CGG-repeat expansion in FMR1 is not associated with amyotrophic lateral sclerosis

Recently, repeat expansions in several genes have been shown to cause or be associated with amyotrophic lateral sclerosis (ALS). It has been demonstrated that an intronic hexanucleotide repeat expansion in C9ORF72 is a major cause of both familial (approximately 40%) and sporadic (approximately 5%) ALS, as well as frontotemporal dementia (FTD). In addition, a CAG-repeat expansion in exon 1 of ATXN2, otherwise known to cause spinocerebellar ataxia type 2, has been identified as a major risk factor for sporadic ALS. Intermediate repeat expansions in the fragile X mental retardation 1 (FMR1) gene (55-200 repeats) are known to cause fragile X-associated premature ovarian insufficiency [(FX)POI; female carriers] or fragile X-associated tremor/ataxia syndrome (FXTAS; male carriers) by CGG-mediated RNA toxicity. The present investigation involves screening FMR1 repeat length in 742 sporadic ALS patients and 792 matched controls. Our conclusion is that FMR1 repeat expansions are not associated with ALS.     

雌性Fmr1基因敲除小鼠生殖功能的初步研究

目的 初步研究敲除Fmr1基因对动物生殖功能的影响.方法 6～8周龄雌性Fmr1基因敲除小鼠24只,分为对照组、春季超排组和冬季超排组,每组8只,进行超排,用放射免疫分析法测定超排前后血清雌二醇(E2)、孕酮(P)、促黄体生成素(LH)和促卵泡生成素(FSH)含量,以及不同季节的超排卵数,并进行统计学处理和分析.结果 超排后小鼠血清中P和LH含量明显增加[(24.43±13.33)比(1.60±0.46);(173.86±112.09)比(0.36±0.23),P＜0.01].与冬季(11.44±5.93)比较,春季(37.25±13.91)的超排卵数明显增加(P＜0.01).结论 雌性Fmr1基因敲除小鼠的生殖系统功能没有明显异常.与正常小鼠一样,Frm 1基因敲除小鼠机体内P和LH的分泌随动物的生理发育时期而变化.其超排效果随季节而有显著不同.     

Deletion of Prdm8 impairs development of upper‐layer neocortical neurons

Upper‐layer (UL) neocortical neurons are the most prominent distinguishing features of the mammalian neocortex compared with those of the avian dorsal cortex and are vastly expanded in primates. However, little is known about the identities of the genes that control the specification of UL neurons. Here, we found that Prdm8, a member of the PR (PRDI‐BF1 and RIZ homology) domain protein family, was specifically expressed in the postnatal UL neocortex, particular those in late‐born RORß‐positive layer IV neurons. We generated homozygous Prdm8 knockout (Prdm8 KO) mice and found that the deletion of Prdm8 causes growth retardation and a reduced brain weight, although the brain weight‐to‐body weight ratio is unchanged at postnatal day 8 (P8). Immunohistochemistry showed that the relative UL thickness, but not the thickness of the deep layer (DL), was significantly reduced in Prdm8 KO mice compared with wild‐type (WT) mice. In addition, we found that a number of late‐born Brn2‐positive UL neurons were significantly decreased in Prdm8 KO mice. To identify genes regulated by Prdm8 during neocortical development, we compared expression profiling analysis in Prdm8 KO and WT mice, and identified some candidate genes. These results suggest that the proper expression of Prdm8 is required for the normal development and construction of UL neurons in the mammalian neocortex.     

Fmr1 knockout mouse has a distinctive strain-specific learning impairment

The Fmr1 gene knockout mouse is a model for the human Fragile X mental retardation syndrome. Fmr1 knockout mice with a C57BL/6-129/OlaHsd hybrid background have been reported to have only a very mild deficiency in learning the Morris water maze task. We compared the effect of this knockout mutation on learning in mice with either an FVB/N-129/OlaHsd hybrid background or a C57BL/6 background. When FVB-129 mice were tested in a cross-shaped water maze task, the knockout mice showed a pronounced deficiency in their ability to learn the position of a hidden escape platform in comparison to normal littermates. In contrast, knockout mice with a C57BL/6 background learned the maze just as well as their normal littermates. Fear conditioning did not reveal differences between knockout and normal mice in either background.These results show that silencing the Fmr1 gene clearly interfered with learning a specific visuospatial task in FVB/N-129 hybrid mice but not in C57BL/6 mice. The strain dependence may model the influence of genetic background in the human Fragile X syndrome.     

Diethylhexyl phthalate exposure impairs follicular development and affects oocyte maturation in the mouse

Diethylhexyl phthalate (DEHP) is an estrogen‐like compound widely used as a commercial plasticizer and present in medical devices, tubing, food containers and packaging. It is considered an endocrine disruptor and studies on experimental animals showed that exposure to DEHP can alter the function of several organs including liver, kidneys, lungs and reproductive system, particularly the developing testes of prenatal and neonatal males. Exposure to DEHP has been proposed as a potential human health hazard. This study assessed the effects of DEHP on folliculogenesis and oocyte maturation using the mouse as the experimental model. Newborn female mice were hypodermically injected with DEHP at doses of 20 and 40 μg/kg per body weight following different exposure regimens during the weaning period. We found that DEHP altered both folliculogenesis and oocyte development. In particular, DEHP exposure significantly decreased the number of the primordial follicles at pubertal and adult age by possibly accelerating the rate of follicle recruitment dynamics, reduced and/or delayed the level of imprinted gene methylation in the oocytes and increased metaphase II spindle abnormalities in oocytes matured in vitro. Furthermore, the weight of pups and litter size of mothers exposed to DEHP were significantly lower than controls. Finally, the number of primordial follicles appeared significantly reduced also in the F1 offspring at the adult age. These results show that DEHP may have a number of adverse effects on oogenesis, especially when exposure occurs during early postnatal age, arising concerns about the exposure of human female infants and children to this compound. Environ. Mol. Mutagen. 54:354–361, 2013. © 2013 Wiley Periodicals, Inc.     

CGG-repeat polymorphism of the BCR gene rules out predisposing alleles leading to the philadelphia chromosome

The Philadelphia Chromosome (Ph) is associated with leukemia, most frequently of the chronic myelogenous variety. The Ph chromosome is a translocation Chromosome which gains oncogenic potential through the fusion of the ABL oncogene of chromosome 9 with the BCR gene of chromosome 22. The Ph is believed to arise from random chromosome rearrangement with a subsequent selective advantage of the malignant cell line. However, alleles may be present in the population which predispose toward this specific rearrangement. We used a highly polymorphic CGG-repeat polymorphism within the first exon of the BCR gene to determine BCR allele frequencies among 26 leukemia patients with the Ph chromosome and 63 control individuals. Eight BCR alleles of variable CGG-repeat length were present in both groups at statistically similar frequencies and in Hardy-Weinberg equilibrium. We therefore concluded that there are no alleles of the BCR gene that have a major predisposing influence on the development of the ph chromosome and subsequent leukemia Genes Chrom Cancer 9:141-144 (1994). Inc.© 1994 Wiley-Liss, Inc.     

Infant Temperament in the FMR1 Premutation and Fragile X Syndrome

Although temperament has been studied for decades as a predictor of psychopathology in the general population, examining temperament in neurogenetic groups has unique potential to inform the genetic and biological factors that may confer risk for psychopathology in later development. The present study examined early temperament in two heritable neurogenetic conditions associated with atypical CGG repeat expansions on the FMR1 gene: the FMR1 premutation (FXpm; 55–200 repeats) and fragile X syndrome (FXS; > 200 repeats). We focus specifically on the FXpm, as the condition is highly prevalent (1:209–291 female individuals, 1:430–855 male individuals) and has been preliminarily associated with increased risk for pediatric psychopathology, including attention problems, autism, and anxiety. In contrast, FXS is a low-incidence disorder (1:7,143 males, 1:11,111 females) often associated with intellectual disability and severe co-occurring psychosocial conditions, particularly in male individuals. Given information on infant clinical phenotypes in the FXpm and FXS is sparse, we aimed to characterize parent-reported infant temperament in infants with the FXpm (n = 22) relative to FXS (n = 24) and controls (n = 24) assessed on 1 to 3 occasions each. Temperament in infants with the FXpm largely fell between TD and FXS groups, with trends toward suppressed negative affect in younger participants, similar to lower negative affect previously reported in FXS. The FXS group consistently demonstrated lower negative affect and surgency than TD controls. These data suggest that FMR1 gene mutations are associated with atypical temperament that emerges as early as infancy, particularly among infants with FXS, warranting further study of whether temperament may index emergent clinical risks in these populations.     

Early postnatal plasticity in neocortex of Fmr1 knockout mice

Fragile X syndrome is produced by a defect in a single X-linked gene, called Fmr1, and is characterized by abnormal dendritic spine morphologies with spines that are longer and thinner in neocortex than those from age-matched controls. Studies using Fmr1 knockout mice indicate that spine abnormalities are especially pronounced in the first month of life, suggesting that altered developmental plasticity underlies some of the behavioral phenotypes associated with the syndrome. To address this issue, we used intracellular recordings in neocortical slices from early postnatal mice to examine the effects of Fmr1 disruption on two forms of plasticity active during development. One of these, long-term potentiation of intrinsic excitability, is intrinsic in expression and requires mGluR5 activation. The other, spike timing-dependent plasticity, is synaptic in expression and requires N-methyl-d-aspartate receptor activation. While intrinsic plasticity was normal in the knockout mice, synaptic plasticity was altered in an unusual and striking way: long-term depression was robust but long-term potentiation was entirely absent. These findings underscore the ideas that Fmr1 has highly selective effects on plasticity and that abnormal postnatal development is an important component of the disorder.     

Dnmt1 deficiency promotes CAG repeat expansion in the mouse germline

Expanded CAG repeat tracts are the cause of at least a dozenneurodegenerative disorders. In humans, long CAG repeats tendto expand during transmissions from parent to offspring, leadingto an earlier age of disease onset and more severe symptomsin subsequent generations. Here, we show that the maintenanceDNA methyltransferase Dnmt1, which preserves the patterns ofCpG methylation, plays a key role in CAG repeat instabilityin human cells and in the male and female mouse germlines. SiRNAknockdown of Dnmt1 in human cells destabilized CAG triplet repeats,and Dnmt1 deficiency in mice promoted intergenerational expansionof CAG repeats at the murine spinocerebellar ataxia type 1 (Sca1)locus. Importantly, Dnmt1^+/– SCA1 mice, unlike their Dnmt1^+/+SCA1 counterparts, closely reproduced the intergenerationalinstability patterns observed in human SCA1 patients. In addition,we found aberrant DNA and histone methylation at sites withinthe CpG island that abuts the expanded repeat tract in Dnmt1-deficientmice. These studies suggest that local chromatin structure mayplay a role in triplet repeat instability. These results areconsistent with normal epigenetic changes during germline developmentcontributing to intergenerational instability of CAG repeatsin mice and in humans.     

Persistent hypersynchronization of neocortical neurons in the mocha mutant of mouse

A recessive mutation in the mouse at the mocha locus (mh, chromosome 10) modulates the synchronous synaptic activation of neocortical neurons, resulting in a constant 6-7 Hz (theta) wave pattern in the electrocorticogram. The gene-linked brain rhythm is unaffected by motor behavior and cannot be desynchronized by sensory stimuli. This exemplary neurological mutation affecting cortical excitability is the first to reveal clearly that the predominance of a specific pattern of spontaneous brain wave activity can be inherited as a recessive trait.     

加味甘麦大枣汤挥发油对Fmr1基因敲除小鼠的旷场行为的影响

目的探讨加味甘麦大枣汤挥发油对Fmr1基因敲除小鼠的旷场行为的影响。方法选用4周龄KO和WT小鼠各45只。各分为3组:生理盐水对照组,加味甘麦大枣汤挥发油高浓度组和低浓度组。所有的小鼠腹腔注射打药加味甘麦大枣汤挥发油30 min后做场行为的实验。结果未用药的WT组和KO组小鼠比较,KO组小鼠的运动性、兴奋性、探索性明显高于WT组小鼠;KO鼠使用加味甘麦大枣汤挥发油用药2个剂量组与生理盐水(0 mg/kg)组比较,KO鼠进入各区的速度、时间、次数和路程均有明显减少(P0.05),WT鼠用药后,与0剂量组比较,高剂量组减少差异有统计学意义(P0.05);加味甘麦大枣汤挥发油治疗使KO鼠路程的活动时间和进入次数减少,接近WT鼠的探索行为方式。结论加味甘麦大枣汤挥发油能够有效地逆转脆性X综合征基因敲除小鼠旷场行为。     

Persistent hypersynchronization of neocortical neurons in the mocha mutant of mouse

A recessive mutation in the mouse at the mocha locus (mh, chromosome 10) modulates the synchronous synaptic activation of neocortical neurons, resulting in a constant 6-7 Hz (theta) wave pattern in the electrocorticogram. The gene-linked brain rhythm is unaffected by motor behavior and cannot be desynchronized by sensory stimuli. This exemplary neurological mutation affecting cortical excitability is the first to reveal clearly that the predominance of a specific pattern of spontaneous brain wave activity can be inherited as a recessive trait.     

Oncornavirus gene expression during embryonal development of the mouse.

BALB/c, C3H, and AKR strains of mice were analyzed for the concentrations of the major internal protein of about 30,000 daltons and the major envelope glycoprotein of about 70,000 daltons of endogenous type-C oncornaviruses in embryos isolated during the second half of gestation, in newborn mice, and in specific organs of adult animals. Each strain showed a different pattern of protein expression. BALB/c tissues contained very low concentrations of both proteins (< 1 ng/mg of protein) in early embryos and adult tissues, whereas moderate levels of both were present in late embryos and newborn animals. C3H tissues contained high concentrations of glycoprotein throughout embryogenesis and in the newborn and the adult spleen; low levels of internal protein were also present throughout. AKR animals contained minimal amounts of glycoprotein in embryos, increased concentrations in the newborn, and high levels in the adult spleen; the major internal protein was present in low levels throughout embryogenesis and in the newborn and rose to high levels in the adult spleen. The results indicated that genetic differences in oncornavirus protein expression are evident during embryogenesis as well as in the adult animals and that this protein expression may be influenced by the state of differentiation of the cell. Our observations do not support the concept that oncornavirus gene expression plays an important role in mammalian embryogenesis.     

Brn-1 and Brn-2 share crucial roles in the production and positioning of mouse neocortical neurons

Formation of highly organized neocortical structure depends on the production and correct placement of the appropriate number and types of neurons. POU homeodomain proteins Brn-1 and Brn-2 are coexpressed in the developing neocortex, both in the late precursor cells and in the migrating neurons. Here we show that double disruption of both Brn-1 and Brn-2 genes in mice leads to abnormal formation of the neocortex with dramatically reduced production of layer IV-II neurons and defective migration of neurons unable to express mDab1. These data indicate that Brn-1 and Brn-2 share roles in the production and positioning of neocortical neuron development.     

Contribution of mGluR and Fmr1 functional pathways to neurite morphogenesis, craniofacial development and fragile X syndrome

Fragile X Syndrome is a leading heritable cause of mental retardation that results from the loss of FMR1 gene function. Studies in mouse and Drosophila model organisms have been critical in understanding many aspects of the loss of function of the FMR1 gene in the human syndrome. Here, we establish that the zebrafish is a useful model organism for the study of the human fragile X syndrome and can be used to examine phenotypes that are difficult or inaccessible to observation in other model organisms. Using morpholino knockdown of the fmr1 gene, we observed abnormal axonal branching of Rohon-Beard and trigeminal ganglion neurons and guidance and defasciculation defects in the lateral longitudinal fasciculus. We demonstrate that this axonal branching defect can be rescued by treatment with MPEP [2-methyl-6-(phenylethynyl) pyridine]. This is consistent with an interaction between mGluR signalling and fmr1 function in neurite morphogenesis. We also describe novel findings of abnormalities in the abundance of trigeminal ganglion neurons and of craniofacial abnormalities apparently due to dysmorphic cartilage formation. These abnormalities may be related to a role for fmr1 in neural crest cell specification and possibly in migration.