Meiosis in NEUROSPORA CRASSA. I. the Isolation of Recessive Mutants Defective in the Production of Viable Ascospores

A scheme has been devised for efficient isolation of recessive meiotic mutants of Neurospora crassa. These mutants were detected by their reduced fertility or by the abortion of ascospores. Their isolation involved the selection and screening of the strains arising from ascospores disomic (n + 1) for linkage group I (LG I), which bears the mating-type locus. These strains are self-fertile heterokaryons that contain two types of haploid nuclei of opposite mating types (A + a). Selfings of these strains are homozygous for genes on all linkage groups except LGI and therefore allow the expression of recessive mutants with an altered sexual cycle. Using this selection procedure, three classes of mutants were detected. In one class, mutants had an early block in perithecial development (class I), and in another mutants had altered perithecia, but apparently unaltered fertility (class III). No recessive mutants were observed and all mutants tested (eight of class I and two of class III) were expressed only when used as the maternal parent. A third mutant class displayed normal production of perithecia, but defective formation of asci (class IIA), or black ascospores (class IIB). Four of 13 class IIA mutants were analyzed, and two of them [asc(DL131) and asc (DL400)] were definitely recessive analysis of 10 of 13 class IIB mutants disclosed six recessive, mutually complementing mutants: ase(DL95), asc(DL243), asc(DL711), asc(DL879), asc(DL917m) and asc(DL961). Mutants asc(DL95), asc(DL243) and the previously studied mei-1 mutant (Smith 1975) complemented one another in crosses, but did not recombine. These may be alleles of the same gene, or they may comprise a gene cluster.     

Allele frequencies in the VRN-A1, VRN-B1 and VRN-D1 vernalization response and PPD-B1 and PPD-D1 photoperiod sensitivity genes,and their effects on heading in a diverse set of wheat cultivars (Triticum aestivum L.)

Heading of cereals is determined by complex genetic and environmental factors in which genes responsible for vernalization and photoperiod sensitivity play a decisive role. Our aim was to use diagnostic molecular markers to determine the main allele types in VRN-A1, VRN-B1, VRN-D1, PPD-B1 and PPD-D1 in a worldwide wheat collection of 683 genotypes and to investigate the effect of these alleles on heading in the field. The dominant VRN-A1, VRN-B1 and VRN-D1 alleles were present at a low frequency. The PPD-D1a photoperiod-insensitive allele was carried by 57 % of the cultivars and was most frequent in Asian and European cultivars. The PPD-B1 photoperiod-insensitive allele was carried by 22 % of the genotypes from Asia, America and Europe. Nine versions of the PPD-B1-insensitive allele were identified based on gene copy number and intercopy structure. The allele compositions in PPD-D1, PPD-B1 and VRN-D1 significantly influenced heading and together explained 37.5 % of the phenotypic variance. The role of gene model increased to 39.1 % when PPD-B1 intercopy structure was taken into account instead of overall PPD-B1 type (sensitive vs. insensitive). As a single component, PPD-D1 had the most important role (28.0 % of the phenotypic variance), followed by PPD-B1 (12.3 % for PPD-B1_overall, and 15.1 % for PPD-B1_intercopy) and VRN-D1 (2.2 %). Significant gene interactions were identified between the marker alleles within PPD-B1 and between VRN-D1 and the two PPD1 genes. The earliest heading genotypes were those with the photoperiod-insensitive allele in PPD-D1 and PPD-B1, and with the spring allele for VRN-D1 and the winter alleles for VRN-A1 and VRN-B1. This combination could only be detected in genotypes from Southern Europe and Asia. Late-heading genotypes had the sensitivity alleles for both PPD1 genes, regardless of the allelic composition of the VRN1 genes. There was a 10-day difference in heading between the earliest and latest groups under field conditions.     

A common cortical substrate activated by horizontal and vertical sound movement in the human brain

Perception of movement in acoustic space depends on comparison of the sound waveforms reaching the two ears (binaural cues) as well as spectrotemporal analysis of the waveform at each ear (monaural cues). The relative importance of these two cues is different for perception of vertical or horizontal motion, with spectrotemporal analysis likely to be more important for perceiving vertical shifts. In humans, functional imaging studies have shown that sound movement in the horizontal plane activates brain areas distinct from the primary auditory cortex, in parietal and frontal lobes and in the planum temporale. However, no previous work has examined activations for vertical sound movement. It is therefore difficult to generalize previous imaging studies, based on horizontal movement only, to multidimensional auditory space perception. Using externalized virtual-space sounds in a functional magnetic resonance imaging (fMRI) paradigm to investigate this, we compared vertical and horizontal shifts in sound location. A common bilateral network of brain areas was activated in response to both horizontal and vertical sound movement. This included the planum temporale, superior parietal cortex, and premotor cortex. Sounds perceived laterally in virtual space were associated with contralateral activation of the auditory cortex. These results demonstrate that sound movement in vertical and horizontal dimensions engages a common processing network in the human cerebral cortex and show that multidimensional spatial properties of sounds are processed at this level.     

Combined monte carlo and molecular dynamics simulation of fully hydrated dioleyl and palmitoyl-oleyl phosphatidylcholine lipid bilayers

We have applied a new equilibration procedure for the atomic level simulation of a hydrated lipid bilayer to hydrated bilayers of dioleyl-phosphatidylcholine (DOPC) and palmitoyl-oleyl phosphatidylcholine (POPC). The procedure consists of alternating molecular dynamics trajectory calculations in a constant surface tension and temperature ensemble with configurational bias Monte Carlo moves to different regions of the configuration space of the bilayer in a constant volume and temperature ensemble. The procedure is applied to bilayers of 128 molecules of POPC with 4628 water molecules, and 128 molecules of DOPC with 4825 water molecules. Progress toward equilibration is almost three times as fast in central processing unit (CPU) time compared with a purely molecular dynamics (MD) simulation. Equilibration is complete, as judged by the lack of energy drift in 200-ps runs of continuous MD. After the equilibrium state was reached, as determined by agreement between the simulation volume per lipid molecule with experiment, continuous MD was run in an ensemble in which the lateral area was restrained to fluctuate about a mean value and a pressure of 1 atm applied normal to the bilayer surface. Three separate continuous MD runs, 200 ps in duration each, separated by 10,000 CBMC steps, were carried out for each system. Properties of the systems were calculated and averaged over the three separate runs. Results of the simulations are presented and compared with experimental data and with other recent simulations of POPC and DOPC. Analysis of the hydration environment in the headgroups supports a mechanism by which unsaturation contributes to reduced transition temperatures. In this view, the relatively horizontal orientation of the unsaturated bond increases the area per lipid, resulting in increased water penetration between the headgroups. As a result the headgroup-headgroup interactions are attenuated and shielded, and this contributes to the lowered transition temperature.     

Steroids and the prostate

Interelationships between steroid and growth factor regulation of cell proliferation has been examined in two androgen sensitive prostatic cell lines, grown in defined medium. The cell lines used were derived from normal (CAPE) and neoplastic (LNCaP) tissues. The growth of both cell lines was elevated by challenge with serum, androgens and epidermal growth factor (EGF) used as single agents. The effects of androgen in CAPE were small, but significant while the profound effects of these agents on the growth of LNCaP were confirmatory of other studies. Androgens upregulated EGF receptor expression in LNCaP measured by both ligand binding capacity and mRNA analysis. This was not observed in the CAPE cells. Addition of serum (whole or charcoal stripped) suppressed the observed androgenic stimulation of EGF receptor expression in LNCaP. This apparent anomaly is discussed in relation to the growth enhancing properties of serum in these cell lines and in the wider context of normal and neoplastic growth control in the prostate.     

On the vapour trail of an atmospheric imprint in insects

Terrestrial arthropods, at constant risk from desiccation, are highly sensitive to atmospheric temperature and humidity. A physiological marker of these abiotic conditions could highlight phenotypic adaptations, indicate niche partitioning, and predict responses to climate change for a group representing three-quarters of the Earth's animal species. We show that the (18)O composition of insect haemolymph is such a measure, providing a dynamic and quantitatively predictable signal for respiratory gas exchange and inputs from atmospheric humidity. Using American cockroaches (Periplaneta americana) under defined experimental conditions, we show that insects respiring at low humidity demonstrate the expected enrichment in the (18)O composition of haemolymph because of evaporation. At high humidity, however, diffusional influx of atmospheric water vapour into the animal forces haemolymph to become depleted in (18)O. Additionally, using cockroaches sampled from natural habitats, we show that the haemolymph (18)O signature is transferred to the organic material of the insect's exoskeleton. Insect cuticle, therefore, exhibits the mean atmospheric conditions surrounding the animals prior to moulting. This discovery will help to define the climatic tolerances of species and their habitat preferences, and offers a means of quantifying the balance between niche partitioning and 'neutral' processes in shaping complex tropical forest communities.     

Deletion of a xenobiotic metabolizing gene in mice affects folate metabolism

The mouse arylamine N-acetyltransferase 2 (Nat2) and its homologue (NAT1) in humans are known to detoxify xenobiotic arylamines and are also thought to play a role in endogenous metabolism. Human NAT1 is highly over-expressed in estrogen receptor positive breast tumours and is implicated in susceptibility to neural tube defects. In vitro assays have suggested an endogenous role for human NAT1 in folate metabolism, but in vivo evidence to support this hypothesis has been lacking. Mouse Nat2 provides a good model to study human NAT1 as it shows similar expression profiles and substrate specificities. We have generated transgenic mice lacking a functional Nat2 gene and compared the urinary levels of acetylated folate metabolite para-aminobenzoylglutamate in Nat2 knockout and Nat2 wild-type mice. These results support an in vivo role for mouse Nat2/human NAT1 in folate metabolism. In addition, effects of the Nat2 deletion on sex ratios and neural tube development are described.     

Report from the second cytomegalovirus and immunosenescence workshop

The Second International Workshop on CMV & Immunosenescence was held in Cambridge, UK, 2-4th December, 2010. The presentations covered four separate sessions: cytomegalovirus and T cell phenotypes; T cell memory frequency, inflation and immunosenescence; cytomegalovirus in aging, mortality and disease states; and the immunobiology of cytomegalovirus-specific T cells and effects of the virus on vaccination. This commentary summarizes the major findings of these presentations and references subsequently published work from the presenter laboratory where appropriate and draws together major themes that were subsequently discussed along with new areas of interest that were highlighted by this discussion.