1 - Development of Mesoderm, Endoderm, Ectoderm

Question 1

Mesoderm Development

Answer 1

Formed during gastrulation from epiblast cells at the primitive streak

Question 2

Mesoderm development - signalling molecules

Answer 2

Nodal, Cerberus1 (Cer1), Lefty1 (regulate primitive streak patterning)

Question 3

Distance of forming mesoderm from ventral midline determines…

Answer 3

its fate - notochord, paraxial, intermediate, lateral

Question 4

Mesodermal subtypes (4)

Answer 4

Axial Mesoderm (Notochord)

Paraxial Mesoderm (Somites)

Intermediate Mesoderm

Lateral Plate Mesoderm (LPM)

Question 5

Axial Mesoderm (Notochord)

Answer 5

Embryonic midline structure, crucial signaling center

Secretes FGF4 (attracts migrating mesodermal cells)

FGF8 secretes by primitive streaks (realises mesoderm cells so they migrate away)

Question 6

Paraxial Mesoderm (Somites)

Answer 6

Forms vertebrae, muscles, dermis / Hox genes regulate anterior-posterior identity

Question 7

Intermediate Mesoderm

Answer 7

Forms kidneys and gonads

Question 8

Lateral Plate Mesoderm (LPM)

Answer 8

Splanchnic layer: Heart, blood vessels, smooth muscle

Somatic layer: Body wall, limb components

Question 9

Somite Formation (Somitogenesis)

Answer 9

Paraxial Mesoderm - segmental pattern

Segmentation clock (cyclic gene expression): Notch, Wnt, Lunatic Fringe

Question 10

Somite differentiation

Answer 10

Sclerotome → Vertebrae and ribs.

Dermomyotome → Muscles, dermis.
Hox genes specify somite identity along the A-P axis

Question 11

Periodicity

Answer 11

Cyclic expression of gene products

Genes involved - notch / Wnt

Question 12

Clock and wavefront model

Answer 12

Gradients of signalling molecules determine which transcription factors are expressed to determine somite formation and rostrocaudal somite patterning

Question 13

Fissure formation

Answer 13

Cyclic gene expression establishes anterior-posterior identity —> induction of Eph-ephrin signalling at borders

Question 14

Eph-ephrin

Answer 14

Signalling involves in cell-cell communication

Question 15

Eph - tyrosine kinases, receptors; ephrin

Answer 15

ligands to Eph

Question 16

Eph function

Answer 16

Separation of presomitic mesoderm

Question 17

Anterior-posterior axis - some differences between this and…

Answer 17

Somites

Question 18

Ribs are formed from…

Answer 18

Somites

Question 19

Where are ribs present

Answer 19

Only in throacic regions

Question 20

Cervical, lumbar, tail somites cant form

Answer 20

Ribs

Question 21

What’s regional specification controlled by

Answer 21

How clusters and genes

Question 22

What’s homeotic genes

Answer 22

Control the identity of body segments

All Hox genes are homeotic genes (they are the most well known homeotic genes)

Question 23

What do homeotic genes encode

Answer 23

homeodomain, which binds to DNA (transcriptional regulation)

Question 24

What’s sclerotome

Answer 24

Form the bones and cartilidge of the spine and ribs

Question 25

What do medial epithelial cells break down to become

Answer 25

Mesenchymal

Question 26

Sclerotome are attracted by…

Answer 26

Notochord (ventral midline) Neural tube

Question 27

Sclerotomes proliferate, condense and differentiate into…

Answer 27

Chondrocytes (from vertebrate and ribs)

Question 28

Endoderm development simple

Answer 28

Forms during gastrulation → Creates the gut tube

Question 29

Endoderm development

Answer 29

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)

Question 30

Folding and tube formation - foregut

Answer 30

Esophagus, stomach, lungs, liver

Question 31

Folding and tube formation - midgut

Answer 31

Small intestine

Question 32

Folding and tube formation - hindgut

Answer 32

Colon, bladder

Question 33

Where do gut associated organs arise from?

Answer 33

endoderm-mesoderm interactions

Question 34

FoxA2 function

Answer 34

Transcription factor Regulates endoderm development

Question 35

Neuraltrion

Answer 35

Neural plate folds → Neural tube (CNS) formation

Question 36

Neural crest cells migrate →

Answer 36

Form PNS, melanocytes, craniofacial structures, Schwann cells

Question 37

Dorsoventral patterning of the neural tube

Answer 37

Shh (ventral) → Motor neurons BMP/Wnt (dorsal) → Sensory neurons

Question 38

Some regions of the brain have evolved to contain huge numbers of neurones via…

Answer 38

Increased progenitor proliferation. These regions are foliated (folded). Folded cerebella are found in all mammals and birds, and folded cortices in many mammalian groups.

Question 39

Summary

Answer 39

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