Download Bio 2175 Developmental Biology Lecture 9: Axis formation

Bio 2175 Developmental Biology
Lecture 9: Axis formation
Establishing the body axes with some introduction to cell signaling during development.
1. News
a. Assignment due in discussion on Thursday
b. Two ways to make a two-headed vertebrate: fusion of two or bifurcation of one
2. The body axes (briefly)
a. Animal/Vegetal (early embryo only)
b. Anterior/Posterior (rostral/caudal)
c. Dorsal/Ventral
d. Left/Right
e. Medial/Lateral (with respect to the midline)
f. Proximal/Distal
g. Planes of section
i. Sagittal
1. Left/right is anterior/posterior, top/bottom is dorsal/ventral
ii. Transverse
1. Left/right is left/right, top/bottom is dorsal/ventral
iii. Horizontal (coronal)
1. Left/right is anterior/posterior, top/bottom is left/right
iv. Zebrafish practice: http://zfatlas.psu.edu/
3. Key vertebrate axial structures for orientation
a. Notochord
i. Axial mesoderm that is typically lost during development
b. Somites
i. Paraxial mesoderm that gives rise to body wall muscle, vertebrae, ribs, etc.
c. Neural plate/tube
i. Neural ectoderm that gives rise to brain, spinal cord, and peripheral neurons
4. Frogs
a. Early Development
i. Meroblastic cleavages
ii. Blastocoel formation & fate map
b. Gastrulation
i. Dorsal lip of the blastopore
ii. Involution and animal pole migration of hypoblast mesendoderm
iii. Archenteron and displacement of blastocoel
iv. Bottle cells (undergo apical constriction, necessary for proper gastrulation)
c. Transplant experiments
i. Most early gastrula cells are not committed (regulative development (signaling))
ii. Most late gastrula cells are committed
iii. However, early gastrula cells at dorsal lip of blastopore are committed
1. Induction of secondary body axes
2. Hans Spemann, Hilde Mangold, and the organizer (1935 Nobel Prize)
a. Mangold was PhD student who died in fuel explosion
Bio 2175 Developmental Biology
Lecture 9: Axis formation
d. D/V axis formation (drawing)
i. D/V axis established at instant of fertilization
ii. Cortical rotation
1. Microtubule dependent
2. Gray crescent
a. Blastopore forms here
b. Animal side of blastopore becomes dorsal
3. A complex, protein-based cytoplasmic determinant mechanism
a. Maternal factor version of the canonical Wnt pathway
b. ß-catenin transcription co-factor for dorsal fates (drawing)
i. Also a cadherin-associated protein (different function)
c. GSK-3 binds to ß-cat and targets for degradation
d. Disheveled (Dsh) binds GSK-3, inhibiting it (Nieuwkoop center)
e. Dsh originally in vegetal cortical cytoplasm
f. Cortical rotation upon sperm entry
i. Microtubules required (tubulin)
4. Example LoF experiments
a. Lithium blocks GSK-3 activity (dorsalizes embryo)
b. Antisense oligo against ß-cat mRNA (ventralizes)
i. Thus required for dorsal fates
5. Example GoF experiment
a. Inject ß-cat to ventral side (sufficient to induce dorsal fates)
5. Fish
a. Different details of embryonic anatomy but the same story as frogs
b. Sperm entry: the micropyle (only one place possible)
c. Dorsal/Ventral
i. The shield or keel
1. The fish organizer
a. Transplant experiment (Visualized with shha mRNA in situ hyb)
ii. Nuclear localization of ß-catenin
6. Drosophila (arthropod)
a. Syncytial blastoderm before cellular blastoderm
i. Thus transcription factors can diffuse between nuclei in the syncytium
b. D/V
i. Arthropods have a ventral CNS and dorsal gut tube
i. Evolutionary flip: Saint-Hilaire’s lobster
ii. Bmp = Dpp, Chordin = Sog
iii. Bmp signals cells to become ventral, chordin inhibits Bmp dorsally
b. A/P specification sequence
i. Bicoid sets off a chain reaction
ii. Gap genes
iii. Pair-rule genes (even-skipped paper in a couple weeks)
iv. Homeotic (Hox) genes
7. Next time: Bicoid discussion and D2 assignment