Studies on karyotype evolution in higher primates in relation to human chromosome 14 and 9 by comparative mapping of immunoglobulin C epsilon genes with fluorescence in situ hybridization.

Karyotypic homologies in relation to human chromosome 14 and 9 were studied through comparative mapping of the immunoglobulin C epsilon genes in higher primates by fluorescence in situ hybridization (FISH) technique. The C epsilon genes will be suitable probes for the analysis of evolutionary rearrangements due to that the multiple recombinational events such as gene duplications and deletions have occurred repeatedly in the immunoglobulin CH gene family (IGH@) during the course of primate evolution. IGH@ locating on the terminal region of human chromosome 14 (HSA14), at band HSA14q32.33, has generated multiple pseudogenes and among subclasses of IGH@ the C epsilon genes have shown most dynamic changes with generating both truncated type (C epsilon 2) and processed type (C epsilon 3) pseudogenes. In this study, chromosomal homologies and rearrangements on HSA14 (C epsilon 1) and HSA9 (C epsilon 3) in relation to the evolutionary genesis of their primate homologous chromosomes in speciation were investigated by comparative mapping with FISH and chromosome painting (ZOO-FISH) techniques. Comparative mapping of the C epsilon 1 gene at HSA14q32.33 was carried out in seven species of nonhuman primates: common chimpanzee (PTR), pygmy chimpanzee (PPA), gorilla (GGO), orangutan (PPY), white-handed gibbon (HLA), agile gibbon (HAG), and Japanese macaque (MFU). The C epsilon 1 gene was assigned to the telomeric region of HSA14 homologues in each species, namely, PTR15q32, PPA15q32, GGO18q16, PPY15q32, HLA17qter, HAG17qter, and MFU7q29, respectively. These results suggested that HSA14 has high degree of syntenic organization with its primate homologues confirmed by ZOO-FISH. Concerning HSA9, comparative mapping of the C epsilon 3 gene at HSA9p24.2-->p24.1 was performed. The mapped positions indicated the HSA9 homologous regions detected by ZOO-FISH in each species, namely, PTR11q34, PPA11q34, GGO13q22, PPY13q16, HLA8qter, HAG8qter, and MFU14q22, respectively, suggesting that several dynamic chromosomal rearrangements including at least twice pericentric inversions have occurred during the course of hominoid evolution. The comparison of syntenic groups and painting results has provided a hypothesis of the evolutionary genesis of HSA9 and its homologues with defined breakpoints on the present chromosomes. Likewise, studies on karyotype evolution will be promoted by combining comparative mapping with ZOO-FISH that can more clearly define the chromosomal rearrangements among species.