NUCLEAR AND CYTOPLASMIC DNA SYNTHESIS IN ADULT AND EMBRYONIC ROTIFERS

Abstract
1. DNA synthesis has been studied in adult and embryonic tissues of the rotifer Asplanchna brightwelli. using autoradiography with tritiated thymidine. 2. Mitosis and mitotic DNA synthesis cease, and nucleoli are formed, approximately simultaneously at the end of the mitotic phase of embryonic development. 3. In the post-mitotic phase of development and in adult females, the large nuclei of the vitellarium (a nurse cell-like organ) incorporate H3-thymidine into metabolically-stable DNA, thus presumably becoming polyploid. 4. The DNA synthesis in the different nuclei of the syncytial vitellarium is not synchronous, showing that the cytoplasm does not control nuclear DNA synthesis. 5. Cytoplasmic DNA synthesis also occurs in embryos and in adult vitellaria. Most or all of the cytoplasmic DNA appears to be in the mitochondria.

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