Redundant type II cadherins define neuroepithelial cell states for cytoarchitectonic robustness

Individual cell shape and integrity must precisely be orchestrated during morphogenesis. Here, we determine function of type II cadherins, Cdh6, Cdh8, and Cdh11, whose expression combinatorially demarcates the mouse neural plate/tube. While CRISPR/Cas9-based single type II cadherin mutants show no obvious phenotype, Cdh6/8 double knockout mice develop intermingled forebrain/midbrain compartments as these two cadherins’ expression opposes at the nascent boundary. Cdh6/8/11 triple, Cdh6/8 double or Cdh8/11 double knockout mice further cause exencephaly just within the cranial region where mutated cadherins’ expression merges. In the Cdh8/11 double knockout midbrain, we observe less-constricted apical actin meshwork, ventrally-directed spreading, and occasional hyperproliferation among dorsal neuroepithelial cells as origins for exencephaly. These results provide rigid evidence that, by conferring distinct adhesive codes to each cell, redundant type II cadherins serve essential and shared roles in compartmentalization and neurulation, both of which proceed under the robust control of the number, positioning, constriction, and fluidity of neuroepithelial cells. The mRNA profiles of the forebrain and midbrain tissues from type II cadherin double and triple knockout mice (E9.5) were generated using the Illumina HiSeq platforms. The numbers of each replicate are three to six, and the total number of samples is 32.

在形态发生过程中，单个细胞的形态与完整性必须得到精准的协调调控。本研究解析了II型钙粘蛋白（type II cadherins）Cdh6、Cdh8与Cdh11的功能，三者的组合表达可界定小鼠神经板/神经管的区域边界。尽管基于CRISPR/Cas9的单-II型钙粘蛋白突变体未表现出明显表型，但Cdh6/8双敲除小鼠的前脑/中脑隔间出现混合现象，原因在于这两种钙粘蛋白在新生边界处的表达相互拮抗。Cdh6/8/11三敲除、Cdh6/8双敲除或Cdh8/11双敲除小鼠则会在突变钙粘蛋白表达重叠的颅区引发露脑畸形（exencephaly）。在Cdh8/11双敲除小鼠的中脑内，我们观察到背侧神经上皮细胞的顶侧肌动蛋白网架收缩不足、向腹侧扩散，以及偶发的过度增殖，这些均为露脑畸形的发生起源。本研究结果提供了确凿证据：通过为每个细胞赋予独特的黏附编码，功能冗余的II型钙粘蛋白在区域化与神经管发生过程中发挥不可或缺的共同作用；而这两个过程均依赖于神经上皮细胞的数量、定位、收缩性与流动性的严格调控。本研究采用Illumina HiSeq测序平台，获取了E9.5天II型钙粘蛋白双敲除与三敲除小鼠的前脑、中脑组织的mRNA表达谱。每组生物学重复的样本量为3至6例，总样本数共计32份。