SRA

Hybridization of eggs and sperm from closely related species can give rise to genetic diversity, or can lead to embryo inviability due to incompatibility. Although central to evolution, the cellular and molecular mechanisms underlying postzygotic barriers that drive reproductive isolation and speciation remain largely unknown. Species of the African Clawed frog Xenopus provide an ideal system to study hybridization and genome evolution. Xenopus laevis is an allotetraploid with 36 chromosomes that arose through interspecific hybridization of diploid progenitors, whereas Xenopus tropicalis is a diploid with 20 chromosomes that diverged from a common ancestor ~48 million years ago. Differences in genome size between the two species are accompanied by organism size differences, and size scaling of the egg and subcellular structures such as nuclei and spindles formed in egg extracts. Nevertheless, early development transcriptional programs, gene expression patterns, and protein sequences are generally conserved. Interestingly, whereas the hybrid produced when X. laevis eggs are fertilized by X. tropicalis sperm (le×ts) is viable, the reverse hybrid (te×ls) dies prior to gastrulation. Here, we applied cell biological tools and high-throughput methods to study the mechanisms underlying hybrid inviability. We reveal that two specific X. laevis chromosomes are incompatible with the X. tropicalis cytoplasm and are mis-segregated during mitosis, leading to unbalanced gene expression at the maternal to zygotic transition, followed by cell-autonomous catastrophic embryo death. Overall design: Collect mRNA from whole embryos; three biological replicates were analyzed