Biomedical subjects

Elizabeth M Simpson

Publications and source records attributed to Elizabeth M Simpson.

14 recordsLinked to original sources

PubMed2006

Hippi is essential for node cilia assembly and Sonic hedgehog signaling.

Hippi functions as an adapter protein that mediates pro-apoptotic signaling from poly-glutamine-expanded huntingtin, an established cause of Huntington disease, to the extrinsic cell death pathway. To explore other functions of Hippi we generated Hippi knock-out mice. This deletion causes randomization of the embryo turning process and heart looping, which are hallmarks of defective left-right (LR) axis patterning. We report that motile monocilia normally present at the surface of the embryonic node, and proposed to initiate the break in LR symmetry, are absent on Hippi-/- embryos. Furthermore, defects in central nervous system development are observed. The Sonic hedgehog (Shh) pathway is downregulated in the neural tube in the absence of Hippi, which results in failure to establish ventral neural cell fate. Together, these findings demonstrate a dual role for Hippi in cilia assembly and Shh signaling during development, in addition to its proposed role in apoptosis signal transduction in the adult brain under pathogenically stressful conditions.

Adaptor Proteins, Signal Transducing↗

PubMed2006

SAGE2Splice: unmapped SAGE tags reveal novel splice junctions.

Serial analysis of gene expression (SAGE) not only is a method for profiling the global expression of genes, but also offers the opportunity for the discovery of novel transcripts. SAGE tags are mapped to known transcripts to determine the gene of origin. Tags that map neither to a known transcript nor to the genome were hypothesized to span a splice junction, for which the exon combination or exon(s) are unknown. To test this hypothesis, we have developed an algorithm, SAGE2Splice, to efficiently map SAGE tags to potential splice junctions in a genome. The algorithm consists of three search levels. A scoring scheme was designed based on position weight matrices to assess the quality of candidates. Using optimized parameters for SAGE2Splice analysis and two sets of SAGE data, candidate junctions were discovered for 5%-6% of unmapped tags. Candidates were classified into three categories, reflecting the previous annotations of the putative splice junctions. Analysis of predicted tags extracted from EST sequences demonstrated that candidate junctions having the splice junction located closer to the center of the tags are more reliable. Nine of these 12 candidates were validated by RT-PCR and sequencing, and among these, four revealed previously uncharacterized exons. Thus, SAGE2Splice provides a new functionality for the identification of novel transcripts and exons. SAGE2Splice is available online at http://www.cisreg.ca.

Algorithms↗

PubMed2005

A mouse atlas of gene expression: large-scale digital gene-expression profiles from precisely defined developing C57BL/6J mouse tissues and cells.

We analyzed 8.55 million LongSAGE tags generated from 72 libraries. Each LongSAGE library was prepared from a different mouse tissue. Analysis of the data revealed extensive overlap with existing gene data sets and evidence for the existence of approximately 24,000 previously undescribed genomic loci. The visual cortex, pancreas, mammary gland, preimplantation embryo, and placenta contain the largest number of differentially expressed transcripts, 25% of which are previously undescribed loci.

Alternative Splicing↗

PubMed2005

Pathological aggression in "fierce" mice corrected by human nuclear receptor 2E1.

"Fierce" mice, homozygous for the deletion of nuclear receptor 2E1 (NR2E1), show abnormal brain-eye development and pathological aggression. To evaluate functional equivalency between mouse and human NR2E1, we generated mice transgenic for a genomic clone spanning the human NR2E1 locus and bred these animals to fierce mice deleted for the corresponding mouse gene. In fierce mutants carrying human NR2E1, structural brain defects were eliminated and eye abnormalities ameliorated. Excitingly, behavior in these "rescue" mice was indistinguishable from controls. Because no artificial promoter was used to drive transgene expression, promoter and regulatory elements within the human NR2E1 clone are functional in mouse. Normal behavior in rescue animals suggests that mechanisms underlying the behavioral abnormalities in fierce mice may also be conserved in humans. Our data support the hypothesis that variation at NR2E1 may contribute to human behavioral disorders. Use of this rescue paradigm with other genes will permit the direct evaluation of human genes hypothesized to play a causal role in psychiatric disease but for which evidence is lacking or equivocal.

Aggression↗

PubMed2005

Of mice and men: will the intersection of social science and genetics create new approaches for intimate partner violence?

The past two decades have yielded a recognition that intimate partner violence is ubiquitous. Although violence within relationships is bidirectional, there is acknowledgment that violence directed against women is more persistent and dangerous. Strategies for treatment of men have been largely unsuccessful, and studies of women centered approaches to prevention are in their infancy. An emerging concept in the brain-behavior field is the recognition of genetics as a powerful influence on aggressive and violent behaviors. Mouse models of human health and disease have facilitated our understanding of the role of genetics in the manifestation of these traits. There is a need to push the boundaries of research on intimate partner violence by adopting biosocial approaches to understand its causes.

Aggression↗

PubMed2004

Engineering embryonic stem cell derived glia for adenosine delivery.

Based on the anticonvulsant and neuroprotective properties of adenosine, and based on the long-term survival potential of stem cell derived brain implants, adenosine releasing stem cells may constitute a novel tool for the treatment of epilepsy. Pluripotency and unlimited self-renewal make embryonic stem (ES) cells a particularly versatile donor source for cell transplantation. With the aim to test the feasibility of a stem cell-based delivery system for adenosine, both alleles of adenosine kinase (ADK), the major adenosine-metabolizing enzyme, were disrupted by homologous recombination in ES cells. Adk-/- ES cells were subjected to a glial differentiation protocol and, as a result, gave rise to proliferating glial precursors, which could be further differentiated into mature astrocytes and oligodendrocytes. Thus, a lack of ADK does not compromise the glial differentiation potential of ES cells. The Adk-/- ES cells yielded glial populations with an adenosine release of up to 40.1 +/- 6.0 ng per 10(5) cells per hour, an amount considered to be sufficient for seizure suppression. Our findings indicate that Adk-/- ES cells constitute a potential source for therapeutic adenosine releasing grafts.

Adenosine↗

PubMed2004

Caspase-7 expanded function and intrinsic expression level underlies strain-specific brain phenotype of caspase-3-null mice.

Caspase-3-deficient mice of the 129S1/SvImJ (129) strain show severe brain development defects resulting in brain overgrowth and perinatal lethality, whereas on the C57BL/6J (B6) background, these mice develop normally. We therefore sought to identify the strain-dependent ameliorating gene. We biochemically isolated caspase-7 from B6-caspase-3-null (Casp3-/-) tissues as being the enzyme with caspase-3-like properties and capability of performing a caspase-3 surrogate function, apoptotic DNA fragmentation. Moreover, we show that, in contrast to the human enzymes, mouse caspase-7 is as efficient as caspase-3 at cleaving and thus inactivating ICAD (inhibitor of caspase-activated DNase), the inhibitor of apoptotic DNA fragmentation. Low levels of caspase-7 expression and activation correlate with lack of DNA fragmentation in 129-Casp3-/- apoptotic precursor neurons, whereas B6-Casp3-/- cells, which can fragment their DNA, show higher levels of caspase-7 expression and activation. The amount of caspase-7 activation in apoptotic precursor neurons is independent of the presence of caspase-3. Together, our findings demonstrate for the first time a strong correlation between caspase-7 activity, normal brain development, and apoptotic DNA fragmentation in Casp3-/- mice.

Animals↗

PubMed2004

Unexpected embryonic stem (ES) cell mutations represent a concern in gene targeting: lessons from "fierce" mice.

The exceptional value of gene targeting technology to generate mouse models of human disease exists under the shadow of potential genetic errors. We previously observed an unexpected brain-behavior phenotype that resulted from a gene-targeting experiment designed to delete the Zfa gene. Given that the transcription of Zfa is restricted to the germ cell lineage of adult testis, it was both a surprise and a concern when the resulting mice had a phenotype present in both sexes that included abnormal brains and violent behavior. We hypothesized that an unrelated mutation may have been responsible for the unexpected phenotype. Here we show that the single gene mutation, Nr2e1(frc) (fierce), which was responsible for the brain-behavior phenotype, existed in the embryonic stem (ES) cell even before the derivation of the Zfa knockout mice. Our work thus highlights a concern in gene targeting, namely, that ES cells can harbor unexpected mutations, which can lead to genotype-phenotype misattribution. Based on our findings, we caution the gene-targeting community to use low-passage ES cells, to characterize mice derived from more than one independently targeted ES cell clone, and to backcross mice to allow for segregation of distant but linked mutations.

Amino Acid Sequence↗

PubMed2003

Selective striatal neuronal loss in a YAC128 mouse model of Huntington disease.

An expanded CAG repeat is the underlying genetic defect in Huntington disease, a disorder characterized by motor, psychiatric and cognitive deficits and striatal atrophy associated with neuronal loss. An accurate animal model of this disease is crucial for elucidation of the underlying natural history of the illness and also for testing experimental therapeutics. We established a new yeast artificial chromosome (YAC) mouse model of HD with the entire human HD gene containing 128 CAG repeats (YAC128) which develops motor abnormalities and age-dependent brain atrophy including cortical and striatal atrophy associated with striatal neuronal loss. YAC128 mice exhibit initial hyperactivity, followed by the onset of a motor deficit and finally hypokinesis. The motor deficit in the YAC128 mice is highly correlated with striatal neuronal loss, providing a structural correlate for the behavioral changes. The natural history of HD-related changes in the YAC128 mice has been defined, demonstrating the presence of huntingtin inclusions after the onset of behavior and neuropathological changes. The HD-related phenotypes of the YAC128 mice show phenotypic uniformity with low inter-animal variability present, which together with the age-dependent striatal neurodegeneration make it an ideal mouse model for the assessment of neuroprotective and other therapeutic interventions.

Age Factors↗

PubMed2003

Metaphase FISHing of transgenic mice recommended: FISH and SKY define BAC-mediated balanced translocation.

The evolving trend to use larger transgenes and their associated increased chance of unexpected genetic events mandates more careful characterization of transgenic mice. In characterizing our five new mouse strains transgenic for the BAC, bEMS4, we have identified the highest copy number reported to date: the stable incorporation of approximately 40 copies of a 194-kb expressed transgene in a single insertion site. We caution, however, that standard molecular techniques failed to identify a balanced translocation in another strain, and an inappropriate site of insertion in a third. Molecular cytogenetic analysis using metaphase FISH was the minimum level of characterization needed to reveal these unexpected genetic events. In addition, we combined FISH and SKY to identify the transgene at the breakpoints of the balanced translocation, t(3;9). This is the first description of a BAC-mediated chromosomal rearrangement and the first application of SKY to identify transgene-induced chromosomal rearrangements.

Animals↗

PubMed2003

Retroposon compensatory mechanism hypothesis not supported: Zfa knockout mice are fertile.

It is hypothesized that autosomal retroposons compensate for the loss of their inactivated essential X-chromosome progenitors during spermatogenesis. Here we test this Retroposon Compensatory Mechanism (RCM) hypothesis using the Zfy gene family. The mouse autosomal retroposon Zfa is expressed in testes at the same developmental time points at which Zfx levels decline, which correspond to the time of male sex chromosome inactivation, suggesting that Zfa may compensate for the loss of Zfx during spermatogenesis. We examined the effect of Zfa-targeted mutagenesis on spermatogenesis in three genetically distinct mouse strains. Surprisingly, Zfa knockout mice showed no detectable fertility, sperm count, or testes morphology defects. We therefore conclude that Zfa is not an essential gene for spermatogenesis and fertility. This surprising finding now challenges the RCM hypothesis at least for the Zfy gene family. It also forces us to reevaluate the original data underpinning the RCM hypothesis for this family and to propose alternative hypotheses.

Aging↗

PubMed2002

Fierce: a new mouse deletion of Nr2e1; violent behaviour and ocular abnormalities are background-dependent.

A new spontaneous mouse mutation named fierce (frc) is deleted for the nuclear receptor Nr2e1 gene (also known as Tlx, mouse homolog of Drosophila tailless). The fierce mutation is genetically and phenotypically similar to Nr2e1 targeted mutations previously studied on segregating genetic backgrounds. However, we have characterized the fierce brain, eye, and behavioural phenotypes on three defined genetic backgrounds (C57BL/6J, 129P3/JEms, and B6129F1). The data revealed many novel and background-dependent phenotypic characteristics. Whereas abnormalities in brain development, hypoplasia of cerebrum and olfactory lobes, were consistent on all three backgrounds, our novel finding of enlarged ventricles in 100% and overt hydrocephalus in up to 30% of fierce mice were unique to the C57BL/6J background. Developmental eye abnormalities were also background-dependent with B6129F1-frc mice having less severe thinning of optic layers and less affected electroretinogram responses. Impaired regression of hyaloid vessels was observed in all backgrounds. Furthermore, retinal vessels were deficient in size and number in 129P3/JEms-frc and B6129F1-frc mice but almost entirely absent in C57BL/6J-frc mice. We present the first standardized behavioural tests conducted on Nr2e1 mutant mice and show that C57BL/6J-frc and B6129F1-frc mice have deficits in sensorimotor assays and are hyperaggressive in both sexes and backgrounds. However, C57BL/6J-frc mice were significantly more aggressive than B6129F1-frc mice. Overall, this extensive characterization of the fierce mutation is essential to its application for the study of behavioural, and brain and eye developmental disorders. In addition, the background-dependent differences revealed will enable the identification of important genetic modifiers.

Aggression↗

PubMed2002

Novel Sxr(a) ES cell line offers hope for Y chromosome gene-targeted mice.

A mouse targeted for a Y Chromosome gene has not been reported. Because the Y Chromosome is present in only one copy, and most of its genes are critical for germ cell development, such a mouse would likely be infertile. Thus, we describe a new reproductive strategy to enable transmission of targeted Y Chromosome genes to subsequent generations. The strategy uses two segregating copies of Y Chromosome genes to mimic the autosomal condition. To achieve this, we developed a new embryonic stem cell line from the XYSxr(a) mouse, which carries a duplication of the gene-rich Y Chromosome short arm. Importantly, we demonstrate germ line transmission of the YSxr(a) chromosome and describe this significant new tool as a practical solution to enable reproduction in mice targeted for Y Chromosome genes.

Animals↗

PubMed2002

Novel vertebrate genes and putative regulatory elements identified at kidney disease and NR2E1/fierce loci.

Fierce (frc) mice are deleted for nuclear receptor 2e1 (Nr2e1), and exhibit cerebral hypoplasia, blindness, and extreme aggression. To characterize the Nr2e1 locus, which may also contain the mouse kidney disease (kd) allele, we compared sequence from human, mouse, and the puffer fish Fugu rubripes. We identified a novel gene, c222389, containing conserved elements in noncoding regions. We also discovered a novel vertebrate gene conserved across its length in prokaryotes and invertebrates. Based on a dramatic upregulation in lactating breast, we named this gene lactation elevated-1 (LACE1). Two separate 100-bp elements within the first NR2E1 intron were virtually identical between the three species, despite an estimated 450 million years of divergent evolution. These elements represent strong candidates for functional NR2E1 regulatory elements in vertebrates. A high degree of conservation across NR2E1 combined with a lack of interspersed repeats suggests that an array of regulatory elements embedded within the gene is required for proper gene expression.

Alternative Splicing↗