Msx1 and Msx2 are expressed in sub‐populations of vascular smooth muscle cells

Abstract

Using an nlacZ reporter gene inserted at the Msx1 and Msx2 loci, we could analyze the expression of these homeogenes in the adult mouse. We observed that Msx genes are prominently expressed in a subset of blood vessels. The Msx2 nlacZ allele is mainly expressed in a restricted population of mural cells in peripheral arteries and veins. Msx1 nlacZ is expressed to a lesser extent by vascular smooth muscle cells of peripheral arteries, but is highly expressed in arterioles and capillaries, making Msx1 a novel marker for a subpopulation of pericytes. Expression is set up early in developing vessels and maintained throughout life. In addition, expression of both genes is observed in a few endothelial cells of the aorta at fetal stages, and only Msx2 continues to be expressed in this layer at the adult stage. These results suggest major functions for Msx genes in vascular mural cell formation and remodeling.

Characterization of Pax3-expressing cells from adult blood vessels

“…No transcripts for myogenic regulatory factors (Myf5, myogenin, MyoD), or for Pax7, were Pax3-expressing cells in blood vessels 3981 detected in RNA preparations from the aorta or femoral arteries, although they were detected in RNA extracts from the diaphragm, a skeletal muscle, which like other skeletal muscles contained blood vessels and thus displayed expression of vascular markers. Expression of the Msx2 gene was observed in the femoral artery but not the aorta, in agreement with previous observations (Goupille et al, 2008) Pax3-GFP-positive cells, directly isolated by flow cytometry after enzymatic digestion of the femoral and brachial arteries of Pax3 GFP/+ mice, could not be expanded in culture (results not shown). However, when explants from these vessels were placed in culture, cells migrated out of the explant, spread over the dish and proliferated (supplementary material Fig.…”

“…The homeodomain protein Msx2 is also implicated in smooth muscle differentiation, notably in the context of mesoangioblasts and other mesodermal progenitor cells where it acts with necdin in the absence of myocardin (Brunelli and Cossu, 2005;Brunelli et al, 2004), and indeed a subset of smooth muscle genes in blood vessels are not regulated by myocardin (Pipes et al, 2005;Yoshida et al, 2004;Yoshida and Owens, 2005). Msx2 is expressed in a subpopulation of vascular smooth muscle cells, mainly in peripheral blood vessels, such as the brachial and femoral arteries (Goupille et al, 2008). These are contractile blood vessels, as distinct from the vessels in the trunk, such as the aorta, that have elastic properties (Gittenberger-de Groot et al, 1999;Megens et al, 2007;Patel et al, 2006).…”

Msx genes define a population of mural cell precursors required for head blood vessel maturation

“…We previously demonstrated that, in the adult mouse, Msx1 and Msx2 are expressed in the VSMCs of peripheral arteries (Goupille et al, 2008). In E11.5 embryos, Msx1 lacZ was detected in a few ECs of the carotid artery (CA) (Fig.…”

“…Furthermore, Msx1 is expressed in pericytes of capillaries and Msx2 in ECs of the dorsal aorta. In the embryo, both Msx1 and Msx2 are detected in some ECs of the aorta from E14.5 and Msx1 additionally in mural cells of the intersomitic arteries from E10.5 (Goupille et al, 2008). We have undertaken the present study to clarify the role of Msx genes in vascular development.…”

“…Immunohistochemistry was performed as described (Goupille et al, 2008) except that X-Gal staining was omitted. Primary antibodies are listed in Table 1.…”