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 mesoderm 2-make dorsal mesoderm 3-pattern mesoderm Very useful model, although “1” likely induces mesoderm throughout the equatorial zone, and “2” and “1” act together on cells dorsally VentralDorsal Wolpert, Principles of Development (1998), Oxford Univ. Press

Evidence for Signal 1: Nieuwkoop Recombinants Signal 1: make mesoderm Figure from S. Sokol, MSSM

FGF Signal 1=Smad2/3-mediated TGF  ligand; Ras/MAPK signaling required for maintenance Adapted from Kimelman and Griffin (1998), Cell 94,

mesoderm induction in Xenopus Adapted from: Massague (1998), Ann. Rev. Biochem. 67, ; Hama et al. (2001), Mech. Dev. 109, 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, Wolpert, Principles of Development (1998), Oxford Univ. Press

Alex Gregorieff et al. Genes Dev. 2005; 19: Figure 1. The Wnt canonical pathway

The “canonical” Wnt pathway

Dorsal stabilization/nuclear localization of  -catenin following cortical rotation Gilbert, Developmental Biology, 7th ed.(2003), Sinauer Associates, Inc.; Tao et al. (2005), Cell 120,

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,

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, ; 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, Gilbert, Developmental Biology, 7th ed.(2003), Sinauer Associates, Inc. Weinstein and Hemmati-Brivanlou (1997), Curr. Opin. Neurobiol. 7, 7-12.

Ectopic germ layer suppression: Xbrachyury promoter analysis Modeled after: Lerchner et al. (2000), Development 127,

Early gastrulaLate gastrula Ectopic germ layer suppression: “rogue cells” Modeled after: Wardle and Smith (2004), Development 131,

Mesendodermal suppression by zygotic Fox proteins Suri et al (2005), Development 132,

Mesodermal suppression by the maternal Smad4 ubiquitin ligase Ectodermin Dupont et al. (2005), Cell 121,

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, ; Perea-Gomez et al. (2002), Dev. Cell 3,

Dual inhibition of BMP and (zygotic) Wnt signaling leads to formation of a complete secondary axis “Head Induction” Glinka et al. (1997) Nature 389,

Cerberus makes extra heads only (no extra trunk)-- Anti-Wnt? + Anti-BMP? + Anti-trunk inducer? Yes. Bouwmeester et al. (1996), Nature 382, ; Piccolo et al. (1999), Nature 397,

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