Endoderm development Flashcards
what are the two types of endoderm
hypoblast tissue: the tissue that separates the embryo from the yolk. occurs very early on in development and will not form embryonic tissue
Definitive Endoderm: the germ layer that forms after gastrulation that will become the gut precursor.
how is endoderm specified
VegT builds up in the vegetal pole of the blastula and causes Sox17 expression.
Sox17 induces endoderm specification
what is the YSL
Yolk Syncytial Layer:
the layer of blastula cells that fuse to the yolk.
They are important in patterning the endoderm and fish organiser in Zebrafish
They do not contribute to the embryo
what is the enveloping Layer
a single layer of cells that form an epithelium over the embryo
This lets it develop in a hypotonic solution where the cells would otherwise lyse
removed after 2 weeks of development
How does the YSL specify endoderm
The YSL induces the expression of Zebrafish nodal related genes Ndr1 and Ndr2 at the blastomere central margin
Ndr proteins diffuse creating a gradient
Cells far become mesendoderm
Cells close to the midline become mesoderm
what are the different structures derived from the endoderm
Digestive system
Respiratory system
Endocrine glands (pancreas, liver)
Allantois
what are the two types of embryo folding
Craniocaudal: head and tail fold inwards ventrally
Lateral: the lateral portion of the embryo and amnion overgrows and fuses ventrally
How does the gut fold
Early on: folding starts from the anterior direction forming the Anterior intestinal portal (AIP)
Later on: folding starts from the posterior direction forming the Caudal directional portal (CIP)
How does the digestive tube form
-Endoderm Associates with splanchnic lateral mesoderm
-endoderm folds laterally across the midline
-the endoderm fuses to form a tube
-the tube then fully dissociates from the yolk sac
How does the mouth form
head region folds forward and makes contact with the ectoderm
These then fuse and forms the mouth
how does the anus form
at the posterior end the organiser makes contact with the surface ectoderm
These then fuse and form the anus
what is Casnova
Casanova is a transcription factor that is both sufficient and required to induce endoderm
This can be seen in the lack of Sox17 expression in Cas- mutants
how is the digestive tube organised
foregut: becomes the oesophagus and stomach
Midgut: becomes the small intestine
Hindgut: becomes the large intestine
how is the early gut tube patterend
the foregut Wnt antagonists that suppress the hindgut
the hindgut expresses Wnt signals that promote hind gut formation
How do the intestines form
-intestines start off as a stratified epithelium
-fold into Villus and inter villus
-within the villus is mesenchyme that secretes BMP
-Intervillus forms crypt cells
what are crypt cells
Stem cells found in the base of the intervillus
the cells in the villi are constantly being replaced
old cells are shed at the villi tip and new ones form from Paneth cells in the crypt
How are foregut derived organs induced
All foregut derived organs are induced by signals from the mesoderm
Lungs: Wnt and FGF from the heart
Liver: BMP and FGF
Pancreas: lack of BMP and FGF
