Evolution of duplicated growth hormone genes in autotetraploid salmonid fishes.

A defining character of the piscine family Salmonidae is autotetraploidy resulting from a genome-doubling event some 25-100 million years ago. Initially, duplicated genes may have undergone concerted evolution and tetrasomic inheritance. Homeologous chromosomes eventually diverged and the resulting reduction in recombination and gene conversion between paralogous genes allowed the re-establishment of disomic inheritance. Among extant salmonine fishes (e.g. salmon, trout, char) the growth hormone (GH) gene is generally represented by two functional paralogs, GH1 and GH2. Sequence analyses of salmonid GH genes from species of subfamilies Coregoninae (whitefish, ciscos) and Salmoninae were used to examine the evolutionary history of the duplicated GH genes. Two divergent GH gene paralogs were also identified in Coregoninae, but they were not assignable to the GH1 and GH2 categories. The average sequence divergence between the coregonine GH genes was more than twofold lower than the corresponding divergence between the salmonine GH1 and GH2. Phylogenetic analysis of the coregonine GH paralogs did not resolve their relationship to the salmonine paralogs. These findings suggest that disomic inheritance of two GH genes was established by different mechanisms in these two subfamilies.

The Tokumasu radish mitochondrial genome contains two complete atp9 reading frames.

Two copies of the gene atp9, encoding subunit 9 of the mitochondrial F1F0-ATPase, have been cloned from the Tokumasu radish (Raphanus sativus L.) cytoplasm. The genomic DNA and the corresponding cDNA sequences of the coding regions were determined. Both alleles contain a 222 bp long and well conserved atp9 reading frame, coding for a 74 amino acid polypeptide. The Tokumasu atp9-1 gene may have a unique N-terminal extension of 11 amino acid residue relative to other plant atp9 genes. In comparison of cDNA and genomic sequences four RNA editing events were found in both atp9 genes. Northern experiments indicate different transcription patterns for the two genes.