On reassessment of the chicken TGFB4 gene as TGFB1.

Three TGFB isoforms, TGFB1-3, are present in mammalian cells. The presence of four TGFB isoforms has been reported in avian species, though the sequence of TGFB4 was not conclusively determined. Our previously published data show that TGFB4 is actually the chicken ortholog of TGFB1. We mapped TGFB1 but not TGFB4 to linkage group E25C31 on GGA32 next to RYR1 forming a conserved segment with human chromosome HSA19q13.1-q13.2 and, therefore, being definitely the ortholog of human TGFB1. We, therefore, suggest that what was once called chicken "TGFB4" is actually TGFB1. Thus, in the evolutionary lineages of birds and mammals there are only three TGFB isoforms.