The Molecular Anatomy of Mammalian Upper Lip and Primary Palate Fusion at Single Cell Resolution

The mammalian lip/primary palate form when coordinated growth and morphogenesis bring the nasal and maxillary processes into contact, the epithelia co-mingle, remodel and clear from the fusion site to allow mesenchyme continuity. Although several genes required for fusion have been identified, an integrated molecular and cellular description of the overall process is lacking. Here we employ single cell RNA sequencing of the developing mouse face to identify ectodermal, mesenchymal, and endothelial populations associated with patterning and fusion of the facial prominences. This analysis indicated that key cell populations at the fusion site exist within the periderm, basal epithelial cells and adjacent mesenchyme. Overall, these data provide a comprehensive high-resolution description of the various cell populations participating in fusion of the lip/primary palate as well as formation of the nasolacrimal groove, and they furnish a powerful resource for those investigating the molecular genetics of facial development and facial clefting that can be mined for critical mechanistic information concerning this prevalent human birth defect. Single cell RNA sequencing were performed on microdissted regions of the upper face where the nasal and maxillary prominences are juxtaposed, including the lambdoid junction, the nasolacrimal groove, and the nasal fin, from E11.5 Wild-type C57BL/6J and E11.5 Crect; ROSA26-lacZ embryos. We obtined about 8000 cells for the C57BL/6J dataset (C57LJ), and about 7000 cells for the Crect; ROSA26-lacZ dataset (CrectLJ). Cells were sequenced to a depth of about 100,000 reads per cell.哺乳动物唇部/原发腭的形成，依赖于协调生长与形态发生过程使鼻突与上颌突相互接触，随后上皮细胞发生混合、重塑并从融合位点清除，从而允许间充质组织实现连续性连接。尽管目前已鉴定出若干参与该融合过程的必需基因，但学界仍缺乏对这一整体过程的整合性分子与细胞层面描述。本研究针对发育中小鼠面部开展单细胞RNA测序（single cell RNA sequencing），成功鉴定出与面部突起模式构建及融合相关的外胚层、间充质与内皮细胞群。分析结果显示，融合位点的关键细胞群分布于周皮、基底上皮细胞以及邻近间充质中。总体而言，本研究数据全面且高分辨率地刻画了参与唇部/原发腭融合以及鼻泪沟形成的各类细胞群；同时为研究面部发育与面部裂隙畸形的分子遗传学提供了极具价值的研究资源，可从中挖掘与这一高发人类出生缺陷相关的关键机制信息。本研究对E11.5天野生型C57BL/6J小鼠以及E11.5天Crect; ROSA26-lacZ胚胎的上面部微解剖区域进行了单细胞RNA测序，所涉区域包括鼻突与上颌突并置处的λ形交界区、鼻泪沟以及鼻鳍。其中C57BL/6J数据集（后文简称C57LJ）共获取约8000个细胞，Crect; ROSA26-lacZ数据集（后文简称CrectLJ）共获取约7000个细胞，所有细胞的测序深度约为每个细胞100000条读段。