Differentiation of lens fiber cells involves a complex interplay of signals from growth factors together with tightly regulated gene expression via transcriptional and post-transcriptional regulators. Various studies have demonstrated that RNA-binding proteins, functioning in ribonucleoprotein granules, have important roles in regulating post-transcriptional expression during lens development. In this study, we examined the expression and localization of two members of the BTG/TOB family of RNA-binding proteins, TOB1 and TOB2, in the developing lens and examined the phenotype of mice that lack Tob1. By RT-PCR, both Tob1 and Tob2 mRNA were detected in epithelial and fiber cells of embryonic and postnatal murine lenses. In situ hybridization showed Tob1 and Tob2 mRNA were most intensely expressed in the early differentiating fibers, with weaker expression in anterior epithelial cells, and both appeared to be downregulated in the germinative zone of E15.5 lenses. TOB1 protein was detected from E11.5 to E16.5 and was predominantly detected in large cytoplasmic puncta in early differentiating fiber cells, often co-localizing with the P-body marker, DCP2. Occasional nuclear puncta were also observed. By contrast, TOB2 was detected in a series of interconnected peri-nuclear granules, in later differentiating fiber cells of the inner cortex. TOB2 did not appear to co-localize with DCP2 but did partially co-localize with an early stress granule marker (EIF3B). These data suggest that TOB1 and TOB2 are involved with different aspects of the mRNA processing cycle in lens fiber cells. In vitro experiments using rat lens epithelial explants treated with or without a fiber differentiating dose of FGF2 showed that both TOB1 and TOB2 were up-regulated during FGF-induced differentiation. In differentiating explants, TOB1 also co-localized with DCP2 in large cytoplasmic granules. Analyses of Tob1^-/- mice revealed relatively normal lens morphology but a subtle defect in cell cycle arrest of some cells at the equator and in the lens fiber mass of E13.5 embryos. Overall, these findings suggest that TOB proteins play distinct regulatory roles in RNA processing during lens fiber differentiation.

晶状体纤维细胞的分化涉及来自生长因子的信号与通过转录和转录后调节因子严格调节的基因表达的复杂相互作用。各种研究表明，在核糖核蛋白颗粒中发挥作用的RNA结合蛋白在调节晶状体发育过程中的转录后表达方面具有重要作用。在这项研究中，我们检查了 RNA 结合蛋白 BTG/TOB 家族的两个成员 TOB1 和 TOB2 在发育中的晶状体中的表达和定位，并检查了缺乏 Tob1 的小鼠的表型。通过 RT-PCR，在胚胎和出生后小鼠晶状体的上皮细胞和纤维细胞中检测到Tob1和Tob2 mRNA。原位杂交显示Tob1和Tob2 mRNA在早期分化纤维中表达最强烈，在前上皮细胞中表达较弱，并且两者在E15.5晶状体的萌发区中似乎表达下调。TOB1 蛋白在 E11.5 至 E16.5 期间检测到，主要在早期分化纤维细胞的大细胞质斑点中检测到，通常与 P 体标记 DCP2 共定位。偶尔也观察到核点。相比之下，TOB2 在一系列相互连接的核周颗粒以及后来分化的内皮层纤维细胞中被检测到。TOB2 似乎并未与 DCP2 共定位，但确实与早期应激颗粒标记 (EIF3B) 部分共定位。这些数据表明 TOB1 和 TOB2 参与晶状体纤维细胞中 mRNA 加工周期的不同方面。使用经或未经纤维分化剂量的 FGF2 处理的大鼠晶状体上皮外植体进行的体外实验表明，TOB1 和 TOB2 在 FGF 诱导的分化过程中均上调。在分化外植体时，TOB1 还与 DCP2 共定位于大细胞质颗粒中。对Tob1 ^-/-小鼠的分析显示，晶状体形态相对正常，但赤道处的一些细胞和 E13.5 胚胎的晶状体纤维团中的细胞周期停滞存在细微缺陷。总的来说，这些发现表明 TOB 蛋白在晶状体纤维分化过程中的 RNA 加工中发挥着独特的调节作用。