Dusp1 modulates activin/smad2 mediated germ layer specification via FGF signal inhibition in Xenopus embryos

Regulation of gene expression downstream of a novel Fgf/Erk pathway during Xenopus development

Activation of Map kinase/Erk signalling downstream of fibroblast growth factor (Fgf) tyrosine kinase receptors regulates gene expression required for mesoderm induction and patterning of the anteroposterior axis during Xenopus development. We have proposed that a subset of Fgf target genes are activated in the embyo in response to inhibition of a transcriptional repressor. Here we investigate the hypothesis that Cic (Capicua), which was originally identified as a transcriptional repressor negatively regulated by receptor tyrosine kinase/Erk signalling in Drosophila, is involved in regulating Fgf target gene expression in Xenopus. We characterise Xenopus Cic and show that it is widely expressed in the embryo. Fgf overexpression or ectodermal wounding, both of which potently activate Erk, reduce Cic protein levels in embryonic cells. In keeping with our hypothesis, we show that Cic knockdown and Fgf overexpression have overlapping effects on embryo development and gene expression. Transcriptomic analysis identifies a cohort of genes that are up-regulated by Fgf overexpression and Cic knockdown. We investigate two of these genes as putative targets of the proposed Fgf/Erk/Cic axis: fos and rasl11b, which encode a leucine zipper transcription factor and a ras family GTPase, respectively. We identify Cic consensus binding sites in a highly conserved region of intron 1 in the fos gene and Cic sites in the upstream regions of several other Fgf/Cic co-regulated genes, including rasl11b. We show that expression of fos and rasl11b is blocked in the early mesoderm when Fgf and Erk signalling is inhibited. In addition, we show that fos and rasl11b expression is associated with the Fgf independent activation of Erk at the site of ectodermal wounding. Our data support a role for a Fgf/Erk/Cic axis in regulating a subset of Fgf target genes during gastrulation and is suggestive that Erk signalling is involved in regulating Cic target genes at the site of ectodermal wounding.

Two Homeobox Transcription Factors, Goosecoid and Ventx1.1, Oppositely Regulate Chordin Transcription in Xenopus Gastrula Embryos

The reciprocal inhibition between two signaling centers, the Spemann organizer (dorsal mesoderm) and ventral region (mesoderm and ectoderm), collectively regulate the overall development of vertebrate embryos. Each center expresses key homeobox transcription factors (TFs) that directly control target gene transcription. Goosecoid (Gsc) is an organizer (dorsal mesoderm)-specific TF known to induce dorsal fate and inhibit ventral/ectodermal specification. Ventx1.1 (downstream of Bmp signaling) induces the epidermal lineage and inhibits dorsal organizer-specific genes from the ventral region. Chordin (Chrd) is an organizer-specific secreted Bmp antagonist whose expression is primarily activated by Gsc. Alternatively, chrd expression is repressed by Bmp/Ventx1.1 in the ventral/epidermal region. However, the regulatory mechanisms underlying the transcription mediated by Gsc and Ventx1.1 remain elusive. Here, we found that the chrd promoter contained two cis-acting response elements that responded negatively to Ventx1.1 and positively to Gsc. In the ventral/ectodermal region, Ventx1.1 was directly bound to the Ventx1.1 response element (VRE) and inhibited chrd transcription. In the organizer region, Gsc was bound to the Gsc response elements (GRE) to activate chrd transcription. The Gsc-mediated positive response on the chrd promoter completely depended on another adjacent Wnt response cis-acting element (WRE), which was the TCF7 (also known as Tcf1) binding element. Site-directed mutagenesis of VRE, GRE, or WRE completely abolished the repressive or activator activity of Ventx1.1 and Gsc, respectively. The ChIP-PCR results confirmed the direct binding of Ventx1.1 and Gsc/Tcf7 to VRE and GRE/WRE, respectively. These results demonstrated that chrd expression is oppositely modulated by homeobox TFs, Ventx1.1, and Gsc/Tcf7 during the embryonic patterning of Xenopus gastrula.

Blood transcriptome comparison between sexes and their function in 4-week Rhode Island red chickens

Sex is a major biological factor in the development and physiology of a sexual reproductive organism, and its role in the growing process is needed to be investigated in various species. We compare blood transcriptome between 5 males and 5 females in 4-week-old Rhode Island Red chickens and perform functional annotation of differentially expressed genes (DEGs). The results are as follows. 141 and 109 DEGs were located in autosomes and sex chromosomes, respectively. The gene ontology (GO) terms are significantly (p < 0.05) enriched, which were limb development, inner ear development, positive regulation of dendrite development, the KEGG pathway the TGF-beta signaling pathway, and melanogenesis (p < 0.05). These pathways are related to morphological maintenance and growth of the tissues. In addition, the SMAD2W and the BMP5 were involved in the TGF-beta signaling pathway, and both play an important role in maintaining tissue development. The major DEGs related to the development of neurons and synapses include the up-regulated NRN1, GDF10, SLC1A1, BMP5, NBEA, and NRXN1. Also, 7 DEGs were validated using RT-qPCR with high correlation (r ² = 0.74). In conclusion, the differential expression of blood tissue in the early growing chicken was enriched in TGF-beta signaling and related to the development of neurons and synapses including SMAD2W and BMP5. These results suggest that blood in the early growing stage is differentially affected in tissue development, nervous system, and pigmentation by sex. For future research, experimental characterization of DEGs and a holistic investigation of various tissues and growth stages will be required.

New developments in the biology of fibroblast growth factors

The fibroblast growth factor (FGF) family is composed of 18 secreted signaling proteins consisting of canonical FGFs and endocrine FGFs that activate four receptor tyrosine kinases (FGFRs 1-4) and four intracellular proteins (intracellular FGFs or iFGFs) that primarily function to regulate the activity of voltage-gated sodium channels and other molecules. The canonical FGFs, endocrine FGFs, and iFGFs have been reviewed extensively by us and others. In this review, we briefly summarize past reviews and then focus on new developments in the FGF field since our last review in 2015. Some of the highlights in the past 6 years include the use of optogenetic tools, viral vectors, and inducible transgenes to experimentally modulate FGF signaling, the clinical use of small molecule FGFR inhibitors, an expanded understanding of endocrine FGF signaling, functions for FGF signaling in stem cell pluripotency and differentiation, roles for FGF signaling in tissue homeostasis and regeneration, a continuing elaboration of mechanisms of FGF signaling in development, and an expanding appreciation of roles for FGF signaling in neuropsychiatric diseases. This article is categorized under: Cardiovascular Diseases > Molecular and Cellular Physiology Neurological Diseases > Molecular and Cellular Physiology Congenital Diseases > Stem Cells and Development Cancer > Stem Cells and Development.

Bmp Signal Gradient Modulates Convergent Cell Movement via Xarhgef3.2 during Gastrulation of Xenopus Embryos

Gastrulation is a critical step in the establishment of a basic body plan during development. Convergence and extension (CE) cell movements organize germ layers during gastrulation. Noncanonical Wnt signaling has been known as major signaling that regulates CE cell movement by activating Rho and Rac. In addition, Bmp molecules are expressed in the ventral side of a developing embryo, and the ventral mesoderm region undergoes minimal CE cell movement while the dorsal mesoderm undergoes dynamic cell movements. This suggests that Bmp signal gradient may affect CE cell movement. To investigate whether Bmp signaling negatively regulates CE cell movements, we performed microarray-based screening and found that the transcription of Xenopus Arhgef3.2 (Rho guanine nucleotide exchange factor) was negatively regulated by Bmp signaling. We also showed that overexpression or knockdown of Xarhgef3.2 caused gastrulation defects. Interestingly, Xarhgef3.2 controlled gastrulation cell movements through interacting with Disheveled (Dsh2) and Dsh2-associated activator of morphogenesis 1 (Daam1). Our results suggest that Bmp gradient affects gastrulation cell movement (CE) via negative regulation of Xarhgef3.2 expression.

The Organizer and Its Signaling in Embryonic Development

Germ layer specification and axis formation are crucial events in embryonic development. The Spemann organizer regulates the early developmental processes by multiple regulatory mechanisms. This review focuses on the responsive signaling in organizer formation and how the organizer orchestrates the germ layer specification in vertebrates. Accumulated evidence indicates that the organizer influences embryonic development by dual signaling. Two parallel processes, the migration of the organizer’s cells, followed by the transcriptional activation/deactivation of target genes, and the diffusion of secreting molecules, collectively direct the early development. Finally, we take an in-depth look at active signaling that originates from the organizer and involves germ layer specification and patterning.

Goosecoid Controls Neuroectoderm Specification via Dual Circuits of Direct Repression and Indirect Stimulation in Xenopus Embryos

Spemann organizer is a center of dorsal mesoderm and itself retains the mesoderm character, but it has a stimulatory role for neighboring ectoderm cells in becoming neuroectoderm in gastrula embryos. Goosecoid (Gsc) overexpression in ventral region promotes secondary axis formation including neural tissues, but the role of gsc in neural specification could be indirect. We examined the neural inhibitory and stimulatory roles of gsc in the same cell and neighboring cells contexts. In the animal cap explant system, Gsc overexpression inhibited expression of neural specific genes including foxd4l1.1, zic3, ncam, and neurod. Genome-wide chromatin immunoprecipitation sequencing (ChIP-seq) and promoter analysis of early neural genes of foxd4l1.1 and zic3 were performed to show that the neural inhibitory mode of gsc was direct. Site-directed mutagenesis and serially deleted construct studies of foxd4l1.1 promoter revealed that Gsc directly binds within the foxd4l1.1 promoter to repress its expression. Conjugation assay of animal cap explants was also performed to demonstrate an indirect neural stimulatory role for gsc. The genes for secretory molecules, Chordin and Noggin, were up-regulated in gsc injected cells with the neural fate only achieved in gsc uninjected neighboring cells. These experiments suggested that gsc regulates neuroectoderm formation negatively when expressed in the same cell and positively in neighboring cells via soluble factors. One is a direct suppressive circuit of neural genes in gsc expressing mesoderm cells and the other is an indirect stimulatory circuit for neurogenesis in neighboring ectoderm cells via secreted BMP antagonizers.

Foxd4l1.1 Negatively Regulates Chordin Transcription in Neuroectoderm of Xenopus Gastrula

Inhibition of the bone morphogenetic proteins (BMPs) is the primary step toward neuroectoderm formation in vertebrates. In this process, the Spemann organizer of the dorsal mesoderm plays a decisive role by secreting several extracellular BMP inhibitors such as Chordin (Chrd). Chrd physically interacts with BMP proteins and inhibits BMP signaling, which triggers the expression of neural-specific transcription factors (TFs), including Foxd4l1.1. Thus, Chrd induces in a BMP-inhibited manner and promotes neuroectoderm formation. However, the regulatory feedback mechanism of Foxd4l1.1 on mesodermal genes expression during germ-layer specification has not been fully elucidated. In this study, we investigated the regulatory mechanism of Foxd4l1.1 on chrd (a mesodermal gene). We demonstrate that Foxd4l1.1 inhibits chrd expression during neuroectoderm formation in two ways: First, Foxd4l1.1 directly binds to FRE (Foxd4l1.1 response elements) within the chrd promoter region to inhibit transcription. Second, Foxd4l1.1 physically interacts with Smad2 and Smad3, and this interaction blocks Smad2 and Smad3 binding to activin response elements (AREs) within the chrd promoter. Site-directed mutagenesis of FRE within the chrd(-2250) promoter completely abolished repressor activity of the Foxd4l1.1. RT-PCR and reporter gene assay results indicate that Foxd4l1.1 strongly inhibits mesoderm- and ectoderm-specific marker genes to maintain neural fate. Altogether, these results suggest that Foxd4l1.1 negatively regulates chrd transcription by dual mechanism. Thus, our study demonstrates the existence of precise reciprocal regulation of chrd transcription during neuroectoderm and mesoderm germ-layer specification in Xenopus embryos.

Functional Roles of FGF Signaling in Early Development of Vertebrate Embryos

Fibroblast growth factors (FGFs) comprise a large family of growth factors, regulating diverse biological processes including cell proliferation, migration, and differentiation. Each FGF binds to a set of FGF receptors to initiate certain intracellular signaling molecules. Accumulated evidence suggests that in early development and adult state of vertebrates, FGFs also play exclusive and context dependent roles. Although FGFs have been the focus of research for therapeutic approaches in cancer, cardiovascular disease, and metabolic syndrome, in this review, we mainly focused on their role in germ layer specification and axis patterning during early vertebrate embryogenesis. We discussed the functional roles of FGFs and their interacting partners as part of the gene regulatory network for germ layer specification, dorsal-ventral (DV), and anterior-posterior (AP) patterning. Finally, we briefly reviewed the regulatory molecules and pharmacological agents discovered that may allow modulation of FGF signaling in research.

Temporal transcriptomic profiling reveals dynamic changes in gene expression of Xenopus animal cap upon activin treatment

Activin, a member of the transforming growth factor-β (TGF-β) superfamily of proteins, induces various tissues from the amphibian presumptive ectoderm, called animal cap explants (ACs) in vitro. However, it remains unclear how and to what extent the resulting cells recapitulate in vivo development. To comprehensively understand whether the molecular dynamics during activin-induced ACs differentiation reflect the normal development, we performed time-course transcriptome profiling of Xenopus ACs treated with 50 ng/mL of activin A, which predominantly induced dorsal mesoderm. The number of differentially expressed genes (DEGs) in response to activin A increased over time, and totally 9857 upregulated and 6663 downregulated DEGs were detected. 1861 common upregulated DEGs among all Post_activin samples included several Spemann's organizer genes. In addition, the temporal transcriptomes were clearly classified into four distinct groups in correspondence with specific features, reflecting stepwise differentiation into mesoderm derivatives, and a decline in the regulation of nuclear envelop and golgi. From the set of early responsive genes, we also identified the suppressor of cytokine signaling 3 (socs3) as a novel activin A-inducible gene. Our transcriptome data provide a framework to elucidate the transcriptional dynamics of activin-driven AC differentiation, reflecting the molecular characteristics of early normal embryogenesis.

Smad2 and Smad3 differentially modulate chordin transcription via direct binding on the distal elements in gastrula Xenopus embryos

Transforming growth factor (TGF)β/activin superfamily regulates diverse biological processes including germ layer specification and axis patterning in vertebrates. TGFβ/activin leads to phosphorylation of Smad2 and Smad3, followed by regulation of their target genes. Activin treatment also induces the essential organizer gene chordin (chrd). The involvement of Smad2/3 in chrd expression has been unclear as to whether Smad2/3 involvement is direct or indirect and whether any cis-acting response elements for Smad2/3 are present in the proximal or distal regions of its promoter. In the present study, we isolated the -2250 bps portion of the chrd promoter, showing that it contained Smad2/3 direct binding sites at its distal portion, separate from the proximal locations of other organizer genes, goosecoid and cerberus. The pattern of transcription activation for the promoter (-2250 bps) was indistinguishable from that of the endogenous chrd in gastrula Xenopus embryos. Reporter gene assays and site-directed mutagenesis analysis of the chrd promoter mapped two active activin/Smad response elements (ARE1 and ARE2) for Smad2 and Smad3. For a differential chrd induction, Smad2 acted on both ARE1 and ARE2, but Smad3 was only active for ARE2. Collectively, the results demonstrate that the distal region of chrd promoter contains the direct binding cis-acting elements for Smad2 and Smad3, which differentially modulate chrd transcription in gastrula Xenopus embryos.