Organization of sperm DNA by the nuclear matrix.

In early years, Dr. Donald S. Coffey fostered the development of a new model for the organization of DNA in the sperm nucleus that had many unexpected similarities to that of somatic cells. This was surprising because it was well known that mammalian sperm DNA is more compact than the DNA in mitotic chromosomes, and the fact that some of the major structural components of somatic cell DNA organization were retained in the sperm cell was not predicted. The highly compact sperm DNA is organized into loop domains that are attached at their bases to a proteinaceous nuclear matrix, at specific matrix attachment regions (MARs). This organization is required for DNA synthesis of the paternal genome hours after fertilization, and also participates in an apoptotic-like degradation of the DNA under certain conditions. The tight packaging of the sperm chromatin is due entirely to the replacement of histones by protamines, but the sperm DNA loop domain organization is not changed by this transition, and is probably inherited by the paternal pronucleus in the newly formed embryo.