Chapter 32-5. Avian Embryology
Recommended post: 【Biology】 Chapter 32. Embryology
1. (Cleavage stage) Axis determination
2. (Gastrulation stage) Organizer 1. Hensen’s node
3. (Gastrulation stage) Germ layer formation
4. (Organogenesis) Organizer 2. Limb bud
5. (Organogenesis) Neural tube development
**1. (Cleavage stage) Axis determination **
⑴ Anterior-posterior axis formation by shh (sonic hedgehog homolog)
⑵ Low shh concentration: Anterior formation
⑶ High shh concentration: Posterior formation
2. (Gastrulation stage) Organizer 1. Hensen’s node
⑴ Ingression site: Primitive streak, formed along the embryo’s anterior-posterior axis
⑵ Hensen’s node
① Cells ingressed at Hensen’s node become notochordal mesoderm
② Evolutionarily conserved: Transplanting the dorsal lip of the amphibian blastopore (Spemann organizer) still results in normal development
3. (Gastrulation stage) Germ layer formation
⑴ High yolk content in the center makes cell movement difficult → Different pattern of germ layer formation
⑵ Epiblast: Forms ectoderm, mesoderm, endoderm
⑶ Hypoblast: Assists germ layer formation
**4. (Organogenesis) Organizer 2. Limb bud **
⑴ Limb bud
Figure 1. Wing bud of a chick embryo on day 3 of development
① Composed of two organizers: Apical ectodermal ridge (AER), zone of polarizing activity (ZPA)
② Depending on the region of action, it is divided into leg bud (forearm) and wing bud (wing)
⑵ Limb buds develop from proximal → distal direction
① The proximal region of the leg/wing bud is destined to become forearm bone/wing bone, while the distal region is destined to become finger bones
② Experiment of transplanting the proximal region of the leg bud into the distal region of the wing bud
○ Transplantation before leg/wing fate is determined: Wing fingers form
○ Transplantation after leg/wing fate is determined but before proximal-distal axis positional information is set: Leg fingers form
○ Transplantation after both leg/wing fate and positional information are determined: Forearm bone forms
⑶ Organizer 2-1. Apical ectodermal ridge (AER): Secretes growth factors
① Substitution with FGF8 (Fibroblast Growth Factor 8) shows little difference in development
⑷ Organizer 2-2. Zone of polarizing activity (ZPA): Secretes shh
① Low shh concentration → Anterior formation → Related to the 4th digit
② High shh concentration → Posterior formation → Related to the 1st digit
③ shh can antagonize BMP and induce motor neurons
5. (Organogenesis) Neural tube development
⑴ shh protein secreted from the notochord determines the ventral-dorsal axis of the neural tube
⑵ Depending on the shh concentration gradient, different types of neurons differentiate in the neural tube
① From closest to the notochord: floor plate, motor neurons, V2 interneurons, V1 interneurons
② Additional notochord transplanted into the neural plate induces extra floor plate and motor neurons
⑶ Anti-shh antibodies inhibit the function of shh
6. Homeoboxgenes
Input: 2019.03.17 14:11