TEMPORAL EXPRESSION AND LOCALIZATION OF PROTEIN FARNESYLTRANSFERASE DURING SPERMIOGENESIS AND POSTTESTICULAR SPERM MATURATION IN THE HAMSTER

Spermiogenesis and posttesticular sperm maturation in the epididymis a re distinct developmental processes that result in a polarized spermat ozoon possessing a plasma membrane partitioned into segment-specific d omains of distinct composition and function. The mechanisms that speci fy the distribution of intracellular organelles and target proteins to restricted membrane domains are not well understood. In this study we examined the expression pattern and distribution of protein farnesylt ransferase (FTase) in hamster spermatids and epididymal spermatozoa to determine if protein lipidation may represent a potential mechanism t o regulate protein association with specific organelles or the plasma membrane. Round spermatids exhibited only weak immunostaining with ant ibody against the beta-subunit of FTase, whereas elongating spermatids exhibited a high level of FTase expression that was segregated to the cytoplasmic lobe surrounding the anterior flagellum. Although FTase w as released with the residual body, mature spermatids retained FTase w ithin the midpiece and cytoplasmic droplet. In epididymal spermatozoa, FTase remained associated with the cytoplasmic droplet during its mig ration to the midpiece-principal piece junction; following release of the cytoplasmic droplet, no immunodetectable FTase was noted in the mi dpiece segment. Immunoblotting demonstrated the presence of both the a lpha and beta subunits of FTase in sperm lysates. The temporal express ion pattern and restricted distribution of FTase in spermatids and epi didymal spermatozoa suggest a potential role in regulating protein ass ociation with specific organelles and/or membrane domains of the matur e spermatozoon. (C) 1997 Wiley-Liss, Inc.