A haystack in the needle: packaging sperm DNA in insects

The global replacement of nucleosomes with nonhistone chromosomal proteins during sperm differentiation is a widespread phenomenon in sexually reproducing animals. In mammals, for instance, sperm chromatin is essentially packaged with protamines, a type of sperm nuclear basic proteins (SNBPs). In contrast to vertebrates, where many taxa retain variable levels of histones in their sperm chromatin, insects seem to systematically eliminate histones during spermiogenesis. This diversity of sperm packaging across metazoa raises questions about the functional significance of the histone-to-protamine transition that occurs during spermiogenesis. Recent studies in Drosophila and other insects have shed light on the function of SNBPs in packaging ultracompact sperm DNA and preparing paternal chromosomes for their integration into the diploid zygote.