Segmentation in Vertebrates

在脊椎动物的早期发育过程中，中胚层在确定和建立身体模式方面起着核心作用。我们的目的是了解中胚层规格的调节机制，主要关注三个主要主题：1)中胚层沿身体背-腹轴的细分，2)侧板的二元决定，3)沿身体前-后轴的Somite分割。1)中胚层被细分为背侧（体突）和腹侧（侧板）区域，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)侧板中胚层可分为躯体层和植骨层两层。前者作用于皮肤下面的外层，后者作用于内脏器官周围的内中胚层。我们发现，身体愉悦是由它的覆盖指定的；外胚层，而内脏受邻近的内胚层影响。3)脊骨、肋骨等大部分前后重复结构都是发育早期的体块分割所致。一对体体沿着前后轴依次从未分节的体体中夹出，从而从头到尾进行分节。我们发现在下一个分割位点，相邻细胞之间的微诱导事件发生，导致形态边界。特别是，位于边界后方的细胞在指导其前细胞形成边界方面起主要作用。我们把这个活动称为“分段”。我们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开辟一条道路。

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.