Institute of Basic Medical Sciences, University of Tsukuba, Ibaraki, Japan.
The cDNA encoding a mouse homologue of porcine epididymis-specific 135kDa alpha-D-mannosidase (MAN2B2, D28521) was cloned from the mouse testis cDNA library. It was found that 1018 amino acids were coded in its open reading frame, and 62% of the amino acid sequence was identical to that of porcine MAN2B2. In the adult mouse, testis contained higher amounts of mRNA encoding the MAN2B2 homologue than the epididymis, though porcine MAN2B2 was mainly expressed in the narrow region between the caput and corpus epididymis. mRNA of the mouse MAN2B2 homologue was localized exclusively in spermatogonia in the testis. It was specifically expressed in type A spermatogonia at stages IX-XI of spermatogenesis and was detected there until the cell developed into type B spermatogonia. We conclude that the expression of the MAN2B2 homologue can serve as a good marker for the late stages of type A spermatogonia and may have an important role to play in the early step of spermatogenesis in mice.