Two novel RXR alpha isoforms from mouse testis.

We report the isolation from mouse testis cDNA of two novel RXR alpha isoforms, mRXR alpha 2 and mRXR alpha 3, with distinct sequences upstream of exon 2. These two isoforms encode a similar protein (mRXR alpha 2/3) which lacks that 28 N-terminal amino acid residues of the major RXR alpha isoform, mRXR alpha 1. The N-terminal activation function (AF-1) of mRXR alpha 2/3 appears altered when compared to that of mRXR alpha 1. mRXR alpha 2 and mRXR alpha 3 are specifically expressed in the testis, and their expression is strongly upregulated in this tissue at puberty. These observations increase the molecular complexity of RXRs, and indicate that RXR alpha may play a specific function during spermatogenesis.