Wray G A, Raff R A
Department of Biology, Indiana University, Bloomington 47405.
Dev Biol. 1990 Sep;141(1):41-54. doi: 10.1016/0012-1606(90)90100-w.
The lineage and fate of each blastomere in the 32-cell embryo of the direct-developing sea urchin Heliocidaris erythrogramma have been traced by microinjection of tetramethylrhodamine-dextran. The results reveal substantive evolutionary modifications of the ancestral cell lineage pattern of indirect sea urchin development. Significant among these modifications are changes in the time and order of cell lineage segregation: vegetal ectodermal founder cells consistently arise earlier than during indirect development, while internal founder cells generally segregate later and in a different sequence. Modifications have also arisen in proportions of the embryo fated to become various cell types and larval structures. Ectodermal fates, particularly vestibular ectoderm, comprise a greater proportion of the total cellular volume in H. erythrogramma. Among internal cell types, coelom consumes more and endoderm less of the remaining cellular volume than during indirect sea urchin development. Evolutionary modifications are also apparent in the positional origin of larval cell types and structures in H. erythrogramma. These include an apparent tilt in the axis of prospective cell fate relative to the animal-vegetal axis as defined by cleavage planes. Together these evolutionary changes in the cell lineage of H. erythrogramma produce an accelerated loss of dorsoventral symmetry in cell fate relative to indirect development. The extent and diversity of rearrangements in its cell lineage indicate that the non-feeding larva of H. erythrogramma is a highly modified, novel form rather than a degenerate pluteus larva. These same modifications underscore the evolutionarily flexible relationship between cell lineage, gene expression, and larval morphology in sea urchin development.
通过向直接发育的海胆红腹海胆（Heliocidaris erythrogramma）的32细胞胚胎中的每个卵裂球注射四甲基罗丹明-葡聚糖，追踪了其谱系和命运。结果揭示了间接海胆发育的祖先细胞谱系模式的实质性进化改变。这些改变中显著的是细胞谱系分离的时间和顺序的变化：植物外胚层祖细胞始终比间接发育时更早出现，而内部祖细胞通常分离得更晚且顺序不同。胚胎中注定成为各种细胞类型和幼虫结构的比例也发生了改变。在红腹海胆中，外胚层命运，特别是前庭外胚层，在总细胞体积中占更大比例。在内部细胞类型中，与间接海胆发育相比，体腔消耗了更多的剩余细胞体积，而内胚层消耗较少。红腹海胆幼虫细胞类型和结构的位置起源也明显存在进化改变。这些包括相对于由卵裂平面定义的动物-植物轴，预期细胞命运轴明显倾斜。红腹海胆细胞谱系中的这些进化变化共同导致相对于间接发育，细胞命运中背腹对称性的加速丧失。其细胞谱系重排的程度和多样性表明，红腹海胆的非摄食幼虫是一种高度修饰的新形式，而不是退化的长腕幼虫。这些相同的修饰强调了海胆发育中细胞谱系、基因表达和幼虫形态之间进化上灵活的关系。
