Abstract Haploid embryonic lethality is a common feature in vertebrates. However, the developmental defects and timing of lethality in haploid embryos differ between non-mammalian and mammalian species. Therefore, it remains unknown whether vertebrates share common principles of haploid intolerance. We investigated haploidy-linked defects at the cellular level in gynogenetic haploid zebrafish larvae that manifest characteristic morphogenetic abnormalities. Haploid larvae suffered severe mitotic arrest and irregular upregulation of p53, leading to unscheduled cell death. Either mitigation of mitotic arrest by spindle assembly checkpoint inactivation or depletion of p53 significantly improved organ growth in haploid larvae, indicating the critical contribution of these cellular defects to haploidy-linked morphogenetic defects. Moreover, haploid zebrafish larvae suffered frequent centrosome loss resulting in mitotic spindle monopolarization, a leading cause of mitotic instability in haploid mammalian cells (1, 2). Haploid larvae also suffered ciliopathy associated with severe centrosome loss. Based on our results, we propose the ploidy-linked alteration in centrosome number control as a common principle constraining the allowable ploidy state for normal development in vertebrates. Significance statement Haploid embryos possessing a single chromosome set are invariably lethal in vertebrates. Though haploid intolerance is attributed to imprinting misregulation in mammals, it remains unknown what limits the developmental capacity of haploid non-mammalian vertebrates free from the imprinting constraint. This study revealed the haploidy-linked mitotic misregulation and p53 upregulation as the leading cause of organ growth retardation in haploid zebrafish larvae. Accompanied by these defects, haploid larvae manifested drastic centrosome loss and mitotic spindle monopolarization, defects also limiting the proliferative capacity of haploid mammalian cells. These findings suggest the ploidy-linked alteration in centrosome number control as a common cell-intrinsic principle of haploid intolerance in vertebrates, providing an insight into an evolutionary constraint on allowable ploidy status in animal life cycles.

Centrosome Loss And Cell Proliferation Defects Underlie Developmental Failure In Haploid Zebrafish Larvae