We report functional analysis of gTub37CD, a maternally synthesized g-tubulin that is highly expressed during oogenesis and utilized at centrosomes in precellular embryos (Tavosanis et al., 1997; Wilson et al., 1997). Three gTub37CD mutants contained missense mutations that altered residues conserved in all g-tubulins, one of which identified a conserved motif unique to g-tubulins. A fourth gTub37CD 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 showed that the structure of the meiotic spindle was close to normal even in the absence of gTub37CD. However, laid eggs lacking the maternal g-tubulin were frequently arrested or delayed in meiosis, indicative of a deficiency in activation. In vitro activation techniques showed that the cortical microtubule cytoskeleton of mature wild-type eggs was reorganized upon activation, expressed as transient assembly of cortical asters, and this cortical reorganization was altered in gTub37CD mutants. Thus, delay or arrest in meiosis may be downstream effects of defects in oocyte activation. In precellular embryos of partial loss of function mutants, spindles were frequently abnormal, typically lacked centrosomes, and cell cycle progression was inhibited. Thus, gTub37CD 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 formation of the mitotic spindle which is directed by centrosomes organized about centrioles.
