Hedgehog–FGF signaling axis patterns anterior mesoderm during gastrulation

Abstract

<jats:p>The mechanisms used by embryos to pattern tissues across their axes has fascinated developmental biologists since the founding of embryology. Here, using single-cell technology, we interrogate complex patterning defects and define a Hedgehog (Hh)–fibroblast growth factor (FGF) signaling axis required for anterior mesoderm lineage development during gastrulation. Single-cell transcriptome analysis of Hh-deficient mesoderm revealed selective deficits in anterior mesoderm populations, culminating in defects to anterior embryonic structures, including the pharyngeal arches, heart, and anterior somites. Transcriptional profiling of Hh-deficient mesoderm during gastrulation revealed disruptions to both transcriptional patterning of the mesoderm and FGF signaling for mesoderm migration. Mesoderm-specific<jats:italic>Fgf4</jats:italic>/<jats:italic>Fgf8</jats:italic>double-mutants recapitulated anterior mesoderm defects and Hh-dependent GLI transcription factors modulated enhancers at FGF gene loci. Cellular migration defects during gastrulation induced by Hh pathway antagonism were mitigated by the addition of FGF4 protein. These findings implicate a multicomponent signaling hierarchy activated by Hh ligands from the embryonic node and executed by FGF signals in nascent mesoderm to control anterior mesoderm patterning.</jats:p>

Ventricular, atrial and outflow tract heart progenitors arise from spatially and molecularly distinct regions of the primitive streak

“…BMPs and Fgfs secreted by the anterior endoderm (Alsan and Schultheiss, 2002;de Soysa et al, 2019;Lough and Sugi, 2000;Schultheiss et al, 1997), retinoic acid expressed in the posterior lateral plate mesoderm (Hochgreb et al, 2003;Xavier-Neto et al, 1999) and signals expressed in the anterior intestinal portal (AIP) at later stages (Anderson et al, 2016) all contribute to the patterning of the cardiac progenitors. A Hedgehog-Fgf signaling axis has also been proposed to pattern the anterior mesoderm to allocate the head and heart during mesodermal migration (Guzzetta et al, 2020). Our analysis shows the primitive streak cells that contribute to either the ventricles or to the poles of the heart are molecularly distinct prior to migration.…”

“…The signalling environment that cells encounter during migration influences the patterning of the heart fields (S13C Fig) (Andersen et al, 2018;Bardot et al 2020;Guzzetta et al, 2020;Hochgreb et al, 2003;Klaus et al, 2007;Sirbu et al, 2008). However, our findings that the ventricles and the outflow/atria arise from distinct primitive streak cell populations raise the possibility that these progenitors are already molecularly distinct in the primitive streak.…”

“…This mode of cellular diversification is reminiscent of temporal programmes in other tissues, such as neural progenitors (Doe, 2017), where sequential expression of distinct sets of transcription factors in progenitors defines the later differentiated cell types. These findings raise the possibility that cardiac progenitors are specified via a combination of both initial conditions set in the primitive streak and inductive events happening during migration (Bardot et al, 2020;Guzzetta et al, 2020) or once cells have reached their final location in the embryo.…”

“…Single cell transcriptomic assays show Mesp1+ cardiac progenitors diversify into molecularly distinct FHF and SHF populations at late embryonic day (E7.25) stage once cells have migrated and reached their final location in the embryo (Lescroart et al, 2018). The signalling environment cells encounter during and after their migration might play a role in the patterning of the cardiac progenitors into FHF and SHF domains (Andersen et al, 2018;Bardot et al 2020;Guzzetta et al, 2020;Hochgreb et al, 2003;Xavier-Neto et al, 1999). Whether initial molecular differences between different sets of cardiac progenitors already exist in the primitive streak remains unclear.…”

The Multifunctional Contribution of FGF Signaling to Cardiac Development, Homeostasis, Disease and Repair

“…FGFR4 and its ligands (FGFs 4 and 8) are involved in the proper left-right patterning of cardiac laterality, which is impaired in congenital heart disease associated with heterotaxy syndrome ( Sempou et al, 2018 ; Guzzetta et al, 2020 ). The functions of FGFs 4 and 8 in mesoderm migration and embryonic axis patterning are dependent on Hedgehog signaling activation (at E.9.5; Guzzetta et al, 2020 ).…”