Molecular cloning and tissue distribution of pig transforming growth factor alpha

Transforming growth factor alpha (TGF alpha) was originally identified as a product of tumour tissues and transformed cells in culture. Although it is now clear that expression of this factor is not restricted to neoplastic cells, there remains relatively little information about the sites of expression of TGF alpha in normal tissues. Therefore, an amplified DNA fragment encoding the pig TGF alpha precursor was cloned by reverse transcription-PCR (RT-PCR) using RNA isolated from normal skin tissue as the template. Nucleotide sequence analysis predicts a 160-residue transmembrane polypeptide that differs from the rat, mouse and human TGF alpha precursors at 14, 15 and six sites respectively. The distribution of TGF alpha mRNA in a wide variety of pig tissues was analysed by RT-PCR, using oligonucleotide primers based on the pig TGF alpha cDNA sequence. TGF alpha transcripts were detected in RNA isolated from 17 of the 22 tissues analysed, including four previously unreported sites. Using an antibody raised against a synthetic TGF alpha peptide, we have immunolocalized TGF alpha protein to cells within the red pulp of the spleen and to the distal convoluted tubules of the kidney.