EVIDENCE THAT EXTRAHEPATIC CELLS EXPRESS VITRONECTIN MESSENGER-RNA ATRATES APPROACHING THOSE OF HEPATOCYTES

Although the liver is the major source of the adhesive glycoprotein vi tronectin (Vn) in vivo, we recently demonstrated low levels of extrahe patic Vn transcription. In this report, in situ hybridization was empl oyed to identify the Vn-producing cells at these extra hepatic sites. In the central nervous system (CNS), high levels of Vn transcripts wer e prominent in arachnoid cells and in cells frequently present in the vicinity of brain capillaries. Significant amounts of Vn mRNA were als o detected in selected peripheral organs. In the myo cardium, the sign al was localized to cells in the endomysium and subepicardial fat. Add itionally, the pulmonary alveolar walls contained Vn-positive cells. T he parenchyma of the kidney and spleen were negative. Moreover, larger blood vessels and adjacent cells in the CNS and peripheral organs wer e devoid of the Vn transcript. Unexpectedly, the rate of Vn gene expre ssion in subsets of cells present in the CNS was similar to that of he patocytes. These results suggest that the low level of Vn gene express ion detected by quantitative PCR may reflect relatively high levels of synthesis by a small subset of cells, and raise the possibility that tissue Vn may, in part, be derived from local biosynthesis rather than from plasma.