endoderm

What are the two major roles of endoderm?

Induces mesoderm formation and forms digestive + respiratory tubes

What mesodermal tissues are induced by endoderm?

Notochord, heart, blood vessels

What two major tubes does endoderm form?

Digestive tube and respiratory tube

What signaling pathway is critical for mesendoderm formation?

Nodal signaling

What germ layers does Nodal specify?

Mesoderm and endoderm (mesendoderm)

What happens when Nodal signaling is disrupted?

Failure to form proper endoderm and mesoderm

What type of signaling specifies mesoderm vs endoderm?

Reciprocal signaling between the two germ layers

What does early endoderm signal mesoderm to do?

Specify distinct mesodermal regions

What transcription factors mark foregut, midgut, and hindgut?

Sox2 (foregut), Pdx1 (midgut/pancreas), Cdx (hindgut)

What determines regional identity along the gut tube?

Hox gene expression along the A–P axis

What signaling influences liver formation?

Positive and negative signals including FGF and BMP

What tissue inhibits liver formation and promotes pancreas development?

The notochord

What does the notochord secrete to inhibit liver fate?

Signals that suppress liver genes and promote pancreatic genes

What experiment shows notochord promotes pancreas?

RT-PCR showing increased pancreatic gene expression when notochord is present

What transcription factor is essential for pancreatic specification?

Pdx1

What happens when Pdx1 is expressed in gut endoderm?

Pancreatic development is initiated

What structures express Pdx1 during development?

Blood vessels and insulin-producing islet cells

What phenotype results from loss of Pdx1?

Failure of pancreas formation

What transcription factors specify dorsal vs ventral foregut?

Sox2 (dorsal esophagus) and Nkx2-1 (ventral trachea)

What signaling pathway is downstream of Sox2/Nkx2-1 patterning?

Ephrin signaling (Efnb2)

What phenotype results from disrupted Sox2/Nkx2-1 balance?

Esophageal–tracheal malformations

What molecule establishes localized Fgf10 expression in respiratory mesoderm?

RA (retinoic acid) and Shh gradients

What does Fgf10 do in lung development?

Promotes lung bud outgrowth and branching

What inhibits Fgf10 on the sides of the respiratory tube?

Retinoic acid (RA)

What molecule inhibits Shh at high levels to refine lung patterning?

Hhip1

What feedback loop regulates Fgf10 signaling?

Fgf10 activates Sprouty proteins (Spry), which inhibit FGF signaling

What experiment shows mesenchyme determines respiratory vs tracheal fate?

Cultured endoderm adopts fate of associated mesenchyme

What are the two major processes in lung formation?

Outgrowth and branching morphogenesis

What signals control lung branching?

Fgf9, Fgf10, BMP/Shh, Wnt, fibronectin, VEGF

What phenotype results from disrupted Fgf10?

Failure of lung bud formation

What phenotype results from disrupted Shh in lung development?

Abnormal branching and patterning defects

What phenotype results from disrupted RA signaling in lung development?

Mispatterned Fgf10 expression and defective branching

What endoderm-derived organs are clinically important due to disease burden?

Liver, pancreas, lungs, thyroid, GI tract

What diseases arise from endoderm-derived organ defects?

Cystic fibrosis, chronic hepatitis, diabetes, congenital GI malformations

What has basic research enabled in endoderm biology?

Directing ESCs to form specific endoderm-derived cell types

What transcription factor marks tracheal endoderm?

Nkx2-1

What transcription factor marks esophageal endoderm?

Sox2

What signaling molecule patterns the respiratory diverticulum?

Fgf10

What is the role of Shh in lung development?

Patterns proximal-distal axis and regulates Fgf10 via Hhip1

What is the role of RA in foregut patterning?

Restricts Fgf10 and helps define lung vs trachea boundaries