Relations entre la visibilité du plumage et la complexité du chant chez des Passeriformes nord-américains

Thèse numérisée par la Direction des bibliothèques de l'Université de Montréal

Transgenic Expression of the Activating Natural Killer Receptor Ly49H Confers Resistance to Cytomegalovirus in Genetically Susceptible Mice

Natural resistance to infection with mouse cytomegalovirus (MCMV) is controlled by a dominant locus, Cmv1. Cmv1 is linked to the Ly49 family of natural killer receptors on distal chromosome 6. While some studies localized Cmv1 as distal to the Ly49 gene cluster, genetic and functional analysis identified Ly49h as a pivotal factor in resistance to MCMV. The role of these two independent genomic domains in MCMV resistance was evaluated by functional complementation using transgenesis of bacterial artificial chromosomes (BAC) in genetically susceptible mice. Phenotypic and genetic characterization of the transgenic animals traced the resistance gene to a single region spanning the Ly49h gene. The appearance of the Ly49H protein in NK cells of transgenic mice coincided with the emergence of MCMV resistance, and there was a threshold Ly49H protein level associated with full recovery. Finally, transgenic expression of Ly49H in the context of either of the two independent susceptibility alleles, Cmv1sBALB or Cmv1sFVB, conferred resistance to MCMV infection. These results demonstrate that Ly49h is necessary and sufficient to confer MCMV resistance, and formally demonstrate allelism between Cmv1 and Ly49h. This panel of transgenic animals provides a unique resource to study possible pleiotropic effect of Cmv1

Snf2h Primes UL Neuron Production

Alterations in the homeostasis of either cortical progenitor pool, namely the apically located radial glial (RG) cells or the basal intermediate progenitors (IPCs) can severely impair cortical neuron production. Such changes are reflected by microcephaly and are often associated with cognitive defects. Genes encoding epigenetic regulators are a frequent cause of intellectual disability and many have been shown to regulate progenitor cell growth, including our inactivation of the Smarca1 gene encoding Snf2l, which is one of two ISWI mammalian orthologs. Loss of the Snf2l protein resulted in dysregulation of Foxg1 and IPC proliferation leading to macrocephaly. Here we show that inactivation of the closely related Smarca5 gene encoding the Snf2h chromatin remodeler is necessary for embryonic IPC expansion and subsequent specification of callosal projection neurons. Telencephalon-specific Smarca5 cKO embryos have impaired cell cycle kinetics and increased cell death, resulting in fewer Tbr2+ and FoxG1+ IPCs by mid-neurogenesis. These deficits give rise to adult mice with a dramatic reduction in Satb2C upper layer neurons, and partial agenesis of the corpus callosum. Mice survive into adulthood but molecularly display reduced expression of the clustered protocadherin genes that may further contribute to altered dendritic arborization and a hyperactive behavioral phenotype. Our studies provide novel insight into the developmental function of Snf2h-dependent chromatin remodeling processes during brain development

Motor Unit Abnormalities in Dystonia musculorum Mice

Dystonia musculorum (dt) is a mouse inherited sensory neuropathy caused by mutations in the dystonin gene. While the primary pathology lies in the sensory neurons of dt mice, the overt movement disorder suggests motor neurons may also be affected. Here, we report on the contribution of motor neurons to the pathology in dt27J mice. Phenotypic dt27J mice display reduced alpha motor neuron cell number and eccentric alpha motor nuclei in the ventral horn of the lumbar L1 spinal cord region. A dramatic reduction in the total number of motor axons in the ventral root of postnatal day 15 dt27J mice was also evident. Moreover, analysis of the trigeminal nerve of the brainstem showed a 2.4 fold increase in number of degenerating neurons coupled with a decrease in motor neuron number relative to wild type. Aberrant phosphorylation of neurofilaments in the perikaryon region and axonal swellings within the pre-synaptic terminal region of motor neurons were observed. Furthermore, neuromuscular junction staining of dt27J mouse extensor digitorum longus and tibialis anterior muscle fibers showed immature endplates and a significant decrease in axon branching compared to wild type littermates. Muscle atrophy was also observed in dt27J muscle. Ultrastructure analysis revealed amyelinated motor axons in the ventral root of the spinal nerve, suggesting a possible defect in Schwann cells. Finally, behavioral analysis identified defective motor function in dt27J mice. This study reveals neuromuscular defects that likely contribute to the dt27J pathology and identifies a critical role for dystonin outside of sensory neurons

The Proteolipid Protein Promoter Drives Expression outside of the Oligodendrocyte Lineage during Embryonic and Early Postnatal Development

The proteolipid protein (Plp) gene promoter is responsible for driving expression of one of the major components of myelin – PLP and its splice variant DM-20. Both products are classically thought to express predominantly in oligodendrocytes. However, accumulating evidence suggests Plp expression is more widespread than previously thought. In an attempt to create a mouse model for inducing oligodendrocyte-specific gene deletions, we have generated transgenic mice expressing a Cre recombinase cDNA under control of the mouse Plp promoter. We demonstrate Plp promoter driven Cre expression is restricted predominantly to mature oligodendrocytes of the central nervous system (CNS) at postnatal day 28. However, crosses into the Rosa26LacZ and mT/mG reporter mouse lines reveal robust and widespread Cre activity in neuronal tissues at E15.5 and E10.5 that is not strictly oligodendrocyte lineage specific. By P28, all CNS tissues examined displayed high levels of reporter gene expression well outside of defined white matter zones. Importantly, our study reinforces the emerging idea that Plp promoter activity is not restricted to the myelinating cell lineage, but rather, has widespread activity both during embryonic and early postnatal development in the CNS. Specificity of the promoter to the oligodendrocyte cell lineage, as shown through the use of a tamoxifen inducible Plp-CreERt line, occurs only at later postnatal stages. Understanding the temporal shift in Plp driven expression is of consequence when designing experimental models to study oligodendrocyte biology

Assessment of motor neuron pathology and potential compensatory mechanisms in phenotypically normal mice with reduced Survival Motor Neuron levels.

Spinal muscular atrophy (SMA) is a destructive pediatric neuromuscular disorder caused by low survival motor neuron (Smn) protein levels due to mutations and deletions within the survival motor neuron 1 (SMN1) gene. Motor neurons are the main pathological targets, and along with neuromuscular junctions (NMJs), they play an early significant role in the pathogenesis of SMA. Previous studies demonstrate that a pathological reduction in Smn levels can lead to significant remodeling defects in both the outgrowth of axonal sprouts and in the nerve-directed clustering of AChRs in mouse models. However, whether this pathological reduction in Smn leads to ubclinical features has not been investigated. Here, we have employed the Smn2B/2B and Smn+/- mouse models to study whether similar SMA pathology is present sub-clinically, and if so whether there is any compensation present. We show a decrease in the motor neuron number in the mouse models, no change in myelin thickness and modest NMJ pathology in both mouse models. Additionally, compensation through the expansion of the motor unit size is suggested.L’amyotrophie spinale (AMS) est un trouble neuromusculaire pédiatrique destructif causé par le niveau bas de protéine du neurone de moteur de survie (NMS) en raison des mutations et des effacements dans le neurone de moteur de survie 1 gène (NMS1). Des neurones du moteur sont les cibles pathologiques principales, et ce, avec des jonctions neuromusculaires (JNMs), ils jouent, en avance, un rôle significatif dans la pathogénie de AMS. Des études précédentes démontrent qu’une réduction pathologique de niveaux de NMS peut mener aux défauts importants de réorganisation tant dans l’excroissance axonale que dans l’agrégation du récepteur de l’acétylcholine (AChR) sous la terminaison nerveuse dans des modèles de souris. Cependant, si cette reduction pathologique de NMS mène aux caractéristiques infracliniques n’a pas été à l’étude. Ici, nous avons employé le NMS2B/2B et NMS +/- des modèles de souris afin de déterminer si une pathologie semblable à l’AMS est présente infracliniquement, ainsi s’il y a présence de quelconque compensation. Nous montrons une diminution dans le nombre des neurones du moteur dans les modèles de souris, aucun changement de l’épaisseur du myelin et une pathologie modeste de JNM dans les deux modèles de souris. De plus, une compensation par l’expansion de la taille d’unité du moteur est suggérée

The mouse dystrophin muscle enhancer-1 imparts skeletal muscle, but not cardiac muscle, expression onto the dystrophin Purkinje promoter in transgenic mice Downloaded from 2 Downloaded from

ABSTRACT A subset of patients harboring mutations in the dystrophin gene suffer from X-linked dilated cardiomyopathy (XLCM), a familial heart disease that is not accompanied by any clinical signs of skeletal muscle myopathy. Since the muscle (M) isoform of dystrophin is not expressed in these patients, the absence of skeletal muscle symptoms has been attributed to expression of the brain (B) and cerebellar Purkinje (CP) isoforms of dystrophin in skeletal, but not cardiac, muscles of XLCM patients. The compensatory mechanism of dystrophin B and CP promoter upregulation is not known but it has been suggested that the dystrophin muscle enhancer from intron 1, DME-1, may be important in this activity. Previous studies have shown that the presence of the DME-1 is essential for a significant increase in dystrophin B and CP promoter activity in skeletal muscle cells in culture. Here, we demonstrate that the mouse dystrophin CP promoter drives expression of a lacZ reporter gene specifically to the cerebellar Purkinje cell layer but not to skeletal or cardiac muscle of transgenic mice. However, if the mouse counterpart of DME-1 is present in the transgene construct, the dystrophin CP promoter is now activated in skeletal muscle, but not in cardiac muscle. Our findings provide in vivo evidence for the importance of the dystrophin muscle enhancer sequences in activating the dystrophin CP promoter in skeletal muscle. Furthermore, they provide support for the model in which muscle enhancers, like DME-1, activate the dystrophin B and CP promoters in skeletal muscle but not in cardiac muscle of XLCM patients

Dystonin loss-of-function leads to impaired autophagy-endolysosomal pathway dynamics

The neuronal dystonin protein (DST-a) is a large cytoskeletal linker important for integrating the various components of the cytoskeleton. Recessive Dst mutations lead to a sensory neuropathy in mice known as dystonia musculorum (DstThe accepted manuscript in pdf format is listed with the files at the bottom of this page. The presentation of the authors' names and (or) special characters in the title of the manuscript may differ slightly between what is listed on this page and what is listed in the pdf file of the accepted manuscript; that in the pdf file of the accepted manuscript is what was submitted by the author

Wnt11 Promotes Cardiomyocyte Development by Caspase-Mediated Suppression of Canonical Wnt Signals ▿ †

Specification and early patterning of the vertebrate heart are dependent on both canonical and noncanonical wingless (Wnt) signal pathways. However, the impact of each Wnt pathway on the later stages of myocardial development and differentiation remains controversial. Here, we report that the components of each Wnt signal conduit are expressed in the developing and postnatal heart, yet canonical/β-catenin activity is restricted to nonmyocardial regions. Subsequently, we observed that noncanonical Wnt (Wnt11) enhanced myocyte differentiation while preventing stabilization of the β-catenin protein, suggesting active repression of canonical Wnt signals. Wnt11 stimulation was synonymous with activation of a caspase 3 signal cascade, while inhibition of caspase activity led to accumulation of β-catenin and a dramatic reduction in myocyte differentiation. Taken together, these results suggest that noncanonical Wnt signals promote myocyte maturation through caspase-mediated inhibition of β-catenin activity