In many mammals, the eyelids migrate over the eye and fuse during embryogenesis to protect the cornea from damage during birth and early life. Loss-of-function mutations affecting the epidermal growth factor receptor (EGFR) signaling pathway cause an eyes-open-at-birth (EOB) phenotype in rodents. We identified an insertional mutation in Spinster homolog 2 (Spns2) in a strain of transgenic rats exhibiting the EOB phenotype. Spns2, a sphingosine 1-phosphate (S1P) transporter that releases S1P from cells, was enriched at the tip of developing eyelids in wild-type rat embryos. Spns2 expression or treatment with S1P or any one of several EGFR ligands rescued the EOB Spns2 mutant phenotype in vivo and in tissue explants in vitro and rescued the formation of stress fibers in primary keratinocytes from mutants. S1P signaled through the receptors S1PR1, S1PR2, and S1PR3 to activate extracellular signal-regulated kinase (ERK) and EGFR-dependent mitogen-activated protein kinase kinase kinase 1 (MEKK1)-c-Jun signaling. S1P also induced the nuclear translocation of the transcription factor MAL in a manner dependent on EGFR signaling. MAL and c-Jun stimulated the expression of the microRNAs miR-21 and miR-222, both of which target the metalloprotease inhibitor TIMP3, thus promoting metalloprotease activity. The metalloproteases ADAM10 and ADAM17 stimulated EGFR signaling by cleaving a membrane-anchored form of EGF to release the ligand. Our results outline a network by which S1P transactivates EGFR signaling through a complex mechanism involving feedback between several intra- and extracellular molecules to promote eyelid fusion in the developing rat.

中文翻译：

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1-磷酸鞘氨醇通过刺激EGFR信号传导刺激发育中大鼠的眼睑闭合。

在许多哺乳动物中，眼睑在眼球上迁移并在胚胎发生过程中融合在一起，以保护角膜免受出生和早期生命的损害。影响表皮生长因子受体（EGFR）信号传导途径的功能丧失突变会导致啮齿动物睁眼睁眼（EOB）表型。我们在展示EOB表型的转基因大鼠品系中发现了Spinster同源物2（Spns2）中的插入突变。Spns2是一种从神经细胞中释放S1P的鞘氨醇1-磷酸（S1P）转运蛋白，在野生型大鼠胚胎的眼睑发育尖端富集。Spns2的表达或用S1P或几种EGFR配体中的任何一种处理在体内和组织外植体中拯救了EOB Spns2突变体表型，并从突变体中拯救了原代角质形成细胞中应力纤维的形成。S1P通过受体S1PR1发出信号，S1PR2和S1PR3激活细胞外信号调节激酶（ERK）和EGFR依赖的有丝分裂原激活的蛋白激酶激酶激酶1（MEKK1）-c-Jun信号传导。S1P还以依赖于EGFR信号传导的方式诱导了转录因子MAL的核易位。MAL和c-Jun刺激了microRNA miR-21和miR-222的表达，两者均靶向金属蛋白酶抑制剂TIMP3，从而促进了金属蛋白酶的活性。金属蛋白酶ADAM10和ADAM17通过切割膜锚定的EGF形式释放配体，从而刺激了EGFR信号传导。我们的研究结果概述了一个网络，S1P通过一个复杂的机制使S1P激活EGFR信号转导，该机制涉及多个细胞内和细胞外分子之间的反馈，以促进发育中大鼠的眼睑融合。S1PR3和S1PR3激活细胞外信号调节激酶（ERK）和EGFR依赖的有丝分裂原激活的蛋白激酶激酶激酶1（MEKK1）-c-Jun信号传导。S1P还以依赖于EGFR信号传导的方式诱导了转录因子MAL的核易位。MAL和c-Jun刺激了microRNA miR-21和miR-222的表达，两者均靶向金属蛋白酶抑制剂TIMP3，从而促进了金属蛋白酶的活性。金属蛋白酶ADAM10和ADAM17通过切割膜锚定的EGF形式释放配体，从而刺激了EGFR信号传导。我们的研究结果概述了一个网络，S1P通过一个复杂的机制使S1P激活EGFR信号转导，该机制涉及多个细胞内和细胞外分子之间的反馈，以促进发育中大鼠的眼睑融合。S1PR3和S1PR3激活细胞外信号调节激酶（ERK）和EGFR依赖的有丝分裂原激活的蛋白激酶激酶激酶1（MEKK1）-c-Jun信号传导。S1P还以依赖于EGFR信号传导的方式诱导了转录因子MAL的核易位。MAL和c-Jun刺激了microRNA miR-21和miR-222的表达，两者均靶向金属蛋白酶抑制剂TIMP3，从而促进了金属蛋白酶的活性。金属蛋白酶ADAM10和ADAM17通过切割膜锚定的EGF形式释放配体，从而刺激了EGFR信号传导。我们的研究结果概述了一个网络，S1P通过一个复杂的机制使S1P激活EGFR信号转导，该机制涉及多个细胞内和细胞外分子之间的反馈，以促进发育中大鼠的眼睑融合。