Maternally expressed gamma Tub37CD in Drosophila is differentially required for female meiosis and embryonic mitosis.

We report functional analysis of gamma Tub37CD, a maternally synthesized gamma-tubulin that is highly expressed during oogenesis and utilized at centrosomes in precellular embryos. Two gamma Tub37CD mutants contained missense mutations that altered residues conserved in all gamma-tubulins and alpha- and/or beta-tubulins. A third gamma Tub37CD missense mutant identified a conserved motif unique to gamma-tubulins. A fourth gamma Tub37CD mutant 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 gamma Tub37CD. Eggs lacking the maternal gamma-tubulin were arrested in meiosis, indicative of a deficiency in activation. Analysis of meiosis with in vitro activation 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 in gamma Tub37CD mutants. In precellular embryos of partial loss of function mutants, spindles were frequently abnormal and cell cycle progression was inhibited. Thus, gamma Tub37CD 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.