A Hedgehog-FGF signaling axis patterns anterior mesoderm during gastrulation

Abstract

The application of single cell technologies to early development holds promise for resolving complex developmental phenotypes. Here we define a novel role for Hedgehog (Hh) signaling for the formation of anterior mesoderm lineages during gastrulation. Single-cell transcriptome analysis of Hh-deficient mesoderm revealed selective deficits in anterior mesoderm populations that later translate to physical defects to anterior embryonic structures including the first pharyngeal arch, heart, and anterior somites. We found that Hh-dependent anterior mesoderm defects were cell non-autonomous to Hh-signal reception.Transcriptional profiling of Hh-deficient mesoderm during gastrulation revealed disruptions to both transcriptional patterning of the mesoderm and a key FGF signaling pathway for mesoderm migration. FGF4 protein application was able to restore cellular migration during gastrulation that was decreased by Hh pathway antagonism. These findings implicate that primitive streak-mediated regulation of anterior mesoderm patterning is controlled by a multicomponent signaling hierarchy activated by Hh signaling and executed by FGF signal transduction.

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 recently 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 (Andersen et al, 2018;Evan 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 (Evan 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;Evan 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.…”

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

“…This is once cells have migrated and reached their final location in the embryo [11]. 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 [8,[12][13][14][15]. Whether initial molecular differences between different sets of cardiac progenitors already exist in the primitive streak remains unclear.…”