Male-enhanced antigen-1 gene flanked by two overlapping genes is expressed in late spermatogenesis.

The male-enhanced antigen-1 gene (Meal) was originally isolated from a murine testicular cDNA library using anti-H-Y antigen antisera and was assigned to chromosome 17. On analysis of its structure and expression, we found that the Meal genomic sequence is flanked by two other genes: Ppp2r5d present in its T-terminus in a tail-to-tail orientation and a novel gene called Peas in its 5'-terminus in a head-to-head orientation. The coding sequences of the two genes embedded in the Meal sequence are located on the opposite DNA strands of Meal. Cap-site analysis of Meal revealed that it is transcribed from at least seven sites. Most splice variants of Meal were abundantly expressed in the testis; the d-type was weakly expressed in the other tissues. AP-2-binding motifs were detected in the transcription-initiation sites. In situ hybridization and immunohistochemical studies revealed Meal expression in pachytene spermatocytes. This expression was most prominent in spermatids and residual bodies. The Meal protein was also localized in the cytoplasm of elongated spermatids and residual bodies. Localization of the Meal suggests that it may function in the very late stages of spermiogenesis. The possibility that Meal is one of the serologically detectable male antigens is discussed.