Coordinate Suppression of Mutations Caused by Robertson''s Mutator Transposons in Maize

Transposable elements from the Robertson's Mutator family are highly active insertional mutagens in maize. However, mutations caused by the insertion of responder (non-autonomous) elements frequently depend on the presence of active regulator (autonomous) elements for their phenotypic effects. The hcf106::Mu1 mutation has been previously shown to depend on Mu activity in this way. The dominant Lesion-mimic 28 mutation also requires Mu activity for its phenotypic effects. We have used double mutants to show that the loss of Mu activity results in the coordinate suppression of both mutant phenotypes. This loss can occur somatically resulting in large clones of cells that have a wild-type phenotype. Autonomous and non-autonomous Mutator elements within these clones are insensitive to digestion with methylation-sensitive enzymes, suggesting extensive methylation of CG and non-CG cytosine residues. Our data are consistent with the sectors being caused by the cycling of MuDR regulatory elements between active and inactive phases. The pattern of sectors suggests that they are clonal and that they are derived from the apical cells of the vegetative shoot meristem. We propose that these cells are more likely to undergo epigenetic loss of Mu activity because of their longer cell division cycle during shoot growth. Coordinate suppression of unlinked mutations can be used to perform mosaic analysis in maize.     

Genetic Dissection of Cerebellar Development: Mutations Affecting Cell Position

SYNOPSIS. The spastic mutation induces swimming coordinationand equilibrium deficiencies in the Mexican axolotl (Ambystomamexicanum). Behavioral ontogeny studies determined that spaslksfail to develop behavior trains of sinusoidal flexures necessaryto mediate escape swimming at the time of onset of cerebellarfunction. Behavior analysis, after lesioning different cranialnerve roots and CNS areas in wild-type animals, confirmed the"behavioral focus" of the mutation to lie in the auricle orvestibulo-cerebellum. Single unit recordings in the cerebellarauricle and adjacent brainstem vestibular zone (area acoustico-lateralis)of mutants revealed a full complement of vestibular unit typesfound in wild-type. However, the gene appears to alter the physicallocation of vestibular units in both areas, including a ventral"translocation" of cerebellar units responding to sustainedipsilateral tilt. Correlated with this unit translocation, mutantPurkinje cells and allied afferent tracts are malpositionedventrally, i.e., "crowded" into an ectopic zone in the ventro-posteriorcerebellum. Studies on cerebellar structure at the time of onsetof spasticity (early feeding stage) confirmed the ventral malpositioningof cerebellar cells and fiber tracts seen in adults. In conjunctionwith these larval studies, mutant larvae injected with tritiatedthymidine during early cerebellogenesis and assayed at the earlyfeeding stage revealed a medio-ventral malpositioning of labelledcells; in wild-type, labelled cells were positioned laterally.Interestingly, the neuropathology of the reeler mutation (rev.,Mariani et al., 1977) found in the mouse is remarkably similarto that of the spastic axolotl. Both cerebella are reduced insize, misshapen, and lack fissures. Purkinje cells appear ectopicallyin the granular layer, white matter and deep cerebellar nuclei.Although both cerebella lack structural integrity, no individualcell type shows marked or progressive degeneration, and cellularuntrastructure appears intact; thus, both genes appear to actindependently of the genesis of cerebellar elements. Instead,they appear to influence morphogenetic movements by which presumptivecerebellar cells attain their proper positions during the neurogeneticsequence.     

Genetic Analysis of Two Mutations Affecting Thymidine Metabolism in Dictyostelium Discoideum

The tmpA600 mutation confers thymidylate synthase deficiency and thymidine auxotrophy to Dictyostelium discoideum. The tdrA600 mutation enhances transport of thymidine and thereby reduces the auxotrophic requirement of tmpA600 strains. The tmpA locus maps to linkage group III. The tdrA600 mutation is dominant and cosegregates with both linkage groups IV and VI, possibly because of a translocation between the two. The tdrA600 allele is sufficient to allow efficient incorporation of exogenous [3H]thymidine or [3H]uridine into TCA-precipitable material and to sensitize the cell to the nucleoside-analog inhibitor, 5-fluorodeoxyuridine. These properties make the tdrA mutation useful for studies requiring labelling of DNA or RNA in vivo.     

Genetic Analysis of Mutations Affecting Growth of SACCHAROMYCES CEREVISIAE at Low Temperature

A large number of genes control growth of the yeast Saccharomyces cerevisiae at low temperatures (< 10 degrees ). Approximately 47 percent of the mutants selected for inability to grow at 4-5 degrees C show increased sensitivity to cycloheximide. In 3 of 4 cases tested, supersensitivity to cycloheximide and inability to grow at the low temperature segregate together and thus appear to be effects of the same mutation. Since many cold-sensitive mutants of bacteria have been found to have altered ribosomes and since cycloheximide resistance in yeast can be caused by ribosomal changes, this suggests that the mutants having low-temperature-sensitive growth may be defective in ribosome-assembly processes at the low temperatures. Two of the lts loci, lts1 and lts3 have been located on chromosome VII and another two, lts4 and lts10 on chromosome IV. A mutation, cyh10, conferring cycloheximide resistance, but not cold sensitivity, has been located close to the centromere on chromosome II.     

玉米籽粒性状的遗传模型研究

用１０个遗传上和籽粒形态性状上具有差异的玉米自交系,依多种可能的交配方法获得亲本Ｐ１、Ｐ２、Ｆ１（Ｐ１× Ｐ２）、Ｆ２、Ｂ１（Ｆ１×Ｐ１）、Ｂ２（Ｆ１× Ｐ２）及其相应反交ＲＦ１、ＲＦ２、ＲＢ１、ＲＢ２共１０个种子世代。种植２年。依广义遗传模型建立包括种子胚乳加性、胚乳显性、母体加性、母体显性和细胞质效应的遗传模型,运用种子数量性状的精细鉴别法［１］和混合模型分析法［２,３］,对粒长、粒宽、粒长宽比、粒厚及百粒重作了性状表达遗传机制的鉴别与探讨。单个组合的遗传模型精细测验表明,５个籽粒性状的遗传主要受母体显性和胚乳基因型（包括加性和灵性）的控制,一个组合的粒宽、粒厚和百粒重上还检测到细胞质效应。对２５对 Ｆ１正反交组合世代均值依ＭＩＮＱＵＥ法分析的结果表明,５个籽粒性状的遗传方差中,母体遗传方差占６０％以上,胚乳基因型方差低于４０％,粒长和百粒重还有细胞质效应,约占１０％～３０％。可见,籽粒性状的遗传特点是受多套遗传系统控制,其中以母体基因型的作用最大。     

玉米籽粒性状的遗传效应分析

采用二倍体胚和三倍体胚乳种子遗传模型及其分析方法,以5个玉米自交系及其配制的F1,F2,BC1,BC2世代为材料,研究5个玉米种子性状的胚直接效应、胚乳直接效应、母体效应和细胞质效应。分析结果表明,除粒宽外,各性状的遗传同时由细胞质效应和胚、胚乳、母体基因效应所控制,百粒重主要受胚乳和母体效应的影响,粒长的遗传以母体效应为主,粒宽和粒厚以胚乳效应为主。各部位籽粒百粒重的胚乳直接加性效应与母体加性效应的协方差达到显著或极显著水平,其余性状的胚、胚乳直接效应与母体效应间的协方差均不显著,通过母体植株的遗传表现可以对这些性状进行有效的选择。S22 是改良百粒重的优良亲本。 Abstract：The embryo,endosperm and cytoplasm effects of seven seed traits were studied by genetic model for diploid embryo and triploid endosperm plant seeds using five inbreds and their F1, F2, BC1 and BC2 generations. The estimates of genetic variance components indicated that the inheritance of all other kernel traits was controlled by the four effects except kernel width. The 100?kernel weight was mainly controlled by endosperm and maternal effects , and kernel length was controlled by the maternal effects,while endosperm conrrolled kernel width and kernel thickness. Except the significant or highly significant covariances between the endosperm direct additive and maternal additive effects for 100－kernel weight,all other traits between the embryo or endosperm direct effect and the maternal were not significant. So,maize inbreds could be developed by direct selection based on maternal plants for these traits. S22 was the best inbred of the improvement for kernel weight in this study.     

影响果蝇心脏发育的基因突变

最近的研究表明,果蝇与脊椎动物及人的心脏早期发育具有极为相似的基因控制机理,果蝇已成为研究人体心脏早期发育基因控制的理想模式动物。利用化学诱变剂甲磺酸乙酯大规模地诱变影响果蝇心脏发育的基因,利用心脏特异性抗体染色进行筛选,获得了112个有心脏突变表型的致死系,其中32个致死系的心脏畸变表型有别于目前已知心脏发育基因的突变表型。细胞遗传学定位研究表明在多线染色体的13个带纹区的某些隐性致死突变基因是目前未知的,其功能可能与发育有关的基因。     

Mitochondrial DNA Mutations in Mutator Mice Confer Respiration Defects and B-Cell Lymphoma Development

Mitochondrial DNA (mtDNA) mutator mice are proposed to express premature aging phenotypes including kyphosis and hair loss (alopecia) due to their carrying a nuclear-encoded mtDNA polymerase with a defective proofreading function, which causes accelerated accumulation of random mutations in mtDNA, resulting in expression of respiration defects. On the contrary, transmitochondrial mito-miceΔ carrying mtDNA with a large-scale deletion mutation (ΔmtDNA) also express respiration defects, but not express premature aging phenotypes. Here, we resolved this discrepancy by generating mtDNA mutator mice sharing the same C57BL/6J (B6J) nuclear background with that of mito-miceΔ. Expression patterns of premature aging phenotypes are very close, when we compared between homozygous mtDNA mutator mice carrying a B6J nuclear background and selected mito-miceΔ only carrying predominant amounts of ΔmtDNA, in their expression of significant respiration defects, kyphosis, and a short lifespan, but not the alopecia. Therefore, the apparent discrepancy in the presence and absence of premature aging phenotypes in mtDNA mutator mice and mito-miceΔ, respectively, is partly the result of differences in the nuclear background of mtDNA mutator mice and of the broad range of ΔmtDNA proportions of mito-miceΔ used in previous studies. We also provided direct evidence that mtDNA abnormalities in homozygous mtDNA mutator mice are responsible for respiration defects by demonstrating the co-transfer of mtDNA and respiration defects from mtDNA mutator mice into mtDNA-less (ρ⁰) mouse cells. Moreover, heterozygous mtDNA mutator mice had a normal lifespan, but frequently developed B-cell lymphoma, suggesting that the mtDNA abnormalities in heterozygous mutator mice are not sufficient to induce a short lifespan and aging phenotypes, but are able to contribute to the B-cell lymphoma development during their prolonged lifespan.     

普通玉米籽粒性状的遗传效应分析

采用二倍体种子遗传模型及其分析方法,研究了５个玉米籽粒性状的直接效应、母体效应和细胞质效应．分析结果表明,各性状的遗传同时受种子直接效应和母体效应的影响,细胞质基因对百粒重和粒宽具有极显著影响．除粒长、粒厚的直接显性效应与母体显性效应间的协方差外,直接效应与母体效应间的协方差均不显著．因此,通过母体植株的表现可对这些性状进行有效的选择．Ｓ_２２和 ８７－１是改良粒重的优良亲本．选择粒较宽的自交系作母本有利于提高后代选系及Ｆ_１的百粒重．     

Analysis of Transient Changes in Fluid Exudation from Isolated Maize Roots

It was found that the fluid exudation rate from isolated maizeroots rapidly decreases when the external concentration of varioussolutes is increased; thereafter a relatively slow increaseto a new value occurs. An analysis of this transient phenomenonhas been achieved on the basis that there is an active transportof salt (KCl) into a compartment within the root. Further, ithas been assumed that fluid exudation is created by a net osmoticwater flow into this compartment. Our analysis of the experimentaldata indicates that the volume of the compartment has a similarmagnitude to the estimated total volume of the xylem vesselsin the root. The transient curve obtained with some solutes (methanol, magnesiumsulphate, mannitol, and raffinose) were significantly differentfrom the usual response. An attempt to apply an appropriate diffusion equation to theinitial phase of the transient curves showed that the time courseof this phase may be interpreted as being controlled by therate of solute diffusion towards an osmotic barrier within theroot.     

Reversion of Frameshift Mutations by Mutator Genes in Escherichia coli

The Escherichia coli mutator genes mutU4, mutS3, and mut-25 (a possible allele of mutL), previously known to induce transitional base changes, increased significantly the frequencies of reversion of lacZ frameshift mutations. mutT1, previously shown to induce only the transversion of adenine-thymine to cytosine-guanine, had no effect on the reversion of lacZ frameshift mutations. With mutator genes other than mutT1, small increases were found in the frequencies of reversion of trpA frameshift mutations.     

Genetic Analysis of Mutations Indirectly Suppressing recB and recC Mutations

Mutations in sbcB inactivate exonuclease I and suppress the UV-sensitive, mitomycin-sensitive, recombination-deficient phenotypes associated with recB and recC mutations. Mapping experiments have located sbcB about 0.4 minutes from the his operon at 38.0 on the standard map of E. coli. This places sbcB between supD and his. A four-point cross shows that sbcB lies between P2 attH and his. P2 eduction deleting the his operon beginning with P2 attH also deletes sbcB and produces the expected exonuclease I deficiency and suppression of recB(-). The occurrence of chemical-mutagen-induced and spontaneous mutations indirectly suppressing recB(-) and recC(-) is examined. Three lines of strains produce only sbcA mutations while only sbcB mutations occur in a fourth line. Explanations for this behavior are proposed in light of the ability of the first three lines to express sbcB mutations which they inherit by transduction.     

玉米ZmCIPK31基因原核表达及启动子序列分析

与钙传感器类钙调磷酸酶B蛋白(calcineurin B-like protein,CBL)互作的蛋白CIPK(CBL-interacting protein kinase)在植物特定的生长发育和应答胁迫过程中起重要作用。对前期研究得到的玉米ZmCIPK31基因构建原核表达重组载体,进行原核表达分析,转化重组质粒的大肠杆菌BL21菌株能够诱导出期望的目的蛋白。蛋白可溶性分析表明,它是可溶性的蛋白,通过淀粉树脂柱对其进行纯化,为下一步激酶活性分析提供了有活性的目的蛋白。同时,克隆了ZmCIPK31基因起始密码子ATG上游包括2189bp的启动子区段,顺式作用元件预测分析表明此区段不仅具有TATA-box和CAAT-box等启动子共有序列,还具有光应答、胁迫应答、发育相关、激素相关及其他功能未知的调控结构域。聚乙二醇(PEG)胁迫下,ZmCIPK31基因的诱导表达进一步表明其能够应答胁迫,且在地上部和根中的表达模式不同。     

Genetic Mutations Affecting the Respiratory Electron-Transport System of the Photosynthetic Bacterium Rhodopseudomonas capsulata

Alternative energy-converting systems permit the nonsulfur purple photosynthetic bacterium Rhodopseudomonas capsulata to grow either with light or (dark) respiration as the source of energy. Respiratory mutants, unable to grow aerobically in darkness, can be readily isolated and the defective step(s) in their respiratory mechanisms can be identified by study of biochemical activities in membrane fragments derived from photosynthetically grown cells. Such analysis of appropriate mutants and revertants permits construction of a model for the respiratory electron-transport system of the wild type. The results obtained indicate differential channeling of electrons derived from succinate and reduced nicotinamide adenine dinucleotide, and are interpreted in terms of a branched electron-transport scheme. The scheme provides a guide for further, more refined analysis of the respiratory mechanisms through biochemical genetic approaches, and several of the mutants isolated can be exploited for investigation of unsolved problems relating to interactions between respiratory and photosynthetic electron transport and the mechanism of inhibition of bacteriochlorophyll synthesis by molecular oxygen.