Integration of Shh and Fgf signaling in controlling Hox expression in cultured limb cells
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ABSTRACT:
ORGANISM(S): Gallus gallus
PROVIDER: GSE92557 | GEO | 2017/03/06
SECONDARY ACCESSION(S): PRJNA358040
REPOSITORIES: GEO
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Project description:During embryonic development, fields of progenitor cells form complex spatial structures through dynamic interactions with external signaling molecules. However, how complex signaling inputs are integrated to yield appropriate gene expression responses is poorly understood. For instance several critical signals have been well characterized in the early limb bud, including Sonic hedgehog (Shh) and Fibroblast growth Factor 8 (Fgf8). While the former is expressed in the distal posterior mesenchyme where it acts as the mediator of anterior to posterior (AP) patterning, the latter is produced by the apical ectodermal ridge (AER) at the distal tip of the limb bud and directs the outgrowth and the proximal to distal (PD) organization of the limb. Here we use cultured limb mesenchyme cells to try and assess the response of the target Hoxd genes to these two factors. We find that they act synergistically and that both factors are required to get activation of Hoxd13 in limb mesenchymal cells. However, the analysis of the enhancer landscapes flanking the HoxD cluster reveals that the bimodal regulatory switch observed in vivo is not fully achieved under these in vitro conditions, suggesting the requirement for other factors.
2017-03-06 | GSE92556 | GEO
Project description:During embryonic development, fields of progenitor cells form complex spatial structures through dynamic interactions with external signaling molecules. However, how complex signaling inputs are integrated to yield appropriate gene expression responses is poorly understood. For instance several critical signals have been well characterized in the early limb bud, including Sonic hedgehog (Shh) and Fibroblast growth Factor 8 (Fgf8). While the former is expressed in the distal posterior mesenchyme where it acts as the mediator of anterior to posterior (AP) patterning, the latter is produced by the apical ectodermal ridge (AER) at the distal tip of the limb bud and directs the outgrowth and the proximal to distal (PD) organization of the limb. Here we use cultured limb mesenchyme cells to try and assess the response of the target Hoxd genes to these two factors. We find that they act synergistically and that both factors are required to get activation of Hoxd13 in limb mesenchymal cells. However, the analysis of the enhancer landscapes flanking the HoxD cluster reveals that the bimodal regulatory switch observed in vivo is not fully achieved under these in vitro conditions, suggesting the requirement for other factors.
2017-03-06 | GSE92555 | GEO
Project description:Integration of Shh and Fgf signaling in controlling Hox expression in cultured limb cells
| PRJNA358040 | ENA
Project description:Vertebrate limb outgrowth is driven by a positive feedback loop that involves Sonic hedgehog (Shh) and Gremlin1 (Grem1) in the posterior limb bud mesenchyme and Fibroblast growth factors (Fgfs) in the overlying epithelium. Proper spatio-temporal control of these signaling activities is required to avoid limb malformations such as polydactyly. Here we show that, in Tbx2-deficient hindlimbs, Shh/Fgf4 signaling is prolonged, resulting in increased limb bud size and duplication of digit 4. In turn, limb-specific Tbx2 overexpression leads to premature termination of this signaling loop with smaller limbs and reduced digit number as phenotypic manifestation. We show that Tbx2 directly represses Grem1 in distal regions of the posterior limb mesenchyme allowing Bone morphogenetic protein (Bmp) signaling to abrogate Fgf4/9/17 expression in the overlying epithelium. Since Tbx2 itself is a target of Bmp signaling, our data identify a growth-inhibiting positive feedback loop (Bmp/Tbx2/Grem1). We propose that proliferative expansion of Tbx2-expressing cells mediates self-termination of limb bud outgrowth due to their refractoriness to Grem1 induction.
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Project description:During limb development, fibroblast growth factors (Fgfs) govern proximal?distal outgrowth and patterning. FGFs also synchronize developmental patterning between the proximal?distal and anterior?posterior axes by maintaining Sonic hedgehog (Shh) expression in cells of the zone of polarizing activity (ZPA) in the distal posterior mesoderm. Shh, in turn, maintains Fgfs in the apical ectodermal ridge (AER) that caps the distal tip of the limb bud. Crosstalk between Fgf and Shh signaling is critical for patterned limb development, but the mechanisms underlying this feedback loop are not well-characterized. Implantation of Fgf beads in the proximal posterior limb bud can maintain SHH expression in the former ZPA domain (evident 3 h after application), while prolonged exposure (24 h) can induce SHH outside of this domain. Although temporally and spatially disparate, comparative analysis of transcriptome data from these different populations accentuated genes involved in SHH regulation. Comparative analysis identified 25 candidates common to both treatments, with eight linked to SHH expression or function. Furthermore, we demonstrated that LHX2, a LIM Homeodomain transcription factor, is an intermediate in the FGF-mediated regulation of SHH. Our data suggest that LHX2 acts as a competency factor maintaining distal posterior SHH expression subjacent to the AER.
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Project description:Anterior-posterior (A-P) patterning of the vertebrate limb is controlled by sonic hedgehog (SHH) signaling, and the precise restriction of Shh expression to the posterior limb bud is essential for its polarizing effect. Fibroblast growth factor (FGF) signaling, a key control of proximal-distal (P-D) limb outgrowth, is known to promote Shh expression in the posterior limb bud. Here, we show that conditional knockout of the FGF-activated transcription factor genes Etv4 and Etv5 in mouse led to ectopic Shh expression in the anterior limb bud and a preaxial polydactyly (PPD) skeletal phenotype. These unexpected results suggest that ETV4 and ETV5 act downstream of FGF signaling to inhibit Shh expression in the anterior limb bud. This finding elucidates a novel aspect of the mechanism coordinating limb development along the A-P and P-D axes.
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Project description:This SuperSeries is composed of the SubSeries listed below.
2021-07-29 | GSE114257 | GEO
Project description:The neurocranium generates most of the craniofacial skeleton and consists of prechordal and postchordal regions. Although development of the prechordal is well studied, little is known of the postchordal region. Here we characterize a signaling hierarchy necessary for postchordal neurocranial development involving Fibroblast growth factor (Fgf) signaling for early specification of mesodermally-derived progenitor cells. The expression of hyaluron synthetase 2 (has2) in the cephalic mesoderm requires Fgf signaling and Has2 function, in turn, is required for postchordal neurocranial development. While Hedgehog (Hh)-deficient embryos also lack a postchordal neurocranium, this appears primarily due to a later defect in chondrocyte differentiation. Inhibitor studies demonstrate that postchordal neurocranial development requires early Fgf and later Hh signaling. Collectively, our results provide a mechanistic understanding of early postchordal neurocranial development and demonstrate a hierarchy of signaling between Fgf and Hh in the development of this structure.
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Project description:The essential roles of SHH in anteroposterior (AP) and AER-FGF signalling in proximodistal (PD) limb bud development are well understood. In addition, these morphoregulatory signals are key components of the self-regulatory SHH/GREM1/AER-FGF feedback signalling system that regulates distal progression of limb bud development. This study uncovers an additional signalling module required for coordinated progression of limb bud axis development. Transcriptome analysis using Shh-deficient mouse limb buds revealed that the expression of proximal genes was distally extended from early stages onwards, which pointed to a more prominent involvement of SHH in PD limb axis development. In particular, retinoic acid (RA) target genes were upregulated proximally, while the expression of the RA-inactivating Cyp26b1 enzyme was downregulated distally, pointing to increased RA activity in Shh-deficient mouse limb buds. Further genetic and molecular analysis established that Cyp26b1 expression is regulated by AER-FGF signalling. During initiation of limb bud outgrowth, the activation of Cyp26b1 expression creates a distal 'RA-free' domain, as indicated by complementary downregulation of a transcriptional sensor of RA activity. Subsequently, Cyp26b1 expression increases as a consequence of SHH-dependent upregulation of AER-FGF signalling. To better understand the underlying signalling interactions, computational simulations of the spatiotemporal expression patterns and interactions were generated. These simulations predicted the existence of an antagonistic AER-FGF/CYP26B1/RA signalling module, which was verified experimentally. In summary, SHH promotes distal progression of limb development by enhancing CYP26B1-mediated RA clearance as part of a signalling network linking the SHH/GREM1/AER-FGF feedback loop to the newly identified AER-FGF/CYP26B1/RA module.
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Project description:Human embryonic stem cells (hESCs) offer a platform to bridge what we have learned from animal studies to human biology. Using oligodendrocyte differentiation as a model system, we show that sonic hedgehog (SHH)-dependent sequential activation of the transcription factors OLIG2, NKX2.2 and SOX10 is required for sequential specification of ventral spinal OLIG2-expressing progenitors, pre-oligodendrocyte precursor cells (pre-OPCs) and OPCs from hESC-derived neuroepithelia, indicating that a conserved transcriptional network underlies OPC specification in human as in other vertebrates. However, the transition from pre-OPCs to OPCs is protracted. FGF2, which promotes mouse OPC generation, inhibits the transition of pre-OPCs to OPCs by repressing SHH-dependent co-expression of OLIG2 and NKX2.2. Thus, despite the conservation of a similar transcriptional network across vertebrates, human stem/progenitor cells may respond differently to those of other vertebrates to certain extrinsic factors.
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