Segmentation in Vertebrates

在脊椎动物的早期发育过程中，中胚层在规范和建立体型方面起着核心作用。我们主要集中在三个方面来研究中胚层的调控机制：1)中胚层沿背腹方向的细分：体轴；2)侧板的二元性决定；3)体节沿体轴方向的分割。1)中胚层分为背侧(体节)区和腹侧(侧板)区，我们发现不同浓度的BMP4(一种属于TGFb家族的信号分子)决定了这些不同的中胚层类型。2)侧板中胚层被细分为两个不同的层，即躯体和背侧胸膜。前者贡献给皮肤下面的外部身体，后者贡献给围绕着“肠道器官”的内部中胚层。我们发现，体细胞是由其覆盖的外胚层决定的，而内脏细胞则受相邻的内胚层的影响。3)大多数前后重复的结构，如背骨和肋骨，都归因于发育早期的体节分裂。一对体节沿前后轴线依次从未分割的体节上夹断下来，从而自头到尾进行分割。我们发现，在下一个分割部位，相邻细胞之间发生了微诱导事件，导致了形态边界。特别是，位于边界后方的细胞在指示它们的前部细胞形成边界方面起着主要作用。关于中胚层细分的新知识将为理解一个简单的结构如何在早期发育过程中产生更复杂的组织打开一条途径。

During early development in vertebrates, the mesoderm plays a central role in specification and: establishment of the body patterning. We aimed at understanding the mechanisms by which the mesoderm specification is regulated by mainly focusing on three major topics : 1) Subdivision of the mesoderm along the dorso-ventral: axis of the body, 2) Binary decision of the lateral plate, 3) Somite segmentation along the antero-posterior axis of the body.1) The mesoderm is subdivided into the dorsal (somite) and ventral (lateral plate) regions, We found that different concentrations of BMP4, a signalling molecule belonging to TGFb family, determine these distinct mesodermal types.2) The lateral plate mesoderm is subdivided into two distinct layers, somatopleure and splanchnopleure., The former one contributes to the outer body underlying the skin and the latter one to the inner mesoderm surrounding the"gut organ. We found that the somatopleure is specified by its overlying; ectoderm whereas the splanchnopleure is influenced by the adjacent endoderm.3) Most of the antero-posteriorly reiterated structures such as back bones and ribs are attributed to the somite segmentation at earlier stages in development. A pair of somites pinches off from the unsegmented somite successively along the antero-posterior axis, thus the segmentation proceeds from head to tail. We found that at the next segmentation site a microinductive event between the adjacent cells takes place leading, to a morphological boundary. Particularly, the posteriorly positioned cells to the boundary play primary roles in instructing their anterior cells to make a boundary. We designated this activity as a "segmenter".Our novel knowledge concerning the mesodermal subdivision will open a way to understand how a simple structure gives rise to more complex organization during early development.