Childs, S. J. | bioRxiv Science

bioRxiv2018

Morphogenesis and differentiation of embryonic vascular smooth muscle cells in zebrafish

Despite the critical role of vascular mural cells (smooth muscle cells and pericytes) in supporting the endothelium of blood vessels, we know little of their early morphogenesis and differentiation. foxc1b:EGFP expressing cells in zebrafish associate with the vascular endothelium (kdrl) and co-express a smooth muscle marker (acta2), but not a pericyte marker (pdgfr{beta}). The expression of foxc1b in early peri-endothelial mesenchymal cells allows us to follow the morphogenesis of mesenchyme into acta2 expressing vascular smooth muscle cells. We show that mural cells expressing different markers associate with vessels of different diameters, depending on their embryonic location and developmental timing, suggesting marker expression is predictive of functional differences. We identify gene expression signatures for an enriched vascular smooth muscle cell population (foxc1b + acta2) and all smooth muscle (acta2) using fluorescence-activated cell sorting and RNA-Seq. Finally, we demonstrate that progressive loss of foxc1a/foxc1b results in decreased smooth muscle cell coverage. Together, our data highlight the early cellular dynamics and transcriptome profiles of smooth muscle cells in vivo, using foxc1b as a unique tool to probe vascular smooth muscle cell differentiation.\n\nSummary StatementTracing the morphogenesis and transcriptome of early vascular smooth muscle cells using foxc1b

developmental biology↗

bioRxiv2018

MicroRNA regulation of BMP signaling; cross-talk between endothelium and vascular smooth muscle cells

Vascular smooth muscle cells (vSMC) are essential to the integrity of blood vessels, and therefore an attractive target of therapeutics aimed at improving vascular function. Smooth muscle cells are one of the few cell types that maintain plasticity and can switch phenotypes from differentiated (contractile) to de-differentiated (synthetic) and vice versa. As small regulatory transcripts, miRNAs act as genetic fine tuners of posttranscriptional events and can act as genetic switches promoting phenotypic switching. The microRNA miR26a targets the BMP signalling effector, smad1. We show that loss of miR26 leads to hemorrhage (a loss of vascular stability) in vivo, suggesting altered vascular differentiation. Reduction in miR26a levels increases smad1 mRNA and phospho-Smad1 (pSmad1) levels. We show that increasing BMP signalling by overexpression of smad1 also leads to hemorrhage and that normalization of Smad1 levels through double knockdown of miR26 and smad1 rescues hemorrhage suggesting a direct relationship between miR26 and smad1 and vascular stability. Using a BMP genetic reporter and pSmad1 staining we show that the effect of miR26 on vascular instability is non-autonomous; BMP signalling is active in embryonic endothelial cells, but not in smooth muscle cells. Nonetheless, increased BMP signalling due to loss of miR26 results in an increase in acta2-expressing smooth muscle cell numbers and promotes a differentiated smooth muscle morphology. Taken together our data suggests that miR26 modulates BMP signalling in endothelial cells and indirectly promotes a differentiated smooth muscle phenotype. Our data also suggests that crosstalk from BMP-responsive endothelium to smooth muscle is important for its differentiation.

developmental biology↗