Centrosomes, the primary microtubule organizing centers (MTOC) of animal cells, consist of a pair of microtubule--based centrioles surrounded by pericentriolar-material (PCM). As in many metazoans, the sperm contributes the sole pair of centrioles to the zygote at fertilization in C. elegans. The paternally provided centrioles and the maternal PCM reconstitute the first centrosome in the embryo. The centrosome duplicates and assembles a bipolar spindle during the first cell cycle. The
sas-1 locus was identified as a parental-effect embryonic lethal mutation [Gonczy et al. (1999)]. In embryos derived from homozygous
sas-1 mutant hermaphrodites, a monopolar spindle assembles in the first cell cycle. The phenotype is rescued by mating
sas-1 mutant hermaphrodites with wild-type males, indicating that
sas-1 is required paternally. We found that the centriolar proteins SAS-4, SAS-5, SAS-6, as well as gamma-tubulin, are present in
sas-1 mutant sperm. Using serial section EM analysis, we show that centrioles are structurally intact during the initial stages of spermatogenesis. However, a microtubule-based structure cannot be detected in mature sperm. Thus,
sas-1 is required for centriole maintenance during spermatogenesis. To address the pattern of centriole biogenesis in
sas-1 mutant embryos we conducted lineage tracing of MTOCs using GFP:beta-tubulin and DIC time-lapse microscopy. This analysis revealed that: 1)
sas-1 mutant sperm provides defective centrioles that are unable to duplicate and result in a monopolar spindle during the first cell cycle. 2) In most cases centriole duplication is rescued in later cell cycles and MTOCs are inherited in a complex pattern. This pattern is compatible with at least two possibilities: defective centrioles could be repaired and resume a normal duplication cycle; alternatively, new functional centrioles could form from
sas-1 defective centrioles. 3) In some cases, MTOCs are lost from given blastomeres, in which cases functional MTOCs do not form thereafter. This suggests that in C. elegans centrioles do not form de novo during early embryogenesis. Identifying the molecular nature of
sas-1 will be key for further understanding the mechanism of centriole biogenesis and maintenance.