Modeling Partial Monosomy for Human Chromosome 21q11.2-q21.1 Reveals Haploinsufficient Genes Influencing Behavior and Fat Deposition

Haploinsufficiency of part of human chromosome 21 results in a rare condition known as Monosomy 21. This disease displays a variety of clinical phenotypes, including intellectual disability, craniofacial dysmorphology, skeletal and cardiac abnormalities, and respiratory complications. To search for dosage-sensitive genes involved in this disorder, we used chromosome engineering to generate a mouse model carrying a deletion of the Lipi–Usp25 interval, syntenic with 21q11.2-q21.1 in humans. Haploinsufficiency for the 6 genes in this interval resulted in no gross morphological defects and behavioral analysis performed using an open field test, a test of anxiety, and tests for social interaction were normal in monosomic mice. Monosomic mice did, however, display impaired memory retention compared to control animals. Moreover, when fed a high-fat diet (HFD) monosomic mice exhibited a significant increase in fat mass/fat percentage estimate compared with controls, severe fatty changes in their livers, and thickened subcutaneous fat. Thus, genes within the Lipi–Usp25 interval may participate in memory retention and in the regulation of fat deposition

Generation of the Sotos syndrome deletion in mice

Haploinsufficiency of the human 5q35 region spanning the NSD1 gene results in a rare genomic disorder known as Sotos syndrome (Sotos), with patients displaying a variety of clinical features, including pre- and postnatal overgrowth, intellectual disability, and urinary/renal abnormalities. We used chromosome engineering to generate a segmental monosomy, i.e., mice carrying a heterozygous 1.5-Mb deletion of 36 genes on mouse chromosome 13 (4732471D19Rik-B4galt7), syntenic with 5q35.2–q35.3 in humans (Df(13)Ms2Dja(+/−) mice). Surprisingly Df(13)Ms2Dja(+/−) mice were significantly smaller for their gestational age and also showed decreased postnatal growth, in contrast to Sotos patients. Df(13)Ms2Dja(+/−) mice did, however, display deficits in long-term memory retention and dilation of the pelvicalyceal system, which in part may model the learning difficulties and renal abnormalities observed in Sotos patients. Thus, haploinsufficiency of genes within the mouse 4732471D19Rik–B4galt7 deletion interval play important roles in growth, memory retention, and the development of the renal pelvicalyceal system. ELECTRONIC SUPPLEMENTARY MATERIAL: The online version of this article (doi:10.1007/s00335-012-9416-0) contains supplementary material, which is available to authorized users

DNA Methylation of α-Synuclein Intron 1 Is Significantly Decreased in the Frontal Cortex of Parkinson’s Individuals with GBA1 Mutations

Parkinson’s disease (PD) is a common movement disorder, estimated to affect 4% of individuals by the age of 80. Mutations in the glucocerebrosidase 1 (GBA1) gene represent the most common genetic risk factor for PD, with at least 7–10% of non-Ashkenazi PD individuals carrying a GBA1 mutation (PD-GBA1). Although similar to idiopathic PD, the clinical presentation of PD-GBA1 includes a slightly younger age of onset, a higher incidence of neuropsychiatric symptoms, and a tendency to earlier, more prevalent and more significant cognitive impairment. The pathophysiological mechanisms underlying PD-GBA1 are incompletely understood, but, as in idiopathic PD, α-synuclein accumulation is thought to play a key role. It has been hypothesized that this overexpression of α-synuclein is caused by epigenetic modifications. In this paper, we analyze DNA methylation levels at 17 CpG sites located within intron 1 and the promoter of the α-synuclein (SNCA) gene in three different brain regions (frontal cortex, putamen and substantia nigra) in idiopathic PD, PD-GBA1 and elderly non-PD controls. In all three brain regions we find a tendency towards a decrease in DNA methylation within an eight CpG region of intron 1 in both idiopathic PD and PD-GBA1. The trend towards a reduction in DNA methylation was more pronounced in PD-GBA1, with a significant decrease in the frontal cortex. This suggests that PD-GBA1 and idiopathic PD have distinct epigenetic profiles, and highlights the importance of separating idiopathic PD and PD-GBA1 cases. This work also provides initial evidence that different genetic subtypes might exist within PD, each characterized by its own pathological mechanism. This may have important implications for how PD is diagnosed and treated

DNA Methylation of α-Synuclein Intron 1 Is Significantly Decreased in the Frontal Cortex of Parkinson’s Individuals with <i>GBA1</i> Mutations

Parkinson’s disease (PD) is a common movement disorder, estimated to affect 4% of individuals by the age of 80. Mutations in the glucocerebrosidase 1 (GBA1) gene represent the most common genetic risk factor for PD, with at least 7–10% of non-Ashkenazi PD individuals carrying a GBA1 mutation (PD-GBA1). Although similar to idiopathic PD, the clinical presentation of PD-GBA1 includes a slightly younger age of onset, a higher incidence of neuropsychiatric symptoms, and a tendency to earlier, more prevalent and more significant cognitive impairment. The pathophysiological mechanisms underlying PD-GBA1 are incompletely understood, but, as in idiopathic PD, α-synuclein accumulation is thought to play a key role. It has been hypothesized that this overexpression of α-synuclein is caused by epigenetic modifications. In this paper, we analyze DNA methylation levels at 17 CpG sites located within intron 1 and the promoter of the α-synuclein (SNCA) gene in three different brain regions (frontal cortex, putamen and substantia nigra) in idiopathic PD, PD-GBA1 and elderly non-PD controls. In all three brain regions we find a tendency towards a decrease in DNA methylation within an eight CpG region of intron 1 in both idiopathic PD and PD-GBA1. The trend towards a reduction in DNA methylation was more pronounced in PD-GBA1, with a significant decrease in the frontal cortex. This suggests that PD-GBA1 and idiopathic PD have distinct epigenetic profiles, and highlights the importance of separating idiopathic PD and PD-GBA1 cases. This work also provides initial evidence that different genetic subtypes might exist within PD, each characterized by its own pathological mechanism. This may have important implications for how PD is diagnosed and treated

Generating a 1.6 Mb deletion between the <i>Lipi</i> and <i>Usp25</i> loci.

<p>(A) The targeting vectors contain a <i>loxP</i> site (arrowhead), a selectable antibiotic resistance gene (<i>N</i> (neomycin) or <i>P</i> (puromycin)), a coat color marker (<i>Ty</i> or <i>Ag</i>) and part of the <i>Hprt</i> gene (5′ or 3′) were targeted as shown. The colored boxes (green and red) indicate the location of the probes (5′ and 3′, respectively) used for Southern blotting (B) The targeting events were confirmed by Southern blot analysis showing an additional <i>Stu</i>I fragment of 17 kb compared with the wildtype allele (15 kb) for the <i>Lipi</i> locus and an additional <i>BamH</i>I fragment of 22.6 kb compared with the wildtype allele (12 kb) for the <i>Usp25</i> locus. B, <i>BamH</i>I; S, <i>Stu</i>I; P, puromycin; N, neomycin; Ty, <i>Tyrosinase</i>; Ag, <i>Agouti</i>. (C) Interphase FISH analysis with BAC probes that map in the region of the deletion (red) and outside (green). Chromosomes from the ES cells double-targeted in <i>cis</i> (<i>Ms1Dja/+</i>) showed two green and only red signal due to the deletion of the <i>Lipi–Usp25</i> region, while chromosomes from the wildtype ES cells showed two green and two red signals.</p

Elevated plus maze test.

<p>(<b>A</b>) Percentage of time spent in the open arms. (<b>B</b>) Number of entries into the open arms. (<b>C</b>) Number of entries into the closed arms. Both monosomic (<i>Ms1Dja/+</i>, n = 12) and control (<i>+/+</i>, n = 12) mice spent similar amount of time in the open arms and had comparable number of entries into the open and closed arms. Tested with two-tailed Student's <i>t</i>-test. The error bars represent the standard error of the mean.</p

Fat percentage estimate of 14-week old control and monosomic mice fed a high-fat diet.

<p>DEXA results showing fat percentage estimate in 14-week old male (n = 7) and female (n = 7) control (<i>+/+</i>) and male (n = 7) and female (n = 6) monosomic (<i>Ms1Dja/+</i>) littermates fed a high-fat diet. Asterisks indicate statistical significance (two-tailed Student's <i>t</i>-test). The error bars represent the standard deviation of the measurements.</p

Schematic representation of HSA21 and the syntenic region on MMU16.

<p>The endpoints of the syntenic regions are indicated (<i>Lipi</i> and <i>Usp25</i>). Genes that map to the human 21q11.2-q21.1 region (NCBI build h36) and the C3.1 band on MMU16 (NCBI build m37) are listed. Studies describing partial Monosomy 21 patients with deletions involving the 21q11.2-q21.1 region (as indicated by the length of the black line) are shown.</p

Analysis of high-fat diet-fed monosomic mice at different ages.

<p>DEXA results showing (<b>A</b>) fat percentage estimate and (<b>B</b>) body weight measurements in 8-, 14- and 25-week old male (n = 8, n = 7 and n = 8, respectively) and female (n = 8, n = 7 and n = 10, respectively) control (<i>+/+</i>) and male (n = 9, n = 7 and n = 7, respectively) and female (n = 10, n = 6 and n = 9, respectively) monosomic (<i>Ms1Dja/+</i>) littermates fed a high-fat diet. Asterisks indicate statistical significance (two-tailed Student's <i>t</i>-test). The error bars represent the standard deviation of the measurements. (<b>C</b>) Photos of 25-week old male and female control (+/+) and monosomic (<i>Ms1Dja/+</i>) littermates fed a high-fat diet. (<b>D</b>) DEXA results showing lean mass measurements in 25-week old male (n = 8) and female (n = 10) control (<i>+/+</i>) and male (n = 7) and female (n = 9) monosomic (<i>Ms1Dja/+</i>) littermates fed a high-fat diet. Analyzed with two-tailed Student's <i>t</i>-test. The error bars represent the standard deviation of the measurements. (<b>E</b>) Haematoxylin and eosin-stained liver and skin sections from 25-week old wildtype (+/+) and monosomic (<i>Ms1Dja/+</i>) littermates fed a high-fat diet. Note markedly increased number and size of adipose cells in liver sections from monosomic (<i>Ms1Dja/+</i>) mice compared to wildtype (+/+) littermates (highlighted by black arrows). Images are representative and taken at ×100 magnification.</p