Sperm Nuclear Architecture

One of the most intriguing questions in sperm biology is how the 3 f long DNA is packaged into an almost crystalline state in an ordered fashion that retains all its biological functions. Several aspects of this process are known; however, a model for the entire packaging still eludes us. We know that the DNA is packaged into very condensed toroids by protamines that protect it from insults during its journey from the male reproductive tract till the time of fertilization with the oocyte. The DNA is also organized by the sperm nuclear matrix to preserve its function and to direct the replication of the DNA in the embryo after fertilization. This particular level of chromatin packaging may also serve as a checkpoint for DNA integrity. At a higher level, sperm chromosomes appear to occupy discrete domains, with the telomeres of each chromosome paired and located at the periphery of the nucleus and the centromeres at the center. However, there are still many unanswered questions about such chromatin structure. There are several different types of sperm DNA damage assays, and each is sensitive to specific aspects of sperm chromatin structure. Understanding how the chromatin is packaged can therefore help to interpret these assays.