DISTINCT TISSUE DISTRIBUTION IN PIGS OF TENASCIN-X AND TENASCIN-C TRANSCRIPTS

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 distributio n of the transcripts in 28 tissues from Large-White pigs, 4.5-42-month s old (called adults) and 17 tissues from 87-day-old fetuses. The hybr idization of Northern blots with tenascin-X probes revealed, in most t issues, a complex pattern of bands including a major band of about 13 kb, assumed to correspond to the main tenascin-X transcript. Hybridiza tion 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 amon g the tissues analysed. Overall, the tenascin-X gene was significantly expressed in two thirds of the tissues, and the tenascin-C gene in ab out 50% of them. The highest tenascin-X signals were observed in tendo ns, ligaments and, unexpectedly, in peripheral nerves. Other tissues, including colon, dermis, skin, heart, uterus, stomach, jejunum, placen tae, aorta, lung, mammary and adrenal glands also exhibited significan t signal intensities. In fetuses, mainly testes and skeletal muscle sh owed higher transcription levels than the adult counterparts. The tena scin-C gene was predominantly transcribed in the ligament, tendon, adr enal gland and colon, and more weakly in the stomach, jejunum, lung an d spinal cord. In fetuses, the tenascin-C signal in the brain was high er 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 i ndependent tenascin-X and tenascin-C transcription regulation mechanis ms; this was particularly obvious in adult and fetal nerves but also i n 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 trans cripts 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.