Beta amyloid gene duplication in Alzheimer's disease and karyotypically normal Down syndrome

With the recently cloned complementary DNA probe, lambda Am4 for the chromosome 21 gene encoding brain amyloid polypeptide (beta amyloid protein) of Alzheimer's disease, leukocyte DNA from three patients with sporadic Alzheimer's disease and two patients with karyotypically normal Down syndrome was found to contain three copies of this gene. Because a small region of chromosome 21 containing the ets-2 gene is duplicated in patients with Alzheimer's disease, as well as in karyotypically normal Down syndrome, duplication of a subsection of the critical segment of chromosome 21 that is duplicated in Down syndrome may be the genetic defect in Alzheimer's disease.     

Gene dosage of the amyloid beta precursor protein in Alzheimer's disease

The progressive deposition in the human brain of amyloid filaments composed of the amyloid beta protein is a principal feature of Alzheimer's disease (AD). Densitometric analysis of Southern blots probed with a complementary DNA for the amyloid protein has been carried out to determine the relative dosage of this gene in genomic DNA of 14 patients with AD, 12 aged normal subjects, and 10 patients with trisomy 21 (Down syndrome). Whereas patients in the last group showed the expected 1.5-fold increase in dosage of this gene, none of the patients with AD had a gene dosage higher than that of the normal controls. These results do not support the hypothesis that the genetic defect in AD involves duplication of a segment of chromosome 21 containing the amyloid gene. Alternative mechanisms for the brain-specific increase in amyloid protein deposition in AD should be considered.     

Amyloid beta protein precursor gene and hereditary cerebral hemorrhage with amyloidosis (Dutch)

Human hereditary cerebral hemorrhage with amyloidosis of the Dutch type (HCHWA-D), an autosomal dominant form of cerebral amyloid angiopathy (CAA), is characterized by extensive amyloid deposition in the small leptomeningeal arteries and cortical arterioles, which lead to an early death of those afflicted in their fifth or sixth decade. Immunohistochemical and biochemical studies have indicated that the amyloid subunit in HCHWA-D is antigenically related to and homologous in sequence with the amyloid beta protein isolated from brains of patients with Alzheimer's disease and Down syndrome. The amyloid beta protein is encoded by the amyloid beta protein precursor (APP) gene located on chromosome 21. Restriction fragment length polymorphisms detected by the APP gene were used to examine whether this gene is a candidate for the genetic defect in HCHWA-D. The data indicate that the APP gene is tightly linked to HCHWA-D and therefore, in contrast to familial Alzheimer's disease, cannot be excluded as the site of mutation in HCHWA-D.     

A chromosome 21 critical region does not cause specific Down syndrome phenotypes

The "Down syndrome critical region" (DSCR) is a chromosome 21 segment purported to contain genes responsible for many features of Down syndrome (DS), including craniofacial dysmorphology. We used chromosome engineering to create mice that were trisomic or monosomic for only the mouse chromosome segment orthologous to the DSCR and assessed dysmorphologies of the craniofacial skeleton that show direct parallels with DS in mice with a larger segmental trisomy. The DSCR genes were not sufficient and were largely not necessary to produce the facial phenotype. These results refute specific predictions of the prevailing hypothesis of gene action in DS.     

Linkage of plasma Abeta42 to a quantitative locus on chromosome 10 in late-onset Alzheimer's disease pedigrees

Plasma Abeta42 (amyloid beta42 peptide) is invariably elevated in early-onset familial Alzheimer's disease (AD), and it is also increased in the first-degree relatives of patients with typical late-onset AD (LOAD). To detect LOAD loci that increase Abeta42, we used plasma Abeta42 as a surrogate trait and performed linkage analysis on extended AD pedigrees identified through a LOAD patient with extremely high plasma Abeta. Here, we report linkage to chromosome 10 with a maximal lod score of 3.93 at 81 centimorgans close to D10S1225. Remarkably, linkage to the same region was obtained independently in a genome-wide screen of LOAD sibling pairs. These results provide strong evidence for a novel LOAD locus on chromosome 10 that acts to increase Abeta.     

Characterization of the supernumerary chromosome in cat eye syndrome

Most individuals with cat eye syndrome (CES) have a supernumerary bisatellited chromosome which, on the basis of cytogenetic evidence, has been reported to originate from either chromosome 13 or 22. To resolve this question, a single-copy DNA probe, D22S9, was isolated and localized to 22q11 by in situ hybridization to metaphase chromosomes. The number of copies of this sequence was determined in CES patients by means of Southern blots and densitometry analysis of autoradiographs. In patients with the supernumerary chromosome, four copies were found, whereas in one patient with a duplication of part of chromosome 22, there were three copies. Therefore, the syndrome results from the presence of either three or four copies of DNA sequences from 22q11; there is no evidence that sequences from other chromosomes are involved. This work demonstrates how DNA sequence dosage analysis can be used to study genetic disorders that are not readily amenable to standard cytogenetic analysis.     

The amyloid beta protein gene is not duplicated in brains from patients with Alzheimer's disease

Complementary DNAs (cDNAs) encoding portions of the amyloid beta protein were used to investigate possible amyloid gene duplication in sporadic Alzheimer's disease. A strategy employing two Eco RI restriction fragment length polymorphisms (RFLPs) detected by the amyloid cDNAs was used. RFLPs allow the detection of a 2:1 gene dosage in the DNA of any individual who is heterozygous for a particular RFLP. The amyloid gene regions homologous to the cDNAs used were not duplicated in the DNA from brains of individuals with sporadic Alzheimer's disease. Similar results were also obtained with a strategy employing a test for 3:2 gene dosage.     

Mutation of the Alzheimer's disease amyloid gene in hereditary cerebral hemorrhage, Dutch type

An amyloid protein that precipitates in the cerebral vessel walls of Dutch patients with hereditary cerebral hemorrhage with amyloidosis is similar to the amyloid protein in vessel walls and senile plaques in brains of patients with Alzheimer's disease, Down syndrome, and sporadic cerebral amyloid angiopathy. Cloning and sequencing of the two exons that encode the amyloid protein from two patients with this amyloidosis revealed a cytosine-to-guanine transversion, a mutation that caused a single amino acid substitution (glutamine instead of glutamic acid) at position 22 of the amyloid protein. The mutation may account for the deposition of this amyloid protein in the cerebral vessel walls of these patients, leading to cerebral hemorrhages and premature death.     

Gene encoding the beta subunit of S100 protein is on chromosome 21: implications for Down syndrome

S100 protein is a calcium-binding protein found predominantly in the vertebrate nervous system. Genomic and complementary DNA probes were used in conjunction with a panel of rodent-human somatic cell hybrids to assign the gene for the beta subunit of S100 protein to the distal half of the long arm of human chromosome 21. This gene was identified as a candidate sequence which, when expressed in the trisomic state, may underlie the neurologic disturbances in Down syndrome.     

鲤45S rDNA的染色体荧光原位杂交定位

应用荧光原位杂交技术,通过设计位于5.8S rDNA、18S rDNA和非转录IGS区域的3条探针CAAG1191、CAAG1845和CAAG3602,分别对散鳞镜鲤Cyprinus carpio var.scattered mirror和松浦鲤Cyprinus carpio Songpu的45S核糖体DNA(ribosomal DNA,rDNA)进行染色体定位及共定位.结果表明:45S rDNA均位于两品种鲤一对近端着丝粒染色体的短臂末端,具有染色体特异性,表明45S rDNA序列的探针能够在鲤细胞遗传学研究中用于标识其所在染色体,并与鲤遗传连锁图谱中长度为227 cM的1号连锁群相对应;两品种鲤的染色体数目均为2n=100,45S rDNA在鲤基因组内仅定位于一对同源染色体,不存在复制位点,证实了鲤基因组在全基因组复制事件之后又经历了重新二倍化过程.     

The fragile X site in somatic cell hybrids: an approach for molecular cloning of fragile sites

Fragile X syndrome is a common form of mental retardation associated with a fragile site on the human X chromosome. Although fragility at this site is usually evident as a nonstaining chromatid gap, it remains unclear whether or not actual chromosomal breakage occurs. By means of somatic cell hybrids containing either a normal human X or a fragile X chromosome and utilizing two genes that flank the fragile site as markers of chromosome integrity, segregation of these markers was shown to be more frequent if they encompass the fragile site under appropriate culture conditions. Hybrid cells that reveal marker segregation were found to contain rearranged X chromosomes involving the region at or near the fragile site, thus demonstrating true chromosomal breakage within this area. Two independent translocation chromosomes were identified involving a rodent chromosome joined to the human X at the location of the fragile site. DNA analysis of closely linked, flanking loci was consistent with the position of the breakpoint being at or very near the fragile X site. Fragility at the translocation junctions was observed in both hybrids, but at significantly lower frequencies than that seen in the intact X of the parental hybrid. This observation suggests that the human portion of the junctional DNA may contain part of a repeated fragility sequence. Since the translocation junctions join heterologous DNA, the molecular cloning of the fragile X sequence should now be possible.     

A mutation in the amyloid precursor protein associated with hereditary Alzheimer's disease

Alzheimer's disease is a form of localized amyloidosis characterized by cerebral cortical amyloid plaques, neurofibrillary tangles, and amyloid deposits within the walls of leptomeningeal vessels. Although most cases of Alzheimer's disease are sporadic, kindreds with autosomal-dominant inheritance of the syndrome suggest that a single mutation may be important in pathogenesis. Direct sequencing of DNA from a family with autopsy-proven Alzheimer's disease revealed a single amino acid substitution (Phe for Val) in the transmembrane domain of the amyloid precursor protein. This mutation correlates with the presence of Alzheimer's disease in all patients in this study, and may be the inherited factor causing both amyloid fibril formation and dementia.     

鸡脾脏重全基因组关联分析

【目的】利用全基因组关联分析（genome-wide association study, GWAS）技术解析产蛋后期母鸡脾脏重的分子机制和遗传特征,为改善产蛋后期母鸡的健康状况提供理论依据。【方法】利用东乡绿壳蛋鸡和白来航蛋鸡构建资源群体,以72周龄F2代501只母鸡脾脏重为研究材料。首先利用高密度600 K 基因芯片对试验群体基因组进行SNPs检测。其次利用APT软件进行质控、BEAGLE软件进行基因型填充、PLINK软件进行主成分分析,GEMMA软件进行全基因组关联分析,最终获得脾脏重的显著和潜在显著关联位点。然后利用GCTA软件计算基于SNP数据的脾脏重遗传力以及染色体遗传力,并利用Haploview软件对显著或潜在关联位点进行连锁不平衡分析。最后通过显著位点区域的相关基因功能注释来筛选影响母鸡产蛋后期脾脏重的候选基因。【结果】由72周龄母鸡脾脏重的表型数据可知,在蛋鸡产蛋后期存在较大的变异系数,脾脏重的遗传力为0.236。通过基因型分析得到43万个高质量的SNP进行进一步分析。群体结构分析发现基因膨胀系数为1.042,表明试验群体没有群体分层的现象,避免了关联分析中假阳性结果的出现。利用单变量混合线性模型分析共发现了412和281个SNPs位点与脾脏重显著和潜在显著关联,位于1、4、16、28号染色体上。显著性关联位点在1号染色体161-174 Mb区间和28号染色体0.47-1.27 Mb区间,潜在性显著位点在4号染色体76 Mb区间和16号染色体175kb区间。由于显著区域可能存在的连锁不平衡,对显著性位点进行了条件分析和连锁不平衡检验,以1号染色体位点rs314001986和28号染色体上位点rs312729296进行条件分析,经分析后原先显著关联的位点均不显著,即以rs314001986和rs312729296作为候选SNP进行基因注释分析。对4号染色体和16号染色体潜在显著位点进行连锁不平衡分析,结果显示潜在性显著位点间存在强的连锁不平衡,即以性状表型方差贡献率最大的SNP rs315270535和rs314065899为候选位点进行进一步分析。参考鸡的galgal4基因组,对各显著及潜在性显著位点及区间初步筛选到KCTD4、LDB2、HEP21和PCASP2候选基因,鉴定的候选基因可能参与了脾脏生长以及免疫应答等过程。此外,将显著位点的基因型与群体的表型数据进行关联分析,发现rs314001986和rs312729296在基因型为GG时对脾脏均有增重效应。此外,基于群体的基因型数据得到1号染色体解释的遗传力为9.25%,28号染色体为4.55%。【结论】初步揭示了母鸡产蛋后期脾脏重的遗传特征,脾脏重的遗传力和染色体遗传力为首次报道。生物信息学分析鉴定到影响脾脏重的区域为新的发现,并初步筛选出4个候选基因。     

The gene for familial polyposis coli maps to the long arm of chromosome 5

The inherited genetic defect in adenomatous polyposis has been localized to a small region on the long arm of chromosome 5. Sixteen DNA marker loci were used to construct a linkage map of the chromosome. When five kindreds segregating a gene for adenomatous polyposis coli were characterized with a number of the markers, significant linkage was found between one marker and the disease gene. Linkage analysis determined the location of the defective gene within a primary genetic map of chromosome 5.     

Two anonymous DNA segments distinguish the Wilms' tumor and aniridia loci

The association of Wilms' tumor with aniridia (the WAGR complex) in children with 11p13 chromosomal abnormalities has been established, but the paucity of molecular probes in 11p13 has hampered identification of the responsible genes. Two new anonymous DNA segments have been identified that map to the WAGR region of 11p13. Both DNA probes identify a cytologically undetectable deletion associated with a balanced chromosome translocation inherited by a patient with familial aniridia, but not Wilms' tumor. The same two DNA segments are also included in the distal p13-p14.1 deletion of another patient, who has aniridia, Wilms' tumor, and hypogonadism, but they are not included in the p12-p13 deletion of a third patient, who does not have aniridia but has had a Wilms' tumor. The discovery of this aniridia deletion and these two DNA segments that physically separate the Wilms' tumor and aniridia loci should facilitate identification of the genes in the WAGR locus, beginning with the aniridia gene.     

水稻CMS-WA恢复基因的遗传和分子标记定位研究进展

综述了近25年来水稻野败型细胞质雄性不育（CMS—WA）恢复基因的遗传及其分子标记定位研究进展．有学者认为，CMS—WA育性的恢复受1对基因控制；大多数研究者认为受2对基因控制，2对基因间互作方式有加性、重叠和显隐性上位作用，也有的认为2对基因是相互独立的；还有人认为受多基因控制或是一种质量一数量性状．在恢复基因分子标记定位方面，有学者发现为1对恢复基因，并将其定位在第10染色体上，也有定位在第7染色体上；发现为2对恢复基因的学者，将其定位在第1和第10染色体上，或定位在第7和第10染色体上，也有将2对恢复基因都定位在第10染色体上；发现为多对恢复基因的学者，有人鉴别出8个基因位点，其中2个Rf-3和Rf-4为主效基因，分别定位在第3和第4染色体上，6个微效基因分别定位在第1，2，5，6，10和第12染色体上；也有人将2个主效基因定位在第1和第10染色体上；还有学者发现为4个QTLs，其中一个主效基因Rf-10被定位在第10染色体上，3个微效基因分别定位在第1，第7和第11染色体上．     

A new DNA marker tightly linked to the fragile X locus (FRAXA)

The fragile X syndrome is the most common cause of familial mental retardation. Genetic counseling and gene isolation are hampered by a lack of DNA markers close to the disease locus. Two somatic cell hybrids that each contain a human X chromosome with a breakpoint close to the fragile X locus have been characterized. A new DNA marker (DXS296) lies between the chromosome breakpoints and is the closest marker to the fragile X locus yet reported. The Hunter syndrome gene, which causes iduronate sulfatase deficiency, is located at the X chromosome breakpoint that is distal to this new marker, thus localizing the Hunter gene distal to the fragile X locus.     

Human prion protein cDNA: molecular cloning, chromosomal mapping, and biological implications

A human complementary DNA whose protein product is considered to be the major component of scrapie-associated fibrils in Creutzfeldt-Jakob disease, kuru, and Gerstmann-Straussler syndrome has been identified and characterized. The extensive homology of this gene sequence to the hamster PrP 27- to 30-kilodalton prion protein complementary DNA clone, and its existence as a single copy in the human genome, leads to the conclusion that this is the human prion gene. This human prion gene has been mapped to human chromosome 20, negating a direct link between the prion protein and Down's syndrome or the amyloid of Alzheimer's disease.     

Brain to plasma amyloid-beta efflux: a measure of brain amyloid burden in a mouse model of Alzheimer's disease

The deposition of amyloid-beta (Abeta) peptides into amyloid plaques precedes the cognitive dysfunction of Alzheimer's disease (AD) by years. Biomarkers indicative of brain amyloid burden could be useful for identifying individuals at high risk for developing AD. As in AD in humans, baseline plasma Abeta levels in a transgenic mouse model of AD did not correlate with brain amyloid burden. However, after peripheral administration of a monoclonal antibody to Abeta (m266), we observed a rapid increase in plasma Abeta and the magnitude of this increase was highly correlated with amyloid burden in the hippocampus and cortex. This method may be useful for quantifying brain amyloid burden in patients at risk for or those who have been diagnosed with AD.     

Induction of mating in Candida albicans by construction of MTLa and MTLalpha strains

Although the diploid fungus Candida albicans, a human pathogen, has been thought to have no sexual cycle, it normally possesses mating-type-like orthologs (MTL) of both of the Saccharomyces cerevisiae mating-type genes (MAT) a and alpha. When strains containing only MTLa or MTLalpha were constructed by the loss of one homolog of chromosome 5, the site of the MTL loci, MTLa and MTLalpha strains mated, but like mating types did not. Evidence for mating included formation of stable prototrophs from strains with complementing auxotrophic markers; these contained both MTL alleles and molecular markers from both parents and were tetraploid in DNA content and mononucleate.