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Frank Costantini - One of the best experts on this subject based on the ideXlab platform.

  • impaired neural development caused by inducible expression of axin in transgenic mice
    Mechanisms of Development, 2007
    Co-Authors: Bo Liu, Frank Costantini, Wei Hsu
    Abstract:

    Ablations of the Axin family genes demonstrated that they modulate Wnt signaling in key processes of mammalian development. The ubiquitously expressed Axin1 plays an important role in formation of the embryonic neural axis, while AXIN2 is essential for craniofacial skeletogenesis. Although AXIN2 is also highly expressed during early neural development, including the neural tube and neural crest, it is not essential for these processes, apparently due to functional redundancy with Axin1. To further investigate the role of Wnt signaling during early neural development, and its potential regulation by Axins, we developed a mouse model for conditional gene activation in the AXIN2-expressing domains. We show that gene expression can be successfully targeted to the AXIN2-expressing cells in a spatially and temporally specific fashion. High levels of Axin in this domain induce a region-specific effect on the patterning of neural tube. In the mutant embryos, only the development of midbrain is severely impaired even though the transgene is expressed throughout the neural tube. Axin apparently regulates b-catenin in coordinating cell cycle progression, cell adhesion and survival of neuroepithelial precursors during development of ventricles. Our data support the conclusion that the development of embryonic neural axis is highly sensitive to the level of Wnt signaling. 2006 Elsevier Ireland Ltd. All rights reserved.

  • mouse axin and AXIN2 conductin proteins are functionally equivalent in vivo
    Molecular and Cellular Biology, 2005
    Co-Authors: Ian V. Chia, Frank Costantini
    Abstract:

    Axin is a central component of the canonical Wnt signal transduction machinery, serving as a scaffold for the β-catenin destruction complex (23, 31, 36, 45, 52). Axin has specific binding sites for many proteins involved in Wnt signal transduction, including β-catenin, glycogen synthase kinase 3 (GSK3), CKI, adenomatous polyposis coli (APC), Dvl, LRP, and protein phosphatase 2A (Fig. ​(Fig.1A)1A) (23, 31). Its key function in this pathway is to bring together β-catenin and the protein kinases CKI and GSK3, thus promoting the phosphorylation and consequent destruction of β-catenin. In the presence of a Wnt signal, this function is overcome, allowing β-catenin to accumulate and enter the nucleus (9, 13). The mechanism by which a Wnt signal leads to the inactivation of the Axin complex is not entirely clear, but it is thought to involve the binding of Axin to the Wnt coreceptor LRP as well as to Dvl (7, 34, 42, 44, 45). This results in the dephosphorylation of Axin, leading to a decrease in its affinity for β-catenin, and in a decrease in the level of Axin (20, 47, 48). Axin also enters the nucleus and appears to play a role in the nuclear-cytoplasmic shuttling of β-catenin (8, 46). FIG.1. Targeted replacement of the Axin gene with myc-tagged AXIN2 cDNA or myc-tagged Axin cDNA. (A) Schematic diagram of Axin and AXIN2 proteins and binding partners. Percent similarities between the conserved RGS and DIX domains and the GSK3 and β-catenin ... The major product of the Axin gene is a protein of 832 or 868 amino acids (depending on alternative splicing) containing two highly conserved domains (52): the RGS domain, which encompasses the binding site for APC (16, 18), and the DIX domain, a region of homology with Dvl proteins that is implicated in the binding of Axin to Dvl as well as in homodimerization (10, 17, 22, 24, 29, 40). (The open reading frame of Axin cDNA potentially encodes proteins of 956 and 992 amino acids, but proteins of this length have not been detected, and the major protein begins at codon Met-125 of the original sequence.) Mutant embryos lacking Axin die at embryonic day 9.5 (E9.5) with abnormalities including truncation of the forebrain, neural tube defects, and embryonic axis duplications (14, 35). Axin is expressed ubiquitously during embryogenesis, and the presence of axis duplications in its absence is thought to be a consequence of the abnormal accumulation of β-catenin, mimicking a Wnt signal, in the early embryo. AXIN2 (also known as Conductin) is 44% identical to Axin and shares the RGS and DIX domains (Fig. ​(Fig.1A)1A) (5, 39, 49) as well as the binding sites for β-catenin, GSK3, Diversin, and Smad3 (Fig. ​(Fig.1A)1A) (5, 11, 39, 49). While AXIN2 has been studied less extensively than Axin, most data suggest that they are similar in function. Thus, when overexpressed in cultured cells, both proteins reduce the levels of β-catenin and the expression of Wnt target genes, and when expressed in frog embryos, both inhibit the development of dorsal structures (5, 19, 37, 49, 52). However, they are not fully redundant in vivo, as AXIN2 is clearly unable to compensate for the absence of Axin in Axin-null embryos (52). Furthermore, humans with heterozygous germ line AXIN2 mutations have familial tooth agenesis (25), while mice homozygous for loss of AXIN2 have skull abnormalities (51), indicating that Axin does not fully substitute for the lack of AXIN2. In addition, deletions or mutations in AXIN or AXIN2 have been observed in a number of types of tumors, including colorectal cancer and hepatocellular carcinoma, indicating that each gene is a tumor suppressor and that neither gene can replace the other for this function (30, 38, 43). One reason for the lack of full redundancy may be the different expression patterns of Axin and AXIN2. While Axin mRNA is ubiquitous (52), AXIN2 is expressed in tissue- and developmental-stage-specific patterns, due (at least in part) to its transcriptional upregulation by canonical Wnt signaling (4, 21, 27). Thus, AXIN2 potentially constitutes a negative-feedback mechanism regulating the response to Wnt signals (21, 27, 32, 50). In the mouse embryo, the inability of AXIN2 to compensate for the lack of Axin might be explained simply by the fact that AXIN2 is not expressed in every cell. However, the two proteins might also differ significantly in function, a possibility supported by their different subcellular localizations in at least some cell types (3). If the functional differences were subtle, they might not be detected using assays that involve overexpression; since the normal level of Axin is extremely low (26), the abnormally high levels of expression in these assays could mask a functional difference. To address the question of functional redundancy in a more physiological way, we generated knockin mice in which the Axin gene was replaced with an AXIN2 cDNA sequence. This gene replacement strategy is similar to those used successfully to compare the functions of other paralogous gene pairs (6, 12, 15, 33, 41). The main advantage of this approach over in vitro assays or other in vivo functional assays (e.g., transgenic rescue) is that targeting of a cDNA to the appropriate genetic locus results in a normal pattern and level of expression. In animals homozygous for the resulting allele, AxinAx2, there will be no Axin, but AXIN2 will be expressed ubiquitously from the Axin locus at a physiological level, as well as in its normal tissue-specific pattern from the unmodified AXIN2 locus. Thus, the total level of Axin plus AXIN2 expression in any cell type should be unchanged from that of the wild type. The ability of these mice to develop and survive normally thus tests the capacity of AXIN2 to replace Axin in vivo.

  • the role of AXIN2 in calvarial morphogenesis and craniosynostosis
    Development, 2005
    Co-Authors: Boris Jerchow, Walter Birchmeier, Frank Costantini, Bo Liu, Tzongjen Sheu, Edward J Puzas, Wei Hsu
    Abstract:

    Axin1 and its homolog AXIN2/conductin/Axil are negative regulators of the canonical Wnt pathway that suppress signal transduction by promoting degradation of β-catenin. Mice with deletion of Axin1 exhibit defects in axis determination and brain patterning during early embryonic development. We show that AXIN2 is expressed in the osteogenic fronts and periosteum of developing sutures during skull morphogenesis. Targeted disruption of AXIN2 in mice induces malformations of skull structures, a phenotype resembling craniosynostosis in humans. In the mutants, premature fusion of cranial sutures occurs at early postnatal stages. To elucidate the mechanism of craniosynostosis, we studied intramembranous ossification in AXIN2 -null mice. The calvarial osteoblast development is significantly affected by the AXIN2 mutation. The AXIN2 mutant displays enhanced expansion of osteoprogenitors, accelerated ossification, stimulated expression of osteogenic markers and increases in mineralization. Inactivation of AXIN2 promotes osteoblast proliferation and differentiation in vivo and in vitro. Furthermore, as the mammalian skull is formed from cranial skeletogenic mesenchyme, which is derived from mesoderm and neural crest, our data argue for a region-specific effect of AXIN2 on neural crest dependent skeletogenesis. The craniofacial anomalies caused by the AXIN2 mutation are mediated through activation of β-catenin signaling, suggesting a novel role for the Wnt pathway in skull morphogenesis.

  • wnt β catenin tcf signaling induces the transcription of AXIN2 a negative regulator of the signaling pathway
    Molecular and Cellular Biology, 2002
    Co-Authors: Tong Zhang, Claire Domon, Jeannoel Freund, Frank Costantini
    Abstract:

    AXIN2/Conductin/Axil and its ortholog Axin are negative regulators of the Wnt signaling pathway, which promote the phosphorylation and degradation of beta-catenin. While Axin is expressed ubiquitously, AXIN2 mRNA was seen in a restricted pattern during mouse embryogenesis and organogenesis. Because many sites of AXIN2 expression overlapped with those of several Wnt genes, we tested whether AXIN2 was induced by Wnt signaling. Endogenous AXIN2 mRNA and protein expression could be rapidly induced by activation of the Wnt pathway, and AXIN2 reporter constructs, containing a 5.6-kb DNA fragment including the promoter and first intron, were also induced. This genomic region contains eight Tcf/LEF consensus binding sites, five of which are located within longer, highly conserved noncoding sequences. The mutation or deletion of these Tcf/LEF sites greatly diminished induction by beta-catenin, and mutation of the Tcf/LEF site T2 abolished protein binding in an electrophoretic mobility shift assay. These results strongly suggest that AXIN2 is a direct target of the Wnt pathway, mediated through Tcf/LEF factors. The 5.6-kb genomic sequence was sufficient to direct the tissue-specific expression of d2EGFP in transgenic embryos, consistent with a role for the Tcf/LEF sites and surrounding conserved sequences in the in vivo expression pattern of AXIN2. Our results suggest that AXIN2 participates in a negative feedback loop, which could serve to limit the duration or intensity of a Wnt-initiated signal.

  • wnt β catenin tcf signaling induces the transcription of AXIN2 a negative regulator of the signaling pathway
    Molecular and Cellular Biology, 2002
    Co-Authors: Eekhoon Jho, Tong Zhang, Claire Domon, Jeannoel Freund, Chounki Joo, Frank Costantini
    Abstract:

    AXIN2/Conductin/Axil and its ortholog Axin are negative regulators of the Wnt signaling pathway, which promote the phosphorylation and degradation of beta-catenin. While Axin is expressed ubiquitously, AXIN2 mRNA was seen in a restricted pattern during mouse embryogenesis and organogenesis. Because many sites of AXIN2 expression overlapped with those of several Wnt genes, we tested whether AXIN2 was induced by Wnt signaling. Endogenous AXIN2 mRNA and protein expression could be rapidly induced by activation of the Wnt pathway, and AXIN2 reporter constructs, containing a 5.6-kb DNA fragment including the promoter and first intron, were also induced. This genomic region contains eight Tcf/LEF consensus binding sites, five of which are located within longer, highly conserved noncoding sequences. The mutation or deletion of these Tcf/LEF sites greatly diminished induction by beta-catenin, and mutation of the Tcf/LEF site T2 abolished protein binding in an electrophoretic mobility shift assay. These results strongly suggest that AXIN2 is a direct target of the Wnt pathway, mediated through Tcf/LEF factors. The 5.6-kb genomic sequence was sufficient to direct the tissue-specific expression of d2EGFP in transgenic embryos, consistent with a role for the Tcf/LEF sites and surrounding conserved sequences in the in vivo expression pattern of AXIN2. Our results suggest that AXIN2 participates in a negative feedback loop, which could serve to limit the duration or intensity of a Wnt-initiated signal.

Roel Nusse - One of the best experts on this subject based on the ideXlab platform.

  • tissue repair in the mouse liver following acute carbon tetrachloride depends on injury induced wnt β catenin signaling
    Hepatology, 2019
    Co-Authors: Ludan Zhao, Yinhua Jin, Katie Donahue, Margaret Tsui, Matt Fish, Catriona Y Logan, Bruce Wang, Roel Nusse
    Abstract:

    In the liver, Wnt/β-catenin signaling is involved in regulating zonation and hepatocyte proliferation during homeostasis. We examined Wnt gene expression and signaling after injury, and we show by in situ hybridization that Wnts are activated by acute carbon tetrachloride (CCl4 ) toxicity. Following injury, peri-injury hepatocytes become Wnt-responsive, expressing the Wnt target gene axis inhibition protein 2 (AXIN2). Lineage tracing of peri-injury AXIN2+ hepatocytes shows that during recovery the injured parenchyma becomes repopulated and repaired by AXIN2+ descendants. Using single-cell RNA sequencing, we show that endothelial cells are the major source of Wnts following acute CCl4 toxicity. Induced loss of β-catenin in peri-injury hepatocytes results in delayed repair and ultimately injury-induced lethality, while loss of Wnt production from endothelial cells leads to a delay in the proliferative response after injury. Conclusion: Our findings highlight the importance of the Wnt/β-catenin signaling pathway in restoring tissue integrity following acute liver toxicity and establish a role of endothelial cells as an important Wnt-producing regulator of liver tissue repair following localized liver injury.

  • tissue repair in the mouse liver following acute carbon tetrachloride depends on injury induced wnt β catenin signaling
    bioRxiv, 2018
    Co-Authors: Ludan Zhao, Yinhua Jin, Katie Donahue, Margaret Tsui, Matt Fish, Catriona Y Logan, Bruce Wang, Roel Nusse
    Abstract:

    In the liver, Wnt/{beta}-catenin signaling is involved in regulating zonation and hepatocyte proliferation during homeostasis. We have examined Wnt gene expression and signaling after injury and we show by in situ hybridization that Wnts are activated by acute carbon tetrachloride (CCl4) toxicity. Following injury, peri-injury hepatocytes become Wnt-responsive, expressing the Wnt target gene AXIN2. Lineage tracing of peri-injury AXIN2+ hepatocytes shows that during recovery, the injured parenchyma becomes repopulated and repaired by AXIN2+ descendants. Using single cell RNA sequencing (scRNA-seq), we show that endothelial cells are the major source of Wnts following acute CCl4 toxicity. Induced loss of {beta}-catenin in peri-injury hepatocytes results in delayed repair and ultimately to injury-induced lethality, while loss of Wnt production from endothelial cells leads to a delay in the proliferative response after injury. Conclusion: Our Findings highlight the importance of the Wnt/{beta}-catenin signaling pathway in restoring tissue integrity following acute liver toxicity and establishes a role of endothelial cells as an important Wnt-producing regulator of liver tissue repair following localized liver injury.

  • interfollicular epidermal stem cells self renew via autocrine wnt signaling
    Science, 2013
    Co-Authors: Xinhong Lim, Si Hui Tan, Winston Koh, Rosanna Man Wah Chau, Kelley S Yan, Calvin J Kuo, Renee Van Amerongen, Allon M Klein, Roel Nusse
    Abstract:

    The skin is a classical example of a tissue maintained by stem cells. However, the identity of the stem cells that maintain the interfollicular epidermis and the source of the signals that control their activity remain unclear. Using mouse lineage tracing and quantitative clonal analyses, we showed that the Wnt target gene AXIN2 marks interfollicular epidermal stem cells. These AXIN2-expressing cells constitute the majority of the basal epidermal layer, compete neutrally, and require Wnt/β-catenin signaling to proliferate. The same cells contribute robustly to wound healing, with no requirement for a quiescent stem cell subpopulation. By means of double-labeling RNA in situ hybridization in mice, we showed that the AXIN2-expressing cells themselves produce Wnt signals as well as long-range secreted Wnt inhibitors, suggesting an autocrine mechanism of stem cell self-renewal.

  • developmental stage and time dictate the fate of wnt β catenin responsive stem cells in the mammary gland
    Cell Stem Cell, 2012
    Co-Authors: Renee Van Amerongen, Angela N Bowman, Roel Nusse
    Abstract:

    Summary The mammary epithelium undergoes extensive growth and remodeling during pregnancy, suggesting a role for stem cells. Yet their origin, identity, and behavior in the intact tissue remain unknown. Using an AXIN2 CreERT2 allele, we labeled and traced Wnt/β-catenin-responsive cells throughout mammary gland development. This reveals a switch in Wnt/β-catenin signaling around birth and shows that, depending on the developmental stage, AXIN2 +  cells contribute differently to basal and luminal epithelial cell lineages of the mammary epithelium. Moreover, an important difference exists between the developmental potential tested in transplantation assays and that displayed by the same cell population in situ. Finally, AXIN2 + cells in the adult build alveolar structures during multiple pregnancies, demonstrating the existence of a Wnt/β-catenin-responsive adult stem cell. Our study uncovers dynamic changes in Wnt/β-catenin signaling in the mammary epithelium and offers insights into the developmental fate of mammary gland stem and progenitor cells.

  • AXIN2 as regulatory and therapeutic target in newborn brain injury and remyelination
    Nature Neuroscience, 2011
    Co-Authors: Stephen P J Fancy, Emily P Harrington, Tracy J Yuen, John C Silbereis, Chao Zhao, Sergio E Baranzini, Charlotte C Bruce, Jose Otero, Eric J Huang, Roel Nusse
    Abstract:

    Permanent damage to white matter tracts, comprising axons and myelinating oligodendrocytes, is an important component of brain injuries of the newborn that cause cerebral palsy and cognitive disabilities, as well as multiple sclerosis in adults. However, regulatory factors relevant in human developmental myelin disorders and in myelin regeneration are unclear. We found that AXIN2 was expressed in immature oligodendrocyte progenitor cells (OLPs) in white matter lesions of human newborns with neonatal hypoxic-ischemic and gliotic brain damage, as well as in active multiple sclerosis lesions in adults. AXIN2 is a target of Wnt transcriptional activation that negatively feeds back on the pathway, promoting β-catenin degradation. We found that AXIN2 function was essential for normal kinetics of remyelination. The small molecule inhibitor XAV939, which targets the enzymatic activity of tankyrase, acted to stabilize AXIN2 levels in OLPs from brain and spinal cord and accelerated their differentiation and myelination after hypoxic and demyelinating injury. Together, these findings indicate that AXIN2 is an essential regulator of remyelination and that it might serve as a pharmacological checkpoint in this process.

Mahtab Lohi - One of the best experts on this subject based on the ideXlab platform.

  • expression of AXIN2 indicates a role for canonical wnt signaling in development of the crown and root during pre and postnatal tooth development
    Developmental Dynamics, 2009
    Co-Authors: Mahtab Lohi
    Abstract:

    Previously two reporter mice, TOPgal and BATgal, have been used to uncover the spatial patterns of canonical Wnt activity up to the bell stage of tooth development. To further understand the function of this pathway, not only at the early developmental stages of odontogenesis but also in postnatal teeth, we have used AXIN2-lacZ mice a direct reporter of canonical Wnt activity. As tooth development progresses, AXIN2 expression becomes localized to the primary and secondary enamel knots, and the underlying mesenchyme. In postnatal teeth, AXIN2 expression is observed in developing odontoblasts, in the dental pulp and concentrated around the developing roots. Expression is excluded from the ameloblasts and associated with the enamel-free zones at the tip of the molar cusps. This expression identifies new roles for Wnt signaling in defining the regions where enamel will form, and controlling root development at late stages of tooth development.

  • expression of AXIN2 indicates a role for canonical wnt signaling in development of the crown and root during pre and postnatal tooth development
    Developmental Dynamics, 2009
    Co-Authors: Mahtab Lohi
    Abstract:

    Previously two reporter mice, TOPgal and BATgal, have been used to uncover the spatial patterns of canonical Wnt activity up to the bell stage of tooth development. To further understand the function of this pathway, not only at the early developmental stages of odontogenesis but also in postnatal teeth, we have used AXIN2-lacZ mice a direct reporter of canonical Wnt activity. As tooth development progresses, AXIN2 expression becomes localized to the primary and secondary enamel knots, and the underlying mesenchyme. In postnatal teeth, AXIN2 expression is observed in developing odontoblasts, in the dental pulp and concentrated around the developing roots. Expression is excluded from the ameloblasts and associated with the enamel-free zones at the tip of the molar cusps. This expression identifies new roles for Wnt signaling in defining the regions where enamel will form, and controlling root development at late stages of tooth development. Developmental Dynamics 239:160–167, 2010. © 2009 Wiley-Liss, Inc.

Ludan Zhao - One of the best experts on this subject based on the ideXlab platform.

  • tissue repair in the mouse liver following acute carbon tetrachloride depends on injury induced wnt β catenin signaling
    Hepatology, 2019
    Co-Authors: Ludan Zhao, Yinhua Jin, Katie Donahue, Margaret Tsui, Matt Fish, Catriona Y Logan, Bruce Wang, Roel Nusse
    Abstract:

    In the liver, Wnt/β-catenin signaling is involved in regulating zonation and hepatocyte proliferation during homeostasis. We examined Wnt gene expression and signaling after injury, and we show by in situ hybridization that Wnts are activated by acute carbon tetrachloride (CCl4 ) toxicity. Following injury, peri-injury hepatocytes become Wnt-responsive, expressing the Wnt target gene axis inhibition protein 2 (AXIN2). Lineage tracing of peri-injury AXIN2+ hepatocytes shows that during recovery the injured parenchyma becomes repopulated and repaired by AXIN2+ descendants. Using single-cell RNA sequencing, we show that endothelial cells are the major source of Wnts following acute CCl4 toxicity. Induced loss of β-catenin in peri-injury hepatocytes results in delayed repair and ultimately injury-induced lethality, while loss of Wnt production from endothelial cells leads to a delay in the proliferative response after injury. Conclusion: Our findings highlight the importance of the Wnt/β-catenin signaling pathway in restoring tissue integrity following acute liver toxicity and establish a role of endothelial cells as an important Wnt-producing regulator of liver tissue repair following localized liver injury.

  • tissue repair in the mouse liver following acute carbon tetrachloride depends on injury induced wnt β catenin signaling
    bioRxiv, 2018
    Co-Authors: Ludan Zhao, Yinhua Jin, Katie Donahue, Margaret Tsui, Matt Fish, Catriona Y Logan, Bruce Wang, Roel Nusse
    Abstract:

    In the liver, Wnt/{beta}-catenin signaling is involved in regulating zonation and hepatocyte proliferation during homeostasis. We have examined Wnt gene expression and signaling after injury and we show by in situ hybridization that Wnts are activated by acute carbon tetrachloride (CCl4) toxicity. Following injury, peri-injury hepatocytes become Wnt-responsive, expressing the Wnt target gene AXIN2. Lineage tracing of peri-injury AXIN2+ hepatocytes shows that during recovery, the injured parenchyma becomes repopulated and repaired by AXIN2+ descendants. Using single cell RNA sequencing (scRNA-seq), we show that endothelial cells are the major source of Wnts following acute CCl4 toxicity. Induced loss of {beta}-catenin in peri-injury hepatocytes results in delayed repair and ultimately to injury-induced lethality, while loss of Wnt production from endothelial cells leads to a delay in the proliferative response after injury. Conclusion: Our Findings highlight the importance of the Wnt/{beta}-catenin signaling pathway in restoring tissue integrity following acute liver toxicity and establishes a role of endothelial cells as an important Wnt-producing regulator of liver tissue repair following localized liver injury.

S S Schmidt - One of the best experts on this subject based on the ideXlab platform.