Differential expression of multiple alternative spliceforms of the Men1 tumor suppressor gene in mouse

The multiple endocrine neoplasia type 1 gene (MEN1) is a tumor suppressor g ene associated with the development of tumors in the parathyroids, the pitu itary, and the pancreas and has also been linked to impaired germ cell prod uction. The murine ortholog, Men1, is highly homologous to the human counte rpart both at DNA and protein levels. The present study was undertaken to f urther approach the function of Men1 and its encoded protein menin. By 5'RA CE and RTPCR four alternative splice variants were identified, indicating a 5' heterogeneity of Men1 similar to the human counterpart. By mRNA in situ hybridization of embryonal and adult mouse tissues, all four splice varian ts were shown to be expressed, albeit at varying timepoints and levels in t he different tissues. However, a putative isoform postulated from the DNA s equence, which would elongate the reading, frame by 15 bases at the exon 2/ intron 2 junction, was not found to occur in mouse. The strongest expressio n was detected in testis, both at the mRNA and protein level and was theref ore further characterized by protein analysis of cells isolated from differ ent stages of the spermatogenesis. Western blotting revealed a single prote in of approximately 70 kDa. detected in total testis, isolated pachytene sp ermatocytes and in haploid spermatids. Notably, no menin expression was det ectable in the extracts from epididymis where the maturation of sperms is a lmost completed, suggesting that menin plays a crucial role during spermato genesis.