MATERNALLY EXPRESSED GAMMA-TUB37CD IN DROSOPHILA IS DIFFERENTIALLY REQUIRED FOR FEMALE MEIOSIS AND EMBRYONIC MITOSIS

We report functional analysis of gamma Tub37CD, a maternally synthesiz ed gamma-tubulin that is highly expressed during oogenesis and utilize d at centrosomes in precellular embryos. Two gamma Tub37CD mutants con tained missense mutations that altered residues conserved in all gamma -tubulins and alpha- and/or beta-tubulins. A third gamma Tub37CD misse nse mutant identified a conserved motif unique to gamma-tubulins. A fo urth gamma Tub37CD mutant contained a nonsense mutation and the corres ponding premature stop codon generated a protein null allele. Immunofl uorescence analysis of laid eggs and activated oocytes derived from th e mutants revealed microtubules and meiotic spindles that were close t o normal even in the absence of gamma Tub37CD. Eggs lacking the matern al 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 assem bly of cortical asters, and this cortical reorganization was altered i n gamma Tub37CD mutants. In precellular embryos of partial loss of fun ction mutants, spindles were frequently abnormal and cell cycle progre ssion was inhibited. Thus, gamma Tub37CD functions differentially in f emale meiosis and in the early embryo; while involved in oocyte activa tion, it is apparently not required or plays a subtle role in formatio n 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, (C) 1998 Academic Press.