The master transcription factor SOX2, mutated in anophthalmia/microphthalmia, is post-transcriptionally regulated by the conserved RNA-binding protein RBM24 in vertebrate eye development

Abstract

Mutations in the key transcription factor, SOX2, alone account for 20% of anophthalmia (no eye) and microphthalmia (small eye) birth defects in humans—yet its regulation is not well understood, especially on the post-transcription level. We report the unprecedented finding that the conserved RNA-binding motif protein, RBM24, positively controls Sox2 mRNA stability and is necessary for optimal SOX2 mRNA and protein levels in development, perturbation of which causes ocular defects, including microphthalmia and anophthalmia. RNA immunoprecipitation assay indicates that RBM24 protein interacts with Sox2 mRNA in mouse embryonic eye tissue. and electrophoretic mobility shift assay shows that RBM24 directly binds to the Sox2 mRNA 3’UTR, which is dependent on AU-rich elements (ARE) present in the Sox2 mRNA 3’UTR. Further, we demonstrate that Sox2 3’UTR AREs are necessary for RBM24-based elevation of Sox2 mRNA half-life. We find that this novel RBM24–Sox2 regulatory module is essential for early eye development in vertebrates. We show that Rbm24-targeted deletion using a constitutive CMV-driven Cre in mouse, and rbm24a-CRISPR/Cas9-targeted mutation or morpholino knockdown in zebrafish, results in Sox2 downregulation and causes the developmental defects anophthalmia or microphthalmia, similar to human SOX2-deficiency defects. We further show that Rbm24 deficiency leads to apoptotic defects in mouse ocular tissue and downregulation of eye development markers Lhx2, Pax6, Jag1, E-cadherin and gamma-crystallins. These data highlight the exquisite specificity that conserved RNA-binding proteins like RBM24 mediate in the post-transcriptional control of key transcription factors, namely, SOX2, associated with organogenesis and human developmental defects.

Rbm24 controls poly(A) tail length and translation efficiency of crystallin mRNAs in the lens via cytoplasmic polyadenylation

“…Moreover, its expression in head sensory organs, particularly in the lens, is also conserved in vertebrates (23,32). Recent studies have associated the rbm24 gene with microphthalmia and anophthalmia (33,34), highlighting its implication in vertebrate eye development. Nevertheless, the molecular and biochemical mechanisms by which it orchestrates lens development remain elusive.…”

RNA-Binding Protein Rbm24 as a Multifaceted Post-Transcriptional Regulator of Embryonic Lineage Differentiation and Cellular Homeostasis

“…At early stages of lens development, Rbm24a may participate in the post-transcriptional regulation of several genes involved in the specification of the lens placode, such as Pax6 and Sox2 . Consistently, Rbm24a deficiency results in decreased stability of Sox2 mRNA [ 39 ]. As lens fiber cell differentiation proceeds, rbm24a exhibits highly localized expression patterns [ 20 ].…”

“…Although much attention has been focused on the Rbm24 function in cardiac and skeletal muscle cell differentiation, several recent works have revealed an interesting expression profile and an important role of this protein during the development of vertebrate head sensory organs [ 20 , 35 , 36 , 39 , 72 ]. In particular, it has been shown that Rbm24 is required for lens fiber cell terminal differentiation in zebrafish and in mice, providing further evidence for an essential regulatory role mediated by RBPs in vertebrate lens development.…”

Modeling ocular lens disease in Xenopus

“…Understanding the involvement of these genes in cataract can be achieved by constructing and characterizing new animal models inactivated for these genes. Indeed, the bioinformatics resource tool iSyTE has predicted several promising candidates that need to be validated in animal models . The cost‐effective pipeline of cataract investigation in Xenopus that we describe here would help to uncover the genetic basis of these rare genetic cataracts as well as to identify/validate new cataract‐linked genes.…”