| Amphioxus or lancelet，a cephalochordate，has long been regarded as the closestliving invertebrate related to the proximate invertebrate ancestor of vertebrates．It iswell-known model organism widely used for interspecies comparative genome studiesand developmental homology analysis．Studies on the gene structure，function andexpression in amphioxus will contribute to the understanding of the origin and evolutionof the veaebrates．Sequencing of the whole genome of Florida amphioxus offers a newopportunity to the research of molecular and evolutionary biology of amphioxus．The transcription factor, activator protein-1(AP-1) is critical functional regulator of cellproliferation and differentiation. AP-1is a multi-protein complex consists of Jun (c-Jun,JunD, JunB) and Fos (c-Fos, Fra-1, Fra-2, FosB) proteins or activating transcriptionfactor subunits that can bind with the high affinity promoter and enhancer regions ofnumerous genes thus altering gene expression. The structures，functions，sequences andexpressions of many kinds of AP-1s have been studied deeply.The AP-1was reported inporcine and rat, yet it has not been previously investigated in amphioxus.Among gene families, Amphioxus always possessed a simple homology tovertebrate genes, so we can speculated that there is a homolog of AP-1in the amphioxus.We have isolated BjAP-1from the gonads of amphioxus, and studied BjAP-1genestructure, expression pattern and evolution. Through revealing the relationship betweenBjAP-1and invertebrate and vertebrate AP-1genes, we can understand the origin andevolution of vertebrates at the molecular level.In this study, an AP-1homologous gene, BjAP-1, was identified in amphioxusBranchiostoma japonicum. The full-length cDNA of BjAP-1contains966nucleotidesencoding321amino acid residues with a predicted molecular mass of approximately35.56kDa. Comparison between BjAP-1and other homologous genes revealed thatBjAP-1shared54.5%,54.1%,52.9%,52.8%,52.8%,51.3%,50.2%,50.5%,52.8%and 48.5%identity to Salmo salar, Danio rerio, Gallus gallus, Homo sapiens, Mus musculus,Sagitella kowalevskii, Acromyrmex echinatior, Xenopus laevis, Alligatormississippiensis, and Ruditapes philippinarum AP-1s, respectively.Phylogenetic analysis indicated that the deduced amino acid sequences of BjAP-1shared a highly conserved Jun domain with invertebrates and vertebrates’AP-1s whichimplied that BjAP-1gene was functional conservative during evolution. Phylogenetictree analysis showed that vertebrate and invertebrate AP-1proteins were each clubbedtogether，with BjAP-1falling at the base of vertebrate AP-1clade suggesting thatamphioxas is a invertebrate most closely related to the proximate invertebrate ancestorof vertebrates．To explore the expression pattern of BjAP-1in adult amphioxus, in situhybridization histochemistry was conducted. It was found that BjAP-1transcripts werelargely appeared in the ovary and hepatic caecum of phase4gonadal development stage,and at a lower level in the muscle, but no signal was observed in the testis, neural tubeand notochord which at the correspondent stage. These indicated that BjAP-1wasexpressed in a tissue and sex-specific manner. It may played an essential role in thedevelopment of ovary.Furthermore, Semi-quantitative RT-PCR results revealed that amphioxus AP-1transcript was most abundant expressed in the ovary of Amphioxus. In contrast, nosignals were detected in the testis. The results presented stable trends of increasing geneexpression levels and forming a peak at certain developmental stage (ovary phase4) inovary. All these results suggest that amphioxus AP-1factor is a specific molecule in theprocessing of female ovary development, agreeing with the in situ hybridization results. |
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