Endoderm - formation and patterning

Concept of reciprocal signaling between epithelium and mesenchyme / endoderm / lateral plate mesoderm

e.g. signals from endoderm induce heart differentiation in the mesoderm which in turn influences the ventral foregut endoderm to form the lung and liver domains

Endoderm gives rise to...

highly specialized epithelial cell types that line the respiratory and digestive systems.

Contributes to associated organs such as thymus, thyroid, lungs, gut, liver, biliary system, and pancreas.

Endodermally derived organs provide essential functions, such as ...

gas exchange (lung), glucose homeostasis (pancreas), detoxification (liver), digestion (gut)

Endoderm induces the formation of ...

several mesodermal organs (heart, blood vessels)

Endoderm instructs the formation of..

the notochord

E(number)

embryonic stage number

Major events of endoderm organogenesis in mice?

Endoderm formation

through gastrulation (ectoderm, endoderm, mesoderm)

Endoderm patterning

2D sheet -> morphogeneis -> 3D gut tube

A-P patterning of the endoderm occurs

- through reciprocal signaling with the mesenchyme

- involving growth factors such as Wnts, Fgfs, and Bmps.

Endoderm organ specification -> differentiation

Mesendoderm

common precursor cell population for endoderm and mesoderm

Mesendoderm -> endoderm? controlled by

nodal signaling and a core group of downstream TFs / network of TFs

high levels of Nodal signaling

endoderm formation

low levels of Nodal signaling

mesoderm formation (FGF + T)

network of TFs, what do they do? -

1. Segregate the endoderm and mesoderm lineages
2. Commit cells to an endodermal fate
3. Integrate signaling events that regionalize the nascent endoderm

Pathways regulating gut tube morphogenesis- function of Convergent extension movements?

control gut tube formation and elongation

Convergent extension movements driven by...

collective cell migration and/or cell intercalation

Convergent extension movements, what?

converge (narrow) along one axis and extend (elongate) along a perpendicular axis

Wnt signalling, the development of the gut tube requires?

both canonical and non-canonical Wnt/Planar cell polarity (PCP) signaling are required for the development of the gut tube.

Wnt-dependent and Wnt-independent mechanisms control gut tube morphogenesis

Wnt5a (PCP signaling) is essential for ..

intestinal elongation in mice

Regionalisation of the gut tube?

along the dorsal-ventral and anterior-posterior axes -> foregut, midgut, and hindgut
-characterized by restricted gene expression pattern.

Endoderm Patterning, dorsal-ventral?

D-V specification poorly understood

Pathways: active Shh signaling, inhibition of Bmp signaling