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Sahin Lab

Summary:

My lab is investigating the normal cellular functions of signaling pathways implicated in neurological disease, with an emphasis on axon growth and guidance. Our research centers upon the proteins affected in tuberous sclerosis complex (TSC) and spinal muscular atrophy (SMA) -- two neurological disorders whose genetic basis is well understood but whose cell biology remains unknown. As a clinical neurologist, I also treat patients with neurological disease. One of the ultimate goals of our research is to guide the development of therapeutics for disorders of neural connectivity. My team is currently conducting clinical trials investigating new treatments for TSC.

Tuberous sclerosis complex

TSC is a multi-system autosomal dominant disease caused by loss-of-function mutations in the TSC1 or TSC2 gene. This disease is characterized by the formation of benign tumors (hamartomas) in several organs. The brain is almost invariably affected, and patients often present with epilepsy, autism and mental retardation. We hypothesize that a miswiring of neuronal connections may underlie these neurological symptoms.

We have recently found that the Tsc1 and Tsc2 proteins restrict axon formation and growth. In mouse models of TSC, we observe ectopic axons and abnormal axon path-finding in the brain. The axonal functions of the Tsc proteins may be important in understanding the neurological features of the disease--and, more generally, in understanding the pathology of the autism spectrum disorders that affect patients both with and without TSC.


Click to see how TSC proteins control axon development.

We are further exploring the molecular network in which the Tsc proteins function, and have found that modulation of the growth-promoting mTOR pathway, which is regulated by Tsc proteins, can promote axon regeneration in the adult central nervous system. We are also interested in other neuronal functions of the Tsc signaling network, such as the control of neuron size, myelination, survival and stress responses. For instance, my lab, in collaboration with others, has shown that in a mouse model of TSC, neurons are sized abnormally, are not sufficiently myelinated and are prone to cell death. In other studies, we have found that Tsc activity mediates mTOR's response to neuronal stress. In particular, neurons lacking a functional Tsc protein complex are more vulnerable to endoplasmic reticulum stress-induced cell death.


Click to see a schematic of the mTOR signaling pathway.

Spinal muscular atrophy

Our second major line of research aims to understand axonal pathology in SMA, an autosomal recessive neuromuscular disease. SMA is characterized by hypotonia and muscle weakness, as spinal motor neurons are lost, and is caused by mutations in the SMN gene.

It is known that the SMN protein controls RNA processing and is important for axon development, but the details remain enigmatic. We hypothesize that axonal RNA transport and/or translation are not properly regulated in the disease. To investigate this, we are characterizing the role of the SMN protein in axon growth and guidance in vivo, as well as identifying proteins and mRNA targets that interact with SMN in neurons. We hope that our work will provide new insight into the signaling mechanisms responsible for establishing brain circuitry, and ultimately suggest therapeutic interventions for disorders in which these signaling mechanisms are perturbed.

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Organisms and Viruses

  • 129S4-Tsc2 Null Mouse ( Mus musculus )

    129S4-Tsc2 null allele "Mice that are heterozygous for the targeted mutation are viable, fertile, normal in size and do not display any gross physical or behavioral abnormalities. Homozygous null mice have an embryonic lethal phenotype, failing to develop past embryonic days 9.5 to 12.5 due to hepatic hypoplasia. Cultured neuroepithelial progenitor cells isolated from embryonic day 10.5 embryos display abnormal growth and differentiation. All heterozygotes develop multiple bilateral renal cystadenomas by 12-15 months of age. By 15 months, about half develop liver hemangiomas (more common in females than in males). Less than 10% develop extremity angiosarcomas or renal carcinoma. Little or no gene product (protein) is detected by Western blot in renal cystadenomas. PCR analysis reveals loss of the wildtype allele in about 30% of lesions. Phenotype variability is dependent on genetic background. This mutant mouse strain may be useful in studies of tuberous sclerosis (TSC). "

  • BMAL cKO Mouse ( Mus musculus )

    BMAL conditional knockout "These targeted mutation mice exhibit a loss of both behavioral and molecular circadian rhythms. When placed in constant darkness, the mice undergo an immediate loss of circadian rhythmicity. Locomotor activity is impaired in both light and constant dark cycles.

    Reduced total activity is seen as the mice age. They display a progressive noninflammatory arthropathy. Little pathology is seen prior to 11 weeks of age, but virtually all homozygotes develop joint ankylosis due to flowing ossification of ligaments and tendons by 35 weeks of age. Bone density and articular cartilage are unaffected.

    Inactivation of the gene suppresses diurnal variation in glucose and triglycerides. Gluconeogenesis is abolished in homozygotes, but the counterregulatory response of corticosterone and glucagon to insulin-induced hypoglycemia is retained. Homozygotes are viable but not fertile and have an increased mortality rate after 26 weeks of age. A truncated, non-functional protein is produced. This strain may be useful in studies of circadian rhythm, arthritis, ankylosis, and glucose homeostasis. "

  • Darpp32-Cre Tg Mouse ( Mus musculus )

    Darpp32-cre transgenic

  • GAN KO Mouse ( Mus musculus )

    GAN knockout

  • HA-ubiquitin Tg Mouse ( Mus musculus )

    HA-ubiquitin trangenic

  • L7-cre Tg Mouse ( Mus musculus )

    "These transgenic mice express a cre gene inserted into exon 4 of a Pcp2 gene. Mice homozygous for the insert are viable, fertile, normal in size and do not display any gross physical or behavioral abnormalities. Recombinase activity is observed in most Purkinje cells and some retinal bipolar neurons. Small amounts of activity are observed in an unidentified population of cells of the central nervous system tissue. Recombination is first observed around postnatal day 6 and is fully established 2 to 3 weeks after birth. " L7-Cre transgene

  • Math1-creER Tg Mouse ( Mus musculus )

    Math1-creER transgenic Mice heterozygous or homozygous for the Gtrosa26tm1Sor targeted mutation may be used to test the tissue/cellular expression pattern of the cre transgene in any transgenic strain carrying cre under the regulation of a specific promoter. Cre expression results in the removal of a loxP-flanked DNA segment that prevents expression of a lacZ gene. When crossed with a cre transgenic strain, lacZ is expressed in cells/tissues where cre is expressed.

  • p62 null allele Mouse ( Mus musculus )

    p62 null allele

  • Paravalbumin-Cre Tg Mouse ( Mus musculus )

    Paravalbumin-Cre transgenic "PV-Cre knockin mice have both endogenous gene and Cre recombinase expression directed to Pvalb-expressing cells by the endogenous promoter/enhancer elements of the parvalbumin locus. These PV-Cre mice are a Cre-lox tool for deleting floxed sequences in Pvalb-expressing cells/tissues, and may be useful in studying neuronal differentiation. "

  • RiboTag-cre Tg Mouse ( Mus musculus )

    The RiboTag targeted mutation of the ribosomal protein L22 locus allows Cre-mediated hemagglutinin epitope tagging of ribosomes from user-defined cell types and/or immunoprecipitation of ribosomes bound to mRNA from those specific cell types. RiboTag-cre transgenic

  • Tg (Hlxb9) Mouse ( Mus musculus )

    "Similar to Stock No. 005024, mice that are homozygous for the targeted mutant Smn1 allele and carry the SMN2 transgene exhibit symptoms and neuropathology similar to patients afflicted with type I proximal spinal muscular atrophy (SMA). As an addition to Stock No. 005024, this line carries a transgene containing a Green Fluorescent Protein (GFP) under the direction of the mouse Hlxb9 promoter. Transgenic mice display distinct expression of GFP in dendrites, axons and soma of spinal motor neurons, allowing identification, isolation and purification of spinal motor neurons by FACS. GFP expression mimics endogenous HLXB9 expression pattern. Fluorescence is detected in axons, dendrites and processes of spinal motor neurons at embryonic day 9.5 to postnatal day 10 aged mice. This mutant mouse strain represents a model that may be useful for purification and in vivo tracking of spinal motor neurons. Mice homozygous for the Hlxb9-GFP transgenic insert are reportedly viable, fertile, do not display any gross behavioral abnormalities, but are smaller in size than wild-type littermates. Homozygous pups born to homozygous females have a high mortality rate. In the initial characterization by the donating investigator, mice that are homozygous for the targeted mutant Smn1 allele and carry the SMN2 transgene exhibit symptoms and mice were either stillborn or survived 4-6 days. Mice that died at or shortly after birth were slightly smaller (1.33 g. vs. 1.51 g.) than normal littermates. Mice that survive for several days are indistinguishable from normal littermates in the first 48 hours, after which they exhibit decreased suckling and movement, labored breathing and tremoring limbs. Mice succumbing at this later time point are noticeably smaller than normal littermates (1.47 g vs. 4.59). A bell-shaped trunk is also noticeable in affected mice, presumably from intercostal muscle weakness, a characteristic of type I SMA. Histological analysis indicates that affected mice that survive to day 5 exhibit a loss of motor neurons from spinal cord (35%) and facial nucleus (40%). A large number of cells with pyknotic nuclei are observed in these tissues. Immunohistochemical analysis indicates low-level expression of the SMN2 protein in the tissues examined (brain, liver, spinal cord) and an absence or near absence of intranuclear aggregates of the SMN protein (`gems?). Homozygous mice bearing the Smn1 targeted mutation without a copy of the SMN2 transgene display an embryonic lethal phenotype with developmental arrest occurring prior to implantation." Hlbx 9 trangenic

  • tg(SMN2) 89 Ahmb Mouse ( Mus musculus )

    SMN1 transgenic "Mice that are homozygous for the targeted mutant Smn1 allele and carry the SMN2 transgene exhibit symptoms and neuropathology similar to patients afflicted with type I proximal spinal muscular atrophy (SMA). In the initial characterization by the donating investigator, mice were either stillborn or survived 4-6 days. Mice that died at or shortly after birth were slightly smaller (1.33 g. vs. 1.51 g.) than normal littermates. Mice that survive for several days are indistinguishable from normal littermates in the first 48 hours, after which they exhibit decreased suckling and movement, labored breathing and tremoring limbs. Mice succumbing at this later time point are noticeably smaller than normal littermates (1.47 g vs. 4.59). A bell-shaped trunk is also noticeable in affected mice, presumably from intercostal muscle weakness, a characteristic of type I SMA. Histological analysis indicates that affected mice that survive to day 5 exhibit a loss of motor neurons from spinal cord (35%) and facial nucleus (40%). A large number of cells with pyknotic nuclei are observed in these tissues. Immunohistochemical analysis indicates low-level expression of the SMN2 protein in the tissues examined (brain, liver, spinal cord) and an absence or near absence of intranuclear aggregates of the SMN protein ('gems'). The donating investigator reports that muscle fibers (quadriceps and gastrocnemius assayed) are atrophied, a characteristic observed in SMA patients. Homozygous mice bearing the Smn1 targeted mutation without a copy of the SMN2 transgene display an embryonic lethal phenotype with developmental arrest occurring prior to implantation. "

  • Tsc2 flox Mouse ( Mus musculus )

    Tsc2 floxed conditional knockout


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Last updated: 2013-09-20T10:40:12.628-05:00

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