Dynamic expression of a native chondroitin sulfate epitope reveals microheterogeneity of extracellular matrix organization in the embryonic chick heart

TC2 is a novel monoclonal antibody produced by in vitro immunization of spl enocytes with a peanut agglutinin-positive fraction from extracts of precho ndrogenic micromass cultures of chick Limb mesenchyme. ELISA results demons trated TC2 reactivity with a native epitope on a glycosaminoglycan (GAG) en riched in chondroitin-4-sulfate and with multiple intact proteoglycans, but not with other GAGs tested. TC2 immunohistochemical reactivity was abolish ed by pretreatment of sections with chondroitinase AC or preadsorption with chondroitin-4-sulfate GAG. Strong TC2 localization occurred throughout the developing heart at stage 9. As looping ensued, a graded reactivity was ob served from lowest in the atrium to highest in the conotruncus that correla ted well with versican localization. The superior atrioventricular cushion stained preferentially with TC2 as compared to the inferior cushion at stag es 16-18. At these later stages TC2 patterns did not agree completely with anti-versican reactivity. By stage 23 there was a marked reduction in TC2 l ocalization in the heart, however strong reactivity remained at certain sit es, including the conotruncus and in subcompartments of both atrioventricul ar cushions. A heterogeneous distribution of other native chondroitin sulfa te glycosaminoglycan epitopes recognized by monoclonal antibodies d1C4 and CS-56 was observed as well. The distribution of the TC2 epitope usually did not overlap with d1C4 or CS-56 localization at the stages examined. Overal l, the spatiotemporal characteristics of TC2 reactivity in the developing c hick heart appear to correlate with subdomains of the endocardial cushions as well as with trabecular and atrial septal formation. Anat Rec 254:181-19 5, 1999. (C) 1999 Wiley-Liss, Inc.