THE HETEROTRIMERIC MOTOR PROTEIN KINESIN-II LOCALIZES TO THE MIDPIECEAND FLAGELLUM OF SEA-URCHIN AND SAND DOLLAR SPERM

We have utilized immunoblotting and light microscopic immunofluorescen t staining methods to examine the expression and localization of sea u rchin kinesin-IT, a heterotrimeric plus end-directed microtubule motor protein (previously referred to as KRP(85/95)), in sea urchin and san d dollar sperm. We demonstrate the presence of the 85 K and 115 K subu nits of kinesin-II in sperm and localize these proteins to the sperm f lagella and midpiece. The kinesin-II localization pattern is punctate and discontinuous, and in the flagella it is quite distinct from the c ontinuous labeling present in sperm labeled with anti-flagellar dynein . The kinesin-II staining is largely insensitive to prefixation deterg ent extraction, suggesting that it is not associated with membranous e lements in the sperm. In the midpiece the kinesin-II staining is simil ar to the pattern present in sperm labeled with an anti-centrosomal an tibody. To our knowledge, this is the first localization of kinesin-li ke proteins in mature sperm and corroborates the recent identification and localization of kinesin-like proteins in the flagella and basal b ody of the unicellular green alga Chlamydomonas. We hypothesize that k inesin-II in the sperm may play functional roles in intraflagellar tra nsport and/or the formation of flagella during spermatogenesis. (C) 19 97 Wiley-Liss,Inc.