Signal Integration During Development

Dan Weinstein

Vertebrate development is characterized by a series of inductive interactions

The three-signal model of mesoderm induction

Germ-layer suppression/ “Head formation”

Xenopus laevis fate maps

Mesoderm formation: the 3 (or 4)-Signal Model

1-make mesoderm2-make dorsal mesoderm3-pattern mesoderm

Very useful model, although “1” likely induces mesoderm throughout the equatorial zone,and “2” and “1” act together on cells dorsally

Ventral Dorsal

Wolpert, Principles of Development (1998), Oxford Univ. Press

Evidence for Signal 1: Nieuwkoop RecombinantsSignal 1: make mesoderm

Figure from S. Sokol, MSSM

FGF

Signal 1=Smad2/3-mediated TGF ligand; Ras/MAPKsignaling required for maintenance

Adapted from Kimelman and Griffin (1998), Cell 94, 419-421

mesoderm induction in Xenopus

Adapted from: Massague (1998), Ann. Rev. Biochem. 67, 753-791; Hama et al. (2001), Mech. Dev. 109, 195-204.

VegT

Nodal-related ligand stimulates 2/3-type R-Smads

Signal 2: Make dorsal mesoderm

Wolpert, Principles of Development (1998), Oxford Univ. Press; Gilbert, Developmental Biology, 7th ed.(2003), Sinauer Associates, Inc.

Evidence for Signal 2

Wolpert, Principles of Development (1998), Oxford Univ. Press

UV irradiation and the DAI

Wolpert, Principles of Development (1998), Oxford Univ. Press

Axial rescue

Slack (1994), Curr. Biol. 4, 116-126Wolpert, Principles of Development (1998), Oxford Univ. Press

Alex Gregorieff et al. Genes Dev. 2005; 19: 877-890

Figure 1. The Wnt canonical pathway

The “canonical” Wnt pathway

http://www.stanford.edu/~rnusse/wntwindow.html

Dorsal stabilization/nuclear localization of -catenin following cortical rotation

Gilbert, Developmental Biology, 7th ed.(2003), Sinauer Associates, Inc.;Tao et al. (2005), Cell 120, 857-871.

Molecular integration of Signal 1 and Signal 2

Gilbert, Developmental Biology, 7th ed.(2003), Sinauer Associates, Inc.

Canonical and non-canonical Wnt pathways

Jessen and Solnica-Krezel (2005), Cell 120, 736-737.

Evidence for a dorsalizing signal secreted by the Organizer

Along these same lines: dorsal recombinants dorsalize ventral explants

Signal 3: Dorsalize Mesoderm/Antagonize Ventralizers of Mesoderm

Wolpert, Principles of Development (1998), Oxford Univ. Press

BMP4 signaling ventralizes mesoderm, and is inhibited dorsally

Glinka et al. (1997) Nature 289, 517-519;Gilbert, Developmental Biology, 7th ed.(2003), Sinauer Associates, Inc.

(dorsalization via inhibition of ventralization)

Phospho-Smad1 localization

Mechanism of action of the dorsalizing, neuralizing, BMP antagonists Chordin, Noggin, and Follistatin

Wolpert, Principles of Development (1998), Oxford Univ. Press

Noggin expression

BMPs and their antagonists represent Signals 3 and 4; these factors pattern all three germ layers during gastrulation

Munoz-Sanjuan and Brivanlou (2002), Nat. Rev. Neurosci. 3, 2721-280.Gilbert, Developmental Biology, 7th ed.(2003), Sinauer Associates, Inc.Weinstein and Hemmati-Brivanlou (1997), Curr. Opin. Neurobiol. 7, 7-12.

Xbrachyury

x

xXbrachyury

Xbrachyury

Ectopic germ layer suppression: Xbrachyury promoter analysis

Modeled after: Lerchner et al. (2000), Development 127, 2729-2739.

Early gastrula Late gastrula

Ectopic germ layer suppression:“rogue cells”

Modeled after: Wardle and Smith (2004), Development 131, 4687-4696.

Mesendodermal suppression by zygotic Fox proteins

Suri et al (2005), Development 132, 2733 - 2742

Mesodermal suppression by the maternal Smad4 ubiquitin ligase Ectodermin

Dupont et al. (2005), Cell 121, 87-99.

Gastrulation in the mouse

Anterior fate requires suppression of posterior (mesodermal) fate

Removal of chick hypoblast (and thus Nodal-antagonist activity),or targeted deletion of Cerl and Lefty1 in the mouse AVE gives rise to multiple primitive streaks (ectopic mesoderm).

Figures adapted from:Weinstein, D.C. (2004). In Stern, C. (ed.), Gastrulation, Cold Spring Harbor Laboratory Press, 563-570;Perea-Gomez et al. (2002), Dev. Cell 3, 745-756.

Dual inhibition of BMP and (zygotic) Wnt signaling leads to

formation of a complete secondary axis

“Head Induction”

Glinka et al. (1997) Nature 389, 517-519.

Cerberus makes extra heads only (no extra trunk)--Anti-Wnt? + Anti-BMP? + Anti-trunk inducer? Yes.

Bouwmeester et al. (1996), Nature 382, 595-601;Piccolo et al. (1999), Nature 397, 707-710

Signal 1/mesendoderm induction--Smad 2/3 + Ras/MAPK

Signal 2/dorsal axis formation--Canonical Wnt pathway, activated maternally

Signal 3/DV patterning (all germ layers)--Smad 1/5 activation/suppression

Ectodermal development--inhibit Smad 1/5, inhibit Smad 2/3,inhibit zygotic canonical Wnt signaling

Formation and patterning of the primary germ layers