Dan Goldowitz

Scrambler and yotari disrupt the disabled gene and produce a reeler- like phenotype in mice

Formation of the mammalian brain requires choreographed migration of neurons to generate highly ordered laminar structures such as those in the cortices of the forebrain and the cerebellum. These processes are severely disrupted by mutations in reelin which cause widespread misplacement of neurons and associated ataxia in reeler mice,. Reelin is a large extracellular protein secreted by pioneer neurons that coordinates cell positioning during neurodevelopment,. Two new autosomal recessive mouse mutations, scrambler and yotari have been described that exhibit a phenotype identical to reeler. Here we report that scrambler and yotari arise from mutations in mdab1 (ref. 12), a mouse gene related to the Drosophila gene disabled ( dab ). Both scrambler and yotari mice express mutated forms of mdab1 messenger RNA and little or no mDab1 protein. mDab1 is a phosphoprotein that appears to function as an intracellular adaptor in protein kinase pathways. Expression analysis indicates that mdab1 is expressed in neuronal populations exposed to Reelin. The similar phenotypes of reeler, scrambler, yotari and mdab1 null mice indicate that Reelin and mDab1 function as signalling molecules that regulate cell positioning in the developing brain.

The cells and molecules that make a cerebellum

The molecular underpinnings of cerebellar development are being established through the identification of naturally occurring mutated genes and the knockout of other genes. Sets of genes expressed in the regions of the mes- and metencephalon have been shown to play a crucial role in specifying the cerebellar anlage. Other genes have been shown to be crucial to early granule-cell development, migration of Purkinje and granule cells, and neuron-glia interactions. However, the process of development will ultimately be understood in terms of cellular interactions and the roles that each cell type plays in the assembly of cerebellar structure. One of the most important interactions is between granule and Purkinje cells. This relationship has been shown to be crucial for the control of cell number, migration of neuroblasts and cell differentiation.

Consensus Paper: Pathological Role of the Cerebellum in Autism

There has been significant advancement in various aspects of scientific knowledge concerning the role of cerebellum in the etiopathogenesis of autism. In the current consensus paper, we will observe the diversity of opinions regarding the involvement of this important site in the pathology of autism. Recent emergent findings in literature related to cerebellar involvement in autism are discussed, including: cerebellar pathology, cerebellar imaging and symptom expression in autism, cerebellar genetics, cerebellar immune function, oxidative stress and mitochondrial dysfunction, GABAergic and glutamatergic systems, cholinergic, dopaminergic, serotonergic, and oxytocin-related changes in autism, motor control and cognitive deficits, cerebellar coordination of movements and cognition, gene–environment interactions, therapeutics in autism, and relevant animal models of autism. Points of consensus include presence of abnormal cerebellar anatomy, abnormal neurotransmitter systems, oxidative stress, cerebellar motor and cognitive deficits, and neuroinflammation in subjects with autism. Undefined areas or areas requiring further investigation include lack of treatment options for core symptoms of autism, vermal hypoplasia, and other vermal abnormalities as a consistent feature of autism, mechanisms underlying cerebellar contributions to cognition, and unknown mechanisms underlying neuroinflammation.

VAC14 nucleates a protein complex essential for the acute interconversion of PI3P and PI(3,5)P2 in yeast and mouse

The signalling lipid PI(3,5)P2 is generated on endosomes and regulates retrograde traffic to the trans‐Golgi network. Physiological signals regulate rapid, transient changes in PI(3,5)P2 levels. Mutations that lower PI(3,5)P2 cause neurodegeneration in human patients and mice. The function of Vac14 in the regulation of PI(3,5)P2 was uncharacterized previously. Here, we predict that yeast and mammalian Vac14 are composed entirely of HEAT repeats and demonstrate that Vac14 exerts an effect as a scaffold for the PI(3,5)P2 regulatory complex by direct contact with the known regulators of PI(3,5)P2: Fig4, Fab1, Vac7 and Atg18. We also report that the mouse mutant ingls (infantile gliosis) results from a missense mutation in Vac14 that prevents the association of Vac14 with Fab1, generating a partial complex. Analysis of ingls and two additional mutants provides insight into the organization of the PI(3,5)P2 regulatory complex and indicates that Vac14 mediates three distinct mechanisms for the rapid interconversion of PI3P and PI(3,5)P2. Moreover, these studies show that the association of Fab1 with the complex is essential for viability in the mouse.

PolymiRTS Database: linking polymorphisms in microRNA target sites with complex traits

Polymorphism in microRNA Target Site (PolymiRTS) database is a collection of naturally occurring DNA variations in putative microRNA target sites. PolymiRTSs may affect gene expression and cause variations in complex phenotypes. The database integrates sequence polymorphism, phenotype and expression microarray data, and characterizes PolymiRTSs as potential candidates responsible for the quantitative trait locus (QTL) effects. It is a resource for studying PolymiRTSs and their implications in phenotypic variations. PolymiRTS database can be accessed at .

Cerebellar Disorganization Characteristic of Reeler in Scrambler Mutant Mice Despite Presence of Reelin

Analysis of the molecular basis of neuronal migration in the mammalian CNS relies critically on the discovery and identification of genetic mutations that affect this process. Here, we report the detailed cerebellar phenotype caused by a new autosomal recessive neurological mouse mutation, scrambler (gene symbolscm). The scrambler mutation results in ataxic mice that exhibit several neuroanatomic defects reminiscent of reeler. The most obvious of these lies in the cerebellum, which is small and lacks foliation. Granule cells, although normally placed in an internal granule cell layer, are greatly reduced in number (∼20% of normal). Purkinje cells are also reduced in number, and the majority are located ectopically in deep cerebellar masses. There is a small population of Purkinje cells (∼5% of the total) that occupy a Purkinje cell layer between the molecular and granule cell layers. Despite this apparent disorganization of Purkinje cells, zebrin-positive and zebrin-negative parasagittal zones can be delineated. The ectopic masses of Purkinje cells are bordered by the extracellular matrix protein tenascin and by processes containing glial fibrillary acidic protein. Antibodies specific for these proteins also identify a novel midline raphe structure in both scrambler and reeler cerebellum that is not present in wild-type mice. Thus, in many respects, the scrambler cerebellum is identical to that of reeler. However, the scrambler locus has been mapped to a site distinct from that of reelin (Reln), the gene responsible for the reeler defect. Here we find that there are normal levels of Reln mRNA in scrambler brain and that reelin protein is secreted normally by scrambler cerebellar cells. These findings imply that the scrambler gene product may function in a molecular pathway critical for neuronal migration that is tightly linked to, but downstream of, reelin.

Anatomical evidence for a projection from the entorhinal cortex to the contralateral dentate gyrus of the rat

Abstract A relatively sparse direct projection from the entorhinal cortex to the rostral part of the contralateral dentate gyrus of the hippocampus has been demonstrated by the Fink-Heimer and autoradiographic techniques in normal rats. The fibers terminate in the outer two-thirds of the molecular layer, similar to the projection to the ipsilateral dentate gyrus. Thus extrinsic cortical input is bilaterally directed, further illustrating the principle of the bilaterality of hippocampal projections. A contralateral entorhinal projection has been reported previously only as a consequence of apparent axon sprouting following a unilateral entorhinal lesion. The demonstration of this projection in normal rats indicates the changes following recovery from unilateral entorhinal lesions need not involve extensive new fiber growth as had been previously hypothesized.

High-throughput behavioral phenotyping in the expanded panel of BXD recombinant inbred strains

Genetic reference populations, particularly the BXD recombinant inbred (BXD RI) strains derived from C57BL/6J and DBA/2J mice, are a valuable resource for the discovery of the bio‐molecular substrates and genetic drivers responsible for trait variation and covariation. This approach can be profitably applied in the analysis of susceptibility and mechanisms of drug and alcohol use disorders for which many predisposing behaviors may predict the occurrence and manifestation of increased preference for these substances. Many of these traits are modeled by common mouse behavioral assays, facilitating the detection of patterns and sources of genetic coregulation of predisposing phenotypes and substance consumption. Members of the Tennessee Mouse Genome Consortium (TMGC) have obtained phenotype data from over 250 measures related to multiple behavioral assays across several batteries: response to, and withdrawal from cocaine, 3,4‐methylenedioxymethamphetamine; “ecstasy” (MDMA), morphine and alcohol; novelty seeking; behavioral despair and related neurological phenomena; pain sensitivity; stress sensitivity; anxiety; hyperactivity and sleep/wake cycles. All traits have been measured in both sexes in approximately 70 strains of the recently expanded panel of BXD RI strains. Sex differences and heritability estimates were obtained for each trait, and a comparison of early (N = 32) and recent (N = 37) BXD RI lines was performed. Primary data are publicly available for heritability, sex difference and genetic analyses using the MouseTrack database, and are also available in GeneNetwork.org for quantitative trait locus (QTL) detection and genetic analysis of gene expression. Together with the results of related studies, these data form a public resource for integrative systems genetic analysis of neurobehavioral traits.

Genetics of the Hippocampal Transcriptome in Mouse: A Systematic Survey and Online Neurogenomics Resource

Differences in gene expression in the CNS influence behavior and disease susceptibility. To systematically explore the role of normal variation in expression on hippocampal structure and function, we generated an online microarray database for a diverse panel of strains of mice, including most common inbred strains and numerous recombinant inbred lines (www.genenetwork.org). Using this resource, coexpression networks for families of genes can be generated rapidly to test causal models related to function. The data set is optimized for quantitative trait locus (QTL) mapping and was used to identify over 5500 QTLs that modulate mRNA levels. We describe a wide variety of analyses and novel synthetic approaches that take advantage of this resource, and demonstrate how both the data and associated tools can be applied to the study of gene regulation in the hippocampus and relations to structure and function.

The weaver granuloprival phenotype is due to intrinsic action of the mutant locus in granule cells: Evidence from homozygous weaver chimeras

The weaver mutation (wv) causes a near total loss of midline granule cells in the mouse cerebellum. The cellular site of mutant locus action leading to the granuloprival phenotype was examined with experimental intraspecific and interspecific homozygous weaver chimeras. It was found that the granule cells which survived and successfully migrated to the internal granular layer of the chimeric cerebellum were all of the wild-type (non-wv) genotype. Using interspecies chimeras, it was determined that the genotype of Purkinje cells and Bergmann glia cells was apparently irrelevant to the survival of granule cells. It is concluded that granule cell death is most likely due to the wv locus acting intrinsically to the weaver granule cells, and not to another cellular site of gene action.