Dmcdc2 kinase is required for both meiotic divisions during Drosophila spermatogenesis and is activated by the Twine/cdc25 phosphatase

We have analyzed the requirement for Drosophila cdc2 kinase during spermatogenesis after generating temperature-sensitive mutant lines (Dmcdc2ts) by re-constructing mutations known to result in temperature sensitivity in fission yeast cdc2+. While meiotic spindles and metaphase plates were never formed in Dmcdc2ts mutants at high temperature, chromosomes still condensed in late spermatocytes and spermatid differentiation (sperm head and tail formation) continued. The same phenotype was also observed in twine and twine, Dmcdc2ts double mutant testes, consistent with the idea that the cdc2 kinase activity required for meiotic divisions is activated by the Twine/cdc25 phosphatase. Confirming this notion, we find that ectopic expression of the String/cdc25 phosphatase, which is known to activate the cdc2 kinase before mitosis, results in a partial rescue of meiotic divisions in twine mutant testis.