Sperm proteomics: potential impact on male infertility treatment

Spermatozoa are unique cells that have highly compact DNA, motility (and hypermotility) patterns, a specific morphology, localized mitochondria and an apical acrosome. They are the end product of a dynamic process termed spermatogenesis. Sperm are therefore produced with specific proteins in order to effect different traits, such as the presence of cysteine-rich protamines in DNA, which effectively compacts DNA. Moreover, specific proteins are transferred during epididymal maturation and after ejaculation in order to render sperm capable of undergoing post-ejaculatory alterations, generally termed capacitation, which confers capacity to fertilize a mature oocyte. In addition, sperm exhibit several post-translational modifications, which are fundamental to their function, such as SUMOylation and ubiquitination. Discussed in this review is the current knowledge of the sperm proteome in terms of its composition and the function that these proteins determine, as well as their post-translational modifications and how these alter sperm functional integrity. Studies are emphasized that focus on shotgun proteomics – untargeted determination of the protein constituent of a cell in a given biological condition – and technologies currently applied toward that end are reviewed.