Debra Silver | Duke University School of Medicine (original) (raw)

Papers by Debra Silver

Neuron, Jan 6, 2016

Embryonic neocortical development depends on balanced production of progenitors and neurons. Gene... more Embryonic neocortical development depends on balanced production of progenitors and neurons. Genetic mutations disrupting progenitor mitosis frequently impair neurogenesis; however, the link between altered mitosis and cell fate remains poorly understood. Here we demonstrate that prolonged mitosis of radial glial progenitors directly alters neuronal fate specification and progeny viability. Live imaging of progenitors from a neurogenesis mutant, Magoh(+/-), reveals that mitotic delay significantly correlates with preferential production of neurons instead of progenitors, as well as apoptotic progeny. Independently, two pharmacological approaches reveal a causal relationship between mitotic delay and progeny fate. As mitotic duration increases, progenitors produce substantially more apoptotic progeny or neurons. We show that apoptosis, but not differentiation, is p53 dependent, demonstrating that these are distinct outcomes of mitotic delay. Together our findings reveal that prolonge...

Cell, 2016

Proper establishment of synapses is critical for constructing functional circuits. Interactions b... more Proper establishment of synapses is critical for constructing functional circuits. Interactions between presynaptic neurexins and postsynaptic neuroligins coordinate the formation of synaptic adhesions. An isoform code determines the direct interactions of neurexins and neuroligins across the synapse. However, whether extracellular linker proteins can expand such a code is unknown. Using a combination of in vitro and in vivo approaches, we found that hevin, an astrocyte-secreted synaptogenic protein, assembles glutamatergic synapses by bridging neurexin-1alpha and neuroligin-1B, two isoforms that do not interact with each other. Bridging of neurexin-1alpha and neuroligin-1B via hevin is critical for the formation and plasticity of thalamocortical connections in the developing visual cortex. These results show that astrocytes promote the formation of synapses by modulating neurexin/neuroligin adhesions through hevin secretion. Our findings also provide an important mechanistic insight into how mutations in these genes may lead to circuit dysfunction in diseases such as autism.

The Journal of neuroscience : the official journal of the Society for Neuroscience, Jan 6, 2015

The cerebral cortex is built during embryonic neurogenesis, a period when excitatory neurons are ... more The cerebral cortex is built during embryonic neurogenesis, a period when excitatory neurons are generated from progenitors. Defects in neurogenesis can cause acute neurodevelopmental disorders, such as microcephaly (reduced brain size). Altered dosage of the 1q21.1 locus has been implicated in the etiology of neurodevelopmental phenotypes; however, the role of 1q21.1 genes in neurogenesis has remained elusive. Here, we show that haploinsufficiency for Rbm8a, an exon junction complex (EJC) component within 1q21.1, causes severe microcephaly and defective neurogenesis in the mouse. At the onset of neurogenesis, Rbm8a regulates radial glia proliferation and prevents premature neuronal differentiation. Reduced Rbm8a levels result in subsequent apoptosis of neurons, and to a lesser extent, radial glia. Hence, compared to control, Rbm8a-haploinsufficient brains have fewer progenitors and neurons, resulting in defective cortical lamination. To determine whether reciprocal dosage change of...

Journal of Biological Chemistry, 1998

Tyrosine phosphorylation of the ␤ 3 subunit of the major platelet integrin ␣ IIb ␤ 3 has been sho... more Tyrosine phosphorylation of the ␤ 3 subunit of the major platelet integrin ␣ IIb ␤ 3 has been shown to occur during thrombin-induced platelet aggregation (1). We now show that a wide variety of platelet stimuli induced ␤ 3 tyrosine phosphorylation, but that this phosphorylation occurred only following platelet aggregation. Several lines of evidence suggest that the ␤ 3 cytoplasmic domain tyrosine residues and/or their phosphorylation function to mediate interactions between ␤ 3 integrins and cytoskeletal proteins. First, phospho-␤ 3 was retained preferentially in a Triton X-100 insoluble cytoskeletal fraction of thrombin-aggregated platelets. Second, in vitro experiments show that the cytoskeletal protein, myosin, associated in a phosphotyrosine-dependent manner with a diphosphorylated peptide corresponding to residues 740 -762 of ␤ 3 . Third, mutation of both tyrosines in the ␤ 3 cytoplasmic domain to phenylalanines markedly reduced ␤ 3 -dependent fibrin clot retraction. Thus, our data indicate that platelet aggregation is both necessary and sufficient for ␤ 3 tyrosine phosphorylation, and this phosphorylation results in the physical linkage of ␣ IIb ␤ 3 to the cytoskeleton. We hypothesize that this linkage may involve direct binding of the phosphorylated integrin to the contractile protein myosin in order to mediate transmission of force to the fibrin clot during the process of clot retraction.

From Melanocytes to Melanoma, 2006

... Cell signaling and adhesion Wnts Wingless-related Dorsal NT Induction, WNT3: Tetra WNT5A: inc... more ... Cell signaling and adhesion Wnts Wingless-related Dorsal NT Induction, WNT3: Tetra WNT5A: increased MMTV ( 2,4,7,9 ) proliferation, Amelia expression ( 44 ) integration site differentiation (#273395) ( 169 ) ( 3,4,37,41,50 ) Catn -catenin Mostly ubiquitous, Induction, ...

Wiley interdisciplinary reviews. RNA, Jan 18, 2015

The cerebral cortex, the brain structure responsible for our higher cognitive functions, is built... more The cerebral cortex, the brain structure responsible for our higher cognitive functions, is built during embryonic development in a process called corticogenesis. During corticogenesis, neural stem cells generate distinct populations of progenitors and excitatory neurons. These new neurons migrate radially in the cortex, eventually forming neuronal layers and establishing synaptic connections with other neurons both within and outside the cortex. Perturbations to corticogenesis can result in severe neurodevelopmental disorders, thus emphasizing the need to better understand molecular regulation of brain development. Recent studies in both model organisms and humans have collectively highlighted roles for post-transcriptional regulation in virtually all steps of corticogenesis. Genomic approaches have revealed global RNA changes associated with spatial and temporal regulation of cortical development. Additionally, genetic studies have uncovered RNA-binding proteins (RBPs) critical fo...

Developmental cell, 2003

New work in Drosophila demonstrates that cdk4 loss causes phenotypes similar to the loss of JAK/S... more New work in Drosophila demonstrates that cdk4 loss causes phenotypes similar to the loss of JAK/STAT pathway components. Cdk4 overexpression can bypass requirements for JAK but not STAT. These results demonstrate a new function for Cdk4 and a new mode of STAT activation.

PLoS genetics, 2008

ADAMTS20 (Adisintegrin-like and metalloprotease domain with thrombospondin type-1 motifs) is a me... more ADAMTS20 (Adisintegrin-like and metalloprotease domain with thrombospondin type-1 motifs) is a member of a family of secreted metalloproteases that can process a variety of extracellular matrix (ECM) components and secreted molecules. Adamts20 mutations in belted (bt) mice cause white spotting of the dorsal and ventral torso, indicative of defective neural crest (NC)-derived melanoblast development. The expression pattern of Adamts20 in dermal mesenchymal cells adjacent to migrating melanoblasts led us to initially propose that Adamts20 regulated melanoblast migration. However, using a Dct-LacZ transgene to track melanoblast development, we determined that melanoblasts were distributed normally in whole mount E12.5 bt/bt embryos, but were specifically reduced in the trunk of E13.5 bt/bt embryos due to a seven-fold higher rate of apoptosis. The melanoblast defect was exacerbated in newborn skin and embryos from bt/bt animals that were also haploinsufficient for Adamts9, a close homol...

Localization of specific mRNAs to distinct sites within the Drosophila oocyte is an early and key... more Localization of specific mRNAs to distinct sites within the Drosophila oocyte is an early and key step in establishing the anterior-posterior and dorsal-ventral axes. We describe a new function for the RNA helicase encoded by the ''posterior'' group gene vasa (vas) in control of localization of the mRNA encoded by the ''dorsal-ventral'' patterning gene gurken (grk). Two new ethyl methane sulfonate-induced, female sterile alleles of vas have been isolated. In these mutants grk mRNA fails to become localized properly and GRK protein is barely detectable. Surprisingly fs(1)K10, a recessive female sterile mutation that results in mislocalization of GRK mRNA to the anterior end of the oocyte, is epistatic to these vas alleles. This result demonstrates that GRK protein levels sufficient to dorsalize the egg chamber can accumulate in vas mutants, if fs(1)K10 is also mutant. Taken together these results suggest that regulation of GRK mRNA localization normally occurs, directly or indirectly, through the VAS RNA-dependent RNA helicase and may suggest that accumulation of GRK protein normally depends on GRK mRNA localization.

ptosis and promote proliferation (Shen et al., 2001). Expression of a constitutively activated fo... more ptosis and promote proliferation (Shen et al., 2001). Expression of a constitutively activated form of STAT3 in 293T cells results in increased expression of cyclin D1, BCL-XL, and c-myc, which promote cell cycle progression, cell survival, and proliferation, respectively. Inhibition of STAT3 in myeloma cells results in apoptosis (Catlett-Falcone et al., 1999b), and dominant-negative Summary STAT3 prevents v-src mediated cellular transformation (Bromberg et al. , 1998). Taken together with the obser-The JAK/STAT signaling pathway, renowned for its vation that STAT3 is frequently constitutively activated effects on cell proliferation and survival, is constituin cancer cells, it is likely that STAT3 plays a role in tively active in various human cancers, including ovartumorigenesis and/or cancer progression. ian. We have found that JAK and STAT are required Most tumors derive from cells of epithelial origin; in to convert the border cells in the Drosophila ovary order to become metastatic, and thereby a serious from stationary, epithelial cells to migratory, invasive threat to human health, these cells must detach from cells. The ligand for this pathway, Unpaired (UPD), is the epithelium of origin and invade surrounding tissues, expressed by two central cells within the migratory ultimately reaching the bloodstream. This step in cancer cell cluster. Mutations in upd or jak cause defects

Advances in Experimental Medicine and Biology, 2006

P igment cells in developing vertebrates are derived from a transient and pluripotent population ... more P igment cells in developing vertebrates are derived from a transient and pluripotent population of cells called neural crest. The neural crest delaminates from the developing neural tube and overlying ectoderm early in development. The pigment cells are the only derivative to migrate along the dorso-lateral pathway. As they migrate, the precursor pigment cell population differentiates and expands through proliferation and pro-survival processes, ultimately contributing to the coloration of organisms. The types of pigment cells that develop, timing of these processes, and final destination can vary between organisms. Studies from mice, chick, Xenopus, zebrafish, and medaka have led to the identification of many genes that regulate pigment cell development. These include several classes of proteins: transcription factors, transmembrane receptors, and extracellular ligands. This chapter discusses an overview of pigment cell development and the genes that regulate this important process. SaintJeannet(Pavan) 7/8/05, 10:21 AM 1 © 2 0 0 5 C o p y r i g h t E u r e k a h / L a n d e s B i o s c i e n c e D o N o t D i s t r i b u t e Neural Crest Induction and Differentiation 2 SaintJeannet(Pavan) 7/8/05, 10:21 AM 2 © 2 0 0 5 C o p y r i g h t E u r e k a h / L a n d e s B i o s c i e n c e D o N o t D i s t r i b u t e

Journal of Visualized Experiments, 2014

Although of short duration, mitosis is a complex and dynamic multi-step process fundamental for d... more Although of short duration, mitosis is a complex and dynamic multi-step process fundamental for development of organs including the brain. In the developing cerebral cortex, abnormal mitosis of neural progenitors can cause defects in brain size and function. Hence, there is a critical need for tools to understand the mechanisms of neural progenitor mitosis. Cortical development in rodents is an outstanding model for studying this process. Neural progenitor mitosis is commonly examined in fixed brain sections. This protocol will describe in detail an approach for live imaging of mitosis in ex vivo embryonic brain slices. We will describe the critical steps for this procedure, which include: brain extraction, brain embedding, vibratome sectioning of brain slices, staining and culturing of slices, and time-lapse imaging. We will then demonstrate and describe in detail how to perform post-acquisition analysis of mitosis. We include representative results from this assay using the vital dye Syto11, transgenic mice (histone H2B-EGFP and centrin-EGFP), and in utero electroporation (mCherry-α-tubulin). We will discuss how this procedure can be best optimized and how it can be modified for study of genetic regulation of mitosis. Live imaging of mitosis in brain slices is a flexible approach to assess the impact of age, anatomy, and genetic perturbation in a controlled environment, and to generate a large amount of data with high temporal and spatial resolution. Hence this protocol will complement existing tools for analysis of neural progenitor mitosis.

PLoS Genetics, 2008

ADAMTS20 (A disintegrin-like and metalloprotease domain with thrombospondin type-1 motifs) is a m... more ADAMTS20 (A disintegrin-like and metalloprotease domain with thrombospondin type-1 motifs) is a member of a family of secreted metalloproteases that can process a variety of extracellular matrix (ECM) components and secreted molecules. Adamts20 mutations in belted (bt) mice cause white spotting of the dorsal and ventral torso, indicative of defective neural crest (NC)-derived melanoblast development. The expression pattern of Adamts20 in dermal mesenchymal cells adjacent to migrating melanoblasts led us to initially propose that Adamts20 regulated melanoblast migration. However, using a Dct-LacZ transgene to track melanoblast development, we determined that melanoblasts were distributed normally in whole mount E12.5 bt/bt embryos, but were specifically reduced in the trunk of E13.5 bt/bt embryos due to a seven-fold higher rate of apoptosis. The melanoblast defect was exacerbated in newborn skin and embryos from bt/bt animals that were also haploinsufficient for Adamts9, a close homolog of Adamts20, indicating that these metalloproteases functionally overlap in melanoblast development. We identified two potential mechanisms by which Adamts20 may regulate melanoblast survival. First, skin explant cultures demonstrated that Adamts20 was required for melanoblasts to respond to soluble Kit ligand (sKitl). In support of this requirement, bt/bt;Kit tm1Alf /+ and bt/bt;Kitl Sl /+ mice exhibited synergistically increased spotting. Second, ADAMTS20 cleaved the aggregating proteoglycan versican in vitro and was necessary for versican processing in vivo, raising the possibility that versican can participate in melanoblast development. These findings reveal previously unrecognized roles for Adamts proteases in cell survival and in mediating Kit signaling during melanoblast colonization of the skin. Our results have implications not only for understanding mechanisms of NC-derived melanoblast development but also provide insights on novel biological functions of secreted metalloproteases.

Journal of Biological Chemistry, 1997

Kinase-related protein, also known as KRP or telokin, is an independently expressed protein produ... more Kinase-related protein, also known as KRP or telokin, is an independently expressed protein product derived from a gene within the gene for myosin light chain kinase (MLCK). KRP binds to unphosphorylated smooth muscle myosin filaments and stabilizes them against ATP-induced depolymerization in vitro. KRP competes with MLCK for binding to myosin, suggesting that both proteins bind to myosin by the KRP domain (Shirinsky, In this study, we investigated which regions of myosin and KRP interact in vitro. Using cosedimentation assays, we determined that KRP binds to unphosphorylated myosin with a stoichiometry of 1 mol of KRP/1 mol of myosin and an affinity of 5.5 M. KRP slows the rate of proteolytic cleavage of the head-tail junction of heavy meromyosin by papain and chymotrypsin, suggesting it is binding to this region of myosin. In addition, competition experiments, using soluble headless fragments of nonmuscle myosin, confirmed that KRP interacts with the regulatory light chain binding region of myosin. The regions important for KRP's binding to myosin were investigated using bacterially expressed KRP truncation mutants. We determined that the acid-rich sequence between Gly 138 and Asp 151 of KRP is required for high affinity myosin binding, and that the amino terminus and ␤-barrel regions weakly interact with myosin. All KRP truncations, at concentrations comparable to their K D values, exhibited some stabilization of myosin filaments against ATP depolymerization in vitro, suggesting that KRP's ability to stabilize myosin filaments is commensurate with its myosin binding affinity. KRP weakened the K m but not the V max of phosphorylation of myosin by MLCK, demonstrating that bound KRP does not prevent MLCK from activating myosin.

Human Molecular Genetics, 2008

Haploinsufficiency for the transcription factor SOX10 is associated with the pigmentary deficienc... more Haploinsufficiency for the transcription factor SOX10 is associated with the pigmentary deficiencies of Waardenburg syndrome (WS) and is modeled in Sox10 haploinsufficient mice (Sox10 LacZ/1 ). As genetic background affects WS severity in both humans and mice, we established an N-ethyl-N-nitrosourea (ENU) mutagenesis screen to identify modifiers that increase the phenotypic severity of Sox10 LacZ/1 mice. Analysis of 230 pedigrees identified three modifiers, named modifier of Sox10 neurocristopathies (Mos1, Mos2 and Mos3). Linkage analysis confirmed their locations on mouse chromosomes 13, 4 and 3, respectively, within regions distinct from previously identified WS loci. Positional candidate analysis of Mos1 identified a truncation mutation in a hedgehog(HH)-signaling mediator, GLI-Kruppel family member 3 (Gli3). Complementation tests using a second allele of Gli3 (Gli3 Xt-J ) confirmed that a null mutation of Gli3 causes the increased hypopigmentation in Sox10 LacZ/1 ;Gli3 Mos1/1 double heterozygotes. Early melanoblast markers (Mitf, Sox10, Dct, and Si) are reduced in Gli3 Mos1/Mos1 embryos, indicating that loss of GLI3 signaling disrupts melanoblast specification. In contrast, mice expressing only the GLI3 repressor have normal melanoblast specification, indicating that the full-length GLI3 activator is not required for specification of neural crest to the melanocyte lineage. This study demonstrates the feasibility of sensitized screens to identify disease modifier loci and implicates GLI3 and other HH signaling components as modifiers of human neurocristopathies.

genesis, 2014

Magoh encodes a core component of the exon junction complex (EJC), which binds mRNA and regulates... more Magoh encodes a core component of the exon junction complex (EJC), which binds mRNA and regulates mRNA metabolism. Magoh is highly expressed in proliferative tissues during development. EJC components have been implicated in several developmental disorders including TAR syndrome, Richieri-Costa-Pereira syndrome, and intellectual disability. Existing germline null Magoh mice are embryonic lethal as homozygotes and perinatal lethal as heterozygotes, precluding detailed analysis of embryonic and postnatal functions. Here, we report the generation of a new genetic tool to dissect temporal and tissue-specific roles for Magoh in development and adult homeostasis. This Magoh conditional allele has two loxP sites flanking the second exon. Ubiquitous Cre-mediated deletion of the floxed allele in a heterozygous mouse (Magoh del/1 ) causes 50% reduction of both Magoh mRNA and protein. Magoh del/1 mice exhibit both microcephaly and hypopigmentation, thus phenocopying germline haploinsufficient Magoh mice. Using Emx1-Cre, we further show that conditional Magoh deletion in neural progenitors during embryonic development also causes microcephaly. We anticipate this novel conditional allele will be a valuable tool for assessing tissue-specific roles for Magoh in mammalian development and postnatal processes. genesis 00:1-7. V C 2014 Wiley Periodicals, Inc. . 2011. A novel frameshift mutation in UPF3B identified in brothers affected with childhood nset schizophrenia and autism spectrum disorders. Mol Psychiatry 16:238-239.

Developmental Cell, 2003

Developmental Biology, 1998