Formation of the male pronuclear lamina in Drosophila melanogaster.

Upon fertilization, a sperm nucleus reorganizes to become a male pronucleus. This reorganization includes breakdown and reformation of the nuclear envelope of the male pronucleus. In this study, we used a maternally encoded nuclear lamina protein, YA, in parallel with another lamina protein, lamin Dm, as probes to study the formation of the male pronuclear lamina in Drosophila melanogaster. Ectopically expressed YA is present in the nuclear envelopes of spermatocytes, but not in mature sperm, similar to endogenous lamin Dm. This suggests that the nuclear envelope of Drosophila sperm differs from that of somatic cells. Upon fertilization, YA and lamin Dm are recruited to the periphery of the male-derived nucleus before or during the early stages of migration by the male pronucleus. Using a paternal effect mutation, snky, we found that recruitment of lamina proteins to the male pronucleus requires, and probably accompanies, reorganization of the sperm nucleus. In order to identify factors that affect the recruitment of nuclear lamina proteins to the male pronucleus, we examined the subcellular localization of YA and lamin Dm in mutant embryos defective for the function of either the male pronucleus (mh, K81, and pal or both pronuclei (gnu, png, and plu). None of these mutations affect the recruitment of YA or lamin Dm to the male pronuclear envelope, suggesting that the mutations affect processes independent of, or after, reorganization of the nuclear envelope. Double mutant analyses between Ya and gnu suggest that YA plays a role in the nuclear envelope permissive for rounds of DNA replication.