Characterization and expression of bone morphogenetic protein 4 gene in postnatal pigs.

Bone morphogenetic protein 4 (BMP4) is involved in animal embryonic development and reproductive physiology. The human and murine BMP4 genes have been isolated and characterized. The objectives of this study were to: (1) characterize the full mRNA and genomic sequence for porcine BMP4, and (2) examine BMP4 gene expression in 10 tissues of postnatal female pigs. Using RT-PCR, RACE and general PCR techniques, a 1,626 bp DNA including the full coding region of BMP4 was isolated and identified as a homologue of human BMP4 transcript variant (TV)-c. The porcine TV-c contained 3 exons and astride 3.6 kb in the isolated 7.8 kb porcine BMP4 genome. The In silicon cloning identified other three forms of mRNAs, including the homologues of human TV-1, TV-a and a novel variant related to human TV-3 (TV-3p). The porcine TV-c, TV-1 and TV-3p bear internal ribosome entry sites (IRES) in 5' untranslated region (UTR), while there are two ARE elements in the 3'UTR. The full genomic sequence of porcine BMP4 gene showed 81.38, 76.23 and 64.00% identity with that of bovine, human and murine, respectively. The expression of BMP4 mRNA was determined by RT-PCR in 7, 14, and 28 day old female piglets and non-gestational sows. The results showed that porcine BMP4 occurred in all 10 examined tissues (heart, lung, liver, kidney, ovary, spleen, spinal medulla, brain, duodenum and thymus). The mRNA expression levels were relatively higher in lung and kidney in 7 day old piglets, thymus in 14 day old piglets, and spleen in 28 day old piglets, respectively, while the higher expressions were detected in liver of non-gestational pigs (P < 0.05). Moreover, the mRNA amounts both in 7 day old piglets and sows were generally higher than those in 14 and 28 day old piglets in nearly all examined tissues, except in thymus. It is concluded that the structure of porcine BMP4 gene is highly conservative with other mammalian BMP4 genes, but some differences may present in the regulation of gene expression. BMP4 mRNAs are expressed in postnatal pigs, and is spatiotemporally regulated.