Fig. S4

Expression of Cei/AurB products in aurB^hi1045 homozygotes. mRNA was injected at the one-cell stage into embryos derived from incrosses of aurB^hi1045 heterozygotes, so that an expected 25% of the progeny are aurB^hi1045 homozygotes. In (A–C,A′–C′), embryos showing overt signs of necrosis are presumed to be aurB^hi1045 homozygotes and are indicated with asterisks. (A–D) At 24 hours p.f., the expected fraction of uninjected embryos begins to show brain necrosis, as indicated by decreased transparency in the head region (A). At this stage, embryos expressing products encoded by the wild-type (B) and maternal-effect mutant (C) alleles show no overt signs of necrosis. Expression of an engineered kinase dead mutant product (AurBK-R; [43]) results in an increased severity of brain necrosis in most embryos (D), showing that this product functions in a dominant negative manner. (A′–D′) Images at 48 hours p.f. of the same groups of embryos as in (A–D). Control uninjected aurB^hi1045 homozygotes now show a greater degree of necrosis in the anterior region, as reflected by increased darkening and a reduction of its size (A′). At this stage, aurB^hi1045 homozygotes injected with mRNA coding for wild-type (B′) and maternal-effect mutant (C′) Cei/AurB products begin to show brain necrosis, although generally to a lesser extent than uninjected mutant embryos. The degree of phenotypic rescue in embryos expressing wild-type product appears higher than that observed in embryos expressing the maternal-effect mutant product (less affected embryos in B′ are indicated by a white asterisk), which is consistent with the postulated hypomorphic nature of the maternal-effect mutant allele. By this stage, all embryos expressing AurBK-R protein exhibit some degree of necrosis (D′). Results shown are representative of duplicate experiments in embryos from two different clutches. Overexpression of neither maternal-effect mutant nor aurBK-R products (as well as wild-type product) did not have any observable effects on cell division at the cleavage stages (data not shown), possibly because of a temporal delay in protein product accumulation after mRNA injection at the one-cell stage.