Cloning and function of morphologyrelated gene HoxB1b in Megalobrama amblycephala

Abstract:

Vertebrate Hox family genes play important roles in growth and development, which encode a helixturnhelix transcription factor and activate downstream target genes by binding the specific DNA region,to regulate the axial pattern formation during ontogeny. Changes in number and in genomic organization of Hox genes are believed to determine various morphology and new species in teleost fish. In this study, the complete cDNAs of blunt snout bream (Megalobrama amblycephala) HoxB1b gene was cloned by rapid amplification of cDNA ends (RACE), and its expression patterns were studied. Our results showed: (1) The whole length of HoxB1b cDNA in blunt snout bream was 1 479 bp, consisting of an open reading frame (ORF) which encodes a 306 amino acid (aa) residues. Phynogenetic analysis showed that blunt snout bream HoxB1b gene demonstrated 89%, 45% and 40% similarity with that of zebrafish, fugu and medaka. (2) During embryogenesis, HoxB1b was stably expressed in all stages except mature eggs, which suggested it was a nonmaternal gene. Further whole embryo in situ hybridization analysis showed HoxB1b obvious spatial expression differences during embryogenesis of blunt snout bream. At early embryonic stage of 20 hours post fertilization (20hpf), HoxB1b expressed mainly in the hindbrain, whereas its expression was also detected in the pectoral fins at the late stage of 40hpf. (3) At adult stage, the expression of HoxB1b was detected in some fish tissues, and there are some differences between male and female in different tissues. In summary, these results suggest that HoxB1b gene plays a crucial role in hindbrain and pectoral fins during embryogenesis, as well as in relative tissues in adult stage at blunt snout bream.