Nucleotide sequence of cDNA and primary structure for hard tail growth hormone

Sequence analysis suggests a recent duplication of the growth hormone-encoding gene in Tilapia nilotica

The sequence of two growth hormone(GH)-encoding genes from tilapia fish (Tilapia nilotica) is reported. Our data indicate that the presence of two GH in the tilapia genome is a consequence of a relatively recent duplication event. The two genes are highly homologous, having a similar intron (five)/exon (six) arrangement, and both encode an identical polypeptide. Sequence similarity extends up to bp -628 upstream to the transcription start point, after which the sequences of the two genes are not related to each other. The presence of two GH in the tilapia genome is supported both by the nucleotide sequence and by genomic DNA blot hybridization analysis. Tilapias, like salmonids, contain an extra intron compared with the mammalian GH structure. We suggest that within the superorder Teleostei, the insertion of intron 5 into GH took place after the evolutionary separation of Cyprinoidea, but before Isospondyli (salmonids) and Acanthopterygii (tilapias) were separated. Thus, the additional intron which is probably present in many teleost fish GH may provide an excellent natural marker for evolution and classification studies.

Cloning and sequencing of the grass carp (Ctenopharyngodon idellus) growth hormone gene

An enriched lambda gt11 library for screening the grass carp (Ctenopharyngodon idellus) growth hormone gene was constructed using HindIII digested genomic DNA extracted from the spleen of the fish. Probing this library with a homologous cDNA, a clone carrying the growth hormone gene was obtained. The gene is 2501 bp long and consists of five exons and four introns. The sequence of nucleotide in the exons is almost identical to that of the cDNA except for ten positions. Analysis of the 5' sequence up to 1220 bp from the +1 position reveals the presence of a TATA box as well as a number of consensus regulatory sequences. Comparison of the grass carp growth hormone gene with those of other fish indicates that there is a high degree of homology with the gene from the common carp but not with those from the rainbow trout and Atlantic salmon.