DEVELOPMENTAL EXPRESSION, INTRACELLULAR-LOCALIZATION, AND SELENIUM CONTENT OF THE CYSTEINE-RICH PROTEIN ASSOCIATED WITH THE MITOCHONDRIAL CAPSULES OF MOUSE SPERM

The outer membranes of mitochondria of mammalian sperm are encased in a keratinous structure known as the mitochondrial capsule. The experim ents in the present study were designed to resolve a controversy surro unding the intracellular localization, developmental expression, and s elenium-content of a cysteine-rich 17-20 kD protein that has been repo rted to constitute the major structural protein in the mitochondrial c apsule of mammals. An antibody to a synthetic oligopeptide based on th e predicted sequence of mouse cysteine-rich protein recognizes a 24 kD protein in epididymal sperm tails of mice. The 24 kD protein does not appear to be a selenoprotein because: (1) it is not labeled with Se-7 5-selenite in seminiferous tubule culture; (2) cleavage with cyanogen bromide and translation of T7 RNA polymerase transcripts in vitro indi cate that the translation start site is located downstream of potentia l UGA selenocysteine codons in the mouse cysteine-rich mRNA; (3) the r eading frame encoding the cysteine-rich protein in rat lacks in-phase UGA selenocysteine codons. Light and electron microscopy immunocytoche mistry detects the cysteine-rich protein first during step 11 of sperm iogenesis in the mouse demonstrating that the cysteine-rich protein mR NA is under temporal translational control. Electron microscope immuno cytochemistry reveals that the cysteine-rich protein is evenly distrib uted in the cytoplasm in spermatids in steps 11 through early step 16 in mouse, and that it is associated with the outer mitochondrial membr anes of spermatids in late step 16 and epididymal spermatozoa. (C) 199 6 Wiley-Liss, Inc.