Cloning and characterization of NM23-Bbt2 gene from amphioxus Branchiostoma belcheri tsingtauense

A full-length amphioxus (Branchiostoma belcheri tsingtauense) NM23-Bbt2, NM23-H2 homologue, cDNA was isolated from the cDNA library and sequenced. The obtained amphioxus NM23-Bbt2 cDNA contains an open reading frame coding for 171 amino acids. Sequence analysis showed that the amphioxus NM23-Bbt2 was highly conserved with that of other species, and all of them contained highly conserved motifs that play important roles in the function of NM23. RT-PCR revealed that NM23-Bbt2 is expressed in the neuronal tissues and is expressed in all stages during the embryogenesis. Nucleoside kinases are thought to have a critical role in regulatory processes such as signal transduction, proliferation, and differentiation. Taken together, these results suggest that nucleoside diphosphate kinases have an important role to play in embryogenic development in amphioxus. Phylogenetic analysis showed that the amphioxus group 1 NDPKs (Bf1-4) may be precursors of the human group 1 NDPKs, NM23-Bf5, NM23-Bf6, NM23-Bf7 and NM23-Bf8 may be precursors of NM23-H5, NM23-H6, NM23-H7 and M23-H8, respectively. Our finding of nine NM23 genes in Branchiostoma floride, the precursor of vertebrates, strongly suggests that the ancestral gene corresponding to each of vertebrates NM23 genes generated before the appearance of vertebrates. Comparison of the gene structures of NM23-H2 homologue from invertebrates to vertebrates suggests that the locations of three of the four introns are conserved in amphioxus and vertebrates.