Wnt Signaling Drives Correlated Changes in Facial Morphology and Brain Shape.

Marta Marchini,Diane Hu,Lucas Lo Vercio,Nathan M Young,Benedikt Hallgrímsson,Ralph Marcucio,Nils D Forkert

doi:10.3389/fcell.2021.644099

Abstract

Canonical Wnt signaling plays multiple roles critical to normal craniofacial development while its dysregulation is known to be involved in structural birth defects of the face. However, when and how Wnt signaling influences phenotypic variation, including those associated with disease, remains unclear. One potential mechanism is via Wnt signaling’s role in the patterning of an early facial signaling center, the frontonasal ectodermal zone (FEZ), and its subsequent regulation of early facial morphogenesis. For example, Wnt signaling may directly alter the shape and/or magnitude of expression of the sonic hedgehog (SHH) domain in the FEZ. To test this idea, we used a replication-competent avian sarcoma retrovirus (RCAS) encoding Wnt3a to modulate its expression in the facial mesenchyme. We then quantified and compared ontogenetic changes in treated to untreated embryos in the three-dimensional (3D) shape of both the SHH expression domain of the FEZ, and the morphology of the facial primordia and brain using iodine-contrast microcomputed tomography imaging and 3D geometric morphometrics (3DGM). We found that increased Wnt3a expression in early stages of head development produces correlated variation in shape between both structural and signaling levels of analysis. In addition, altered Wnt3a activation disrupted the integration between the forebrain and other neural tube derivatives. These results show that activation of Wnt signaling influences facial shape through its impact on the forebrain and SHH expression in the FEZ, and highlights the close relationship between morphogenesis of the forebrain and midface.

Highlights

Craniofacial development is a highly orchestrated process that involves both physical and molecular interactions between neuroectoderm, mesenchyme, and surface ectoderm
We used 3D geometric morphometrics (3DGM) to quantify the shape of the head and the brain, and we developed four novel metrics based on geometry for quantifying shape and size of a gene expression domain to assess sonic hedgehog (SHH) expression in the frontonasal ectodermal zone (FEZ)
Wnt3a overexpression, and to examine whether infection and expression was restricted to the frontonasal process (FNP), we quantified the level of expression of WNT3A, GAG, and AXIN2 indicators of Wnt signaling in neural crest cells (Yu et al, 2007) in the mesenchyme and ectoderm together derived from the FNP from four WT and four RCAS-Wnt3a samples (Supplementary Figure 1D)

Summary

Introduction

Craniofacial development is a highly orchestrated process that involves both physical and molecular interactions between neuroectoderm, mesenchyme, and surface ectoderm. The brain helps to physically shape the face and molecular signals from the brain are required for facial development (Marcucio et al, 2015). Recent evidence indicates that signals from neural crest cells contribute to development of the forebrain (Creuzet et al, 2004; Aguiar et al, 2014; Garcez et al, 2014). We altered signals that participate in development of the face and brain and assess covariance in these structures in order to determine the extent to which development of the brain and face are integrated.

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