Segmentation in Vertebrates

在脊椎动物的早期发育过程中，中胚层在身体形态的特化和建立中起着核心作用。我们的目标是通过主要关注三个主要主题来理解调节中胚层特化的机制：1）中胚层沿着背腹侧的细分：中胚层分为背侧和腹侧两部分，背侧部分为体节，腹侧部分为体节，体节沿体的前后轴沿着分布我们发现，不同浓度的BMP 4，一种属于TGF β家族的信号分子，决定了这些不同的中胚层类型。2）侧板中胚层分为两个不同的层，体侧板和脏侧板。前一种作用于皮肤下的外体，后一种作用于围绕“肠器官”的内中胚层。我们发现，体侧板由其上覆的外胚层所决定，而脏侧板则受相邻的内胚层所影响。3）大多数前后重复的结构，如脊骨和肋骨，在发育的早期阶段都归因于体节的分割。一对体节从未分节的体节上沿前后轴沿着连续夹断，从而使分节从头到尾进行。我们发现，在下一个分割网站之间的相邻细胞的微感应事件发生导致，形态边界。特别是，位于边界后方的细胞在指示其前方细胞形成边界方面起主要作用。我们将这一活动称为“分段器”。我们关于中胚层细分的新知识将为理解在早期发育过程中简单结构如何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.