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Open Access Publications from the University of California

Scholarly Works (23 results)

  • Thesis
  • Peer Reviewed
UC San Francisco Electronic Theses and Dissertations (2009)

The Dact family (also known as Dapper/Frodo) of cytoplasmic scaffold proteins are expressed during embryonic development and have been shown to modulate developmentally important signaling pathways such as the Wnt pathway. To gain a better understanding of the developmental stages and tissues in which Dacts function, the embryonic expression pattern of the mouse Dact family was characterized. Dact1 is expressed in mesoderm derived tissue (i.e. presomitic mesoderm and somites) and in the primitive streak, where gastrulation occurs. To determine if Dact1 is required for gastrulation, mouse mutants in the Dact1 gene were analyzed during gastrulation stages (e7.0-e8.5). These data indicate that at the 6 somite stage, Dact1 mutants have posterior morphological defects in the region of the primitive streak reminiscent of phenotypes associated with abnormalities in convergent extension movements necessary to elongate the embryo. These posterior defects are associated with disruptions in downstream readouts of the Planar Cell Polarity Pathway and not the Wnt/β-catenin pathway. The morphological differences seen in Dact1 mutants arise due to the abnormal upregulation of membrane Vangl2 and E-cadherin protein levels in primitive streak cells undergoing epithelial-mesenchymal transition (EMT) preceeding cell migration. Vangl2 Loop-tail mutants show the opposite effect with a reduction in Vangl2 membrane localization in these cells. Importantly, crossing these two mutations (i.e. making Dact1 mutants also heterozygous for the Vangl2 Loop-tail mutation) restored Vangl2 membrane levels at the primitive streak and rescued Dact1 embryological phenotypes. These data identify a role for Dact1 in regulating appropriate levels of the Planar Cell Polarity protein Vangl2 necessary for EMT and cell migration during mouse gastrulation.

    Cover page: Dact1 functions in the planar cell polarity pathway during vertebrate gastrulation
    • Article
    • Peer Reviewed
    UC San Francisco Previously Published Works (2013)
    In mice, genetically engineered knockout of the Dapper Antagonist of Catenin-1 (Dact1) locus, which encodes a scaffold protein involved in Wnt signaling, leads to decreased excitatory input formation on dendrites of developing forebrain neurons. We have previously demonstrated this in both (excitatory, glutamatergic) pyramidal neurons of the hippocampus and in (inhibitory GABAergic) interneurons of the cortex. We have also demonstrated that knockout of the Dact1 locus leads to decreased dendrite complexity in cultured hippocampal pyramidal neurons, and to decreased spine formation on dendrites of forebrain pyramidal neurons in vitro and in vivo. Synapse phenotypes resulting from Dact1 loss in cultured cortical interneurons can be rescued by recombinant overexpression of the Dact1 binding partner, Dishevelled-1 (Dvl1), but not by recombinant expression of a constitutively active form of the small GTPase Rac1. This contrasts with dendrite spine phenotypes resulting from Dact1 loss in cultured hippocampal pyramidal neurons, which can be fully rescued by recombinant expression of activated Rac1. Taken together, these data suggest that in maturing forebrain neurons there are molecularly separate requirements for Dact1 in dendrite arborization/spine formation vs. synaptogenesis. Here, we show that the developmental requirement for Dact1 during dendrite arborization, which we previously demonstrated only in hippocampal pyramidal neurons, is also present in cortical interneurons, and we discuss mechanistic implications of this finding.
      Cover page: Dapper Antagonist of Catenin-1 (Dact1) contributes to dendrite arborization in forebrain cortical interneurons
      • Article
      • Peer Reviewed
      UC San Francisco Previously Published Works (2012)
      Members of the Wnt family of secreted signaling proteins influence many aspects of neural development and function. Wnts are required from neural induction and axis formation to axon guidance and synapse development, and even help modulate synapse activity. Wnt proteins activate a variety of downstream signaling pathways and can induce a similar variety of cellular responses, including gene transcription changes and cytoskeletal rearrangements. This review provides an introduction to Wnt signaling pathways and discusses current research on their roles in vertebrate neural development and function.
        Cover page: Wnt Signaling in Vertebrate Neural Development and Function
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        • Peer Reviewed
        UC San Francisco Previously Published Works (2016)
        Mounting evidence indicates that Wnt signaling is relevant to pathophysiology of diverse mental illnesses including schizophrenia, bipolar disorder, and autism spectrum disorder. In the 35 years since Wnt ligands were first described, animal studies have richly explored how downstream Wnt signaling pathways affect an array of neurodevelopmental processes and how their disruption can lead to both neurological and behavioral phenotypes. Recently, human induced pluripotent stem cell (hiPSC) models have begun to contribute to this literature while pushing it in increasingly translational directions. Simultaneously, large-scale human genomic studies are providing evidence that sequence variation in Wnt signal pathway genes contributes to pathogenesis in several psychiatric disorders. This article reviews neurodevelopmental and postneurodevelopmental functions of Wnt signaling, highlighting mechanisms, whereby its disruption might contribute to psychiatric illness, and then reviews the most reliable recent genetic evidence supporting that mutations in Wnt pathway genes contribute to psychiatric illness. We are proponents of the notion that studies in animal and hiPSC models informed by the human genetic data combined with the deep knowledge base and tool kits generated over the last several decades of basic neurodevelopmental research will yield near-term tangible advances in neuropsychiatry.
          • Article
          • Peer Reviewed
          UC San Francisco Previously Published Works (2013)
          The planar cell polarity (PCP) pathway is a conserved non-canonical (β-catenin-independent) branch of Wnt signaling crucial to embryogenesis, during which it regulates cell polarity and polarized cell movements. Disruption of PCP components in mice, including Vangl2 and Dact1, results in defective neural tube closure and other developmental defects. Here, we show that Sestd1 is a novel binding partner of Vangl2 and Dact1. The Sestd1-Dact1 interface is formed by circumscribed regions of Sestd1 (the carboxyl-terminal region) and Dact1 (the amino-terminal region). Remarkably, we show that loss of Sestd1 precisely phenocopies loss of Dact1 during embryogenesis in mice, leading to a spectrum of birth malformations, including neural tube defects, a shortened and/or curly tail, no genital tubercle, blind-ended colons, hydronephrotic kidneys, and no bladder. Moreover, as with Dact1, a knock-out mutation at the Sestd1 locus exhibits reciprocal genetic rescue interactions during development with a semidominant mutation at the Vangl2 locus. Consistent with this, examination of Wnt pathway activities in Sestd1 mutant mouse embryonic tissue reveals disrupted PCP pathway biochemistry similar to that characterized in Dact1 mutant embryos. The Sestd1 protein is a divergent member of the Trio family of GTPase regulatory proteins that lacks a guanine nucleotide exchange factor domain. Nonetheless, in cell-based assays the Sestd1-Dact1 interaction can induce Rho GTPase activation. Together, our data indicate that Sestd1 cooperates with Dact1 in Vangl2 regulation and in the PCP pathway during mammalian embryonic development.
            Cover page: SEC14 and Spectrin Domains 1 (Sestd1) and Dapper Antagonist of Catenin 1 (Dact1) Scaffold Proteins Cooperatively Regulate the Van Gogh-like 2 (Vangl2) Four-pass Transmembrane Protein and Planar Cell Polarity (PCP) Pathway during Embryonic Development in Mice* ♦
            • Thesis
            • Peer Reviewed
            UC San Francisco Electronic Theses and Dissertations (2010)

            Dact1 (Dapper/Frodo), an interactor with Dishevelled and Catenin proteins that can modulate Wnt signaling, is located at synapses and involved in development of dendritic spines, structures that support excitatory postsynaptic contacts. Hippocampal neurons from Dact1 knockout mice have simpler dendritic arbors and fewer spines than hippocampal neurons from wild type littermates. This correlates with reductions in excitatory synapses and miniature excitatory postsynaptic currents. In contrast, inhibitory synapses are not affected by loss of Dact1, revealing a differential requirement for this protein in the development of excitatory and inhibitory synapses. Loss of Dact1 results in loss of active Rac, and recombinant expression of either Dact1 or constitutively active Rac, but not Rho or Cdc42, rescues dendrite and spine phenotypes in Dact1 mutant hippocampal neurons. Combined with other evidence, this suggests that the function of Dact1 during these aspects of neuronal differentiation are mediated through activation of Rac.

              Cover page: Dact1 is a postsynaptic protein required for dendrite, spine, and excitatory synapse formation in mammalian forebrain
              • Article
              • Peer Reviewed
              UC San Francisco Previously Published Works (2011)
              Abstract Background The Dact family of scaffold proteins was discovered by virtue of binding to Dvl proteins central to Wnt and Planar Cell Polarity (PCP) signaling. Subsequently Dact proteins have been linked to a growing list of potential partners implicated in β-catenin-dependent and β-catenin-independent forms of Wnt and other signaling. To clarify conserved and non-conserved roles for this protein family, we systematically compared molecular interactions of all three murine Dact paralogs by co-immunoprecipitation of proteins recombinantly expressed in cultured human embryonic kidney cells. Results Every Dact paralog readily formed complexes with the Vangl, Dvl, and CK1δ/ε proteins of species ranging from fruit flies to humans, as well as with PKA and PKC. Dact proteins also formed complexes with themselves and with each other; their conserved N-terminal leucine-zipper domains, which have no known binding partners, were necessary and sufficient for this interaction, suggesting that it reflects leucine-zipper-mediated homo- and hetero-dimerization. We also found weaker, though conserved, interactions of all three Dact paralogs with the catenin superfamily member p120ctn. Complex formation with other previously proposed partners including most other catenins, GSK3, LEF/TCF, HDAC1, and TGFβ receptors was paralog-specific, comparatively weak, and/or more sensitive to empirical conditions. Conclusions Combined with published functional evidence from targeted knock-out mice, these data support a conserved role for Dact proteins in kinase-regulated biochemistry involving Vangl and Dvl. This strongly suggests that a principal role for all Dact family members is in the PCP pathway or a molecularly related signaling cascade in vertebrates.
                Cover page: All Dact (Dapper/Frodo) scaffold proteins dimerize and exhibit conserved interactions with Vangl, Dvl, and serine/threonine kinases
                • Article
                • Peer Reviewed
                UC San Francisco Previously Published Works (2016)
                We report a case of irritable bowel syndrome (IBS), diarrhea subtype, characterized by daily 'morning rush' and episodic acute exacerbations brought on by common IBS trigger foods including insoluble fiber, red wine and large/rich meals. The patient also had a history of migraine headaches, and a family history suggesting a common diathesis for both disorders. Given hypothesized contributions to IBS from dysregulation of the enteric serotonergic system, a trial of low-dose triptan medication was implemented in the context of the patient's known IBS triggers, with highly satisfactory results.
                  • Article
                  • Peer Reviewed
                  UC San Francisco Previously Published Works (2013)
                  We previously reported that Sestd1 KO phenocopies Dact1 KO in mice, consistent with a model in which Sestd1 and Dact1 act together to form a crucial functional complex that regulates Vangl2 in the Wnt/Planar Cell Polarity (PCP) pathway. Here, we show that Dvl2, a binding partner of Dact1, also forms complexes with Sestd1, and does so independently of both Dact1 and Vangl2. In cell-based assays, whereas Sestd1 does not alter Dvl2 activation of the Wnt/β-catenin signaling pathway, Dvl2 enhances activation of Rho family GTPases by Dact1 and Sestd1, consistent with a role in the PCP pathway. In mice, although Dvl2 KO is recessive in an otherwise wild type background, it leads to dominant embryonic lethality in either the Sestd1 or Dact1 KO background. This genetic synergy stands in contrast to the epistasis we have previously reported between Sestd1 and Dact1 KO, and suggests independent or semi-independent functions for Dvl2 vs. Sestd1/Dact1 in the regulation of the PCP pathway during development. In conclusion, biochemical and genetic interactions between Dvl2, Sestd1, and Dact1, in addition to prior reported interactions between these same molecules and Vangl2, suggest that all these gene products can form complexes together and regulate the PCP pathway during mammalian development. However, Sestd1 and Dact1 have a closely allied function in the post-translational regulation of Vangl2 that is at least partially distinct from the functions of Dvl2 in this pathway.
                    Cover page: SEC14 and Spectrin Domains 1 (Sestd1), Dishevelled 2 (Dvl2) and Dapper Antagonist of Catenin-1 (Dact1) co-regulate the Wnt/Planar Cell Polarity (PCP) pathway during mammalian development.
                    • Article
                    • Peer Reviewed
                    UC San Francisco Previously Published Works (2013)
                    We previously reported that Sestd1 KO phenocopies Dact1 KO in mice, consistent with a model in which Sestd1 and Dact1 act together to form a crucial functional complex that regulates Vangl2 in the Wnt/Planar Cell Polarity (PCP) pathway. Here, we show that Dvl2, a binding partner of Dact1, also forms complexes with Sestd1, and does so independently of both Dact1 and Vangl2. In cell-based assays, whereas Sestd1 does not alter Dvl2 activation of the Wnt/β-catenin signaling pathway, Dvl2 enhances activation of Rho family GTPases by Dact1 and Sestd1, consistent with a role in the PCP pathway. In mice, although Dvl2 KO is recessive in an otherwise wild type background, it leads to dominant embryonic lethality in either the Sestd1 or Dact1 KO background. This genetic synergy stands in contrast to the epistasis we have previously reported between Sestd1 and Dact1 KO, and suggests independent or semi-independent functions for Dvl2 vs. Sestd1/Dact1 in the regulation of the PCP pathway during development. In conclusion, biochemical and genetic interactions between Dvl2, Sestd1, and Dact1, in addition to prior reported interactions between these same molecules and Vangl2, suggest that all these gene products can form complexes together and regulate the PCP pathway during mammalian development. However, Sestd1 and Dact1 have a closely allied function in the post-translational regulation of Vangl2 that is at least partially distinct from the functions of Dvl2 in this pathway.
                      Cover page: SEC14 and Spectrin Domains 1 (Sestd1), Dishevelled 2 (Dvl2) and Dapper Antagonist of Catenin-1 (Dact1) co-regulate the Wnt/Planar Cell Polarity (PCP) pathway during mammalian development
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