TRANSPOSITION OF RHOA TO THE MURINE Y-CHROMOSOME

In an effort to produce a more complete transcription map of the short (similar to 5 Mb) arm of the mouse Y chromosome, we have initiated ex on trapping from Yp-derived YACs. Sequence analysis of the trapped pro ducts has identified exons of previously cloned mouse Y-located genes Zfy and SSty and potential exons homologous to the human Y-located Tsp y gene family. In addition, a family of three Yp-located transcripts t hat show close homology to human RHOA (locus designation ARHA), a memb er of the Ras family of small GTPases, has been identified. To determi ne whether these Yp sequences had been transposed from an autosomal an cestor, we used this trapped product to isolate a full-length autosoma l mouse RhoA cDNA that is 80% identical at the nucleotide level and 98 % identical at the amino acid level to human RHOA and maps to mouse Ch romosome 2 (locus designation ArhA). Sequence analysis indicates that the Y-linked copies have diverged from the autosomal form, with small deletions precluding maintenance of a significant open reading frame i n all Yp copies. Yet RT-PCR analysis indicates that two of these pseud ogenes, RhoAy1 and 3, are expressed in a testis-specific manner, in sh arp contrast to the nearly ubiquitous expression pattern of the autoso mal ancestor. The data indicate that the Y copies of RhoA have been tr ansposed from an autosome, followed by subsequent duplication, sequenc e divergence, and acquisition of a testis-specific promoter/enhancer. (C) 1998 Academic Press.