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Summary Part 2 -- Body axes and cell fate
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This is a summary of part 2 Body axes and cell fate of Evolutionary Development. With all of my summaries for this course I passed it with an 7,7 !
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Body axes and cell fateAxes
• Anterior (front) / posterior (rear – achterkant)
• Dorsal (back) / ventral (belly)
• Left / right (bilateral)
Chordates (they have a chorda – elastische weefsel-achtige streng die
langs de gehele rug loopt)
Notochord
• Dorsal rod with tightly packed highly vacuolized (vacuum) cells
surround by membrane
• Derived from mesoderm
• Present in all embryos and disappears later contributing to
intervertebral discs
• Induces the neural tube
Neural tube
Induced by notochord – take place at dorsal side
Somites
Outside to inside: dermatome (skin) → myotome (muscle) →
sclerotome (vertebrate)
Neural crest cells
Migration of neural crest cells contribute to organogenesis:
• Parts of skull (occipital bone)
• Parts of the heart (aorta valves)
• Neurons and glia cells of PNS
• Chromaffin cells in kidney cortex
• Melanocytes in the skin
Nervous system
• Ventral nervous system: invertebrates
o Nervous system – axochord (median ventral
longitudinal muscle) (help to crawl over surface) –
ventral artery
o Protostomia (annelida (ringwormen), mollusca
(weekdieren), arthropoda (geleedpotigen), nematoda
(rondwormen))
▪ Blastopore (notch (inkeping) in gastrulation)
becomes mouth
▪ Mesoderm develops from
designated (aangewezen) cell
(blastomere)
▪ Determinate cleavages
▪ Coelom (second body cavity)
develops from a fission (splijting)
in the mesoderm (schizocoel)
• Dorsal nervous system: vertebrates:
, o Nervous system – notochord – aorta
o Deuterostomia (chordate, echninodermata (stekelhuidigen) (zee-egel,
zeester))
▪ Blastopore becomes anus
▪ Mesoderm develops as a split form the ectoderm
▪ indeterminate cleavages
▪ Coelom develops as pouches (zakjes) from the gut (enterocoel)
Axocord and notochord are homologues to each other except that notochord is on
dorsal side and axocord on ventral side
Development of genes across insects and vertebrates
• Drosophilia (fruitvliegjes)
o Bicoid: A-P gradient
o Decapentaplegic (dpp): dorsal identity
o Sog: ventral development
o Hedgehog: specification of segments
• Mammals
o Goosecoid: P-A gradient
o BMP4: ventral identity
o Chordin: dorsal development
o Sonic Hedgehog: specification of segments
All these genes are homologous to each other
Model axis formation
Drosophila anterior-posterior axis – cells outside the blastula play a role
Drosophila dorsal-ventral axis – cells in blastula play a role
Egg has already a dorsal-ventral and anterior-
posterior axis induced by the mother
Specification of body axis by maternal RNA:
mRNA is synthesized by the mother by the follicle
cells. After fertilization mRNA will be translated
into protein
1. Deposit of Bicoid (Bcd) mRNA in egg cell
2. Gurken signalling to posterior follicle cell
3. Differentiation of posterior follicle cells
4. Posterior follicle cells signal back to egg
5. Reorientation of microtubules
6. Transport of Bicoid mRNA to anterior end
Fertilization!
7. Bicoid protein accumulate anterior (head + thorax) + Nanon
protein accumulate posterior
8.9. Gurken (dorsal) signalling are inhibited to secrete ventral signal
(Toll-Spätzle)
10. Ventral follicle synthesize & secrete Toll-Spätzle
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