The molecular genetics of Alzheimer's disease

The major pathological characteristic of Alzheimer's disease (AD) is the abnormal deposition of β-amyloid peptide (Aβ) in the brain. In some early onset cases, the disease develops because of mutations in the gene coding for β-amyloid precursor protein (βAPP). However, the majority of AD families in the early onset subgroup are linked to a locus on chromosome 14. The genetic analysis and age of onset correlates of both the βAPP gene and the chromosome 14 locus are discussed. We speculate on the mechanisms by which the βAPP mutations cause the disease and discuss recent advances in βAPP processing that may be relevant to the pathogenesis of the late-onset (common) form of the disease. In addition, we review the association of theAPOE locus with late-onset familial and nonfamilial disease. Further work is required to establish the effects of this locus on disease occurrence, age of onset, and progression. The molecular pathology of ApoE in relation to AD development and the identification of the chromosome 14 gene will greatly contribute to a general pathogenic model of AD, and will clarify the role of βAPP and its derivatives.     

In situ hybridization to metaphase chromosomes in six species ofPhaseolus andVigna using ribosomal DNA as the probe

In situ hybridization with a biotin-labeled rice ribosomal DNA (rDNA) probe to the somatic metaphase chromosomes of six species ofPhaseolus andVigna (P. angularis, P. calcaratus, P. coccineus, P. vulgaris, V. sesquipedalis andV. sinensis) was done to determine the sites of rDNA. Hybridization signals were present in the terminal and subterminal chromosome regions of each of the six species. The number of rDNA sites was two inP. angularis andP. calcaratus, four inP. coccineus andP. vulgaris, and six inV. sesquipedalis andV. sinensis.     

玉米胚性愈伤组织的长期继代及其染色体分析

对５种基因型幼胚诱导的愈伤组织继代培养表明,玉米胚性愈伤组织的长期继代受基因型,培养基成分,激素,培养条件的影响。适时继代,逐代筛选对胚性保持起重要作用。适当降低培养温度（１２±２℃）有利于愈伤组织的保存和胚性保持,可以减少愈伤组织长期继代所需的物质和工作量。长期继代培养的胚性愈伤组织,胚状体发生能力和植株再生率无显著变化,但正常苗的再生频率显著下降。观察愈伤组织细胞染色体发现：（１）基因型对不同倍性细胞的比例有明显影响。（２）随着继代时间的延长,二倍体细胞下降,四倍体和非二倍体细胞增多。（３）愈伤组织中出现多种染色体结构变异,这些结构变异有可能导致非整倍体细胞的形成。     

Telomeric repeat [TTAGGG]n sequences of human chromosomes are conserved in chimpanzee (Pan troglodytes)

Summary Using a series of genetic parameters, attempts have been made for more than two decades to establish the close kinship of human (Homo sapiens) with chimpanzee (Pan troglodytes). Molecular and cytogenetic data presently suggest that the two species are closely related. The recent isolation of a human telomeric probe (P5097-B.5) has prompted us to cross hybridize it to chimpanzee chromosomes in order to explore convergence and/or divergence of the telomeric repeat sequences (TTAGGG)_n. On hybridization, the human probe bound to both ends (telomeres) of chimpanzee chromosomes, suggesting a concerted evolution of tandemly repeated short simple sequences (TTAGGG)_n. Even the terminal heterochromatin of chimpanzee chromosomes was found to be endowed with telomeric repeats, suggesting that evolution of heterochromatin and capping with tandemly repeated short sequences are highly complex phenomena.     

Fractionation of bovine spermatozoa for sex selection: A rapid immunomagnetic technique to remove spermatozoa that contain the H-Y antigen

A study was conducted to rapidly fractionate bovine spermatozoa on the basis of cell-surface H-Y antigen (i.e., Y chromosome-bearing spermatozoa). A novel, rapid immunomagnetic method was developed for removal of spermatozoa that bound to anti-H-Y IgG. Fluorescent labeling and flow cytometry were used to measure the efficiency with which spermatozoa binding to anti-H-Y were removed by the immunomagnetic technique. Washed bovine spermatozoa (n=7 bulls) were treated with a mouse monoclonal IgG antibody to H-Y antigen (MoAb 12/49). Fluorescent labeled goat antibody against mouse IgG was added to label those spermatozoa with cell-surface H-Y antigens. Supermagnetized polymer beads coated with an anti-antibody to the MoAb 12/49 were then added to the spermatozoa. After 20 min of incubation, spermatozoa were exposed for 2 min to a magnet, causing the magnetized particles to adhere to the sides of the tube. Nonmagnetized spermatozoa in the supernatent were aspirated and analyzed for fluorescent label by flow cytometry. Approximately 50% of spermatozoa not subjected to immunomagnetic separation were fluorescent labeled, and about one-half of the spermatozoa were observed microscopically to be bound to the magnetized polymer beads prior to magnetic separation (P<0.05). Following magnetic separation, only 1.2% (P<0.05) of the spermatozoa in the magnetic supernatent were fluorescent labeled. Assuming that only Y chromosome-bearing spermatozoa have cell-surface H-Y antigens, the present immunomagnetic fractionation removed almost all of the Y chromosome-bearing spermatozoa, leaving a population that was greater than 98% X chromosome-bearing spermatozoa.     

黑松,马尾松及其杂种的核型比较

分析了黑松、马尾松及其杂种的核型。其核型公式：黑松为Ｋ（２ｎ）＝２４－２０ｍ（６＿（ＳＡＴ）））＋４ｓｍ;杂种为Ｋ（２ｎ）＝２４＝２３ｍ＋１ｓｍ;马尾松为Ｋ（２ｎ）＝２４－２４ｍ（４＿（ＳＡＴ））。相对长度和臂比方差分析表明,两亲本和杂种差异显著。杂种在相对长度、全组染色体总长、最长与最短染色体比、臂比平均值以及染色体类型上均处于双亲之间。这些研究结果为进一步研究该天然杂种提供必要的细胞学资料。     

Genetic differentiation of house mice in the fauna of the former U.S.S.R.: results of cytogenetic studies

A cytogenic study of nearly 200 house mice (Mus musculus sensu stneto) and aboriginal mice (Mus hortulanus, Mus abbotti) of the subgenus Mus was carried out. Mice were sampled from most localities in the former U.S.S.R., from the western borders to the Far East, and it was shown that it is possible to use cytogenetic markers to classify the species and rare subspecies of the subgenus. Such markers included the characteristic morphology of the sex chromosomes and the pattern of distribution of the C-heterochromatin in the karyotype. Thus, the aboriginal mice, together with M. spretus , are characterized by a significant reduction in the size of the Y chromosome. In addition, the variant of the X chromosome (so called 'molossinus' lype) previously only observed in Japanese M. in. molossinus was found in all the Mus musculus sampled from the fauna of the former U.S.S.R. Another type, the so called 'domeslicus' is a plesiomorphic variant of the X chromosome which is normally found in M. domestuus. M. hortulanus, M. abbotti and possibly in M. spretus. The presence of the common variant X chromosome in the house mice of the various subspecies in the fauna of the former U.S.S.R., Mongolia (raddei) and Japan (molossinus) provides the basis for the integration of Asian house mice into the one species, At. musculus sensu stricto. The problems of morphology, ecology and systematics of the mouse fauna of the former U.S.S.R. are also discussed with special attention being paid to the studies of the so called 'wagnen' form.     

Towards an understanding of the Sarcostemma viminale (Asclepiadaceae) complex

LIEDE, S. & MEVE, U., 1993. Towards an understanding of the Sarcostemma viminale (Asclepiadaceae) complex. All names in Sarcostemma sensu Bullock (Asclepiadaceae, Asclepiadeae, Cynanchinae) are listed and their current status evaluated. Chromosome numbers are given for most taxa. The typification of S. viminale is clarified. A new subspecies of S. viminale is described from the Orange Free State, South Africa, and relationships of the Namaqualand/Namibia populations are discussed.     

Cloning and molecular genetic analysis of Drosopbila melanogaster interband DNA

Interband DNA of Drosophila melanogaster polytene chromosomes was studied using a novel approach based on the electron microscopic (EM) analysis of chromosome regions carrying DNA fragements of known molecular genetic composition, inserted by P element-mediated transformation. Insertion of such fragments predominantly into interbands makes it possible to clone interband DNA by constructing genomic libraries from transformed strains and probing them with the insert DNA. The transformed strain P[H-sp70:Adh](61C) has insertion in the 61 C7-8 interband on the left arm of chromosome 3. This DNA consists of part of the hsp70 gene promoter fused to the coding region of the Adh gene, and is flanked on either side by P element sequences. We constructed a genomic library from DNA of this strain and isolated a clone containing the insert and the interband DNA. Subsequently the genomic library of wild-type strain was probed with a subclone composed of interband DNA only. We have thus isolated a clone containing the entire native interband. 1289 by of interband DNA was sequenced and found to be AT-rich (53.4%) with numerous regions of overlapping direct and inverted repeats, regulatory sites, and two overlapping open reading frames (ORFs).     

Examination of DNA sequences undergoing chromatin conformation changes at a variegating breakpoint in Drosophila melanogaster

Position effect variegation in Drosophila melanogaster is associated with the inability of certain genes to be correctly expressed in a proportion of cells, giving a mosaic phenotype. The lack of expression is thought to be due to alterations in the gene's chromatin structure due to its proximity to a region of heterochromatin. Because of the difficulties involved, there is little biochemical data to support the intuitively appealing model of heterochromatin spreading used to explain this phenomenon.Differences in restriction fragment length were used to distinguish DNA regions from either normal (non-position affected) or rearranged (position affected) chromosomes so as to examine possible changes in gene copy number and the effects of endogenous nucleases. DNA sequences at the breakpoint of In (1)w ^m4, which variegates for the white gene, were assayed under conditions where the chromatin conformation was altered using second site modifier mutations (Su(var) or En(var)). No change in the DNA sequerice copy number was observed at either chromosome breakpoint, relative to wild type, when either suppressor or enhancer mutations were present. Therefore copy number change, through differential polyploidization or somatic gene loss, is not affected by Su(var) or En(var) induced changes in the chromatin conformation.Initial experiments showed a gross difference in the sensitivity of DNA to endogenous nucleases that appeared associated with Su(var) and En(var) mutations. En(var) mutation bearing samples appeared delayed in the digestion, relative to Su(var). This differential sensitivity seemed to be genome-wide as there was no detectable difference between either breakpoint of In(1)w ^m4 or the sequences on the homologous w ^- chromosome. However, after isogenizing the genetic background, the previously noted difference between the Su(var) and En(var) mutations was eliminated. In studies dealing with nuclease digestion of chromatin, the isogenization of genetic background is essential before meaningful comparisons can be made.