Signalling Pathway

Question 1

Fgf

Answer 1

Limb development:
- FGF10 from mesenchyme induces AER;
- FGF8 from AER maintains mesenchyme proliferation.

Somite formation:
- FGF gradients regulate segmentation and somitogenesis.

Neural development:
- FGF signals specify neural progenitors and regulate anterior-posterior patterning.

Question 2

Hedgehog (Sonic Hedgehog, Shh):

Answer 2

Limb development:
- Shh from the zone of polarizing activity (ZPA) establishes anterior-posterior limb axis (e.g., thumb-pinky patterning).

Neural patterning:
- Shh from the notochord induces ventral neural tube differentiation, forming the floor plate and motor neurons.

Somite differentiation:
- Shh induces sclerotome formation from somites.

Question 3

Wnt

Answer 3

Dorsal patterning:
- Wnt signalling from the ectoderm patterns dorsal structures of somites (e.g., dermomyotome).

Neural crest induction:
- Wnt triggers EMT in neural crest cells, allowing migration.

Limb development:
- Wnt regulates AER formation and outgrowth.

Question 4

TGF-β/BMP (Bone Morphogenetic Protein):

Answer 4

Limb development: BMP signals regulate apoptosis in interdigital regions, shaping digits.

Neural crest: BMP induces neural crest cell fate and EMT during migration.

Somite patterning: BMP signals dorsalize the somites, promoting dermomyotome formation.

Gastrulation: BMP inhibits neural induction and promotes ectodermal fates.

Question 5

ECM (Extracellular Matrix):

Answer 5

Cell adhesion and migration:
- ECM provides a substrate for migration during gastrulation, neural crest migration, and limb outgrowth.

Somite boundary formation:
- ECM proteins like fibronectin organize segmentation.

Question 6

Limb Development Process

Answer 6

FGF: Outgrowth (FGF10 → FGF8 loop).
Shh: Anterior-posterior patterning (thumb to pinky).
Wnt: AER formation and dorsal-ventral polarity.
BMP: Apoptosis shapes digits.

Question 7

Neural Patterning

Answer 7

Shh: Ventral neural tube (floor plate, motor neurons).
Wnt/BMP: Dorsal neural tube (sensory neurons).

Question 8

Somites

Answer 8

FGF: Regulates segmentation clock.
Shh: Induces sclerotome (bone).
Wnt/BMP: Dorsal dermomyotome (muscle, dermis)

Question 9

Neural Crest Development

Answer 9

Wnt/BMP: EMT initiation, neural crest migration.
ECM: Substrate for migration.

Question 10

EMT and MET

Answer 10

EMT:
Neural crest delamination (Wnt/BMP).
Mesoderm formation during gastrulation.

MET:
Somite epithelialization during somitogenesis.

Question 11

Types of Cell Movement & Their Occurrence

Answer 11

Invagination:
Infolding of epithelial sheets during gastrulation (e.g., mesoderm formation).

Ingression:
Migration of individual cells from an epithelial layer during neural crest formation.

Epiboly:
Spreading of epithelial sheets during gastrulation.

Convergent Extension:
Cells intercalate and elongate during gastrulation and neural tube closure.

Migration:
Neural crest cells migrating along ECM pathways.

Apoptosis:
Sculpting of digits, neural pruning, or eliminating transient structures.