Molecular cloning of equine transforming growth factor-beta 1 reveals equine-specific amino acid substitutions in the mature peptide sequence

This study cloned and sequenced equine transforming growth factor (TGF)-bet a 1, yielding a unique nucleotide structure which predicted amino acid subs titutions not seen in other mammalian species. The nucleotide sequence homo logy was 89% to bovine, 91% to man, 90% to ovine, and 86% to rat. Derived a mino acid sequence comparison showed that the equine protein was unique, di ffering by two residues from man, cow, sheep, pig, and dog, and by three re sidues in the rat. Subsequent use of the cDNA clones to examine the express ion of the TGF-beta 1 gene in various tissues indicated predominant express ion in adult spleen and kidney, with an age-related peak in cartilage expre ssion at 12 months, followed by a decline as the animals matured. Northern blots showed that the predominant transcript sizes were 2.5 and 1.9 kb. Mor e sensitive mRNA detection using PCR reaction showed peak cartilage TGF-bet a mRNA levels in horses 0.7 and 1 year of age, with declining expression in older animals (2.5 and 5.5 years of age). In conclusion, although the prim ary nucleotide sequence of equine TGF-beta was relatively homologous to tha t of other species, the resulting amino acid sequence was unique to the hor se, differing by two residues from the majority of mammalian sequences, whe re the peptide structure is identical. Expression of TGF-beta was particula rly evident in spleen and kidney, and showed an age-related increase in exp ression in cartilage as the animals approached maturity and then a decline with progressive aging.