Four loci on abnormal chromosome 10 contribute to meiotic drive in maize

We provide a genetic analysis of the meiotic drive system on maize abnormal chromosome 10 (Ab10) that causes preferential segregation of specific chromosomal regions to the reproductive megaspore. The data indicate that at least four chromosomal regions contribute to meiotic drive, each providing distinct functions that can be differentiated from each other genetically and/or phenotypically. Previous reports established that meiotic drive requires neocentromere activity at specific tandem repeat arrays (knobs) and that two regions on Ab10 are involved in trans-activating neocentromeres. Here we confirm and extend data suggesting that only one of the neocentromere-activating regions is sufficient to move many knobs. We also confirm the localization of a locus/loci on Ab10, thought to be a prerequisite for meiotic drive, which promotes recombination in structural heterozygotes. In addition, we identified two new and independent functions required for meiotic drive. One was identified through the characterization of a deletion derivative of Ab10 [Df(L)] and another as a newly identified meiotic drive mutation (suppressor of meiotic drive 3). In the absence of either function, meiotic drive is abolished but neocentromere activity and the recombination effect typical of Ab10 are unaffected. These results demonstrate that neocentromere activity and increased recombination are not the only events required for meiotic drive.     

Beta 2 subunit propeptides influence cooperative proteasome assembly

Vertebrate proteasomes are structurally heterogeneous, consisting of both "constitutive" (or "standard") proteasomes and "immunoproteasomes." Constitutive proteasomes contain three ubiquitously expressed catalytic subunits, Delta (beta 1), Z (beta 2), and X (beta 5), whereas immunoproteasomes contain three interferon-gamma-inducible catalytic subunits, LMP2 (beta 1i), MECL (beta 2i), and LMP7 (beta 5i). We recently have demonstrated that proteasome assembly is biased to promote immunoproteasome homogeneity when both types of catalytic subunits are expressed in the same cell. This cooperative assembly is due in part to differences between the LMP7 (beta 5i) and X (beta 5) propeptides. In the current study we demonstrate that differences between the MECL (beta 2i) and Z (beta2) propeptides also influence cooperative assembly. Specifically, replacing the MECL propeptide with that of Z enables MECL incorporation into otherwise constitutive (Delta(+)/X(+)) proteasomes and facilitates X incorporation into otherwise immunoproteasomes (MECL(+)/LMP2(+)). We also show, using MECL(-/-) mice, that LMP2 incorporation does not require MECL, in contrast with previous suggestions that their incorporation is mutually codependent. These results enable us to refine our model for cooperative proteasome assembly by determining which combinations of inducible and constitutive subunits are favored over others, and we propose a mechanism for how propeptides mediate cooperative assembly.     

Compartmentation of metabolism probed by [2-13C]alanine: improved 13C NMR sensitivity using a CryoProbe detects evidence of a glial metabolon

The labelling of metabolites with the NMR active nucleus 13C allows not only metabolite enrichments to be monitored, but also the relative fluxes through competing pathways to be delineated. [2-13C, 15N]alanine was used as a metabolic probe to investigate compartmentation in superfused cerebral slices. Perchloric acid extracts of the tissue were investigated using 13C NMR spectroscopy. The spectra were obtained using a CryoProbe optimised for 13C detection (dual CryoProbe [13C, 1H]) in which the receiver and transmitter coils are cooled to approximately 20K to reduce contributions to noise in the signal obtained. Compared with conventional inverse geometry probe, the signal-to-noise ratio (S/N) was increased by approximately 17-fold using this device. A large proportion of alanine was initially metabolised over the first 20 min by glial cells, as indicated by the relative importance of the glial, only enzyme pyruvate carboxylase to the labelling pattern of glutamate, with the ratio of pyruvate carboxylase to pyruvate dehydrogenase derived glutamate being 0.25, and exported [2-13C, 15N]aspartate.Using the increased sensitivity of the CryoProbe, [2-13C, 15N]aspartate was also detected in the extracts of cerebral tissue. This metabolite could only have been derived via the pyruvate carboxylase pathway, and given the large export of the metabolite into the superfusion buffer suggests the occurrence of a "metabolon" arrangement of enzymes within glial cells.     

Influence of environmental pH on G2-phase arrest caused by ionizing radiation

We investigated the effects of an acidic environment on the G2/M-phase arrest, apoptosis, clonogenic death, and changes in cyclin B1-CDC2 kinase activity caused by a 4-Gy irradiation in RKO.C human colorectal cancer cells in vitro. The time to reach peak G2/M-phase arrest after irradiation was delayed in pH 6.6 medium compared to that in pH 7.5 medium. Furthermore, the radiation-induced G2/M-phase arrest decayed more slowly in pH 6.6 medium than in pH 7.5 medium. Finally, there was less radiation-induced apoptosis and clonogenic cell death in pH 6.6 medium than in pH 7.5 medium. It appeared that the prolongation of G2-phase arrest after irradiation in the acidic environment allowed for greater repair of radiation-induced DNA damage, thereby decreasing the radiation-induced cell death. The prolongation of G2-phase arrest after irradiation in the acidic pH environment appeared to be related at least in part to a prolongation of the phosphorylation of CDC2, which inhibited cyclin B1-CDC2 kinase activity.     

A supramodal number representation in human intraparietal cortex

The triple-code theory of numerical processing postulates an abstract-semantic "number sense." Neuropsychology points to intraparietal cortex as a potential substrate, but previous functional neuroimaging studies did not dissociate the representation of numerical magnitude from task-driven effects on intraparietal activation. In an event-related fMRI study, we presented numbers, letters, and colors in the visual and auditory modality, asking subjects to respond to target items within each category. In the absence of explicit magnitude processing, numbers compared with letters and colors across modalities activated a bilateral region in the horizontal intraparietal sulcus. This stimulus-driven number-specific intraparietal response supports the idea of a supramodal number representation that is automatically accessed by presentation of numbers and may code magnitude information.     

The role of neurotrophin receptors in female germ-cell survival in mouse and human

During mammalian ovary formation, the production of ovarian follicles is accompanied by an enormous loss of germ cells. It is not known how this loss is regulated. We have investigated the role of the Trk tyrosine kinase receptors, primarily TrkB, in this process. The ovaries of TrkB-/- and TrkC-/- mice with a mixed (129Sv x C57BL/6) genetic background were examined shortly after birth. Around 50% of TrkB-/- mice had grossly abnormal ovaries that contained greatly reduced numbers of follicles. No defects were found in the ovaries of TrkC-/- mice. Congenic TrkB-/- mice were generated on 129Sv and C57BL/6 backgrounds: whereas the former had a mixed ovarian phenotype similar to that of the original colony of mice, the ovaries of all offspring of the C57BL/6 congenic line contained reduced numbers of follicles. RT-PCR showed that mRNA encoding TrkB and its two ligands, neurotrophin 4 (NT4) and brain-derived neurotrophic factor (BDNF), were present throughout the period of follicle formation in the mouse. In situ hybridisation showed that TrkB was expressed primarily in the germ cells before and after follicle formation. Mouse neonatal and fetal ovaries and human fetal ovaries were cultured in the presence of K252a, a potent inhibitor of all Trk receptors. In mice, K252a inhibited the survival of germ cells in newly formed (primordial) follicles. This effect was rescued by the addition of basic fibroblast growth factor (bFGF) to the culture medium. Combined addition of both BDNF and NT4 blocking antibodies lowered germ-cell survival, indicating that these TrkB ligands are required in this process. The results indicate that signalling through TrkB is an important component of the mechanism that regulates the early survival of female germ cells.     

Enantiotracin

The enantiomer of the antibiotic bacitracin A was prepared by solid-phase total synthesis. ent-Bacitracin A was found to be equally potent to the natural enantiomer in in vitro susceptibility assays. This supports the notion that bacitracin exerts its antibacterial effects through interaction with bactoprenylpyrophosphate, an achiral ligand.     

Discovery and biological evaluation of potent dual ErbB-2/EGFR tyrosine kinase inhibitors: 6-thiazolylquinazolines

We have identified a novel class of 6-thiazolylquinazolines as potent and selective inhibitors of both ErbB-2 and EGFR tyrosine kinase activity, with IC(50) values in the nanomolar range. These compounds inhibited the growth of both EGFR (HN5) and ErbB-2 (BT474) over-expressing human tumor cell lines in vitro. Using xenograft models of the same cell lines, we found that the compounds given orally inhibited in vivo tumor growth significantly compared with control animals.