Gofflot F, Hall M, Morriss-Kay G M
Department of Human Anatomy, University of Oxford, United Kingdom.
Dev Dyn. 1997 Dec;210(4):431-45. doi: 10.1002/(SICI)1097-0177(199712)210:4<431::AID-AJA7>3.0.CO;2-H.
Posterior neuropore (PNP) closure coincides with the end of gastrulation, marking the end of primary neurulation and primary body axis formation. Secondary neurulation and axis formation involve differentiation of the tail bud mesenchyme. Genetic control of the primary-secondary transition is not understood. We report a detailed analysis of gene expression in the caudal region of day 10 mouse embryos during primary neuropore closure. Embryos were collected at the 27-32 somite stage, fixed, processed for whole mount in situ hybridisation, and subsequently sectioned for a more detailed analysis. Genes selected for study include those involved in the key events of gastrulation and neurulation at earlier stages and more cranial levels. Patterns of expression within the tail bud, neural plate, recently closed neural tube, notochord, hindgut, mesoderm, and surface ectoderm are illustrated and described. Specifically, we report continuity of expression of the genes Wnt5a, Wnt5b, Evx1, Fgf8, RARgamma, Brachyury, and Hoxb1 from primitive streak and node into subpopulations of the tail bud and caudal axial structures. Within the caudal notochord, developing floorplate, and hindgut, HNF3alpha, HNF3beta, Shh, and Brachyury expression domains correlate directly with known genetic roles and predicted tissue interdependence during induction and differentiation of these structures. The patterns of expression of Wnt5a, Hoxb1, Brachyury, RARgamma, and Evx1, together with observations on proliferation, reveal that the caudal mesoderm is organised at a molecular level into distinct domains delineated by longitudinal and transverse borders before histological differentiation. Expression of Wnt5a in the ventral ectodermal ridge supports previous evidence that this structure is involved in epithelial-mesenchymal interaction. These results provide a foundation for understanding the mechanisms facilitating transition from primary to secondary body axis formation, as well as the factors involved in defective spinal neurulation.
后神经孔（PNP）闭合与原肠胚形成结束同时发生，标志着初级神经胚形成和初级体轴形成的结束。次级神经胚形成和轴形成涉及尾芽间充质的分化。初级 - 次级转变的遗传控制尚不清楚。我们报告了对第10天小鼠胚胎在初级神经孔闭合期间尾部区域基因表达的详细分析。在27 - 32体节阶段收集胚胎，固定，进行全胚胎原位杂交处理，随后切片进行更详细的分析。选择用于研究的基因包括那些在早期和更颅侧水平参与原肠胚形成和神经胚形成关键事件的基因。展示并描述了尾芽、神经板、最近闭合的神经管、脊索、后肠、中胚层和表面外胚层内的表达模式。具体而言，我们报告了基因Wnt5a、Wnt5b、Evx1、Fgf8、RARγ、Brachyury和Hoxb1从原条和节点到尾芽亚群和尾轴结构的表达连续性。在尾脊索、发育中的底板和后肠内，HNF3α、HNF3β、Shh和Brachyury的表达域与这些结构诱导和分化过程中已知的遗传作用以及预测的组织相互依赖性直接相关。Wnt5a、Hoxb1、Brachyury、RARγ和Evx1的表达模式，连同对增殖的观察结果表明，在组织学分化之前，尾中胚层在分子水平上被组织成由纵向和横向边界界定的不同区域。Wnt5a在腹侧外胚层嵴中的表达支持了先前的证据，即该结构参与上皮 - 间充质相互作用。这些结果为理解促进从初级到次级体轴形成转变的机制以及参与脊柱神经胚形成缺陷的因素提供了基础。
