Embryology - Biology 104, Spring 2006 - Albert Harris and Corey Johnson
OUTLINE OF THIRD LECTURE: Jan 18, 2006, by Corey Johnson
Compare embryology of sea urchin, frog, bird and mammal
similarities and differences - continued
Cell movements defined (see also p. 88 for examples):
Invagination: infolding of an epithelial sheet
Ingression: movement of cells into the blastocoel
Involution: movement cell sheets over an interior surface
Delamination: separation of one sheet into two
Epiboly: movement cell sheets over an exterior surface
Convergence: movement of cells toward a central location
Extension: formation of a narrow group of cells
Sea Urchin Gastrulation (continued)
Archenteron: the pocket (endoderm) continues to expand as a tube toward the animal pole
(convergent-extension: cells group together forming a longer and narrower structure)
Blastopore: the opening to the archenteron
Outer cells: ectoderm Inner cells: endoderm Micromeres: mesoderm
Amphibian Gastrulation
Part of the gray crescent (if present) begins to invaginate
A combination of epiboly and involution move cells into the interior of the blastocoel
Involution: the inward migration of a dividing sheet of cells along those cells lining the blastocoel
Epiboly: the movement of a dividing sheet of cells over the outside of the embryo
The involuting cells form a new cavity, the archenteron
The first cells that move in are mesoderm, followed by endoderm
Outer cells: ectoderm Lining the archenteron: endoderm Those in between: mesoderm
link to movie
Vegetal View of Gastrulation & Neurulation: (15.0 hours elapsed, 48
minutes/second). This movie shows gastrulation and neurulation viewed
from the vegetal pole, the future dorsal side at the top.
diagram comparing gastrulation in different organisms
includes teleost fish, which will be covered in a later lecture
Avian Gastrulation:
Formation of the primitive streak: A longitudinal thickening of the epiblast
Cells pass through a groove and migrate right, left, and anteriorly (cranially)
Hensen's Node: the anterior boundary of the streak
First cells through displace the hypoblast and form endoderm
Second group slips between endoderm and the epiblast (ectoderm) forming mesoderm
Mammalian Gastrulation:
Basically the same as avian without the yolk
Hensen's node is called "the node"
Mouse development is unusual at this point - inverted
Neurulation:
Formation of the neural tube - ectoderm folds up forming a tube
Similar in all vertebrate groups (except fish)
Formation of mesodermal subpopulations: similar (but not identical) in all vertebrate groups
Lateral plate mesoderm (LPM)
Intermediate mesoderm (IM)
Somitic mesoderm (SM) - has segmented pairs called somites
Notochord Ð central mesodermal column runs from anterior to posterior (chordamesoderm)
-------------------------ectoderm------------------------
LMP - IM - SM - notochord - SM - IM - LPM
-------------------------endoderm------------------------
diagram comparing frog and chick body plan after neurulation
Organogenesis: things start to diverge substantially from one group to the next
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