Gene expression in early development of Lymnaea stagnalis

Pond snails (Lymnaea stagnalis) were irradiated with doses of 2760 r or 5520 r in order to induce lethal factors in the germ cells. The descendants of these irradiated snails were individually reared to adulthood, when by self-fertilization they produced egg masses. The occurrence of lethal factors was studied in these egg masses and the stage at which they manifested themselves was determined. No developmental disturbance was found during cleavage, but gastrulation was affected. This indicates that gastrulation in Lymnaea is controlled by the genome of the embryo. The stage at which most genes interfere with development is the early trochophore stage. At later stages the number of genes, which for the first time are active in development, declines. Since the late veliger stage was never affected, all genes essential for development, are apparently functioning before this stage.