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

slide 2), (7 MB, for http://www.wormclassroom.org/movies/edu/nancegast.mov

slide 21 & slide 24 left), http://www.wormclassroom.org/movies/edu/goldgast2.mov

slide 24 right), (2.3 MB, for (3MB, for http://www.wormclassroom.org/movies/edu/goldgast3.mov

slide 27) (4MB, for

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 muscle and pharynx endoderm 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 P2 removed Pharynx Priess & Thomson (1986) Cell 48:241

SKN-1 (

sk

i

n

excess) is responsible for mesoderm fate Mutation of

skn-1

results in EMS producing muscle and hypodermis Wild-type

skn-1

mutant Pharynx Gut Gilbert 7th ed. Fig. 8.45

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

mex-1

2-cell 4-cell Gilbert 5e, Fig. 13.19

SKN-1 activates transcription Nuclei of

med-1

&

med-2

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 (

p

haryngeal &

i

ntestinal

e

xcess) 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 Gilbert 7th ed. Fig. 8.46

Gut and pharynx; EMS makes 1 E cell and 1 MS cell

Blastomere identity in C. elegans: P2 induces E remove P2

ABa ABp EMS

normal

ABa ABp P2 EMS

move P2

ABa ABp EMS P2

adapted from work by Bob Goldstein gut granules

Wnt signaling activates transcription of certain genes

Wnt Wnt

b

-catenin degraded

b

-catenin levels accumulate

Gilbert 7th ed. Fig. 6.24

No transcription Transcription

mom-2/Wnt

and

mom-5/Fz

are required for E specification

mom-2

mutant

mom =

mo

re

m

esoderm 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 b catenin 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 P4

Lee & Goldstein Development (2003) 130:307

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