Sherwood D R, McClay D R
Developmental, Cell and Molecular Biology Group, Duke University, Durham, NC 27708, USA.
Development. 1997 Sep;124(17):3363-74. doi: 10.1242/dev.124.17.3363.
The specifications of cell types and germ-layers that arise from the vegetal plate of the sea urchin embryo are thought to be regulated by cell-cell interactions, the molecular basis of which are unknown. The Notch intercellular signaling pathway mediates the specification of numerous cell fates in both invertebrate and vertebrate development. To gain insights into mechanisms underlying the diversification of vegetal plate cell types, we have identified and made antibodies to a sea urchin homolog of Notch (LvNotch). We show that in the early blastula embryo, LvNotch is absent from the vegetal pole and concentrated in basolateral membranes of cells in the animal half of the embryo. However, in the mesenchyme blastula embryo LvNotch shifts strikingly in subcellular localization into a ring of cells which surround the central vegetal plate. This ring of LvNotch delineates a boundary between the presumptive secondary mesoderm and presumptive endoderm, and has an asymmetric bias towards the dorsal side of the vegetal plate. Experimental perturbations and quantitative analysis of LvNotch expression demonstrate that the mesenchyme blastula vegetal plate contains both animal/vegetal and dorsoventral molecular organization even before this territory invaginates to form the archenteron. Furthermore, these experiments suggest roles for the Notch pathway in secondary mesoderm and endoderm lineage segregation, and in the establishment of dorsoventral polarity in the endoderm. Finally, the specific and differential subcellular expression of LvNotch in apical and basolateral membrane domains provides compelling evidence that changes in membrane domain localization of LvNotch are an important aspect of Notch receptor function.
海胆胚胎植物极板产生的细胞类型和胚层的特化被认为是由细胞间相互作用调控的，但其分子基础尚不清楚。Notch细胞间信号通路在无脊椎动物和脊椎动物发育过程中介导了众多细胞命运的特化。为了深入了解植物极板细胞类型多样化的潜在机制，我们鉴定并制备了针对海胆Notch同源物（LvNotch）的抗体。我们发现，在早期囊胚胚胎中，植物极没有LvNotch，它集中在胚胎动物半侧细胞的基底外侧膜中。然而，在间充质囊胚胚胎中，LvNotch的亚细胞定位显著转移到围绕中央植物极板的一圈细胞中。这圈LvNotch划定了假定的次生中胚层和假定的内胚层之间的边界，并且对植物极板的背侧具有不对称偏向。对LvNotch表达的实验性扰动和定量分析表明，间充质囊胚植物极板甚至在该区域内陷形成原肠之前就已经包含了动物/植物和背腹分子组织。此外，这些实验表明Notch通路在次生中胚层和内胚层谱系分离以及内胚层背腹极性建立中的作用。最后，LvNotch在顶端和基底外侧膜结构域中的特异性和差异性亚细胞表达提供了令人信服的证据，表明LvNotch膜结构域定位的变化是Notch受体功能的一个重要方面。
