The Mechanism of the binary dicision of the lateral plate mesoderm

包括脊椎动物在内的大多数三倍体动物都有一个体腔腔，将身体的外部和内部组件分开。体腔由来自侧板区的两种不同的组织成分--躯体和内脏--构成。因此，在侧板的早期规范过程中，通过二元判决来构建体腔。在这份报告中，我们研究了这种二元决定的分子机制。我们首先证明了侧板分裂成两个细胞片的过程是以前后顺序进行的，这一过程与体细胞分裂的过程不协调。通过一系列的胚胎学操作，我们发现年轻的内脏中胚层仍然有能力重新分化为体细胞中胚层，而覆盖在侧板上的外胚层足以进行这种重定向。侧外胚层也是维持中胚层的体细胞特征所必需的。因此，外胚层在侧板的早期分裂中至少起着两个作用：体细胞中胚层的具体化和维持。我们还表明，后一种相互作用是由定位于外侧外胚层的BMP分子介导的。还考虑了体腔形成的进化方面。

Most triploblastic animals including vertebrates have a coelomic cavity that separates the outer and inner components of the body. The coelom is lined by two different tissue components, somatopleure and splanchnopleure, which are derived from the lateral plate region. Thus, the coelom is constructed by the binary decision during early specification of the lateral plate. In this report we studied the molecular mechanisms of this binary decision. We first demonstrate that the splitting of the lateral plate into the two cell sheets progresses in an antero posterior order and this progression is not coordinated with that of the somitic segmentation. By a series of embryological manipulations we found that a young splanchnic mesoderm is still competent to be respecified to the somatic mesoderm, and the ectoderm overlying the lateral plate is sufficient for this redirection. The lateral ectoderm is also required for maintenance of the somatic character of the mesoderm. Thus, the ectoderm plays at least two roles in the early subdivision of the lateral plate : specification and maintenance of the somatic mesoderm. We also show that the latter interactions are mediated by BMP molecules that are localized in the lateral ectoderm. Evolutionary aspects of the coelom formation are also considered.