Ransick A, Davidson E H
Division of Biology, California Institute of Technology, Pasadena 91125, USA.
Dev Biol. 1998 Mar 1;195(1):38-48. doi: 10.1006/dbio.1997.8814.
Single blastomeres of the sixth-cleavage veg1 and veg2 tiers of Strongylocentrotus purpuratus embryos were labeled with DiI lineage tracer, and the disposition of the progeny was followed through the blastula and gastrula stages in order to determine their respective endodermal and ectodermal contributions. In the endoderm of postgastrula embryos, veg1-derived cells constituted nearly all of the prospective hindgut and about half of the prospective midgut, while veg2-derived cells made up the prospective foregut and half the midgut. Oral veg1 clones consistently contributed more cells to endoderm than aboral veg1 clones. Oral veg1 clones extended along the archenteron up to the foregut region, while aboral veg1 clones contributed only small numbers of hindgut cells but large patches of ectoderm cells that extended out to the prospective larval vertex. The oral/aboral asymmetry in veg1 allocations was also demonstrated using chimeric embryos, the animal halves of which were labeled with a rhodamine-dextran. Lineages expressing the vegetal plate marker Endo16 were more precisely determined by combining lineage tracer injection with whole-mount in situ hybridization. Endo16 expression was found in all cells that are going to participate in gastrulation. Recruitment of new cells to the Endo16 domain occurs in advance of the actual invagination of those cells. During the blastula stages Endo16 expression expands radially until all cells in the veg2 lineages express this gene. The first phase of gastrulation, including the normal buckling of the vegetal plate and primary invagination of the archenteron, involves only the Endo16-expressing cells of the veg2 lineages. As the archenteron begins to elongate, marking the onset of the second phase of gastrulation, there is an asymmetric expansion of Endo16 into the veg1-derived cells that will contribute to the hindgut and midgut in accordance with lineage tracing observations. The results indicate a relatively late specification of veg1-derived cells, resulting in late recruitment to the periphery of the vegetal plate territory as gastrulation proceeds. Differential recruitment of veg1-derived cells on the oral side of the embryo introduces an oral bias to gastrulation by disproportionately increasing the number of cells on the oral side that are competent to participate in gastrulation.
用DiI谱系示踪剂标记紫海胆胚胎第六次卵裂时veg1和veg2层的单个卵裂球，并追踪其后代在囊胚期和原肠胚期的分布情况，以确定它们各自对内胚层和外胚层的贡献。在原肠胚后期胚胎的内胚层中，veg1来源的细胞几乎构成了所有预期的后肠和大约一半的预期中肠，而veg2来源的细胞构成了预期的前肠和一半的中肠。口侧的veg1克隆向内胚层贡献的细胞始终比反口侧的veg1克隆多。口侧的veg1克隆沿着原肠延伸至前肠区域，而反口侧的veg1克隆仅贡献少量后肠细胞，但有大片外胚层细胞延伸至预期的幼虫顶端。使用嵌合胚胎也证明了veg1分配中的口/反口不对称性，其动物半球用罗丹明-葡聚糖标记。通过将谱系示踪剂注射与整体原位杂交相结合，更精确地确定了表达植物极板标记Endo16的谱系。在所有将要参与原肠形成的细胞中都发现了Endo16的表达。新细胞向Endo16区域的募集发生在这些细胞实际内陷之前。在囊胚期，Endo16的表达呈放射状扩展，直到veg2谱系中的所有细胞都表达该基因。原肠形成的第一阶段，包括植物极板的正常弯曲和原肠的初级内陷，仅涉及veg2谱系中表达Endo16的细胞。随着原肠开始伸长，标志着原肠形成第二阶段的开始，Endo16不对称地扩展到veg1来源的细胞中，根据谱系追踪观察，这些细胞将对后肠和中肠做出贡献。结果表明veg1来源的细胞特化相对较晚，导致随着原肠形成的进行，它们较晚被募集到植物极板区域的周边。胚胎口侧veg1来源细胞的差异性募集通过不成比例地增加口侧能够参与原肠形成的细胞数量，给原肠形成带来了口侧偏向性。
