ASSEMBLY OF THE ZYGOTIC CENTROSOME IN THE FERTILIZED DROSOPHILA EGG

Zygotic centrosome assembly in fertilized Drosophila eggs was analyzed with the aid of an antiserum Rb188, previously shown to be specific f or CP190, a 190 kDa centrosome-associated protein (Whitfield et al. (1 988) J. Cell Sci. 89, 467-480; Whitfield et al. (1995) J. Cell Sci. 10 8, 3377-3387). The CP190 protein was detected in two discrete spots, a ssociated with the anterior and posterior ends of the elongating nucle us of Drosophila spermatids. As the spermatids matured, this labelling gradually disappeared and was no longer visible in sperm dissected fr om spermathecae and ventral receptacles. gamma-Tubulin was also found in association with the posterior end of the sperm nucleus during sper miogenesis, but was not detected in mature sperm. This suggests that C P190 and gamma-tubulin are not present in detectable quantities in fer tilizing sperm. CP190 was not detected in association with the sperm n ucleus of newly fertilized eggs removed from the uterus, whereas many CP190-positive particles were associated with microtubules of the sper m aster from anaphase I to anaphase II. These particles disappeared du ring early telophase II and only one pair of CP190-positive;pots remai ned visible at the microtubule focus of the sperm aster. These spots w ere associated with one aster through telophase, and then moved away t o form two smaller asters from which the first mitotic spindle was org anized. Colchicine treatment suggested that at least some CP190 protei n is an integral part of the centrosome rather than merely being trans ported along microtubules. Centrosomal localization of the CP190 antig en was prevented by incubation of the permeabilized zygote in 20 mM ED TA. (C) 1997 Elsevier Science Ireland Ltd.