Figure 3. SAS-7 is required for newly formed daughter centrioles to become mother centrioles.

(A) Random defects model for centriole duplication in sas-7 mutants. If both mother and daughter centrioles fail to duplicate with a probability of a (p=a), the distribution of 4 cell stage monopolar spindles will be as shown. (B) Daughter-mother transition defects model for sas-7 mutants. If mother centrioles are never defective for centriole duplication while daughter centrioles fail to duplicate with a probability of b (p=b), the distribution of 4 cell stage monopolar spindles will be as shown. (C) Distribution of 4 cell stage monopolar spindles in sperm(+), oocyte(-) embryos from sas-7(or452ts) mutant females crossed with wild-type males. (D) SAS-7 may also be required for mother centrioles to maintain duplication competence. In sas-7(or452ts) mutants, centriole duplication in meiosis I is normal but is sometimes defective in meiosis II resulting in the P₀ monopolar spindle phenotype. However, the observed P₀ monopolar spindle penetrance (62%; see Table 1) is higher than even the case where all daughter centrioles fail to duplicate (b = 1.0, in which case all sperm would have centrioles depicted in the right-most box, such that 50% of P₀ spindles would be monopolar); even fewer would be monopolar at lower values of b. These results suggest that SAS-7 is required for some of the mother centrioles to duplicate in sperm(-), oocyte(-) sas-7(or452ts) embryos. Mother centrioles are blue; daughters are orange.

DOI: http://dx.doi.org/10.7554/eLife.20353.010

Figure 3—figure supplement 1. sas-7(or452ts) mother centrioles lose duplication competence.

(A) If the daughter-to-mother transition defects model in Figure 3D is applied, the probability of monopolar spindle formation in sperm(-), oocyte(-) P₀ division becomes as shown. (B) If the daughter-to-mother transition defects model in Figure 3D is applied, the probability that monopolar spindles will form in both AB and P₁ is at most 11%. However, we observed monopolar spindles in both P₁ and AB in 27% of the sperm(-), oocyte(-) embryos examined (A). These results as well as the data in Figure 3D suggest that that some mother centrioles lose duplication competence in the absence of SAS-7. Mother centrioles are blue; daughters are orange. Note that in our calculations, we did not consider the possibility that daughter centrioles become mothers even if they duplicate; if that possibility were included, the probability that monopolar spindles will form in both AB and P₁ is even lower.

DOI: http://dx.doi.org/10.7554/eLife.20353.011