Note to Instructors

1
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.m
  ov (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)

2
C. elegans Blastomere Specification and
Gastrulation
Insert movie earlyemb.mov
By Tim Walston at University of Wisconsin in
Madison
3
EMS daughters form two major germ layers
mesoderm muscle and pharynx
endoderm gut
4
Blastomere Identity in C. elegans
makes mesoderm (muscle, pharynx)
progeny make pharynx and epidermis due to
induction from MS
makes gut
5
EMS displays both autonomous and conditional
specification

• Cytoplasmic determinants specify MS fate.
• Cell-cell inductions specify E fate.

6
Mesoderm is autonomously specified
AB removed
P1 killed
P2 removed
Pharynx
Priess Thomson (1986) Cell 48241
7
SKN-1 (skin excess) is responsible for mesoderm
fate
Mutation of skn-1 results in EMS producing muscle
and hypodermis
skn-1 mutant
Wild-type
Pharynx
Gut
Gilbert 7th ed. Fig. 8.45
8
SKN-1 is present in EMS and P2
Modified from Riddle et al. Figure 14.5
9
MEX-1 restricts SKN-1 to MS P2
Wildtype
mex-1
2-cell
4-cell
Gilbert 5e, Fig. 13.19
10
SKN-1 activates transcription of med-1 med-2
Nuclei
MED-1GFP
Maduro et al. Molec. Cell (2001) 7475
11
SKN-1 is present in EMS and P2
Modified from Riddle et al. Figure 14.5
12
PIE-1 (pharyngeal intestinal excess) represses
SKN-1 in P2
MED-1GFP
Maduro et al. Molec. Cell (2001) 7475
Modified from Riddle et al. Figure 14.5
13
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.

14
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
15
Blastomere identity in C. elegans P2 induces E
normal
remove P2
move P2
ABp
ABp
ABp
ABa
ABa
ABa
P2
EMS
EMS
EMS
P2
gut granules
adapted from work by Bob Goldstein
16
Wnt signaling activates transcription of certain
genes
Wnt
b-catenin levels accumulate
b-catenin degraded
Transcription
No transcription
Gilbert 7th ed. Fig. 6.24
17
mom-2/Wnt and mom-5/Fz are required for E
specification
mom-2 mutant
mom more mesoderm
Thorpe et al. Cell (1997) 90695
18
P2 specifies gut through MOM-2
Gut
Thorpe et al. Cell (1997) 90695
19
MOM-2/Wnt from P2 signals EMS to induce E
MOM-2 Wnt MOM-5 Frizzled
adapted from Gilbert 6e, Fig. 8.46
20
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
  b-catenin levels and activating transcription

21
C. elegans gastrulation
Insert movie nancegast.mov
Nance et al.Development (2003) 1305339
22
Gastrulation creates multiple body layers
Gilbert 7th ed. Fig. 8.48
23
C. elegans has a small blastocoel
Nance Priess Development (2002) 129387
24
Ea Ep begin ingression
Insert movie goldgast2.mov
Insert movie nancegast.mov
Nance et al.Development (2003) 1305339
Lee Goldstein Development (2003) 130307
25
Apical constriction draws Ea Ep into the
bloastocoel
Lee Goldstein Development (2003) 130307
26
P4 and MS cells actively extend over ingressing
cells
Nance Priess Development (2002) 129387
27
C. elegans gastrulationApical constriction and
directed migrations
Insert movie goldgast3.mov
Lee Goldstein Development (2003) 130307
28
Ingression of other cell types follow Ea Ep
Nance Priess Development (2002) 129387
29
Gastrulation creates multiple body layers
Gilbert 7th ed. Fig. 8.48