Reciprocal inheritance of centrosomes in the parthenogenetic Hymenopteran Nasonia vitripennis

Background: In the majority of animals, the centrosome - the microtubule-or ganizing center of the cell - is assembled from components of both the sper m and the egg. How the males of the insect order Hymenoptera acquire centro somes is a mystery, as they originate from virgin birth. Results: To address this issue, we observed centrosome, spindle and nuclear behavior in real time during early development in the parthenogenetic hyme nopteran Nasonia vitripennis. Female meiosis was identical in unfertilized eggs. Centrosomes were assembled before the first mitotic division but were inherited differently in unfertilized and fertilized eggs. In both, large numbers of asters appeared at the cortex of the egg after completion of mei osis. In unfertilized eggs, the asters migrated inwards and two of them bec ame stably associated with the female pronucleus and the remaining cytoplas mic asters rapidly disappeared. In fertilized eggs, the Nasonia sperm broug ht in paternally derived centrosomes, similar to Drosophila melanogaster. A t pronuclear fusion, the diploid zygotic nucleus was associated only with p aternally derived centrosomes. None of the cytoplasmic asters associated wi th the zygotic nucleus and, as in unfertilized eggs, they rapidly degenerat ed. Conclusions: Selection and migration of the female pronucleus is independen t of the sperm and its aster. Unfertilized male eggs inherit maternal centr osomes whereas fertilized female eggs inherit paternal centrosomes. This is the first system described in which centrosomes are reciprocally inherited . The results suggest the existence of a previously undescribed mechanism f or regulating centrosome number in the early embryo.