Bio 2175 Developmental Biology
Lecture 6: Gastrulation
The basics of how cell division and early cell movements lay out the embryonic body plan with a focus
on sea urchins and zebrafish. Vocabulary is especially important today.
1.
News
a. Exam next Thursday
i. Practice questions this Friday, example answers Monday
ii. Review session next Tuesday 8:30PM, Searles 215
1. No new material—please bring specific questions
b. Teach-in
i. No labs next week so you can attend the afternoon sessions (if you want)
ii. If you want to attend a teach-in event during the exam time, please email me
ASAP three other times you could take the exam and we’ll work something out
c. Fetal (embryonic) tissue use in research
2.
Antibody label (next labs)
a. Bindin example; illustrating primary antibodies, secondary antibodies, and visualization
3.
Embryonic cell division
a. Fertilized egg, 1-cell stage embryo = zygote
b. Cytoskeleton
i. Cell division is a directed process--not just bags of water
ii. Microfilaments (actin) and microtubules (tubulin)
1. e.g. Inhibiting tubulin with colchicine blocks cell division
iii. Visualization: phalloidin-fluorophore + anti-tubulin antibody with secondary
1. Phalloidin is deathcap mushroom toxin
iv. Distribution of determinants (next week)
c. Cleavage divisions
i. Very fast, no growth, often asymmetrical cytoplasmic distribution
1. As opposed to exponential growth (e.g. stem cells)
ii. Holoblastic vs meroblastic
iii. Radial vs spiral (and others)
1. Complex phylogenetic positioning (e.g. lophotrochozoa ~ spiralia)
d. Embryonic tissue morphology
i. Epithelium vs Mesenchyme
1. Cuboidal vs squamous epithelium
2. Epithelial to mesenchymal (and vice versa) transition (EMT)
e. Morphogenetic movements
i. Condensation, cavitation, epiboly, involution, invagination, convergent extension,
branching, intercalation (we will see examples of most of these)
ii. Apical construction during invagination
1. Basal extracellular matrix (ECM)
a. (a.k.a. basement membrane or basal lamina)
4.
Germ layers
a. Fate maps: ectoderm (blue), mesoderm (red), endoderm (yellow)
i. e.g. by fluorescent cell transplant
ii. e.g. Kaede (maple leaf, “kye-duh”) labeling
Bio 2175 Developmental Biology
Lecture 6: Gastrulation
5.
Urchins
a. Time-lapse movie
b. Holoblastic radial cleavage
c. Orientation
i. Animal vs Vegetal axes
1. No other body axes yet (more information about axis formation later)
ii. Mesomers, macromeres, and micromeres
1. FYI: these are urchin-specific designations we won’t use much
d. Blastulation
i. Blastula, blastomere, blastocoel
ii. Make a hollow ball of cells (adhesion, channels)
e. Gastrulation
i. Invagination of primitive gut (archenteron, coelom)
ii. Ingression of mesenchyme (mesoderm)
iii. Convergent extension (intercalation)
iv. Pulling(?) by the secondary mesenchyme (Hardin 1988 on Thursday)
1. Filopodia
6.
Zebrafish
a. Meroblastic cleavage
b. No blastocoel
c. Gastrulation
i. Epiboly
ii. Involution
1. A layer sliding under another
iii. Ingression (mesendoderm)
1. A cell changing layers
7.
Evolution (if time)
a. Protostome vs deuterostome
i. The blastopore fate map that we mentioned previously
b. The strange developmental origin of the adult echinoderm body plan
i. Which came first in evolution?
ii. Lots of evolution of larval form
1. Has led some to speculate about genome fusions (unlikely)
8.
Next time
a. Discussion of Hardin 1988 urchin gastrulation paper
b. No assignment due but please prepare for discussion
c. Laptops will be helpful to bring to look up things