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.

眼部晶状体混浊，即白内障（cataract），是引发失明的常见病因。为实现晶状体透明化，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：信号转导与转录过程是否足以解释细胞向转录潜能受损状态分化的机制？本研究发现，保守型RNA结合蛋白Celf1可通过转录后调控关键基因，进而调控晶状体纤维细胞的分化。经Celf1靶向敲除的小鼠，以及celf1敲低的斑马鱼与爪蟾吗啉代敲低胚胎（morphants），均出现严重眼部缺陷与白内障表型。Celf1可通过与细胞周期蛋白依赖性激酶（cyclin-dependent kinase, Cdk）抑制剂p27Kip1的5'非翻译区（5’ UTR）结合并介导翻译抑制，实现对该靶点的时空特异性下调。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Dnase2b的mRNA，以维持其高水平表达。上述事件共同作用，是Cdk1介导的核纤层蛋白A/C磷酸化启动纤维细胞核膜破裂与DNA降解的必要前提。此外，Celf1还可调控膜组织因子β-血影蛋白的可变剪接，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的全新调控分子机制，提示转录后调控型RNA结合蛋白已演化出保守功能，以调控脊椎动物的眼发生过程。