongation and in later stages, defective fiber cell nuclear degradation. Furthermore, SEM analysis demonstrates disruption of both cortical and nuclear fiber cell packing, leading to vacuole formation in postnatal mutant lens. Expression profiling by microarrays identified 102 differentially regulated RNAs in Celf1 cKO lens, among which, we identified several direct ligands of Celf1 by CLIP and RIP analyses. Interestingly, mRNAs for a fiber cell-enriched DNase (Dnase2b) necessary for nuclear degradation, and that for a spectrin (Spnb2), are down-regulated in Celf1 mutants and directly interact with Celf1. Celf1 expression is conserved in Zebrafish and Xenopus lens fiber cells and Celf1-knockdown in these animal models causes eye defects, suggesting its conserved function in vertebrate lens development.

Conclusions: We have identified an RNA binding protein Celf1 that is essential for vertebrate eye development. Celf1 regulates gene expression in lens fiber cell differentiation by directly binding to lens-expressed mRNAs, and is essential for degradation of fiber cell nuclei. Along with Tdrd7, these data confirm that conserved post-transcriptional regulatory networks function to control gene expression in vertebrate eye development.

Keywords: 445 cataract • 539 genetics • 497 development