Project description:The morphogen Indian Hedgehog plays a very important role during intestinal embryogenesis, but also maintains homeostasis in the adult gut. Intestinal Hedgehog is expressed by the intestinal epithelium and signals in paracrine manner to fibroblasts in the stromal compartment. We studied the colonic changes upon activation of the Hedgehog pathway by deleting the Hedgehog receptor Patched1 in order to alleviate its repressive function.
Project description:The morphogen Indian Hedgehog plays a very important role during intestinal embryogenesis, but also maintains homeostasis in the adult gut. Intestinal Hedgehog is expressed by the intestinal epithelium and signals in paracrine manner to fibroblasts in the stromal compartment. We studied the stromal changes upon simultaneous homozygous deletion of Ihh and the tumor-suppressor gene Apc in the colon.
Project description:Sivakumar2011 - Hedgehog Signaling Pathway
This is the current model for the Hedgehog signaling pathway. The best data for mechanism of signaling has been worked out in Drosophila, so this model is based largely on Drosophila data. Hedgehog target genes vary from tissue to tissue, so the identities of individual target genes have not been listed. The main difference between the Drosophila and mammalian Hedgehog signaling pathways is the fact that there are three mammalian homologs of Cubitus interruptus, Gli1 Gli2 and Gli3. Some or all of the mammalian homologs may be proteolytically processed, but the data are controversial. There are two mammalian Ptc genes and three mammalian Hedgehog genes as well. The pathway for Sonic Hedgehog appears to be most similar to the Drosophila hedgehog pathway.
References:
Hedgehog signaling in animal development: paradigms and principles.
Sonic hedgehog in the nervous system: functions, modifications and mechanisms.
Hedgehog signal transduction: recent findings.
Hedgehog signaling: Costal-2 bridges the transduction gap.
This model is described in the article:
A systems biology approach to model neural stem cell regulation by notch, shh, wnt, and EGF signaling pathways.
Sivakumar KC, Dhanesh SB, Shobana S, James J, Mundayoor S.
Omics: a Journal of Integrative Biology. 2011; 15(10):729-737
Abstract:
The Notch, Sonic Hedgehog (Shh), Wnt, and EGF pathways have long been known to influence cell fate specification in the developing nervous system. Here we attempted to evaluate the contemporary knowledge about neural stem cell differentiation promoted by various drug-based regulations through a systems biology approach. Our model showed the phenomenon of DAPT-mediated antagonism of Enhancer of split [E(spl)] genes and enhancement of Shh target genes by a SAG agonist that were effectively demonstrated computationally and were consistent with experimental studies. However, in the case of model simulation of Wnt and EGF pathways, the model network did not supply any concurrent results with experimental data despite the fact that drugs were added at the appropriate positions. This paves insight into the potential of crosstalks between pathways considered in our study. Therefore, we manually developed a map of signaling crosstalk, which included the species connected by representatives from Notch, Shh, Wnt, and EGF pathways and highlighted the regulation of a single target gene, Hes-1, based on drug-induced simulations. These simulations provided results that matched with experimental studies. Therefore, these signaling crosstalk models complement as a tool toward the discovery of novel regulatory processes involved in neural stem cell maintenance, proliferation, and differentiation during mammalian central nervous system development. To our knowledge, this is the first report of a simple crosstalk map that highlights the differential regulation of neural stem cell differentiation and underscores the flow of positive and negative regulatory signals modulated by drugs.
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Project description:Colorectal cancer is one of the most common cancers worldwide with increasing incidence, the presence of metastasis is one of the major causes for poor outcome. BEX2 has been reported to be involved in tumor development in several types of cancer, but is poorly understood in metastatic colorectal cancer. Here we demonstrated that knockout of BEX2 resulted in the enhancement of the migratory and metastatic potential of colorectal cancer cells in vivo and in vitro, re-expression of BEX2 in knockout cells could reverse the migratory enhancement. Expression profile chip indicated that hedgehog signaling pathway was activated after knockout of BEX2, and hedgehog Signaling inhibitor GANT61 and GDC-0449 could somehow reverse the migratory enhancement of BEX2-/- colorectal cancer cells. We also demonstrated that it is the nucleus translocation of Zic2 after BEX2 silenced, that activated hedgehog signaling pathway, while knockdown Zic2 could also abrogated migratory enhancement of BEX2-/- cells. In summary, our findings suggest that BEX2 is a negative modulator of hedgehog signaling pathway by retaining Zic2 in the cytoplasm of colorectal cancer cells, thus to inhibit colorectal cancer cell migration and metastasis.
Project description:The Hedgehog (Hh) signaling pathway is a developmentally conserved regulator of stem cell function. Several reports suggested that Hh signaling is an important regulator of hematopoietic stem cell (HSC) maintenance and differentiation. Here we test this hypothesis in vivo using both gain- and loss-of-function Hh genetic models. Surprisingly, our studies demonstrate that conditional Smoothened (Smo) deletion or over-activation has no significant effects on adult HSC self-renewal and function. Moreover, they indicate a lack of synergism between the Notch and Hh pathways in HSC function, as RBPJ- and Smo-deficiency do not affect hematopoiesis. In agreement with this notion, detailed genome-wide transcriptome analysis reveals that silencing of Hh signaling does not significantly alter the HSC-specific gene expression “signature”. Our studies demonstrate that the Hh signaling pathway is dispensable for adult HSC function and suggest that the Hh pathway can be targeted in future clinical trials addressing the effect of Hh inhibition on leukemia-initiating cell maintenance. Transcriptional consequences of inactivating Smo (hh loss-of-function) in LKS cells.
Project description:The Hedgehog (Hh) signaling pathway is a developmentally conserved regulator of stem cell function. Several reports suggested that Hh signaling is an important regulator of hematopoietic stem cell (HSC) maintenance and differentiation. Here we test this hypothesis in vivo using both gain- and loss-of-function Hh genetic models. Surprisingly, our studies demonstrate that conditional Smoothened (Smo) deletion or over-activation has no significant effects on adult HSC self-renewal and function. Moreover, they indicate a lack of synergism between the Notch and Hh pathways in HSC function, as RBPJ- and Smo-deficiency do not affect hematopoiesis. In agreement with this notion, detailed genome-wide transcriptome analysis reveals that silencing of Hh signaling does not significantly alter the HSC-specific gene expression âsignatureâ. Our studies demonstrate that the Hh signaling pathway is dispensable for adult HSC function and suggest that the Hh pathway can be targeted in future clinical trials addressing the effect of Hh inhibition on leukemia-initiating cell maintenance. Transcriptional consequences of inactivating Smo (hh loss-of-function) in LKS cells. Experiment Overall Design: Four samples were analyzed: wild-type (WT) control and Smo-deficient (SMO) Lin-ckit+Sca1+ (LSK) cells, as well as Lin-ckit+Sca1- myeloid progenitor (MP) cells, which served as a control for LSK-enriched/specific genes. Total bone marrow cells were pooled from four WT and four SMO mice before sorting LSK and MP populations.
Project description:Older age is a major risk factor for damage to many tissues, including liver. Aging undermines resiliency (i.e., the ability to recover from injury) and impairs liver regeneration. The mechanisms whereby aging reduces resiliency are poorly understood. Hedgehog is a signaling pathway with critical mitogenic and morphogenic functions during development. Recent studies indicate that Hedgehog regulates metabolic homeostasis in adult liver. The present study evaluates the hypothesis that Hedgehog signaling becomes dysregulated in hepatocytes during aging, resulting in decreased resiliency and therefore, impaired regeneration and enhanced vulnerability to damage. Methods: Partial hepatectomy (PH) was performed on young and old wild type mice and Smoothened (Smo)-floxed mice treated with AAV8-TBG luciferase (control) or AAV8-TBG-Cre vectors to conditionally delete Smo and disrupt Hedgehog signaling specifically in hepatocytes. Changes in signaling were correlated with changes in regenerative responses and compared among groups. Results: Old livers had fewer hepatocytes proliferating after PH. RNA sequencing identified Hedgehog as a top down-regulated pathway in old hepatocytes before and after the regenerative challenge. Deleting Smo in healthy young hepatocytes before PH prevented Hedgehog pathway activation after PH and inhibited regeneration. GO analysis demonstrated that both old and Smo-deleted young hepatocytes had activation of pathways involved in innate immune responses and suppression of several signaling pathways that control liver growth and metabolism including insulin-like growth factor, Wnt and NOTCH. Hedgehog inhibition promoted telomere shortening and mitochondrial dysfunction in hepatocytes, consequences of aging that promote inflammation and impair tissue growth and metabolic homeostasis. Conclusion: Hedgehog signaling is dysregulated in old hepatocytes. This accelerates aging, resulting in decreased resiliency and therefore, impaired liver regeneration and enhanced vulnerability to damage.