Kinesin light-chain KLC3 expression in testis is restricted to spermatids

Kinesins are tetrameric motor molecules, consisting of two kinesin heavy ch ains (KHCs) and two kinesin light chains (KLCs) that are involved in transp ort of cargo along microtubules. The function of the light chain may be in cargo binding and regulation of kinesin activity. In the mouse, two KLC gen es, KLC1 and KLC2, had been identified. KLC1 plays a role in neuronal trans port, and KLC2 appears to be more widely expressed. We report the cloning f rom a testicular cDNA expression library of a mammalian light chain, KLC3. The KLC3 gene is located in close proximity to the ERCC2 gene. KLC3 can be classified as a genuine light chain: it interacts in vitro with the KHC, th e interaction is mediated by a conserved heptade repeat sequence, and it as sociates in vitro with microtubules. In mouse and rat testis, KLC3 protein expression is restricted to round and elongating spermatids, and KLC3 is pr esent in sperm tails. In contrast, KLC1 and KLC2 can only be detected befor e meiosis in testis. Interestingly, the expression profiles of the three kn own KHCs and KLC3 differ significantly: Kif5a and Kif5b are not expressed a fter meiosis, and Kif5c is expressed at an extremely low level in spermatid s but is not detectable in sperm tails. Our characterization of the KLC3 ge ne suggests that it carries out a unique and specialized role in spermatids .