The lower chordate amphioxus is the closest living invertebrate relative of the vertebrates. To elucidate the relationship between gene expression and embryonic development of the complex vertebrate body, 3?075 bp cDNA of an amphioxus novel gene, named sfy1, was cloned from Qingdao amphioxus neurulae by RT-PCR, subsequent cDNA library screening and 5′RACE (rapid amplification of cDNA ends) reaction. It contained a complete open reading frame encoding a putative protein of 325 amino acid residues, with a 650 bp 5′untranslational region (UTR) and a 1?435 bp 3′UTR. No significant alignment was found between sfy1 amino acids and any other sequences in GenBank. Whole mount in situ hybridization followed by sectioning revealed its expression in endoblast of the whole alimentary canal, including pharynx and gut at neurula and early larva stages. Very little has been known about the gut development in amphioxus. As whole mount in situ hybridization showed,no positive signal was detected in blastula, gastula and neurula of younger embryos (12 hours); at 8 hours development, a positive staining was visible in the endoderm of whole alimentary canal, including the pharynx and gut, and by 18 hours the mRNA level of sfy 1 gene was highest in endoderm of whole amphioxus embryo,and thereafter the expression level gradually declined.The spatial and temporal characteristics of sfy1 expression coincided with that of primitive pharynx and gut development in amphioxus. Because of the endoderm specific expression pattern, sfy1 could be used as an endoderm marker.
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