Autoradiographic patterns of [3H]uridine incorporation during the development of the mollusc, Acmaea scutum

Autoradiographic experiments on eggs and embryos of the gastropod mollusc, Acmaea scutum, have provided information on the time of initiation of [3H]uridine incorporation into RNA, the relative degree to which different embryonic regions are participating, and the relative rates of incorporation at different times of development. The unfertilized egg does not incorporate exogenous [3H]uridine. After fertilization the first indication of incorporation in the stages examined was at the beginning of the sixth cleavage. There is a marked increase in the level of incorporation during the sixth cleavage which marks the beginning of gastrulation in these embryos. After this stage there is a gradual increase in incorporation per embryo, throughout development to the mid-veliger. Very little indication of significant differences in the level of incorporation among the cells of any embryo was found. The most pronounced exception was the lower activity of the anterior ectodermal cells of the trochophore larva. At later stages the derivatives of these cells were as active as the cells of other regions.