Spermatogenesis in the mouse 2. Amino acid incorporation into basic nucleoproteins of mouse spermatids and spermatozoa

The present studies were designed to identify mouse spermatid proteins into which intratesticularly injected [³H]arginine [³H]lysine were initially incorporated and to determine the fates of those proteins during subsequent spermatid differentiation. At intervals between 2 h and 7 days after injections, elongated spermatid nuclei were isolated from the testes by virtue of their resistance to sonication, and mature sperm nuclei were isolated from the epididymides. Basic proteins were extracted from isolated spermatid and sperm nuclei and subjected to electrophoresis on acid-urea polyacrylamide gels. Two hours after injection, [³H]arginine was seen in a number of spermatid basic proteins, including both the 'testis-specific'protein (TP) and the protamines. As expected from previous studies, only one case of these labeled proteins, protamine, was retained through the completion of spermiogenesis and sperm maturation 7 days later. In striking contrast, [³H]lysine was initially incorporated only into the spermatid TP protein, was retained for only 3 days, and was then lost. Our previous autoradiographic study (Mayer and Zirkin, 1979) demonstrated that intratesticularly injected [³H]lysine was initially incorporated into elongating spermatid nuclei at the initiation of chromatin condensation (late step 12 and step 13), was retained for 3 days through the completion of chromatin condensation (step 14), and was then lost. The present results, taken together with the results of our previous autoradiographic study, demonstrate striking temporal relationships between the first appearance of newly synthesized TP protein and the initiation of chromatin condensation in spermatid nuclei of late step 12, and between the loss of TP protein and the completion of chromatin condensation in spermatid nuclei of step 14.