Genomic, cDNA, and embryonic expression analysis of zebrafish transforming growth factor beta 3 (tgfβ3)

TGF beta 3, a member of the transforming growth factor P family, regulates a spectrum of biological processes and is involved in mammalian pulmonary and craniofacial development. Homologs of human TGF beta 3 have been identified in several vertebrate species. We sequenced a cDNA clone of zebrafish tgf beta 3, consisting of a 271-bp 5' untranslated region, a 1,233-bp open reading frame that encodes a predicted 410 amino acid peptide, and a 527-bp 3' untranslated region. Using 5' rapid amplification of eDNA ends, the transcription start site of this gene was determined to lie an additional 29 nucleotides upstream. The gene is composed of seven exons and maps to a segment of linkage group 17 that is syntenic to the human TGF beta 3 locus on chromosome l4q24. One stimulating protein 1 (Sp1) and two (TATA binding protein) (TBP) transcription factor binding sites were identified in the putative promoter segment upstream of the transcription start site. Comparative alignment analysis revealed a high degree of tgf beta 3 nucleotide and amino acid identity between zebrafish and other species, including complete conservation of the cysteine knot structure that facilitates protein-protein interaction. Also, 9 of 10 amino acid residues critical for ligand/receptor binding in human TGF beta 3 are conserved in zebrafish, suggesting a high degree of functional conservation even in lower vertebrates. Zebrafish tgf beta 3 transcripts were first detected in the notochord (10 somite to high-pec stage), followed by expression in the developing pharyngeal arch and neurocranial cartilage (18 somite to protruding mouth stage), lens and heart (21 somite to protruding mouth stage), and pectoral fins (prim-25 to protruding mouth stage). The strong expression in the pectoral fins, not reported in the orthologous mammalian forelimb, suggests a modified or novel function of tgf beta 3 during early fish development. (c) 2005 Wiley-Liss, Inc.