The special systems biology of the sperm.

Spermatozoa represent a highly specialized cell type, with a minimalist structure designed to fulfil a single principal function: the transport of an intact single-copy haploid genome to the site of fertilization in the oviduct, and consequent zygote formation. They have lost most of their original cytoplasm, and remaining organelles are extremely modified. One result of this is that biochemical dynamics are restricted by a lack of cytoplasmic diffusion and a dramatic compartmentalization, with an increased emphasis on the physicochemical modulation of membranes. This is also reflected in a truncated apoptotic pathway, described in this issue of the Biochemical Journal in an article by Koppers et al., which leads to a so-called 'silent response' in the female tract, whereby unused sperm are removed without inflammatory consequences that might otherwise be detrimental to the new embryo. This new study shows that sperm have not simply jettisoned unwanted cellular components, but have evolved a very appropriate systems biology adapted to the specialist role they have to perform.