RESTRICTED LOCALIZATION OF THROMBOSPONDIN-2 PROTEIN DURING MOUSE EMBRYOGENESIS - A COMPARISON TO THROMBOSPONDIN-1

Thrombospondin-l and -2 (TSP1 and TSP2) are multifunctional, multimodu lar extracellular matrix proteins encoded by separate genes. We compar ed the distributions of TSP1 and TSP2 in mouse embryos (day 10 and lat er) by immunohistochemistry. TSP1 was detected on day 10 in the heart and intestinal epithelium, on day 11 in megakaryocytes, and on day 14 in the lung. TSP2 was not detected until day 14, with strongest staini ng in mesenchymal condensation that gives rise to cartilage and bone. The distribution of TSP2 was different from but overlapped with the di stribution of TSP1. TSP1 was found in cartilage proper with diminished staining around chondrocytes undergoing differentiation and hypertrop hy, whereas TSP2 was restricted to the matrix surrounding chondrocytes of the growth zone cartilage. TSP2 and TSP1 were both expressed in ce nters of intramembranous ossification that form the skull bones, in re ticular dermis, on the apical surface of nasal epithelium, in skeletal muscle, and in the sheath surrounding vibrissae. Areas of exclusive s taining for TSP2 included the perichondrium surrounding the cartilage of the nasal cavities, developing bone of the lower mandible, and adre nal gland. The distinct localizations of TSP1 and TSP2, indicate that the two proteins have specific functions during mouse embryogenesis.