Upon fertilization, the sperm nucleus undergoes reactivation. The pore
less sperm nuclear envelope is replaced by a functional male pronuclea
r envelope and the highly compact male chromatin decondenses. Here som
e recent evidence is examined: that disassembly of the sperm lamina is
required for chromatin decondensation, that remnant portions of the s
perm nuclear envelope target the binding of egg membrane vesicles that
form the male pronuclear envelope, that functional male pronuclear en
velopes containing iamin B receptor assemble prior to lamin import and
lamina formation, and that lamina assembly drives male pronuclear swe
lling. Several unresolved issues are discussed.