Autoradiography ofCoelopa frigida (Diptera) embryos, after labeling with3H-uridine during various phases of oogenesis.

The distribution of tritiated (3H) uridine or its derivatives in embryos of the kelp flyCoelopa frigida is analyzed by autoradiography. The radioactive label is introduced into the growing oocyte, after injectio into females at different time periods post eclosion. The majority of the label remains in the cytoplasm for the entire embryonic development and is presumably incorporated into stable RNA. Only when the precursor is injected toward the final stages of oogenesis, can presence of label be detected in the nuclei, for a short time period during the blastodern stage. Since no preferential location in nucleoli is found, it appears possible that labeled cytidine could have been derived from the original precursor which would be available for incorporation into DNA.