The sperm
protein associated with nucleus in the X chromosome (SPANX) gene family is constituted by only a few members, clustered at Xq27, encoding small
proteins which range from 15 to 20 kDa. These
proteins have been shown to be present both in mature spermatozoa and in tumours, such as
melanoma and some leukaemias. We developed polyclonal sera in order to study the distribution of the
protein in human-ejaculated spermatozoa and their precursors. A synthetic
peptide was designed from a domain common to the SPANX
protein family and polyclonal sera were raised in mice. Seven healthy volunteer men with normal sperm parameters were recruited and the expression of SPANX
proteins was evaluated in spermatozoa and ejaculated sperm precursors by immunocytochemistry and immunofluorescence analyses. SPANX
proteins, present in a large fraction (96%) of mature spermatozoa, were localized in the sperm head (39.2%), midpiece (22.8%) or in both sites (34.4%). Spermatids also showed the presence of SPANX
proteins in their cytoplasm, although a significantly higher number of spermatids were SPANX-negative compared with spermatozoa. In conclusion, SPANX
proteins are expressed in an elevated percentage of spermatids and mature spermatozoa. In the latter, they are preferentially located in the sperm head. The greater number of SPANX-negative spermatids observed could relate to their easier exfoliation from the seminiferous tubules.