MGP (Matrix Gla Protein) is an extracellular matrix vitamin K dependent protein previously identified as a physiological inhibitor of calcification and shown to be well conserved among vertebrates during evolution. MGP is involved in other mechanisms such as TGF-b and BMP activity, and a proposed modulator of cell-matrix interactions. MGP is expressed early in vertebrate development although its role has not been clarified. Previous work in the chicken embryo found MGP localization predominantly in the aorta and aortic valve base, but no data is available earlier in development. Here we examined MGP expression pattern using whole-mount in situ hybridization and histological sectioning during the initial stages of chick development. MGP was first detected at HH10 in the head and in the forming dorsal aorta. At the moment of the onset of blood circulation, MGP was expressed additionally in the venous plexus which will remodel into the vitelline arteries. By E2.25, it is clear that the vitelline arteries are MGP positive. MGP expression progresses centrifugally throughout the area vasculosa of the yolk sac. Between stages HH17 and HH19 MGP is seen in the dorsal aorta, heart, notochord, nephric duct, roof plate, vitelline arteries and in the yolk sac, beneath main arterial branches and in the vicinity of several vessels and venules. MGP expression persists in these areas at least until E4.5. These data suggest that MGP expression could be associated with cell migration and differentiation and to the onset of angiogenesis in the developing chick embryo. This data has biomedical relevance by pointing to the potential use of chick embryo explants to study molecules involved in artery calcification.
KEY WORDS: MGP, angiogenesis, heart development, brain development, yolk sacMatrix Gla Protein (MGP) is a small secreted protein present in the extracellular matrix (ECM) that is known to be a physiological inhibitor of calcification. The correlation between the absence of functional MGP and aberrant calcification of both arteries and cartilage was clearly established following the development of the MGP knock-out mice (Luo et al., 1997). In humans, MGP mutations are the genetic basis of the Keutel syndrome (KS), a rare autosomal recessive disease characterized by abnormal cartilage calcification, brachytelephalangism, peripheral pulmonary artery stenosis, hearing loss, and facial abnormalities (Keutel et al., 1971;Hur et al., 2005).Multiple functions have been associated to MGP. These functions include the regulation of calcium phosphate transport (Price et al., 2002), the activity of TGF-b1 (Bostrom et al., 2004), the inhibition of BMP2 (Wallin et al., 2000), BMP4, and BMP7 by direct binding Int. J. Dev. Biol. 60: 71-76 (2016) ( Yao et al., 2011), the maintenance of BMP and Notch signaling balance and the maintenance of normal endothelial cell function (Sharma and Albig, 2013;Yao et al., 2013).Nonetheless, MGP appears early in development, being expressed in a specific pattern in embryonic tissues, suggesting a...