Transcript C. elegans Blastomere Specification and Gastrulation

Note to Instructors
•
The material is kindly contributed by Tim Walston at the University of
Wisconsin in Madison
•
About the material: the lecture is about early embryonic development in
C. elegans. In it, the author looked at fate specification of the 4 cell
embryo by PIE-1, SKN-1 and Wnt signaling. He also presented a
detailed description of C. elegans gastrulation.
•
There are total 4 movies accompanying this Power Point Presentation
(earlyemb.mov, nancegast.mov, goldgast2.mov and goldgast3.mov).
•
The movies can be found in the links:
http://www.wormclassroom.org/movies/edu/earlyemb.mov (7 MB, for
slide 2),
http://www.wormclassroom.org/movies/edu/nancegast.mov (2.3 MB, for
slide 21 & slide 24 left),
http://www.wormclassroom.org/movies/edu/goldgast2.mov (3MB, for
slide 24 right),
http://www.wormclassroom.org/movies/edu/goldgast3.mov (4MB, for
slide 27)
C. elegans Blastomere
Specification and Gastrulation
Insert movie “earlyemb.mov”
By Tim Walston
at University of Wisconsin in Madison
EMS daughters form two
major germ layers
mesoderm
endoderm
muscle and pharynx
gut
Blastomere Identity in C. elegans
progeny make pharynx
and epidermis
due to induction from MS
makes
mesoderm
(muscle,
pharynx)
makes
gut
EMS displays both
autonomous and conditional
specification
• Cytoplasmic determinants specify MS
fate.
• Cell-cell inductions specify E fate.
Mesoderm is autonomously specified
AB removed
P1 killed
Pharynx
Priess & Thomson (1986) Cell 48:241
P2 removed
SKN-1 (skin excess) is
responsible for mesoderm fate
Mutation of skn-1 results in EMS producing muscle and hypodermis
Wild-type
Pharynx
Gut
Gilbert 7th ed. Fig. 8.45
skn-1 mutant
SKN-1 is present in EMS and P2
Modified from Riddle et al. Figure 14.5
MEX-1 restricts SKN-1 to MS & P2
Wildtype
2-cell
4-cell
Gilbert 5e, Fig. 13.19
mex-1
SKN-1 activates transcription
of med-1 & med-2
Nuclei
MED-1::GFP
Maduro et al. Molec. Cell (2001) 7:475
SKN-1 is present in EMS and P2
Modified from Riddle et al. Figure 14.5
PIE-1 (pharyngeal & intestinal
excess) represses SKN-1 in P2
MED-1::GFP
Modified from Riddle et al. Figure 14.5
Maduro et al. Molec. Cell (2001) 7:475
EMS displays both
autonomous and conditional
specification
• Cytoplasmic determinants specify MS
fate.
– SKN-1 activates transcription of med-1 &
med-2
• Cell-cell inductions specify E fate.
EMS requires P2 to make gut
No gut;
EMS produces 2 MS-like cells
No gut;
EMS produces 2 MS-like cells
Gut and pharynx;
EMS makes 1 E cell and 1 MS cell
Gilbert 7th ed. Fig. 8.46
Blastomere identity in C. elegans:
P2 induces E
remove P2
ABa
ABp
EMS
normal
ABp
move P2
ABp
ABa
P2
EMS
ABa
EMS
P2
gut granules
adapted from work by Bob Goldstein
Wnt signaling
activates transcription
of certain genes
Wnt
b-catenin
degraded
Gilbert 7th ed. Fig. 6.24
No transcription
Wnt
b-catenin levels
accumulate
Transcription
mom-2/Wnt and mom-5/Fz are
required for E specification
mom-2 mutant
mom =
more
mesoderm
Thorpe et al. Cell (1997) 90:695
P2 specifies gut through MOM-2
Gut
Thorpe et al. Cell (1997) 90:695
MOM-2/Wnt from P2 signals EMS
to induce E
MOM-2 = Wnt
MOM-5 = Frizzled
adapted from Gilbert 6e, Fig. 8.46
EMS displays both
autonomous and conditional
specification
• Cytoplasmic determinants specify MS fate.
– SKN-1 activates transcription of med-1 & med-2
• Cell-cell inductions specify E fate.
– Wnt signaling from P2 induces EMS by regulating bcatenin levels and activating transcription
C. elegans gastrulation
Insert movie “nancegast.mov”
Nance et al.Development (2003) 130:5339
Gastrulation creates
multiple body layers
Gilbert 7th ed. Fig. 8.48
C. elegans has a small blastocoel
Nance & Priess Development (2002) 129:387
Ea & Ep begin ingression
Insert movie
“goldgast2.mov”
Insert movie “nancegast.mov”
Nance et al.Development (2003) 130:5339
Lee & Goldstein Development (2003) 130:307
Apical constriction draws Ea & Ep
into the bloastocoel
Ea
Ep
Lee & Goldstein Development (2003) 130:307
P4
P4 and MS cells
actively extend
over ingressing
cells
Nance & Priess Development (2002) 129:387
C. elegans gastrulation:
Apical constriction and
directed migrations
Insert movie “goldgast3.mov”
Lee & Goldstein Development (2003) 130:307
Ingression of other cell types
follow Ea & Ep
Nance & Priess Development (2002) 129:387
Gastrulation creates
multiple body layers
Gilbert 7th ed. Fig. 8.48