Duplication of an amphioxus myogenic bHLH gene is independent of vertebrate myogenic bHLH gene duplication.
Gene duplication is thought to be a major genetic change that may have permitted the evolution of vertebrates from invertebrates. The myogenic genes encode basic helix-loop-helix (bHLH) transcriptional factors essential for the formation of skeletal muscle. The invertebrate genome contains only a single myogenic bHLH gene, whereas the vertebrate genome contains four (MyoD, Myf-5, myogenin and MRF4). Since the tunicate genome contains a single myogenic bHLH gene, its duplication might have occurred some time during chordate evolution. To determine whether the duplication of the myogenic bHLH gene occurred prior to, or after the divergence of vertebrates from the cephalochordate lineage, we amplified target fragments from the amphioxus, Branchiostoma floridae, by means of PCR. Sequence analysis and genomic Southern analysis revealed that the amphioxus genome contains two myogenic bHLH genes (BMD1 and BMD2). A comparison of the amino acid sequences in the bHLH domain between BMD1, BMD2 and four vertebrate myogenic bHLH gene products, however, showed that neither BMD1 nor BMD2 resembled any of the four genes. These results suggested that the duplication of amphioxus myogenic bHLH gene occurred independently of that leading to the four myogenic bHLH genes in vertebrates.
Araki
I
I
Department of Zoology, Graduate School of Science, Kyoto University, Japan.
Terazawa
K
K
Satoh
N
N
D000595:Amino Acid Sequence; D000818:Animals; D001483:Base Sequence; D051792:Basic Helix-Loop-Helix Proteins; D005075:Biological Evolution; D002816:Chordata, Nonvertebrate / Q000235:genetics*; D004268:DNA-Binding Proteins / Q000235:genetics*; D019143:Evolution, Molecular; D005787:Gene Frequency; D006801:Humans; D008969:Molecular Sequence Data; D005810:Multigene Family; D009124:Muscle Proteins; D018006:Myogenic Regulatory Factors; D017386:Sequence Homology, Amino Acid; D014157:Transcription Factors / Q000235:genetics*; D014714:Vertebrates
D051792:Basic Helix-Loop-Helix Proteins; D004268:DNA-Binding Proteins; D009124:Muscle Proteins; D018006:Myogenic Regulatory Factors; D014157:Transcription Factors; C099925:BMD1 protein, Branchiostoma floridae; C099926:BMD2 protein, Branchiostoma floridae