Biology 624 - Developmental Genetics
Lecture #4 – Gastrulation Movements
GASTRULATION is a complex series of cell
movements that:
--rearranges cells, giving them new neighbors
--results in the formation of 3 GERM LAYERS that will
form the subsequent embryo: ectoderm, endoderm and
mesoderm
--forms the main body axes of the embryo (they were
specified earlier but not formed)
cleavage
*
1.5h
0h
organogenesis
GASTRULATION
16h
6h
*
organogenesis
cleavage GASTRULATION
2.5h
0h
cleavage
2.8h
24h
10h
cleavage
3.5h
dorsal closure
*GASTRULATION
neurulation organogenesis
36h
18h
*
GASTRULATION
segmentation
5h
10h
organogenesis
24h
48-72h
*
GASTRULATION
cleavage
organogenesis
segmentation
24h
first cleavage
24h
4d
21d
7d
*
implantation GASTRULATION
organogenesis
4.5d
6.5d
segmentation
14d
20d
Invagination- the infolding of a region of cells
Involution- the inturning of an expanding outer
layer of cells
Ingression- the migration of individual cells
from surface to interior
Delamination- the splitting of one sheet of cells
into two parallel sheets of cells
Epiboly- the movement of epithelial sheets that
spread as a unit to cover the embryo
Convergent Extension
Convergent extension- the lengthening of a
group of cells in the long axis while shortening
in the perpendicular axis
Cell Movements during
Convergent Extension in Zebrafish
Fate map of the fly embryo at cellular blastoderm stage
Early Gastrulation in Drosophila
Figure 9.40 Gastrulation in
Drosophila
Schematic Representation of Mid-Gastrulation in
Drosophila
Germ Band Extension in Drosophila
GERM BAND EXTENDED PROCESSES:
--organogenesis – e.g. nervous system forms by
neuroblast ingression from ectoderm
--segmentation – A-P segment unique identity set up
--imaginal disc specification – cells set aside that will
survive pupation
Germ Band Retraction in Drosophila
Gastrulation in Drosophila - lateral view
Gastrulation in Drosophila – Vade Mecum Movie
FGF Signaling is Critical to Gastrulation in Drosophila
Stage 7
Stage 8
early
gastrulation
midgastrulation
Stage 9
WildType
Mutant
Neurotactin, membrane marker
Twist, mesoderm marker
extended
germ band
(Gryzik and Muller, 2004)
Model for FGF signaling in Drosophila gastrulation
(Leptin and Affolter, 2004)
Fate Map of the Blastula of the Frog Xenopus laevis
Cell Movements During Frog Gastrulation - Early
Cell Movements During Frog Gastrulation - Mid
Cell Movements During Frog Gastrulation - Late
Epiboly of the Ectoderm Is Accomplished by Cell
Division and Intercalation
Convergent Extension
Convergent extension- the lengthening of a
group of cells in the long axis while shortening
in the perpendicular axis
Movie of Xenopus Gastrulation
Xenopus Gastrulation – Vade Mecum
Fibronectin and Amphibian Gastrulation
Normal
FN block
peptides
Blastocoel Roof Explants deposit matrix that
directs the migration of mesoderm
from Nagel et al, 2004
FGF Expression during avian gastrulation and
the putative role of Sprouty/spred
from Keller, 2005
Wnt Signaling Mediates Two Distinct Aspects of
Gastrulation
Convergent Extension
Tissue Separation
(Huelsken and Birchmeier, 2001)
Amphibian Convergence Extension Requires Noncanonical Wnt Signaling
(Habas et al, 2003)
CE in Zebrafish Requires Oriented Cell Division
(Gong et al, 2004)
This is the dorsal ectoderm of embryos in
gastrulation, Xdd is a Disheveled mt, animal
pole is up
papc Expression is Defective in spt Mutant Embryos
WT
spt-
At the end of gastrulation---the basic body plan is set up
--the three germ layers have formed
and will produce all embryonic
structures except the germline
ECTODERM---skin, nervous system, neural crest
MESODERM---muscle, bones, blood and vessels, kidney,
gonads, connective tissue
ENDODERM---gut, liver, lungs, pancreas
C. elegans embryogenesis
cleavage
0h
* GASTRULATION
1.5h
6h
organogenesis
16h
Drosophila embryogenesis
*
organogenesis
cleavage GASTRULATION
0h 2.5h
dorsal closure
10h
24h
Frog embryogenesis
* GASTRULATION
3.5h 18h
cleavage
neurulation
organogenesis
36h
Zebrafish embryogenesis
* GASTRULATION segmentation
2.8h 5h
10h 24h
cleavage
organogenesis
48-72h
Chick embryogenesis
Egg laid
*
GASTRULATION
cleavage
organogenesis
24h
segmentation
4d
7d
21d
Mouse embryogenesis
first cleavage
24h
implantation
4.5d
* GASTRULATION
organogenesis
6.5d
segmentation
14d
20d