1 - Development of Mesoderm, Endoderm, Ectoderm Flashcards
Mesoderm Development
Formed during gastrulation from epiblast cells at the primitive streak
Mesoderm development - signalling molecules
Nodal, Cerberus1 (Cer1), Lefty1 (regulate primitive streak patterning)
Distance of forming mesoderm from ventral midline determines…
its fate - notochord, paraxial, intermediate, lateral
Mesodermal subtypes (4)
Axial Mesoderm (Notochord)
Paraxial Mesoderm (Somites)
Intermediate Mesoderm
Lateral Plate Mesoderm (LPM)
Axial Mesoderm (Notochord)
Embryonic midline structure, crucial signaling center
Secretes FGF4 (attracts migrating mesodermal cells)
FGF8 secretes by primitive streaks (realises mesoderm cells so they migrate away)
Paraxial Mesoderm (Somites)
Forms vertebrae, muscles, dermis / Hox genes regulate anterior-posterior identity
Intermediate Mesoderm
Forms kidneys and gonads
Lateral Plate Mesoderm (LPM)
Splanchnic layer: Heart, blood vessels, smooth muscle
Somatic layer: Body wall, limb components
Somite Formation (Somitogenesis)
Paraxial Mesoderm - segmental pattern
Segmentation clock (cyclic gene expression): Notch, Wnt, Lunatic Fringe
Somite differentiation
Sclerotome → Vertebrae and ribs.
Dermomyotome → Muscles, dermis.
Hox genes specify somite identity along the A-P axis
Periodicity
Cyclic expression of gene products
Genes involved - notch / Wnt
Clock and wavefront model
Gradients of signalling molecules determine which transcription factors are expressed to determine somite formation and rostrocaudal somite patterning
Fissure formation
Cyclic gene expression establishes anterior-posterior identity —> induction of Eph-ephrin signalling at borders
Eph-ephrin
Signalling involves in cell-cell communication
Eph - tyrosine kinases, receptors; ephrin
ligands to Eph
Eph function
Separation of presomitic mesoderm
Anterior-posterior axis - some differences between this and…
Somites
Ribs are formed from…
Somites
Where are ribs present
Only in throacic regions
Cervical, lumbar, tail somites cant form
Ribs
What’s regional specification controlled by
How clusters and genes
What’s homeotic genes
Control the identity of body segments
All Hox genes are homeotic genes (they are the most well known homeotic genes)
What do homeotic genes encode
homeodomain, which binds to DNA (transcriptional regulation)
What’s sclerotome
Form the bones and cartilidge of the spine and ribs
What do medial epithelial cells break down to become
Mesenchymal
Sclerotome are attracted by…
Notochord (ventral midline)
Neural tube
Sclerotomes proliferate, condense and differentiate into…
Chondrocytes (from vertebrate and ribs)
Endoderm development simple
Forms during gastrulation → Creates the gut tube
Endoderm development
The outer surface area of large groups of cells is too small to supply their needs, gastrulation evolved to allow animals to become larger and to form an extra surface dedicated to food uptake and digestion in the gut. The extra surface is the endoderm.
At the posterior end of the embryo, the posterior intestinal portal forms (the first form on a tube)
Folding and tube formation - foregut
Esophagus, stomach, lungs, liver
Folding and tube formation - midgut
Small intestine
Folding and tube formation - hindgut
Colon, bladder
Where do gut associated organs arise from?
endoderm-mesoderm interactions
FoxA2 function
Transcription factor
Regulates endoderm development
Neuraltrion
Neural plate folds → Neural tube (CNS) formation
Neural crest cells migrate →
Form PNS, melanocytes, craniofacial structures, Schwann cells
Dorsoventral patterning of the neural tube
Shh (ventral) → Motor neurons
BMP/Wnt (dorsal) → Sensory neurons
Some regions of the brain have evolved to contain huge numbers of neurones via…
Increased progenitor proliferation.
These regions are foliated (folded). Folded cerebella are found in all mammals and birds, and folded cortices in many mammalian groups.
Summary
Mesoderm forms muscles, bones, cardiovascular, urogenital systems
Endoderm develops into digestive and respiratory organs
Ectoderm gives rise to skin, CNS, PNS, neural crest derivatives
Transcription factors & signaling pathways (e.g., Hox genes, Shh, BMPs, FGF) regulate development
