Rapid divergency of rodent CD99 orthologs: implications for the evolution of the pseudoautosomal region.
The human pseudoautosomal region 1 (PAR1) is essential for the obligatory X-Y crossover in male meiosis. Despite its critical role, comparative studies of human and mouse pseudoautosomal genes have been limited owing to the scarcity of genes conserved between the two species. Human CD99 is a 32-kDa cell surface protein that is encoded by the MIC2 gene localized to the PAR1. Although several sequences such as CD99L2, PBDX, and CD99L1 are related to CD99, its murine ortholog, Cd99, has not yet been identified. Here we report a novel mouse Cd99, designated D4, which shows overall sequence homology to CD99, with the highest conservation between the two genes being found in the transmembrane regions. In addition, the D4 protein displays biochemical characteristics, functional homology, and expression patterns similar to those of CD99. The D4 gene is localized on an autosome, chromosome 4, reflecting a common mapping feature with other mouse orthologs of human PAR1 genes. Furthermore, a phylogenetic analysis of CD99-related genes confirmed that the D4 gene is indeed an ortholog of CD99 and exhibits the accelerated evolution pattern of CD99 orthologs, as compared to the CD99L2 orthologs. On the basis of these findings, we suggest that CD99 belongs to the ancient PAR genes, and that the rapid interspecies divergence of its present sequence and map position is due to a high recombination frequency and the occurrence of chromosomal translocation, supporting the addition-attrition hypothesis for PAR evolution.
Department of Pathology, Seoul National University College of Medicine, 28 Yongon-dong Chongno-gu, Seoul 110-799, South Korea. pshoe@plaza.snu.ac.kr
Seong Hoe
SH
Park
Young Kee
YK
Shin
Young Ho
YH
Suh
Won Seo
WS
Park
Young Larn
YL
Ban
Hueng-Sik
HS
Choi
Hyo Jin
HJ
Park
Kyeong Cheon
KC
Jung
D000071443:12E7 Antigen; D000595:Amino Acid Sequence; D000818:Animals; D015703:Antigens, CD / Q000737:chemistry / Q000235:genetics*; D001483:Base Sequence; D015815:Cell Adhesion Molecules / Q000737:chemistry / Q000235:genetics*; D002874:Chromosome Mapping; D022202:Chromosomes, Artificial, Bacterial; D003001:Cloning, Molecular; D017931:DNA Primers; D018076:DNA, Complementary; D005434:Flow Cytometry; D006801:Humans; D017404:In Situ Hybridization, Fluorescence; D051379:Mice; D008969:Molecular Sequence Data; D010802:Phylogeny; D012377:Rodentia / Q000145:classification / Q000235:genetics; D017386:Sequence Homology, Amino Acid; D014981:Xenopus
D000071443:12E7 Antigen; D015703:Antigens, CD; C061828:CD99 protein, human; D015815:Cell Adhesion Molecules; D017931:DNA Primers; D018076:DNA, Complementary