Wt1-expressing progenitors contribute to multiple tissues in the developing lung

Abstract

Cano E, Carmona R, Muñoz-Chápuli R. Wt1-expressing progenitors contribute to multiple tissues in the developing lung. Am J Physiol Lung Cell Mol Physiol 305: L322-L332, 2013. First published June 28, 2013 doi:10.1152 doi:10. /ajplung.00424.2012velop from paired endodermal outgrowths surrounded by a mesodermal mesenchyme. Part of this mesenchyme arises from epithelialmesenchymal transition of the mesothelium that lines the pulmonary buds. Previous studies have shown that this mesothelium-derived mesenchyme contributes to the smooth muscle of the pulmonary vessels, but its significance for lung morphogenesis and its developmental fate are still little known. We have studied this issue using the transgenic mouse model mWt1/IRES/GFP-Cre (Wt1 cre ) crossed with the Rosa26R-EYFP reporter mouse. In the developing lungs, Wt1, the Wilms' tumor suppressor gene, is specifically expressed in the embryonic mesothelium. In the embryos obtained from the crossbreeding, the Wt1-expressing cell lineage produces the yellow fluorescent protein (YFP), allowing for colocalization with differentiation markers. Wt1 cre -YFP cells were very abundant from the origin of the lung buds to postnatal stages, contributing significantly to pulmonary endothelial and smooth muscle cells, bronchial musculature, tracheal and bronchial cartilage, as well as CD34 ϩ fibroblast-like interstitial cells. Thus Wt1 cre -YFP mesenchymal cells show the very same differentiation potential as the splanchnopleural mesenchyme surrounding the lung buds. FSP1 ϩ fibroblast-like cells were always YFP Ϫ ; they expressed the common leukocyte antigen CD45 and were apparently recruited from circulating progenitors. We have also found defects in pulmonary development in Wt1 Ϫ/Ϫ embryos, which showed abnormally fused lung lobes, round-shaped and reduced pleural cavities, and diaphragmatic hernia. Our results suggest a novel role for the embryonic mesothelium-derived cells in lung morphogenesis and involve the Wilms' tumor suppressor gene in the development of this organ. pulmonary development; coelomic epithelium; mesothelium; Wilms' tumor suppressor gene THE DEVELOPMENT OF THE RESPIRATORY system was a key evolutionary event for the air-breathing vertebrates. Lungs arose as specialized endodermal sacs from the digestive tract, and this phylogenetic origin is recapitulated in lung ontogeny. The contribution of mesodermal cells to the endodermal structures is essential for pulmonary development and function. In mouse embryos, the lung primordium sprouts from the ventral foregut by embryonic day (E) 9.5. It consists of a simple tube of endodermal epithelium surrounded by mesenchyme derived from the splanchnic mesoderm and lined by a layer of mesothelium. This primary tube branches in the pair of pulmonary sacs (reviewed in Ref. 17).

Contribution of Fetal, but Not Adult, Pulmonary Mesothelium to Mesenchymal Lineages in Lung Homeostasis and Fibrosis

“…We used the highest tamoxifen dose that was compatible with survival of embryos to term, and labeled the large majority (81 6 1.7%) of mesothelial cells. PMC-derived mesenchymal cells (PMCDCs) were found within the lung mesenchyme ( Figure 1B), consistent with having undergone an EMT, as reported previously (9)(10)(11). The entry of fetal PMCs into lung mesenchyme was confirmed using cultured fetal lung explants, where mesothelium was selectively labeled using the cell-tracking dye, 5-chloromethylfluorescein diacetate (CMFDA) ( Figure E2).…”

“…These cells, like other mesothelial cells, express the transcription factor, Wilms' tumor 1 (Wt1), and Wt1-driven expression of constitutive Cre or inducible CreERT2 alleles has been used to trace the fate of PMCs during lung development, postnatal lung homeostasis, and lung disease, with conflicting results (3,(9)(10)(11). During lung development, one study using a constitutive Wt1-Cre transgene reported that PMCs contribute to vascular SMCs (11).…”

“…1 fibroblasts, bronchial SMCs, and tracheal and bronchial cartilage, as well as vascular SMCs (9). A third study used pulse mesothelial labeling of the fetal lung mesothelium to show that its differentiation is restricted to subpopulations of bronchial and vascular SMCs and desmin 1 fibroblasts, whereas differentiation into ECs was not reported (10).…”

Lung Pericytes and Resident Fibroblasts

“…Both Tbx4 À and Wt1-based experimental systems traced the progeny of mesothelial cells to smooth muscle and endothelial populations, as well as fibroblasts identified by desmin and/or the absence of other lineage markers. 34,35,42 These results also indicate that mesothelium is not the main source of pericytes or fibroblasts in the adult lung, but may instead contribute to rare fibroblast subgroups whose distinguishing features and ancestry remain ambiguous. Together, these largely concordant findings demonstrate both the close relationships between pericytes and resident fibroblasts and the heterogeneity among these populations ( Figure 2 and Table 2).…”

Heterogeneity of adipose tissue in development and metabolic function

“…Wt1 expression is restricted to the intermediate and lateral plate mesoderm during development, structures that give rise to the omentum, mesentery and the mesothelium lining the organs of the visceral cavity. Consequently, these studies showed that the mesothelium provides a source of adipocyte progenitors for VAT but not SAT (Asahina et al, 2011;Cano et al, 2013;Chau et al, 2014;Rinkevich et al, 2012). These studies also showed that Wt1 positive progenitors are not the sole source of adipocytes because, depending on the individual VAT depot, only 30-80% of adipocytes in adult mice derive from cells that express Wt1 during embryonic development (Chau et al, 2014) (Fig.…”