Portal de Periódicos da CAPES

Cellular mechanisms in the morphogenesis of the sea urchin embryo

1963; Elsevier BV; Volume: 32; Issue: 3 Linguagem: Inglês

10.1016/0014-4827(63)90195-2

1090-2422

T. Gustafson,

Echinoderm biology and ecology

The contacts between various pseudopodal elements and the ectoderm in the sea urchin gastrula have been investigated by means of time-lapse cinematography and interference contrast microscopy on slightly compressed larvae, where the ectoderm is more or less extended and the cells tend to separate to a varying extent. In zones of the ectoderm where cell contact is moderate, the cells are joined up by points of attachment which are restricted to the margin of the inner and outer end of the cells. Where the contact is low, only the outer ends are involved in these mutual attachments, whereas in the animal plate, where the contact is strongest, the cells are attached to each other along the whole of their length. An increased packing of the cells can thus be correlated with the occurrence of inner contact points or broad contacts. The pseudopods of the primary mesenchyme, the archenteron tip, and the free secondary mesenchyme cells only attach at the points where the ectoderm cells attach to each other, and particularly to the inner points of attachment. The distribution of the inner points of attachment explains the correlation between the location of the primary mesenchyme cells and the thickened zones within the ectoderm. The inability of pseudopods to make strong contacts with the animal plate and the tendency of the archenteron tip pseudopods to attach to the dorsal side during gastrulation are tentatively explained in terms of availability of free contact surface within the ectoderm, but other factors may also be involved. The basis of the apparent differences between the pattern of primary and secondary mesenchyme is discussed. The inner and the outer contact points appear to be structurally different. The nature and origin of the cell contacts within the ectoderm is discussed, and it is suggested that the mutual adhesion between the cells is rather low, but that the cells tend to spread at the hyaline membrane and an inner layer which promotes a direct adhesion between the cells. The broad contact within the animal plate, however, indicates a high mutual adhesiveness of the cell surface as a whole. The results suggest that many of the complex morphological features of the young sea urchin embryo have a simple background.