Spindle dynamics and the role of gamma-tubulin in early Caenorhabditis elegans embryos

gamma -Tubulin is a ubiquitous and highly conserved component of centrosome s in eukaryotic cells. Genetic and biochemical studies have demonstrated th at gamma -tubulin functions as part of a complex to nucleate microtubule po lymerization from centrosomes. We show that, as in other organisms, Caenorh abditis elegans gamma -tubulin is concentrated in centrosomes. To study cen trosome dynamics in embryos, we generated transgenic worms that express GFP ::gamma -tubulin or GFP::beta -tubulin in the maternal germ line and early embryos. Multiphoton microscopy of embryos produced by these worms revealed the time course of daughter centrosome appearance and growth and the diffe rential behavior of centrosomes destined for germ line and somatic blastome res. To study the role of gamma -tubulin in nucleation and organization of spindle microtubules, we used RNA interference (RNAi) to deplete C. elegans embryos of gamma -tubulin. gamma -Tubulin (RNAi) embryos failed in chromos ome segregation, but surprisingly, they contained extensive microtubule arr ays. Moderately affected embryos contained bipolar spindles with dense and long astral microtubule arrays but with poorly organized kinetochore and in terpolar microtubules. Severely affected embryos contained collapsed spindl es with numerous long astral microtubules. Our results suggest that,gamma - tubulin is not absolutely required for microtubule nucleation in C. elegans but is required for the normal organization and function of kinetochore an d interpolar microtubules.