INSULIN-LIKE GROWTH FACTOR-II MANNOSE-6-PHOSPHATE RECEPTOR EXPRESSIONDURING EARLY HEART DEVELOPMENT

Expression of the insulin-like growth factor-II/mannose-6-phosphate (I GF-II/M6P) receptor was examined during the major stages of heart morp hogenesis in the chicken embryo. By using an affinity-purified antibod y, Western blot analysis of total embryonic proteins from stages 5-24 revealed little if any IGF-II/M6P receptor protein until stage 7, appr oximately 8 hours prior to the appearance of the rudimentary myocardia l tubes, Thereafter, receptor accumulation increased until stage 14, a fter which receptor protein levels remained constant, up to 7 days in ovo, Immunohistochemical localization revealed that, among all embryon ic tissues at stages 10-24, the predominant site of receptor expressio n was the developing myocardium. Receptor expression was also immunohi stochemically evaluated in a defined in vitro model of cardiogenesis i n which explanted precardiac mesoderm is induced to undergo differenti ation by co-explanted endoderm. In this system, as in vivo, IGF-II/M6P receptors were only detected after precardiac mesoderm had differenti ated into a synchronously contractile multilayer which expressed cardi ac ol-actin. These findings indicate that the IGF-II/M6P receptor has an important role during early heart development. (C) 1996 Wiley-Liss, Inc.