A NOVEL DROSOPHILA NUCLEAR-PROTEIN SERINE THREONINE KINASE EXPRESSED IN THE GERMLINE DURING ITS ESTABLISHMENT

Nuclear protein kinases are believed to play important roles in regula ting gene expression. We report here the identification and developmen tal expression of Dmnk (Drosophila maternal nuclear kinase), a Drosoph ila gene encoding a putative nuclear protein serine/threonine kinase w ith no apparent homology to previously identified protein kinases and located at 38B on the second chromosome. Dmnk mRNAs are transcribed in nurse cells and are subsequently localized in the anterior of oocytes during oogenesis, in a manner similar to several maternal transcripts regulating oogenesis and early embryogenesis. At early cleavage-stage s Dmnk transcripts are transiently present throughout the embryo, but become restricted to the posterior pole and then to the newly-formed p rimordial germ cells (pole cells) by the blastoderm stage. The transcr ipts are sustained in the pole cells during gastrulation until they pa ss through the midgut pocket wall into the body cavity. Immunostaining with specific antibodies revealed that Dmnk proteins are localized to the nuclei in a speckled pattern. Dmnk proteins become detectable in both somatic and germ line cell nuclei upon their arrival at the perip lasm of the syncytial embryo, but then disappear from the somatic cell nuclei. Consistent with mRNA expression, Dmnk proteins in pole cell n uclei are sustained during gastrulation. Taken together, Dmnk represen ts a novel class of nuclear protein kinases and the dynamic expression of Dmnk suggests a role in germ line establishment. The results are d iscussed in the light of recent findings concerning germ line establis hment in Caenorhabditis and Drosophila. (C) 1998 Elsevier Science Irel and Ltd.