Packing for the journey: CHD5 remodels the genome.

Nearly 2 m of DNA is so tightly packaged that it fits neatly within the nucleus of each cell of our body. As if this was not mind-blowing enough, the problem is intensified in the male germline, as the nucleus of a sperm cell is about 6 times smaller than that of a somatic cell. Sperm are highly specialized cells charged with the sole responsibility of delivering the paternal genome to offspring. Thus, future generations depend upon the faithful delivery device of the sperm. The haploid genome of the father needs to be intricately packaged so that it fits within the confines of the sperm nucleus, and also so the genome is protected from the harsh environment that the sperm encounters during its epic journey from the safety of the testes, through the female reproductive tract, to its ultimate destination, the receptive oocyte.