A novel transcript encoding truncated LIM kinase 2 is specifically expressed in male germ cells undergoing meiosis

LIM kinases, composed of LIMK1 and LIMK2, have unique structural features that contain two LIM motifs at the N-terminus and a catalytic domain at the C-terminus. We report evidence of a novel type of mouse LIMK2 (Limk2) transcript specifically expressed in testis. cDNA cloning showed this Limk2 variant, designated tLimk2, lacked LIM domains at the N-terminus, due to usage of a testis-specific, alternative initiation exon. In Northern blot analysis, tLimk2 was detected in intact adult testis, but not in germ-cell-deficient or immature testis, indicating the stage-specific expression of tLimk2 in spermatogenic cells. In situ hybridization clearly demonstrated that tLimk2 was restrictedly expressed in differentiated germ cells (pachytene spermatocytes to round spermatids) and not expressed in early stages of spermatogenic cells and somatic cells in testis. These results suggested the possibility that the tLimk2 product is involved in spermatogenesis, especially in meiotic and/or postmeiotic processes.