Maternally Expressed γTub37CD inDrosophilaIs Differentially Required for Female Meiosis and Embryonic Mitosis

AbstractWe report functional analysis of γTub37CD, a maternally synthesized γ-tubulin that is highly expressed during oogenesis and utilized at centrosomes in precellular embryos. TwoγTub37CDmutants contained missense mutations that altered residues conserved in all γ-tubulins and α- and/or β-tubulins. A thirdγTub37CDmissense mutant identified a conserved motif unique to γ-tubulins. A fourthγTub37CDmutant contained a nonsense mutation and the corresponding premature stop codon generated a protein null allele. Immunofluorescence analysis of laid eggs and activated oocytes derived from the mutants revealed microtubules and meiotic spindles that were close to normal even in the absence of γTub37CD. Eggs lacking the maternal γ-tubulin were arrested in meiosis, indicative of a deficiency in activation. Analysis of meiosis within vitroactivation techniques showed that the cortical microtubule cytoskeleton of mature wild-type eggs was reorganized upon activation and expressed as transient assembly of cortical asters, and this cortical reorganization was altered inγTub37CDmutants. In precellular embryos of partial loss of function mutants, spindles were frequently abnormal and cell cycle progression was inhibited. Thus, γTub37CD functions differentially in female meiosis and in the early embryo; while involved in oocyte activation, it is apparently not required or plays a subtle role in formation of the female meiotic spindle which is acentriolar, but is essential for assembly of a discrete bipolar mitotic spindle which is directed by centrosomes organized about centrioles