SPERMATID PERINUCLEAR RIBONUCLEIC ACID-BINDING PROTEIN BINDS MICROTUBULES IN-VITRO AND ASSOCIATES WITH ABNORMAL MANCHETTES IN-VIVO IN MICE

Spermatid perinuclear RNA-binding protein (SPNR) is a microtubule-asso ciated RNA-binding protein that localizes to the manchette in developi ng spermatids. The RNA target of SPNR in vivo is unknown, although we have previously suggested the possibility that SPNR is involved in the translational activation of the protamine 1 mRNA in elongated spermat ids. To increase our understanding of SPNR's association with the manc hette, we sought to determine SPNR's subcellular localization in sever al mouse mutants that show reduced fertility or sterility and that hav e structurally abnormal manchettes. We show here that despite the high ly abnormal manchettes and microtubule aggregates formed in azh, hop-s terile, t(w2) and t(w8) mutants, SPNR remains associated with the manc hettes. Localization of SPNR to the abnormal manchettes suggests that SPNR is tightly bound to the manchette. SPNR could bind manchette micr otubules directly, or it could bind indirectly via an interaction with a microtubule-associated protein (MAP). We sought to determine whethe r SPNR binds microtubules in vitro, and if so, whether it requires a M AP. We show by Western analysis that the endogenous SPNR protein can b e pelleted with murine testis microtubules in a taxol-dependent manner in vitro. A recombinant version of SPNR produced in bacteria can also be pelleted with testis microtubules, as well as microtubules polymer ized from purified bovine brain tubulin, an association that is salt-s ensitive. These results suggest that SPNR, in addition to its function as an RNA-binding protein, is also a bona fide MAP.