Distinct Tissue Distribution in Pigs of Tenascin-X and Tenascin-C Transcripts

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Abstract
Tenascin-X and tenascin-C glycoproteins are phylogenetically conserved components of the extracellular matrix, although their specific roles remain to be determined. cDNA probes were produced from pig tenascin-X and tenascin-C genes and were used to examine the tissue distribution of the transcripts in 28 tissues from Large-White pigs, 4.5-42-months old (called adults) and 17 tissues from 87-day-old fetuses. The hybridization of Northern blots with tenascin-X probes revealed, in most tissues, a complex pattern of bands including a major band of about 13 kb, assumed to correspond to the main tenascin-X transcript. Hybridization with the tenascin-C probe showed two transcripts of 6.8 kb and 8.2 kb. The data from the ribonuclease-protection technique showed that both genes displayed large variations in the transcription levels among the tissues analysed. Overall, the tenascin-X gene was significantly expressed in two thirds of the tissues, and the tenascin-C gene in about 50% of them. The highest tenascin-X signals were observed in tendons, ligaments and, unexpectedly, in peripheral nerves. Other tissues, including colon, dermis, skin, heart, uterus, stomach, jejunum, placentae, aorta, lung, mammary and adrenal glands also exhibited significant signal intensities. In fetuses, mainly testes and skeletal muscle showed higher transcription levels than the adult counterparts. The tenascin-C gene was predominantly transcribed in the ligament, tendon, adrenal gland and colon, and more weakly in the stomach, jejunum, lung and spinal cord. In fetuses, the tenascin-C signal in the brain was higher than the signal in the brain of adult, whereas the reverse was true for the adrenal gland and the colon. Within a given tissue, the level of tenascin-X and tenascin-C transcripts varied greatly, indicating independent tenascin-X and tenascin-C transcription regulation mechanisms; this was particularly obvious in adult and fetal nerves but also in the dermis, skin, heart, uterus, placentae and aorta, where tenascin-X RNA molecules were much more abundant than those of tenascin-C. In addition, similar differences were observed in the skeletal muscle and adrenal gland of fetuses. In contrast, the amount of tenascin-C transcripts in the fetal brain and adult spinal cord was higher than those for tenascin-X. Our results draw attention to a possible specific role of tenascin-X in the peripheral nerve physiology.