Correlation between SPANX gene expression and testicular germ cell tumours

The sperm protein associated with the nucleus (SpanX) is a gene family recently identified in the X chromosome. According to the Build 36 database, seven genes belonging to this family have been described and named SpanX-A1, SpanX-A2, SpanX-B1, SpanX-B2, SpanX-C, SpanX-D, and SpanX-E. These genes, made up by two exons separated by a small intron of 648 bp, map in a 600 Kb interval of the human Xq27.1. Although the function of the proteins codified by each SpanX gene is not yet clear, we showed that about 95% of spermatozoa and about 90% of sperm precursors were SpanX positive using a new polyclonal antibody directed against a common SpanX protein epitope. It is intriguing that the SpanX gene family maps on the so-called testicular germ cell tumour (TGCT1) locus which has been shown to predispose to testicular cancer development. In addition, it has been shown that CTp11 (cancer/testis-associated protein of 11 KDa), which is 100% homologous to Spanx-C, is expressed in many tumours, such as melanoma, myeloma, glioblastoma, leukemias. Moreover the Xq27 region is interested by duplications, inversions and deletions and LDOC1, a potential oncosuppressor, is located in this region. These observations suggested that SpanX genes, or some of them, may be involved in the development of TGCT. We reported that SpanX proteins are expressed in germ cells-derived testicular tumours by immunohistochemical analysis of paraffin-embedded sections. In seminomas, they were present in the nucleus and 81±2% of the cells were SpanX-positive. In embryonal cell carcinomas only 53±5% of the cells were found to be SpanX-positive. In a subsequent study, we confirmed, by RT-PCR on mRNA obtained from paraffined testicular sections, the expression of SpanX mRNA in seminomas and embryonal cell carcinomas. Both tumours exhibited a strong expression.