Species-Specific Heterochromatin Prevents Mitotic Chromosome Segregation to Cause Hybrid Lethality in Drosophila
(A) Hybrid male and female embryos at different stages of early embryogenesis. Embryos were sexed using FISH probes to the D. melanogaster X (359-bp satellite) and Y (AATAGAC satellite) chromosomes. Higher magnifications of the nuclei are shown in the insets. Hybrid male embryos develop normally, while hybrid female embryos show abnormal nuclear spacing beginning during nuclear divisions 10–13 of the syncytial blastoderm stage. (B) Hybrid female embryos exhibit mitotic asynchrony. Left panel, a hybrid male embryo showing wild-type pattern. Right panel, a hybrid female embryo. Both embryos were stained with anti-phospho-Histone 3 (PH3) antibodies. (C) Chromosome mis-segregation in hybrid female embryos. White arrows in right panel indicate lagging chromatin during anaphase in a hybrid female embryo. (D) Left panel is a high magnification of two dividing chromosome sets during anaphase. Right panel is a high magnification of two daughter nuclei during late telophase. White arrows indicate lagging chromatin. Scale bar is 90 µm in (A) and (B), 8 µm in (C), and 5 µm in (D).