Data from: The RNA-binding protein Celf1 post-transcriptionally regulates p27Kip1 and Dnase2b to control fiber cell nuclear degradation in lens development

Opacification of the ocular lens, termed cataract, is a common cause of blindness. To become transparent, lens fiber cells undergo degradation of their organelles, including their nuclei, presenting a fundamental question: does signaling/transcription sufficiently explain differentiation of cells progressing toward compromised transcriptional potential? We report that a conserved RNA-binding protein Celf1 post-transcriptionally controls key genes to regulate lens fiber cell differentiation. Celf1-targeted knockout mice and celf1-knockdown zebrafish and Xenopus morphants have severe eye defects/cataract. Celf1 spatiotemporally down-regulates the cyclin-dependent kinase (Cdk) inhibitor p27Kip1 by interacting with its 5’ UTR and mediating translation inhibition. Celf1 deficiency causes ectopic up-regulation of p21Cip1. Further, Celf1 directly binds to the mRNA of the nuclease Dnase2b to maintain its high levels. Together these events are necessary for Cdk1-mediated lamin A/C phosphorylation to initiate nuclear envelope breakdown and DNA degradation in fiber cells. Moreover, Celf1 controls alternative splicing of the membrane-organization factor beta-spectrin and regulates F-actin-crosslinking factor Actn2 mRNA levels, thereby controlling fiber cell morphology. Thus, we illustrate new Celf1-regulated molecular mechanisms in lens development, suggesting that post-transcriptional regulatory RNA-binding proteins have evolved conserved functions to control vertebrate oculogenesis.

眼部晶状体（ocular lens）混浊即白内障（cataract），是引发失明的常见病因。为实现眼晶状体的透明化，晶状体纤维细胞会降解包括细胞核在内的各类细胞器，这引出了一个核心科学问题：信号转导与转录调控是否足以解释细胞向转录潜能受损方向分化的过程？本研究发现，保守型RNA结合蛋白（RNA-binding protein）Celf1通过转录后调控关键基因，参与调控晶状体纤维细胞的分化。Celf1基因敲除小鼠以及celf1基因敲低的斑马鱼和爪蟾（Xenopus）morphant胚胎均出现严重眼部缺陷或白内障。Celf1可通过结合细胞周期蛋白依赖性激酶抑制剂（cyclin-dependent kinase (Cdk) inhibitor）p27Kip1的5'非翻译区（5’ UTR）并介导翻译抑制，实现对该蛋白的时空表达下调。Celf1功能缺失会导致p21Cip1出现异位上调表达。此外，Celf1可直接结合核酸酶（nuclease）Dnase2b的mRNA，以维持其表达水平。上述协同事件是细胞周期蛋白依赖性激酶1（Cdk1）介导的核纤层蛋白A/C（lamin A/C）磷酸化，进而启动纤维细胞核膜破裂与DNA降解的必要条件。此外，Celf1可调控膜组织因子β-血影蛋白（beta-spectrin）的可变剪接，并调节F-肌动蛋白交联因子Actn2的mRNA水平，进而控制晶状体纤维细胞的形态。综上，本研究阐明了Celf1在晶状体发育过程中全新的调控分子机制，提示转录后调控型RNA结合蛋白通过演化获得保守性功能，以此调控脊椎动物的眼发生（oculogenesis）过程。