Genomic organisation of rainbow trout, Oncorhynchus mykiss TGF-beta

The genomic organisation of Oncorhynchus mykiss TGF-beta has been determine d through the generation of contiguous clones by PCR, The O. mykiss TGF-bet a gene is approximately 3.4 Kb in length and consists of 7 coding exons wit h no introns in the 5'-UTR. Whilst this is the same number of exons found i n TGF-beta genes of amphibians, birds and mammals, in the O. mykiss gene in tron 2 of other vertebrates is absent and an additional intron is present a t the 3' end of the molecule, splitting exon 7 of the other known TGF-beta genes into two exons (trout exons 6 and 7). Comparison of exon sizes in the coding region support the suggestion that the Xenopus TGF-beta 5 and trout TGF-beta sequences are the forerunners of TGF-beta 1. Conservation of exon s coding for the mature TGF-beta peptide is relatively high (63-73% identit y) but other exons show lower identities (37-58%). Comparison of the TGF-be ta intron sequences reveals that in general the O. mykiss introns are consi derably shorter than the avian homologs. The impact of the teleost TGF-beta gene organisation on theories of the gene evolution of this cytokine famil y are discussed. (C) 1999 Elsevier Science Ltd. All rights reserved.