The murine Spam1 gene: RNA expression pattern and lower steady-state levels associated with the Rb(6.16) translocation.

Recently we mapped the murine Spam1 gene to the proximal region of chromosome 6 (MMU 6). Based on the map location and physiological characteristics of its encoded sperm antigen, the gene is an attractive candidate for the sperm dysfunction seen in Rb(6.16) translocation heterozygotes and the reduced fertility of homozygotes. We have analyzed the expression of Spam1 mRNA in normal and Rb(6.16) mice. The expression of Spam1 mRNA was found to be: 1) tissue specific; it is expressed exclusively in testis; and 2) developmentally regulated, with a haploid expression. Notably, the steady-state mRNA level of Spam1 in Rb(6.16) homozygotes was 25-30% of that in chromosomally normal consomic mice and those homozygous for Rb(2.8) (7.18). In Rb(6.16) and Rb(6.15) heterozygotes the levels were 61% and 66% of the normal. Studies are currently under way to determine the protein levels and gene structure of Spam1, to detect the underlying cause of the mRNA reduction associated with these translocations.