RESUMO
Aromatic amino acid hydroxylase (AAAH) genes and insulin-like genes form part of an extensive paralogy region shared by human chromosomes 11 and 12, thought to have arisen by tetraploidy in early vertebrate evolution. Cloning of a complementary DNA (cDNA) for an amphioxus (Branchiostoma floridae) hydroxylase gene (AmphiPAH) allowed us to investigate the ancestry of the human chromosome 11/12 paralogy region. Molecular phylogenetic evidence reveals that AmphiPAH is orthologous to vertebrate phenylalanine (PAH) genes; the implication is that all three vertebrate AAAH genes arose early in metazoan evolution, predating vertebrates. In contrast, our phylogenetic analysis of amphioxus and vertebrate insulin-related gene sequences is consistent with duplication of these genes during early chordate ancestry. The conclusion is that two tightly linked gene families on human chromosomes 11 and 12 were not duplicated coincidentally. We rationalize this paradox by invoking gene loss in the AAAH gene family and conclude that paralogous genes shared by paralogous chromosomes need not have identical evolutionary histories.
Assuntos
Evolução Molecular , Fator de Crescimento Insulin-Like II/genética , Fator de Crescimento Insulin-Like I/genética , Neuropeptídeos/genética , Fenilalanina Hidroxilase/genética , Sequência de Aminoácidos , Animais , Sequência de Bases , Caenorhabditis elegans/genética , Bovinos , Galinhas , Cordados não Vertebrados/genética , Mapeamento Cromossômico/métodos , Clonagem Molecular , DNA Complementar/genética , Drosophila melanogaster , Peixes , Duplicação Gênica , Humanos , Camundongos , Dados de Sequência Molecular , Família Multigênica/genética , Filogenia , Codorniz , Coelhos , Ratos , Homologia de Sequência do Ácido Nucleico , Triptofano Hidroxilase/genética , Tirosina 3-Mono-Oxigenase/genética , Xenopus laevisRESUMO
Previous studies of the Robertsonian polymorphism in the Atlantic dog-whelk, Nucella lapillus (2n = 26-36), have been limited by the inability to identify unequivocally individual chromosomes in the karyotype. This species, as with many other marine invertebrates, has proven largely refractory to the standard (mammalian) chromosome-banding techniques. In this study, fluorescence in situ hybridization (FISH) using a rDNA probe was applied to the metaphase chromosomes of the 2n = 26 and 2n = 36 forms of N. lapillus. The results were compared with silver-staining of the nucleolar organizer regions (NORs). The FISH technique was shown to be more sensitive and less intrinsically prone to variation than the silver-staining method. An additional NOR/rDNA locus was observed in the 2n = 36 form which, to date, has not been seen in any 2n = 26 population. The 2n = 36 karyotype is described for a south-west UK population that differs from that reported previously in the literature. After fission, Robertsonian metacentrics are shown to correspond to at least one subtelocentric product.
