Spermatid manchette: Plugging proteins to zero into the sperm tail

Spermiogenesis pursues three major objectives: (1) The safeguard of the mal e genome within the confines of a compact nucleus. (2) The accumulation of enzymes in the acrosome of be released at fertilization. (3) The developmen t of a sperm propelling tail consisting of an axoneme surrounded by a scaff old of keratin-containing outer dense fibers and a fibrous sheath. Recent e xperimental data indicate that three keratins-Sak57, Odf1 and Odf2- and oth er proteins (the 26S proteasome and the Odf1-binding protein Spag4) are tem porarily stored in the manchette before being sorted to the developing sper m tail. These findings support a general model for the manchette as an ephe meral structure timely developed and strategically positioned to provide a transient storage to both structural and signaling proteins. Some of the pr oteins are later sorted to the developing tail; others may participate in t he reciprocal nuclear-cytoplasmic signaling pathways as the gene activity o f the male genome gradually becomes silent. (C) 2001 Wiley-Liss, Inc.