Mesothelium contributes to vascular smooth muscle and mesenchyme during lung development

Abstract

During mouse development, the sophisticated vascular network of the lung is established from embryonic day (E)Ϸ10.5 and continues to develop postnatally. This network is composed of endothelial cells enclosed by vascular smooth muscle, pericytes, and other mesenchymal cells. Recent in vivo lineage labeling studies in the developing heart and intestine suggest that some of the vascular smooth muscle cells arise from the surface mesothelium. In the developing lung, the Wilm's tumor 1 gene (Wt1) is expressed only in the mesothelial cells. Therefore, we lineage-labeled the mesothelium in vivo by using a Wt1-Cre transgene in combination with either Rosa26R lacZ , Rosa26R CAG-hPLAP , or Rosa26R EYFP reporter alleles. In all three cases, cells derived from lineage-labeled mesothelium are found inside the lung and as smooth muscle actin (SMA) and PDGF receptor-beta positive cells in the walls of pulmonary blood vessels. To corroborate this finding, we used 5-(and-6)-carboxy-2 ,7 -dichlorofluorescein diacetate, succinimidyl ester ''mixed isomers'' (CCFSE) dye to label mesothelial cells on the surface of the embryonic lung. Over the course of 72-h culture, dye-labeled cells also appear within the lung mesenchyme. Together, our data provide evidence that mesothelial cells serve as a source of vascular smooth muscle cells in the developing lung and suggest that a conserved mechanism applies to the development of blood vessels in all coelomic organs.lineage tracing ͉ blood vessel ͉ embryo ͉ pleura

The building blocks of mammalian lung development

“…These were not specifically identified and could have been alveolar myofibroblasts, microvascular pericytes, or even endothelial cells (Que et al, 2008). This finding warrants further investigation, preferably with an inducible Cre line, to identify all of the mesothelial-derived cells and the developmental stage at which they are produced; moreover, to determine how many different progenitor populations the embryonic lung mesothelium contains and whether any of these also function in the adult.…”

“…lineage-tracing experiments in the lung demonstrated that the mesothelium contributes $30% of the vascular smooth muscle in both arteries and veins, but that it makes no contribution to the parabronchial smooth muscle (Que et al, 2008;Morimoto et al, 2010;Fig. 5).…”

“…It is now incontrovertible that epithelial mesothelial cells delaminate and undergo EMT (epithelial-mesenchymal transitions) during lung development (Que et al, 2008;Morimoto et al, 2010). By contrast, all of the available evidence suggests that the endodermally derived epithelium does not undergo EMT during normal development.…”

Proper formation of whisker barrelettes requires periphery-derived Smad4-dependent TGF-β signaling

“…into pregnant female mice at E12.5 and E13.5. Smad4 flox/flox and Rosa26R-CAG-STOP-hPLAP mice (Rosa PLAP ) have been described previously (24,25). All experiments were conducted according to protocols approved by the Duke University Institutional Animal Care and Use Committee.…”

“…Furthermore, we assessed axonal outgrowth in vivo by examining the projections of trigeminal axonal collaterals using the Rosa PLAP reporter line (24,25). No apparent differences were detected in the growth of sensory axonal collaterals into brainstem nuclei between control and mutant mice in embryonic and postnatal stages (Fig.…”