Immunolocalization of the transcription factor Slug in the developing avian heart

Abstract

Slug is a transcription factor involved in processes such as the formation of mesoderm and neural crest, two developmental events that imply a transition from an epithelial to a mesenchymal phenotype. During late cardiac morphogenesis, mesenchymal cells originate from two epithelia--epicardial mesothelium and cushion endocardium. We aimed to check if Slug is expressed in these systems of epithelial-mesenchymal transition. We have immuno-located the Slug protein in the heart of quail embryos between Hamburger and Hamilton stages HH16 and HH30. In the proepicardium (the epicardial primordium), Slug was detected in most cells, mesothelial as well as mesenchymal. Slug immunoreactivity was strong in the mesenchyme of the endocardial cushions and subepicardium from its inception until HH24, but the immunoreactivity disappeared in later embryos. Only a small portion of the endocardial cells located in the areas of epithelial-mesenchymal transition (atrioventricular groove and outflow tract) were immuno-labelled, mainly between HH16 and HH20. Endocardial cells from other cardiac segments were always negative, except for a transient, weak immunoreactivity that coincided with the development of the intertrabecular sinusoids of the ventricle. In contrast, virtually all cells of the epicardial mesothelium were immunoreactive until stage HH24. The mesenchymal cells that migrate to the heart through the spina vestibuli were also conspicuously immunoreactive. The myocardium was not labelled in the stages studied. Our results stress the involvement of Slug in the epithelial to mesenchymal transition. We suggest that Slug can constitute a reliable marker of the cardiac epithelial cells that are competent to transform into mesenchyme as well as a transient marker of the epithelial-derived mesenchymal cells in the developing heart.

Podoplanin deficient mice show a rhoa‐related hypoplasia of the sinus venosus myocardium including the sinoatrial node

“…An important feature of EMT is downregulation of E-cadherin (Batlle et al, 2000;Cano et al, 2000;Carmona et al, 2000) which is correlated with podoplanin (Martin-Villar et al, 2005). We have observed up-regulation of Ecadherin in the coelomic cavity epithelium of the podoplanin knockout embryos.…”

The role of endothelial-to-mesenchymal transition in cancer progression

“…Downstream of these signalling events, the transcriptional networks mediating EndMT also remain largely unidentified. In one series of experiments, cells that undergo EndMT exhibited an increased expression of the Snail family of transcriptional repressors (Carmona et al, 2000;Romano and Runyan, 2000;Timmerman et al, 2004). Snail proteins are also known to be upregulated during EMT, where they play a critical role in disrupting cell -cell junctions (Batlle et al, 2000;Cano et al, 2000;Nieto, 2002).…”

The epicardium and epicardially derived cells (EPDCs) as cardiac stem cells

“…Thus it appears that the molecular mechanisms controlling EMT in different areas of the heart might not be the same. It is important to emphasize that despite the controversy about the factors that induce EMT, it has also been reported that some transcription factors (i.e., ets-1, slug) are found in both endocardial and epicardial transforming cells (Carmona et al, 2000;Macias et al, 1998;Romano and Runyan, 1999). The spatiotemporal expression of ets-1, slug, WT1, and RALDH2 in avian cardiac development is summarized in Figure 5.…”

“…After EMT the EPDC is a relatively undifferentiated cell. This EPDC expresses genes characteristic for undifferentiated cells such as Slug (Carmona et al, 2000) and WT1 (Moore et al, 1999, Carmona et al, 2001, Pérez-Pomares et al, 2002b, and, in general, does not express any markers for advanced stages of differentiation (e.g., smooth muscle markers (actin, caldesmon) and endothelial markers (PE-CAM, Flk1, QH1)). Several in vitro studies demonstrate high proliferative activity of the epicardial epithelium and EPDCs.…”