Antagonistic BMP–cWNT signaling in the cnidarian Nematostella vectensis reveals insight into the evolution of mesoderm

Abstract

Gastrulation was arguably the key evolutionary innovation that enabled metazoan diversification, leading to the formation of distinct germ layers and specialized tissues. Differential gene expression specifying cell fate is governed by the inputs of intracellular and/or extracellular signals. Beta-catenin/Tcf and the TGF-beta bone morphogenetic protein (BMP) provide critical molecular signaling inputs during germ layer specification in bilaterian metazoans, but there has been no direct experimental evidence for a specific role for BMP signaling during endomesoderm specification in the early branching metazoan Nematostella vectensis (an anthozoan cnidarian). Using forward transcriptomics, we show that beta-catenin/Tcf signaling and BMP2/4 signaling provide differential inputs into the cnidarian endomesodermal gene regulatory network (GRN) at the onset of gastrulation (24 h postfertilization) in N. vectensis. Surprisingly, beta-catenin/Tcf signaling and BMP2/4 signaling regulate a subset of common downstream target genes in the GRN in opposite ways, leading to the spatial and temporal differentiation of fields of cells in the developing embryo. Thus, we show that regulatory interactions between beta-catenin/Tcf signaling and BMP2/4 signaling are required for the specification and determination of different embryonic regions and the patterning of the oral-aboral axis in Nematostella. We also show functionally that the conserved "kernel" of the bilaterian heart mesoderm GRN is operational in N. vectensis, which reinforces the hypothesis that the endoderm and mesoderm in triploblastic bilaterians evolved from the bifunctional endomesoderm (gastrodermis) of a diploblastic ancestor, and that slow rhythmic contractions might have been one of the earliest functions of mesodermal tissue.cell signaling | cell fate | evodevo | heart kernel | gene regulatory network G astrulation is the morphogenetic event in metazoan embryonic development that leads to germ layer specification and organismal axial patterning (1). The complex cell signaling events that regulate both morphogenetic and cell-type specification is controlled temporally and spatially by complex networks of hierarchical regulatory inputs and outputs referred to as gene regulatory networks (GRNs) (1-5). During germ layer specification in triplobloblastic bilaterians with three germ layers (ectoderm, mesoderm, and endoderm), early endomesoderm (the embryonic precursor of both endoderm and mesoderm) induction is followed by the segregation of endodermal (e.g., lining of the gut and its derivatives) from mesodermal (e.g., muscle, connective tissue, kidney, somatic gonad, and coelomic lining) derivatives. Generally accepted to have evolved at the base of the bilaterian lineage, the presence of a mesoderm has played a crucial role in the evolution of complex animal body plans (5, 6). GRNs regulating initial embryonic endomesoderm specification are relatively well known in a variety of model bilaterian systems (7-12). Canonical Wnt (cWnt) signaling (13-17) and BMP signal...

Germ layer specific regulation of cell polarity and adhesion gives insight into the evolution of mesoderm

“…For example, TGFß, BMP, NANOS, FGF, and MEK/ERK/ERG take on roles during the specification of mesoderm, NCC migration, tumorigenesis, and other EMT-related processes (Barrallo-Gimeno & Nieto, 2005; Lim & Thiery, 2012; Nieto et al, 2016). Concordantly in N. vectensis embryos, cells of the pharyngeal and endomesodermal tissues express components of all these pathways (Amiel et al, 2017; Extavour, Pang, Matus, & Martindale, 2005; Matus, Thomsen, & Martindale, 2006, 2007; Röttinger et al, 2012; N. Wijesena, Simmons, & Martindale, 2017) that may modify their cellular characteristics. For example, one cadherin ( Nv CDH2 (Clarke, Miller, Lowe, Weis, & Nelson, 2016): 1g244010), and kinases that modify tubulin and histones are differentially regulated between ecto- and endomesodermal epithelium (N. Wijesena et al, 2017).…”

“…Target sites, off-target sites, and CFD scores were identified and sgRNA were designed using CRISPRscan (Doench et al, 2014; Moreno-Mateos et al, 2015). We delivered the RNP complex by microinjection as previously described (Ikmi, McKinney, Delventhal, & Gibson, 2014; Servetnick et al, 2017; N. Wijesena et al, 2017). Lyophilized Cas9 (PNA Bio., Inc. Cat.# CP01) was reconstituted in nuclease-free water with 20% glycerol to a final concentration of 2µg/µl.…”

On the evolution of bilaterality

“…4A). We are just beginning to understand how the regulatory systems of the two cnidarian body axes are wired and coordinated (Wijesena et al, 2017); however, some interesting details are already known. Owing to differences in the wiring of the gene regulatory network in Nematostella, dpp and chordin are expressed on the same side of the body axis, unlike in Drosophila or frog (Genikhovich et al, 2015;Rentzsch et al, 2006).…”

Genomic analysis of the tryptome reveals molecular mechanisms of gland cell evolution

“…Nematostella vectensis, the starlet sea anemone, has become a valuable model for studies of animal body plan evolution (Finnerty et al, 2004; Fritzenwanker et al, 2007; Kusserow et al, 2005; Leclere and Rentzsch, 2014; Wijesena et al, 2017); yet, little is known about the extent of cell diversity in the tissues that comprise the pharynx and mesenteries. The endodermal component of the mesenteries houses the germ cell precursors and two types of muscle cells and the few recent studies of the mesenteries in Nematostella have focused largely on these endodermal functions (Jahnel et al, 2014; Moiseeva et al, 2017; Renfer et al, 2010).…”