Abstract
ABSTRACTFGF signaling is involved in mesoderm induction in members of deuterostomes (e.g. tunicates, hemichordates), but not in flies and nematodes, in which it has a role in mesoderm patterning and migration. However, we need comparable studies in other protostome taxa in order to decipher whether this mesoderm-inducing function of FGF extends beyond the lineage of deuterostomes. Here, we investigated the role of FGF signaling in mesoderm development in three species of lophophorates, a clade within the protostome group Spiralia. Our gene expression analyses show that the mesodermal molecular patterning is conserved between brachiopods and phoronids, but the spatial and temporal recruitment of transcription factors differs significantly. Moreover, the use of the inhibitor SU5402 demonstrates that FGF signaling is involved in different steps of mesoderm development, as well as in morphogenetic movements of gastrulation and axial elongation. Our findings suggest that the mesoderm-inducing role of FGF extends beyond the group of deuterostomes.
Highlights
Mesoderm is an embryonic germ layer of bilaterians that gives rise to tissues residing between the ectoderm and endoderm, such as coeloms and muscles (Hyman, 1951; Ruppert, 1991)
Sprouty genes are downstream of fibroblast growth factor (FGF) signaling pathway in lophophorates We looked for putative downstream modulators of FGF signaling
The same was not true for T. transversa, where the expression of both sprouty genes remained unaffected in treated gastrulae (Fig. 5Ca-d′), suggesting that FGF signaling is acting at a later developmental stage in this species. These results suggest that sprouty genes are downstream of FGF signaling in all three investigated species, as shown in other organisms
Summary
Mesoderm is an embryonic germ layer of bilaterians that gives rise to tissues residing between the ectoderm and endoderm, such as coeloms and muscles (Hyman, 1951; Ruppert, 1991). Despite the differences in the embryological origin and morphogenesis, the molecular underpinnings of mesoderm induction, migration and differentiation into various derivatives shares similarities within bilaterians (Amin et al, 2009, 2010; Andrikou et al, 2013; Chiodin et al, 2013; Fritzenwanker et al, 2014; Grifone et al, 2005; Harfe et al, 1998; Hinman and Degnan, 2002; Imai et al, 2004; Kozin et al, 2016; Kozmik et al, 2007; Mahlapuu et al, 2001; Mankoo et al, 1999; Materna et al, 2013; Nederbragt et al, 2002; Osborne et al, 2018; Passamaneck et al, 2015; Perry et al, 2015; Rudnicki et al, 1993; Sandmann et al, 2007; Schubert et al, 2003; Shimeld et al, 2010; Zaffran et al, 2001) (Table S1) These molecular similarities have been commonly used as an argument for the homology of this germ layer (Burton, 2008; Lartillot et al, 2002; Martindale et al, 2004; Seipel and Schmid, 2005; Technau and Scholz, 2003). To gain insight into the ancestral role of FGF signaling for mesoderm development, data from other protostomes and, in particular, members of the Spiralia, are needed
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