DBA/2J genetic background exacerbates spontaneous lethal seizures but lessens amyloid deposition in a mouse model of Alzheimer's disease.

Alzheimer's disease (AD) is a leading cause of dementia in the elderly and is characterized by amyloid plaques, neurofibrillary tangles (NFTs) and neuronal dysfunction. Early onset AD (EOAD) is commonly caused by mutations in amyloid precursor protein (APP) or genes involved in the processing of APP including the presenilins (e.g. PSEN1 or PSEN2). In general, mouse models relevant to EOAD recapitulate amyloidosis, show only limited amounts of NFTs and neuronal cell dysfunction and low but significant levels of seizure susceptibility. To investigate the effect of genetic background on these phenotypes, we generated APPswe and PSEN1de9 transgenic mice on the seizure prone inbred strain background, DBA/2J. Previous studies show that the DBA/2J genetic background modifies plaque deposition in the presence of mutant APP but the impact of PSEN1de9 has not been tested. Our study shows that DBA/2J.APPswePSEN1de9 mice are significantly more prone to premature lethality, likely to due to lethal seizures, compared to B6.APPswePSEN1de9 mice-70% of DBA/2J.APPswePSEN1de9 mice die between 2-3 months of age. Of the DBA/2J.APPswePSEN1de9 mice that survived to 6 months of age, plaque deposition was greatly reduced compared to age-matched B6.APPswePSEN1de9 mice. The reduction in plaque deposition appears to be independent of microglia numbers, reactive astrocytosis and complement C5 activity.

Kidney adysplasia and variable hydronephrosis, a new mutation affecting the odd-skipped related 1 gene in the mouse, causes variable defects in kidney development and hydronephrosis.

Many genes, including odd-skipped related 1 (Osr1), are involved in regulation of mammalian kidney development. We describe here a new recessive mutation (kidney adysplasia and variable hydronephrosis, kavh) in the mouse that leads to downregulation of Osr1 transcript, causing several kidney defects: agenesis, hypoplasia, and hydronephrosis with variable age of onset. The mutation is closely associated with a reciprocal translocation, T(12;17)4Rk, whose Chromosome 12 breakpoint is upstream from Osr1. The kavh/kavh mutant provides a model to study kidney development and test therapies for hydronephrosis.

3-Dimensional histological reconstruction and imaging of the murine pancreas.

Visualization of important disease-driving tissues in their native morphological state, such as the pancreas, given its importance in glucose homeostasis and diabetes, provides critical insight into the etiology and progression of disease and our understanding of how cellular changes impact disease severity. Numerous challenges to maintaining tissue morphology exist when one attempts to preserve or to recreate such tissues for histological evaluation. We have overcome many of these challenges and have developed new methods for visualizing the whole murine pancreas and single islets of Langerhans in an effort to gain a better understanding of how islet cell volume, spatial distribution, and vascularization are altered as diabetes progresses. These methods are readily adaptable without requirement for costly specialized equipment, such as magnetic resonance imaging, positron emission tomography, or computed tomography, and can be used to provide additional robust analysis of diabetes susceptibility in mouse models of Type 1 and Type II diabetes.

Complex oncogenic translocations with gene amplification are initiated by specific DNA breaks in lymphocytes.

Chromosomal instability is a hallmark of many tumor types. Complex chromosomal rearrangements with associated gene amplification, known as complicons, characterize many hematologic and solid cancers. Whereas chromosomal aberrations, including complicons, are useful diagnostic and prognostic cancer markers, their molecular origins are not known. Although accumulating evidence has implicated DNA double-strand break repair in suppression of oncogenic genome instability, the genomic elements required for chromosome rearrangements, especially complex lesions, have not been elucidated. Using a mouse model of B-lineage lymphoma, characterized by complicon formation involving the immunoglobulin heavy chain (Igh) locus and the c-myc oncogene, we have now investigated the requirement for specific genomic segments as donors for complex rearrangements. We now show that specific DNA double-strand breaks, occurring within a narrow segment of Igh, are necessary to initiate complicon formation. By contrast, neither specific DNA breaks nor the powerful intronic enhancer Emu are required for complicon-independent oncogenesis. This study is the first to delineate mechanisms of complex versus simple instability and the first to identify specific chromosomal elements required for complex chromosomal aberrations. These findings will illuminate genomic cancer susceptibility and risk factors.

A mouse model for Meckel syndrome type 3.

Meckel-Gruber syndrome type 3 (MKS3; OMIM 607361) is a severe autosomal recessive disorder characterized by bilateral polycystic kidney disease. Other malformations associated with MKS3 include cystic changes in the liver, polydactyly, and brain abnormalities (occipital encephalocele, hydrocephalus, and Dandy Walker-type cerebellar anomalies). The disorder is hypothesized to be caused by defects in primary cilia. In humans, the underlying mutated gene, TMEM67, encodes transmembrane protein 67, also called meckelin (OMIM 609884), which is an integral protein of the renal epithelial cell and membrane of the primary cilium. Here, we describe a spontaneous deletion of the mouse ortholog, Tmem67, which results in polycystic kidney disease and death by 3 wk after birth. Hydrocephalus also occurs in some mutants. We verified the mutated gene by transgenic rescue and characterized the phenotype with microcomputed tomography, histology, scanning electron microscopy, and immunohistochemistry. This mutant provides a mouse model for MKS3 and adds to the growing set of mammalian models essential for studying the role of the primary cilium in kidney function.

Synaptojanin 1-linked phosphoinositide dyshomeostasis and cognitive deficits in mouse models of Down's syndrome.

Phosphatidylinositol-4,5-bisphosphate [PtdIns(4,5)P(2)] is a signaling phospholipid implicated in a wide variety of cellular functions. At synapses, where normal PtdIns(4,5)P(2) balance is required for proper neurotransmission, the phosphoinositide phosphatase synaptojanin 1 is a key regulator of its metabolism. The underlying gene, SYNJ1, maps to human chromosome 21 and is thus a candidate for involvement in Down's syndrome (DS), a complex disorder resulting from the overexpression of trisomic genes. Here, we show that PtdIns(4,5)P(2) metabolism is altered in the brain of Ts65Dn mice, the most commonly used model of DS. This defect is rescued by restoring Synj1 to disomy in Ts65Dn mice and is recapitulated in transgenic mice overexpressing Synj1 from BAC constructs. These transgenic mice also exhibit deficits in performance of the Morris water maze task, suggesting that PtdIns(4,5)P(2) dyshomeostasis caused by gene dosage imbalance for Synj1 may contribute to brain dysfunction and cognitive disabilities in DS.

Chromosomal inversion discovered in C3H/HeJ mice.

Mice of the inbred mouse strain C3H/HeJ have been shown to be homozygous for a chromosomal inversion on Chromosome (Chr) 6. The inversion encompasses about 20% of the chromosome from approximately 73 Mb to approximately 116 Mb. The importance of this finding is that linkage crosses using C3H/HeJ will show no recombination in this region of Chr 6. The inversion has no apparent effect on the phenotype of C3H/HeJ mice and its presence should not affect biological studies; however, use of C3H/HeJ mice for genetic analysis of Chr 6 should be avoided or the results interpreted with the inversion in mind. The inversion has been named In(6)1J (inversion Chr 6, Jackson 1).