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Abstract：
The zebrafish pronephros provides a conserved model to study kidney development, in particular to delineate the poorly understood processes of how nephron segment pattern and cell type choice are established. Zebrafish nephrons are divided into distinct epithelial regions that include a series of proximal and distal tubule segments, which are comprised of intercalated transporting epithelial cells and multiciliated cells (MCC). Previous studies have shown that retinoic acid (RA) regionalizes the renal progenitor field into proximal and distal domains and that Notch signaling later represses MCC differentiation, but further understanding of these pathways has remained unknown. The transcription factor mecom (mds1/evi1 complex) is broadly expressed in renal progenitors, and then subsequently marks the distal tubule. Here, we show that mecom is necessary to form the distal tubule and to restrict both proximal tubule formation and MCC fate choice. We found that mecom and RA have opposing roles in patterning discrete proximal and distal segments. Further, we discovered that RA is required for MCC formation, and that one mechanism by which RA promotes MCC fate choice is to inhibit mecom. Next, we determined the epistatic relationship between mecom and Notch signaling, which limits MCC fate choice by lateral inhibition. Abrogation of Notch signaling with the γ-secretase inhibitor DAPT revealed that Notch and mecom did not have additive effects in blocking MCC formation, suggesting that they function in the same pathway. Ectopic expression of the Notch signaling effector, Notch intracellular domain (NICD), rescued the expansion of MCCs in mecom morphants, indicating that mecom acts upstream to induce Notch signaling. These findings suggest a model in which mecom and RA arbitrate proximodistal segment domains, while MCC fate is modulated by a complex interplay in which RA inhibition of mecom, and mecom promotion of Notch, titrates MCC number. Taken together, our studies have revealed several essential and novel mechanisms that control pronephros development in the zebrafish.
摘要：
斑马鱼pronephros提供了一个保守的模型来研究肾脏发育，特别是描述如何建立肾单位节段模式和细胞类型选择的知之甚少的过程。斑马鱼肾单位分为不同的上皮区域，包括一系列近端和远端小管段，其由插入的转运上皮细胞和多纤毛细胞(MCC)组成。先前的研究表明，视黄酸（RA）将肾脏祖细胞区域划分为近端和远端结构域，而Notch信号后来抑制了MCC分化，但是对这些途径的进一步理解仍然未知。转录因子mecom（mds1/evi1复合物）在肾祖细胞中广泛表达，然后标记远端小管。这里,我们表明，mecom是形成远端小管并限制近端小管形成和MCC命运选择的必要条件。我们发现mecom和RA在图案化离散的近端和远端段中具有相反的作用。Further,我们发现RA是MCC形成所必需的，RA促进MCC命运选择的一种机制是抑制mecom。接下来,我们确定了mecom和Notch信号之间的上位关系，通过侧向抑制限制了MCC命运的选择。γ-分泌酶抑制剂DAPT对Notch信号的消除表明，Notch和mecom在阻断MCC形成方面没有累加作用，表明它们在同一途径中发挥作用。Notch信号效应子的异位表达，Notch胞内域(NICD),拯救了mecom形态中MCC的扩张，表明mecom在上游起作用以诱导Notch信号传导。这些发现表明了一个模型，在该模型中，mecom和RA对近端远端节段域进行仲裁，而MCC的命运是由复杂的相互作用来调节的，其中RA对Mecom的抑制，以及Notch的推广，滴定MCC编号。一起来看,我们的研究揭示了控制斑马鱼pronephros发育的几个基本和新颖的机制。
