Visual stabilization of the eyes in primates

Observers moving through a texture three-dimensional world experience potentially confusing patterns of optic flow. Recent experiments on monkeys and humans have revealed the existence of rapid, yet cortically mediated, reflex eye movements that automatically single out images in the plane of fixation for stabilization and ignore images that are nearer or further.     

Control of respiration and growth yield in ammonium-assimilating cultures of Azotobacter vinelandii

Azotobacter vinelandii was grown in continuous culture at constant dilution rate and at different molar ratios of sucrose to ammonium (C/N) in the inflowing medium. The organisms used up essentially all of the carbon and fixed nitrogen sources. Therefore, the (C/N)-ratio in the influent was the same as the (C/N)-ratio of consumption. Starting close to unity, slight increases of the (C/N)-ratio resulted in increases of cellular respiration. Concomitantly, growth yield coefficients on sucrose decreased while the total biomass stayed constant. At there low (C/N)-ratios growth was limited by ammonium with a yield coefficient on ammonium of about 0.07 g protein per mmol of ammonium. Eventually, however, upon furhter increasing the (C/N)-ratio, respiration as well as the yield coefficient on sucrose approached constant values while the biomass levels increased linearly. This result indicated that a transition to sucrose-limited growth had occurred. The (C/N)-ratio, above which respiration and yield coefficients on sucrose approached constancy, increased when the cultures were grown at higher oxygen tension. When the oxygen tension was higher, and at the same (C/N)-ratios, respiratory values increased, and biomass levels as well as yield coefficients decreased. The data suggest control of respiration and thus of growth yield by the ratio of sucrose to ammonium consumed. These observations infer that commencement of dinitrogen fixation kept the internal (C/N)-ratio constant and consequently respiration as well as yield coefficients on sucrose were maintained.     

Wheat kernel dimensions: how do they contribute to kernel weight at an individual QTL level?

Kernel dimensions (KD) contribute greatly to thousand-kernel weight (TKW) in wheat. In the present study, quantitative trait loci (QTL) for TKW, kernel length (KL), kernel width (KW) and kernel diameter ratio (KDR) were detected by both conditional and unconditional QTL mapping methods. Two related F(8:9) recombinant inbred line (RIL) populations, comprising 485 and 229 lines, respectively, were used in this study, and the trait phenotypes were evaluated in four environments. Unconditional QTL mapping analysis detected 77 additive QTL for four traits in two populations. Of these, 24 QTL were verified in at least three trials, and five of them were major QTL, thus being of great value for marker assisted selection in breeding programmes. Conditional QTL mapping analysis, compared with unconditional QTL mapping analysis, resulted in reduction in the number of QTL for TKW due to the elimination of TKW variations caused by its conditional traits; based on which we first dissected genetic control system involved in the synthetic process between TKW and KD at an individual QTL level. Results indicated that, at the QTL level, KW had the strongest influence on TKW, followed by KL, and KDR had the lowest level contribution to TKW. In addition, the present study proved that it is not all-inclusive to determine genetic relationships of a pairwise QTL for two related/causal traits based on whether they were co-located. Thus, conditional QTL mapping method should be used to evaluate possible genetic relationships of two related/causal traits.     

Two new cytotypes reinforce that <Emphasis Type="Italic">Micronycteris hirsuta</Emphasis> Peters, 1869 does not represent a monotypic taxon

Background

The genus Micronycteris is a diverse group of phyllostomid bats currently comprising 11 species, with diploid number (2n) ranging from 26 to 40 chromosomes. The karyotypic relationships within Micronycteris and between Micronycteris and other phyllostomids remain poorly understood. The karyotype of Micronycteris hirsuta is of particular interest: three different diploid numbers were reported for this species in South and Central Americas with 2n?=?26, 28 and 30 chromosomes. Although current evidence suggests some geographic differentiation among populations of M. hirsuta based on chromosomal, morphological, and nuclear and mitochondrial DNA markers, the recognition of new species or subspecies has been avoided due to the need for additional data, mainly chromosomal data.

Results

We describe two new cytotypes for Micronycteris hirsuta (MHI) (2n?=?26 and 25, NF?=?32), whose differences in diploid number are interpreted as the products of Robertsonian rearrangements. C-banding revealed a small amount of constitutive heterochromatin at the centromere and the NOR was located in the interstitial portion of the short arm of a second pair, confirmed by FISH. Telomeric probes hybridized to the centromeric regions and weakly to telomeric regions of most chromosomes. The G-banding analysis and chromosome painting with whole chromosome probes from Carollia brevicauda (CBR) and Phyllostomus hastatus (PHA) enabled the establishment of genome-wide homologies between MHI, CBR and PHA.

Conclusions

The karyotypes of Brazilian specimens of Micronycteris hirsuta described here are new to Micronycteris and reinforce that M. hirsuta does not represent a monotypic taxon. Our results corroborate the hypothesis of karyotypic megaevolution within Micronycteris, and strong evidence for this is that the entire chromosome complement of M. hirsuta was shown to be derivative with respect to species compared in this study.

     

Conditional and unconditional QTL mapping of drought-tolerance-related traits of wheat seedling using two related RIL populations

For discovering the quantitative trait loci (QTLs) contributing to early seedling growth and drought tolerance during germination, conditional and unconditional analyses of 12 traits of wheat seedlings: coleoptile length, seedling height, longest root length, root number, seedling fresh weight, stem and leaves fresh weight, root fresh weight, seedling dry weight, stem and leaves dry weight, root dry weight, root to shoot fresh weight ratio, root-to-shoot dry weight ratio, were conducted under two water conditions using two F_8:9 recombinant inbred line (RIL) populations. The results of unconditional analysis are as follows: 88 QTLs accounting for 3.33–77.01% of the phenotypic variations were detected on chromosomes 1A, 1B, 1D, 2A, 2B, 2D, 3A, 3B, 4A, 4B, 4D, 5A, 5B, 5D, 6A, 6B, 6D, 7A, 7B and 7D. Among these QTLs, 19 were main-effect QTLs with a contribution rate greater than 10%. The results of the conditional QTL analysis of 12 traits under osmotic stress on normal water conditions were as follows: altogether 22 QTLs concerned with drought tolerance were detected on chromosomes 1B, 2A, 2B, 3B, 4A, 5D, 6A, 6D, 7B, and 7D. Of these QTLs, six were main-effect QTLs. These 22 QTLs were all special loci directly concerned with drought tolerance and most of them could not be detected by unconditional analysis. The finding of these QTLs has an important significance for fine-mapping technique, map-based cloning, and molecular marker-assisted selection of early seedling traits, such as growth and drought tolerance.     

SIRAC: Supervised Identification of Regions of Aberration in aCGH datasets

Background  

Array comparative genome hybridization (aCGH) provides information about genomic aberrations. Alterations in the DNA copy number may cause the cell to malfunction, leading to cancer. Therefore, the identification of DNA amplifications or deletions across tumors may reveal key genes involved in cancer and improve our understanding of the underlying biological processes associated with the disease.     

新生隐球菌转录共激活因子MBF1基因的鉴定与敲除

目的构建新生隐球菌转录共激活因子MBF1基因缺陷菌株。方法采用套叠PCR方法 ,构建含有抗性基因NEO以及靶基因上下游同源DNA片段的基因敲除框,通过基因枪将重组片段转化入新生隐球菌,应用PCR筛选和DNA序列测序方法对基因突变株进行鉴定与验证。结果成功构建了新生隐球菌基因突变株mbf1裣。结论通过基因突变株mbf1裣的构建,为深入研究新生隐球菌转录辅助因子Mbf1的功能机制奠定基础。     

Reversible and irreversible inactivation of cellular nitrogenase upon oxygen stress in Azotobacter vinelandii growing in oxygen controlled continuous culture

Azotobacter vinelandii growing in oxygen controlled chemostat culture was subjected to sudden increases of ambient oxygen concentrations (oxygen stress) after adaptation to different oxygen concentrations adjustable with air (100% air saturation corresponds to 225±14 M O₂). Inactivations of cellular nitrogenase during stress (switch off) as well as after release of stress (switch on) were evaluated in vivo as depending on stress duration and stress height (pO₂). Switch off was at its final extent within 1 min of stress. The extent of switch off, however, increased with stress height and was complete at pO₂ between 8–10% air saturation irrespective of different oxygen concentrations the organisms were adapted to before stress, indicating that switch off is adaptable. Inactivation of nitrogenase measurable after switch on represents irreversible loss of activity. Irreversible inactivation was at its characteristic level within less than 3 min of stess and at a pO₂ of less than 1% air saturation. The level of irreversible inactivation increased linearly with the oxygen concentration the organisms were adapted to before stress. Thus adaptation of cells to increased oxygen concentrations did not prevent increased susceptibility of nitrogenase to irreversible inhibition during oxygen stress. The fast response of irreversible inactivation at low stress heights suggests that it takes place already during stress. Thus switch off comprised both a reversible and an irreversible phase. The data showed that reversible inactivation of nitrogenase was less susceptible to oxygen stress than irreversible inactivation. A basic pre-requisite of the hypothesis of respiratory protection of nitrogenase, i.e. the proposed relationship between respiratory activities and the protection of nitrogenase from irreversible inhibition by oxygen, was not supported by the results of this report.     

Blood–Brain Barrier Pericytes Are the Main Source of γ-Glutamyltranspeptidase Activity in Brain Capillaries

Cerebral endothelial cells form the selective permeability barrier between brain and blood by virtue of their impermeable tight junctions and the presence of specific carrier systems. These specialized properties of brain capillaries are reflected in the presence of proteins that are not found in other capillaries of the body. gamma-Glutamyltranspeptidase (GGT) has been widely used as a marker for brain capillaries and differentiated properties of brain endothelial cells. By using histochemical and biochemical methods we have investigated the expression of GGT in isolated capillaries, cultured brain endothelial cells and pericytes, and cocultures of astrocytes and brain endothelial cells. It was surprising that the majority of GGT activity was associated with pericytes, but not endothelial cells, suggesting that GGT is a specific marker for brain pericytes. The remaining GGT activity that was associated with endothelial cells rapidly disappeared from cultured cells but was reinduced in cocultures with astrocytes. Our results emphasize the need for pure endothelial cells for the investigation of blood-brain barrier characteristics.     

Mitochondrial DNA sequence variation in the spruce budworm species complex (Choristoneura: Lepidoptera)

A combination of polymerase-chain-reaction amplification and automated DNA sequencing was used to survey variation in a species complex of pest insects, the spruce budworms (Choristoneura fumiferana species group), and an outgroup species, C. rosaceana. We sequenced an mtDNA region of 1,573 bp that extends from the middle of cytochrome oxidase subunit I (COI) through tRNA leucine (UUR) to the end of cytochrome oxidase subunit II. In addition, we examined levels of intraspecific variation within a 470-bp region of the COI gene. Choristoneura fumiferana clearly represented the oldest lineage within its species group, with 2.7%-2.9% sequence divergence from the other species. In contrast, the four remaining species (C. pinus, C. biennis, C. occidentalis, and C. orae) had closely related or identical mtDNA, with < 1% divergence among most of their haplotypes. Despite its older lineage and widespread geographic distribution, C. fumiferana showed significantly lower intraspecific genetic diversity than did C. occidentalis. Choristoneura orae shared haplotypes with C. occidentalis and C. biennis, and species-level separation of these three species was not supported. Two divergent, uncommon haplotypes were also found in C. occidentalis and C. biennis. The divergent haplotype in C. biennis had an unusually high number of inferred amino acid replacements, suggesting selective differences between mitochondrial DNA haplotypes. Transition:transversion ratios in Choristoneura paralleled those found in Drosophila; transition:transversion ratios were highest in closely related sequences but decreased with increasing sequence divergence. Nucleotide composition showed an A+T bias that was near the high end of the range known for insects. This work illustrates the potential utility of direct DNA sequencing in assessing population structures, species limits, and phylogenetic relationships among organisms that have not previously been subjected to DNA analysis.