Microfibril-associated Glycoprotein-2 (MAGP-2) Is Specifically Associated with Fibrillin-containing Microfibrils but Exhibits More Restricted Patterns of Tissue Localization and Developmental Expression Than Its Structural Relative MAGP-1

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Abstract
SUMMARY We developed an affinity-purified anti-MAGP-2 peptide antibody that specifically identified MAGP-2 on Western blots of purified matrix proteins and extracts of nuchal ligament. Immunolocalization studies on tissues from a 210-day-old fetus and a mature bovine showed that MAGP-2 was located in similar regions to MAGP-1 and fibrillin-1 but that the distribution of MAGP-2 was more restricted. In fetal nuchal ligament, skeletal muscle, and spleen the distribution of MAGP-2 was indistinguishable from that of MAGP-1. In contrast to MAGP-1, MAGP-2 was not detected in the medial layer of fetal thoracic aorta and in much of the peritubular matrix of fetal and mature kidney and in the mature ocular zonule. Some differences in the immunolocalization patterns were also evident in fetal lung, cartilage, skin, and heart. Immunoelectron microscopy confirmed that MAGP-2 was specifically associated with fibrillin-containing microfibrils in nuchal ligament, dermis, adventitia of aorta, glomerular mesangium and perimysium. Northern blotting of RNA from tissues of a 210-day-old fetus indicated that steady-state MAGP-2 mRNA levels were highest in nuchal ligament. Significant expression was also detected in lung, heart, skeletal muscle, skin, and Achilles tendon. The tissue pattern of MAGP-2 expression differed significantly from that of MAGP-1. MAGP-2 expression appeared to be higher in nuchal ligament, heart, and skeletal muscle and lower in aorta and kidney. In nuchal ligament, MAGP-2 mRNA expression appeared to peak around 180 days of fetal development, which correlates with the period of onset of elastinogenesis in this tissue. Overall, the immunolocalization and expression patterns of MAGP-2 appeared to be distinct from those of other microfibrillar components. This is consistent with the view that MAGP-2 plays a unique role in the biology of the microfibrils, perhaps by mediating their interaction with cell surfaces at specific stages of development and differentiation.

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