Evolution of messenger RNA structure and regulation in the genus Mus: the androgen-inducible RP2 mRNAs.

The RP2 gene is one of several genes that are regulated by androgens in the mouse kidney. Previous studies have demonstrated that androgen inducibility of RP2 transcription varies among species within the genus Mus, indicating extensive evolutionary modification of the participating regulatory elements. Thus, while a five-fold induction of transcription occurs in M. domesticus, none is detectable in M. hortulanus or M. caroli. In the present paper, we have sequenced cDNAs representing the RP2 mRNAs of M. caroli and M. saxicola and have compared them with each other and with M. domesticus. Several findings from the sequence comparisons indicate that the encoded 41-kD polypeptide is physiologically functional. First, divergence within noncoding regions of the mRNAs exceeds that within coding regions. Second, the 357-codon open reading frame has been maintained among the species, with approximately 90% of the amino acid replacements being conservative. Finally, substitution rates at synonymous sites within the coding regions are from twofold to threefold greater than those at nonsynonymous sites. The genetic elements responsible for variations in RP2 inducibility among species were studied by cis/trans analyses of mice heterozygous for RP2 alleles, using a primer extension assay to measure expression of species-specific mRNAs. The results show that the absence of transcriptional induction in M. hortulanus is due to a cis-acting genetic element, while that in M. caroli is due to a trans-acting element. Thus, the androgen-resistant RP2 phenotypes of these two species derive from distinct genetic events.