Xp. Shao et al., Spag4, a novel sperm protein, binds outer dense-fiber protein Odf1 and localizes to microtubules of manchette and axoneme, DEVELOP BIO, 211(1), 1999, pp. 109-123
Outer dense fibers are structures unique to the sperm tail. No definite fun
ction for these fibers has been found, but they may play a role in motility
and provide elastic recoil. Their composition had been described before, b
ut only two of the fiber proteins, Odf1 and Odf2, are cloned. We cloned Odf
2 by virtue of its functional and specific interaction with Odf1, which, we
show, is mediated by a leucine zipper. Further work demonstrated that the
84-kDa Odf2 protein localizes to both the cortex and the medulla of the fib
ers, whereas the 27-kDa Odf1 protein is present only in the medulla. Here w
e report the cloning and characterization of a new Odf1-interacting protein
, Spag4. Spag4 mRNA is spermatid specific, and the 49-kDa Spag4 protein com
plexes specifically with Odf1, but not Odf2, mediated by a leucine zipper.
It also self-associates. In contrast to Odf1 and Odf2, Spag4 protein locali
zes to two microtubule-containing spermatid structures. Spag4 is detectable
in the transient manchette and it is associated with the axoneme in elonga
ting spermatids and epididymal sperm. Our data suggest a role for Spag4 in
protein localization to two major sperm tail structures. (C) 1999 Academic
Press.