Reiterative use of FGF signaling in mesoderm development during embryogenesis and metamorphosis in the hemichordate Ptychodera flava

Functional evidence that FGFR regulates MAPK signaling in organizer specification in the gastropod mollusk Lottia peitaihoensis

The D-quadrant organizer sets up the dorsal-ventral (DV) axis and regulates mesodermal development of spiralians. Studies have revealed an important role of mitogen-activated protein kinase (MAPK) signaling in organizer function, but the related molecules have not been fully revealed. The association between fibroblast growth factor receptor (FGFR) and MAPK signaling in regulating organizer specification has been established in the annelid Owenia fusiformis. Now, comparable studies in other spiralian phyla are required to decipher whether this organizer-inducing function of FGFR is prevalent in Spiralia. Here, we indicate that treatment with the FGFR inhibitor SU5402 resulted in deficiency of organizer specification in the mollusk Lottia peitaihoensis. Subsequently, the bone morphogenetic protein (BMP) signaling gradient and DV patterning were disrupted, suggesting the roles of FGFR in regulating organizer function. Changes in multiple aspects of organizer function (the morphology of vegetal blastomeres, BMP signaling gradient, expression of DV patterning markers, etc.) indicate that these developmental functions have different sensitivities to FGFR/MAPK signaling. Our results reveal a functional role of FGFR in organizer specification as well as DV patterning of Lottia embryos, which expands our knowledge of spiralian organizers.

Supplementary Information

The online version contains supplementary material available at 10.1007/s42995-023-00194-x.

Exploring the Structural and Functional Diversity among FGF Signals: A Comparative Study of Human, Mouse, and Xenopus FGF Ligands in Embryonic Development and Cancer Pathogenesis

Fibroblast growth factors (FGFs) encode a large family of growth factor proteins that activate several intracellular signaling pathways to control diverse physiological functions. The human genome encodes 22 FGFs that share a high sequence and structural homology with those of other vertebrates. FGFs orchestrate diverse biological functions by regulating cellular differentiation, proliferation, and migration. Dysregulated FGF signaling may contribute to several pathological conditions, including cancer. Notably, FGFs exhibit wide functional diversity among different vertebrates spatiotemporally. A comparative study of FGF receptor ligands and their diverse roles in vertebrates ranging from embryonic development to pathological conditions may expand our understanding of FGF. Moreover, targeting diverse FGF signals requires knowledge regarding their structural and functional heterogeneity among vertebrates. This study summarizes the current understanding of human FGF signals and correlates them with those in mouse and Xenopus models, thereby facilitating the identification of therapeutic targets for various human disorders.

Comparisons of cell proliferation and cell death from tornaria larva to juvenile worm in the hemichordate Schizocardium californicum

Background

There are a wide range of developmental strategies in animal phyla, but most insights into adult body plan formation come from direct-developing species. For indirect-developing species, there are distinct larval and adult body plans that are linked together by metamorphosis. Some outstanding questions in the development of indirect-developing organisms include the extent to which larval tissue undergoes cell death during the process of metamorphosis and when and where the tissue that will give rise to the adult originates. How do the processes of cell division and cell death redesign the body plans of indirect developers? In this study, we present patterns of cell proliferation and cell death during larval body plan development, metamorphosis, and adult body plan formation, in the hemichordate Schizocardium californium (Cameron and Perez in Zootaxa 3569:79–88, 2012) to answer these questions.

Results

We identified distinct patterns of cell proliferation between larval and adult body plan formation of S. californicum. We found that some adult tissues proliferate during the late larval phase prior to the start of overt metamorphosis. In addition, using an irradiation and transcriptomic approach, we describe a genetic signature of proliferative cells that is shared across the life history states, as well as markers that are unique to larval or juvenile states. Finally, we observed that cell death is minimal in larval stages but begins with the onset of metamorphosis.

Conclusions

Cell proliferation during the development of S. californicum has distinct patterns in the formation of larval and adult body plans. However, cell death is very limited in larvae and begins during the onset of metamorphosis and into early juvenile development in specific domains. The populations of cells that proliferated and gave rise to the larvae and juveniles have a genetic signature that suggested a heterogeneous pool of proliferative progenitors, rather than a set-aside population of pluripotent cells. Taken together, we propose that the gradual morphological transformation of S. californicum is mirrored at the cellular level and may be more representative of the development strategies that characterize metamorphosis in many metazoan animals.

Supplementary Information

The online version contains supplementary material available at 10.1186/s13227-022-00198-1.

Gain of gene regulatory network interconnectivity at the origin of vertebrates

In this manuscript, we address an essential question in developmental and evolutionary biology: How have changes in gene regulatory networks contributed to the invertebrate-to-vertebrate transition? To address this issue, we perturbed four signaling pathways critical for body plan formation in the cephalochordate amphioxus and in zebrafish and compared the effects of such perturbations on gene expression and gene regulation in both species. Our data reveal that many developmental genes have gained response to these signaling pathways in the vertebrate lineage. Moreover, we show that the interconnectivity between these pathways is much higher in zebrafish than in amphioxus. We conclude that this increased signaling pathway complexity likely contributed to vertebrate morphological novelties during evolution.

Signaling pathways control a large number of gene regulatory networks (GRNs) during animal development, acting as major tools for body plan formation [A. Pires-daSilva, R. J. Sommer, Nat. Rev. Genet. 4, 39–49 (2003)], although only a few of these pathways operate during this period [J. J. Sanz-Ezquerro, A. E. Münsterberg, S. Stricker, Front. Cell Dev. Biol. 5, 76 (2017)]. Moreover, most of them have been largely conserved during metazoan evolution [L. S. Babonis, M. Q. Martindale, Philos. Trans. R. Soc. Lond. B Biol. Sci. 372, 20150477 (2017)]. How evolution has generated a vast diversity of animal morphologies with such a limited number of tools is still largely unknown. Here, we show that gain of interconnectivity between signaling pathways and the GRNs they control may have critically contributed to the origin of vertebrates. We perturbed the retinoic acid, Wnt, FGF, and Nodal signaling pathways during gastrulation in the invertebrate chordate amphioxus and zebrafish and compared the effects on gene expression and cis-regulatory elements (CREs). We found that multiple developmental genes gain response to these pathways through vertebrate-specific CREs. Moreover, in contrast to amphioxus, many of these CREs responded to multiple pathways in zebrafish, which reflects their high interconnectivity. Furthermore, we found that vertebrate-specific cell types are more enriched in highly interconnected genes than in tissues with more ancient origin. Thus, the increase of CREs in vertebrates integrating inputs from different signaling pathways probably contributed to gene expression complexity and to the formation of new cell types and morphological novelties in this lineage.

Structural and Functional Characterization of the FGF Signaling Pathway in Regeneration of the Polychaete Worm Alitta virens (Annelida, Errantia)

Epimorphic regeneration of lost body segments is a widespread phenomenon across annelids. However, the molecular inducers of the cell sources for this reparative morphogenesis have not been identified. In this study, we focused on the role of fibroblast growth factor (FGF) signaling in the posterior regeneration of Alitta virens. For the first time, we showed an early activation of FGF ligands and receptor expression in an annelid regenerating after amputation. The expression patterns indicate that the entire regenerative bud is competent to FGFs, whose activity precedes the initiation of cell proliferation. The critical requirement of FGF signaling, especially at early stages, is also supported by inhibitor treatments followed by proliferation assay, demonstrating that induction of blastemal cells depends on FGFs. Our results show that FGF signaling pathway is a key player in regenerative response, while the FGF-positive wound epithelium, ventral nerve cord and some mesodermal cells around the gut could be the inducing tissues. This mechanism resembles reparative regeneration of vertebrate appendages suggesting such a response to the injury may be ancestral for all bilaterians.

FGF signaling acts on different levels of mesoderm development within Spiralia

FGF 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.

Molecular insights into deuterostome evolution from hemichordate developmental biology

Hemichordates, along with echinoderms and chordates, belong to the lineage of bilaterians called the deuterostomes. Their phylogenetic position as an outgroup to chordates provides an opportunity to investigate the evolutionary origins of the chordate body plan and reconstruct ancestral deuterostome characters. The body plans of the hemichordates and chordates are organizationally divergent making anatomical comparisons very challenging. The developmental underpinnings of animal body plans are often more conservative than the body plans they regulate, and offer a novel data set for making comparisons between morphologically divergent body architectures. Here I review the hemichordate developmental data generated over the past 20 years that further test hypotheses of proposed morphological affinities between the two taxa, but also compare the conserved anteroposterior, dorsoventral axial patterning programs and germ layer specification programs. These data provide an opportunity to determine which developmental programs are ancestral deuterostome or bilaterian innovations, and which ones occurred in stem chordates or vertebrates representing developmental novelties of the chordate body plan.