NOVEL MOUSE ENDOTHELIAL-CELL SURFACE MARKER IS SUPPRESSED DURING DIFFERENTIATION OF THE BLOOD-BRAIN-BARRIER

Few markers specific for mouse endothelium exist, We describe here one such marker, MECA-32, a monoclonal antibody which shows high specific ity for mouse endothelium in both embryonic and mature tissues, The ME CA-32 antigen has a M(r) of 50-55 x 10(3) under reducing conditions an d M(r) of 100-120 x 10(3) under nonreducing conditions. It is expresse d on most endothelial cells in the embryonic and in the adult mouse, w ith the exception of the brain, skeletal, and cardiac muscle, where it has a more restricted distribution. In skeletal and cardiac muscle on ly small arterioles and venules express the MECA-32 antigen, while in the brain its expression is negatively correlated with the differentia tion of the vasculature to form the blood brain barrier. Interestingly , during embryonic development the antigen occurs on the brain vascula ture up to day 16 of gestation (E16), whereupon it, disappears. The em bryonic brain is an avascular organ anlage which is vascularized by in growth of external blood vessels, Differentiation of the vasculature t o form the blood brain barrier occurs at approximately E16 in the mous e, This differentiation correlates with the downregulation of MECA-32 antigen expression. Between E12 and E16 MECA-32 detects most endotheli al cell surfaces of the blood vessels in the brain. No MECA-32 antigen is found in the brain at E17 or any later stage of development with t he exception of the vasculature of the circumventricular organs. The r esults suggest that MECA-32 antigen expression is temporally and spati ally correlated with the development of the blood brain barrier. (C) 1 995 Wiley-Liss, Inc.