The schematics depict transverse sections through the gut tube at the level of the liver diverticulum at different developmental stages in liver bud formation. After hepatic specification by FGF and BMP signals from the heart and septum transversum mesenchyme (STM) the hepatoblasts begin to express liver markers, the hepatic epithelium thickens then and transitions from a columnar to a pseudostratified epithelium (e8.75-e9.0). At this stage the hepatic epithelium is embedded in the STM and surrounded by a laminin rich basement membrane and endothelial cell precursors. By e9.5 the basal lamina breaks down and hepatoblasts delaminate and migrate into the STM to form the liver bud. Signals from the endothelial cells, the STM, as well as the activity of the indicated genes are required for this process.
From: Liver development
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