Distinct features in fish Bouncer proteins determine sperm-egg compatibility

Abstract

All sexually reproducing organisms depend on fertilization to survive as species. Despite the importance of fertilization, the mechanisms that drive sperm-egg compatibility are poorly understood. In fish, the egg protein Bouncer is necessary for fertilization and is species-specific between medaka and zebrafish. Here, we investigate whether Bouncer is generally species-specific in fish and identify features mediating its medaka/zebrafish specificity. In vitro fertilization experiments using zebrafish and medaka show that Bouncer is not a general specificity factor. Instead, its homologs exhibit wide compatibility with sperm, in line with the pervasive purifying selection that dominates Bouncer's evolution. We further uncover specific features of Bouncer - distinct amino acid residues and N-glycosylation patterns - that differentially influence the function of medaka and zebrafish Bouncer homologs and contribute to medaka/zebrafish specificity. This work reveals important themes central to understanding Bouncer's function in sperm binding and clarifying the molecular requirements for Bouncer's sperm interaction partner.

Evolutionary conservation of embryonic DNA methylome remodelling in distantly related teleost species

“…Hybrid organisms are valuable assets in exploring the relationship between genome evolution, epigenetic control, and cytoplasmic components. For example, hybrids were used to elucidate factors controlling fertilisation and ZGA timing [32,58,59] and to explore genome evolution as exemplified by studies in Xenopus [60][61][62]. Here we have generated first base-resolution DNA methylome profiles of an inter-order hybrid organism [32] to explore the evolution and conservation of DNA remodelling pathways and machinery over large evolutionary distances.…”