Roles of small ubiquitin-related modifiers in male reproductive function.

Spermatogenesis consists of the mitotic division of spermatogonia, meiosis of spermatocytes, and postmeiotic differentiation of spermatids, processes tightly controlled by hormones and growth factors secreted by testicular somatic cells. The events during spermatogenesis are precisely regulated by the sequential appearance of different proteins and their posttranslational modifications. Sumoylation (covalent modification by small ubiquitin-like modifiers; SUMO proteins) has emerged as an important regulatory mechanism in different cell types, and data obtained from studies on germ cells imply that SUMO proteins are involved in multiple aspects of spermatogenesis. Although progress has been made in the initial characterization of sumoylated proteins during spermatogenesis, the targets of sumoylation, their corresponding pathways in the testis, are mostly unknown. In this chapter, I review what we know about sumoylation in somatic cells, summarize the expression patterns, suggest possible functions of SUMO proteins in testicular cells, and discuss some difficulties and perspectives on the studies of sumoylation during spermatogenesis.