Smad4 controls signaling robustness and morphogenesis by differentially contributing to the Nodal and BMP pathways

Luca Guglielmi,Claire Heliot,James Mcginty,Sunil Kumar,Ilaria Gori,Yuriy Alexandrov,Christopher Barrington,Andrew D Economou,Philip East,Caroline S Hill,Paul M W French,Foteini Papaleonidopoulou

doi:10.1038/s41467-021-26486-3

Luca Guglielmi, Claire Heliot + Show 10 more

Open Access

https://doi.org/10.1038/s41467-021-26486-3

Copy DOI

Abstract

The transcriptional effector SMAD4 is a core component of the TGF-β family signaling pathways. However, its role in vertebrate embryo development remains unresolved. To address this, we deleted Smad4 in zebrafish and investigated the consequences of this on signaling by the TGF-β family morphogens, BMPs and Nodal. We demonstrate that in the absence of Smad4, dorsal/ventral embryo patterning is disrupted due to the loss of BMP signaling. However, unexpectedly, Nodal signaling is maintained, but lacks robustness. This Smad4-independent Nodal signaling is sufficient for mesoderm specification, but not for optimal endoderm specification. Furthermore, using Optical Projection Tomography in combination with 3D embryo morphometry, we have generated a BMP morphospace and demonstrate that Smad4 mutants are morphologically indistinguishable from embryos in which BMP signaling has been genetically/pharmacologically perturbed. Smad4 is thus differentially required for signaling by different TGF-β family ligands, which has implications for diseases where Smad4 is mutated or deleted.

Highlights

The transcriptional effector SMAD4 is a core component of the transforming growth factor β (TGF-β) family signaling pathways
SMAD4 is described as the “common SMAD”, given its involvement in signal transduction in both arms of the TGF-β family signaling pathways; the SMAD1/5 arm, which is canonically activated by BMPs and some GDF ligands, and the SMAD2/ 3 arm, activated by NODAL, Activins, TGF-β, and other GDF family members[10,11]
We have comprehensively characterized a Smad[4] mutant in zebrafish and shown that Smad[4] is differentially required for the two arms of the TGF-β family signaling pathways. We have demonstrated this by interrogating Smad[4] function downstream of BMP and Nodal, which signal through pSmad1/5 and pSmad[2], respectively

Summary

Introduction

The transcriptional effector SMAD4 is a core component of the TGF-β family signaling pathways. Specific features of the signal, such as concentration and duration, are interpreted by receiving cells via highly regulated cellular responses[1] These are typically mediated by intracellular effectors, transcription factors, and cofactors[3]. The transcriptional effector SMAD4 mediates signaling responses to the transforming growth factor β (TGF-β) family of morphogens in a variety of biological contexts, ranging from embryo development to adult tissue homeostasis[4,5,6]. Consistent with this central role, loss of SMAD4 is associated with human disease, most commonly cancer, where it acts as a prominent tumor suppressor[7,8,9]. SMADs (R-SMADs) SMAD1/5 and SMAD2/3 are phosphorylated by activated type I receptors and form complexes with

Methods

Results

Conclusion