MAPK signaling is necessary for neurogenesis in Nematostella vectensis

Abstract

BackgroundThe nerve net of Nematostella is generated using a conserved cascade of neurogenic transcription factors. For example, NvashA, a homolog of the achaete-scute family of basic helix-loop-helix transcription factors, is necessary and sufficient to specify a subset of embryonic neurons. However, positive regulators required for the expression of neurogenic transcription factors remain poorly understood.ResultsWe show that treatment with the MEK/MAPK inhibitor U0126 severely reduces the expression of known neurogenic genes, Nvath-like, NvsoxB(2), and NvashA, and known markers of differentiated neurons, suggesting that MAPK signaling is necessary for neural development. Interestingly, ectopic NvashA fails to rescue the expression of neural markers in U0126-treated animals. Double fluorescence in situ hybridization and transgenic analysis confirmed that NvashA targets represent both unique and overlapping populations of neurons. Finally, we used a genome-wide microarray to identify additional patterning genes downstream of MAPK that might contribute to neurogenesis. We identified 18 likely neural transcription factors, and surprisingly identified ~40 signaling genes and transcription factors that are expressed in either the aboral domain or animal pole that gives rise to the endomesoderm at late blastula stages.ConclusionsTogether, our data suggest that MAPK is a key early regulator of neurogenesis, and that it is likely required at multiple steps. Initially, MAPK promotes neurogenesis by positively regulating expression of NvsoxB(2), Nvath-like, and NvashA. However, we also found that MAPK is necessary for the activity of the neurogenic transcription factor NvashA. Our forward molecular approach provided insight about the mechanisms of embryonic neurogenesis. For instance, NvashA suppression of Nvath-like suggests that inhibition of progenitor identity is an active process in newly born neurons, and we show that downstream targets of NvashA reflect multiple neural subtypes rather than a uniform neural fate. Lastly, analysis of the MAPK targets in the early embryo suggests that MAPK signaling is critical not only to neurogenesis, but also endomesoderm formation and aboral patterning.Electronic supplementary materialThe online version of this article (doi:10.1186/s12915-016-0282-1) contains supplementary material, which is available to authorized users.

A bipolar role of the transcription factor ERG for cnidarian germ layer formation and apical domain patterning

“…Interestingly, cWnt/TCF represses expression of the potential FGF ligand, fgf8A , in the central ring (animal hemisphere) restricting its expression to the central domain, suggesting a role of FGF induced ERK/MAPK signaling in endomesoderm formation [24]. However, a recent study that focuses on the role of ERK/MAPK signaling in the initiation of the neurogenic program in Nematostella development, suggest that FGFR might not be the (sole) activator of this pathway in the presumptive endomesoderm [35]. The same authors have also shown that pharmacologically inhibition of ERK/MAPK signaling using U0126, a potent inhibitor of the ERK activating kinase MEK [36,37], after fertilization blocks gastrulation and endomesoderm formation [35].…”

“…However, a recent study that focuses on the role of ERK/MAPK signaling in the initiation of the neurogenic program in Nematostella development, suggest that FGFR might not be the (sole) activator of this pathway in the presumptive endomesoderm [35]. The same authors have also shown that pharmacologically inhibition of ERK/MAPK signaling using U0126, a potent inhibitor of the ERK activating kinase MEK [36,37], after fertilization blocks gastrulation and endomesoderm formation [35]. As this treatment perturbs gene expression within the animal hemisphere as well as the apical domain, this further suggests a dual role of this pathway in germ layer formation and axial patterning [35].…”

“…The same authors have also shown that pharmacologically inhibition of ERK/MAPK signaling using U0126, a potent inhibitor of the ERK activating kinase MEK [36,37], after fertilization blocks gastrulation and endomesoderm formation [35]. As this treatment perturbs gene expression within the animal hemisphere as well as the apical domain, this further suggests a dual role of this pathway in germ layer formation and axial patterning [35]. In addition, by using a genome wide expression array approach, the authors have identified a large set of putative downstream targets of this pathway of which only the genes potentially involved in neurogenesis have been reported [35].…”

“…As this treatment perturbs gene expression within the animal hemisphere as well as the apical domain, this further suggests a dual role of this pathway in germ layer formation and axial patterning [35]. In addition, by using a genome wide expression array approach, the authors have identified a large set of putative downstream targets of this pathway of which only the genes potentially involved in neurogenesis have been reported [35]. …”

Regulation of AP-1 by MAPK Signaling in Metal-Stressed Sea Anemone

“…However, we found only one homolog of ERK1/2 in Nematostella , most resembling ERK2 (80.7% protein identity). To directly test the role of ERK2 and ERK5 signaling cascades in Hg-treated anemone we used the MEK1/2-specific inhibitor U0126, which was shown to inhibit ERK1/2 phosphorylation and activation in Nematostella [30, 31], the ERK5 inhibitor XMD 8-92 [48], or a combination of the two. Results showed that Hg induces Nematostella ERK2 phosphorylation and that U0126 completely inhibits ERK2 phosphorylation (Fig.…”