The 14-kDa dynein light chain-family protein Dlc1 is required for regular oscillatory nuclear movement and efficient recombination during meiotic prophase in fission yeast

A Schizosaccharomyces pombe spindle pole body (SPB) protein interacts in a two-hybrid system with Dlc1, which belongs to the 14-kDa Tctex-1 dynein light chain family. Green fluorescent protein-tagged Dlc1 accumulated at the SPB throughout the life cycle. During meiotic prophase, Dlc1 was present along astral microtubules and microtubule-anchoring sites on the cell cortex, reminiscent of the cytoplasmic dynein heavy chain Dhc1. In a dlc1-null mutant, Dhc1-dependent nuclear movement in meiotic prophase became irregular in its duration and direction. Dhc1 protein was displaced from the cortex anchors and the formation of microtubule bundle(s) that guide nuclear movement was impaired in the mutant. Meiotic recombination in the dlc1 mutant was reduced to levels similar to that in the dhc1 mutant. Dlc1 and Dhc1 also have roles in karyogamy and rDNA relocation during the sexual phase. Strains mutated in both the dlc1 and dhc1 loci displayed more severe defects in recombination, karyogamy, and sporulation than in either single mutant alone, suggesting that Dlc1 is involved in nuclear events that are independent of Dhc1. S. pombe contains a homolog of the 8-kDa dynein light chain, Dlc2. This class of dynein light chain, however, is not essential in either the vegetative or sexual phases.     

Conformational change in full-length mouse prion: a site-directed spin-labeling study

The structure of the mouse prion (moPrP) was studied using site-directed spin-labeling electron spin resonance (SDSL-ESR). Since a previous NMR study by Hornemanna et al., [Hornemanna, Korthb, Oeschb, Rieka, Widera, Wüthricha, Glockshubera, Recombinant full-length murine prion protein, mPrP (23-231): purification and spectroscopic characterization, FEBS Lett. 413 (1997) 277-281] has indicated that N96, D143, and T189 in moPrP are localized in a Cu²⁺ binding region, Helix1 and Helix2, respectively, three recombinant moPrP mutations (N96C, D143C, and T189C) were expressed in an Escherichia coli system, and then refolded by dialysis under low pH and purified by reverse-phase HPLC. By using the preparation, we succeeded in preserving a target cystein residue without alteration of the α-helix structure of moPrP and were able to apply SDSL-ESR with a methane thiosulfonate spin label to the full-length prion protein. The rotational correlation times (τ) of 1.1, 3.3, and 4.8 ns were evaluated from the X-band ESR spectra at pH 7.4 and 20 °C for N96R1, D143R1, and T189R1, respectively. τ reflects the fact that the Cu²⁺ binding region is more flexible than Helix1 or Helix2. ESR spectra recorded at various temperatures revealed two phases together with a transition point at around 20 °C in D143R1 and T189R1, but not in N96R1. With the variation of pH from 4.0 to 7.8, ESR spectra of T189R1 at 20 °C showed a gradual increase of τ from 2.9 to 4.8 ns. On the other hand, the pH-dependent conformational changes in N96R1 and D143R1 were negligible. These results indicated that T189 located in Helix2 possessed a structure sensitive to physiological pH changes; simultaneously, N96 in the Cu²⁺ binding region and D143 in Helix1 were conserved.     

Importance of local structures of second and third repeat fragments of microtubule-binding domain for tau filament formation

To investigate the importance of the seventh residue of the second and third repeat fragments (R2 and R3 peptides) of the microtubule-binding domain (MBD) for tau filamentous assembly, the residues Lys and Pro were substituted (R2-K7P and R3-P7K). The filament formations of the R2 and R3 peptides were almost lost due to their substitutions despite their overall conformational similarities. The NOE analyses showed the importance of the conformational flexibility for the R2 peptide and the coupled extended and helical conformations for the R3 peptide in their limited N-terminal regions around their seventh residues. The result shows that the filament formation of MBD is initiated from a short fragment region containing the minimal conformational or functional motif.     

Cytological affinities and interfertilities between Lolium temulentum and L. persicum (Poaceae) accessions

Interspecific crossing between L. temulentum L. and L. persicum Boiss. & Hohen. ex Boiss. was performed to clarify their interfertility based on the results of chromosome pairing, pollen fertility and seed set. Both parents were normal with a high percentage of chromosome association of ring bivalents in contrast to rod bivalents at metaphase I, pollen fertility and seed set, but F1 hybrids showed different proportions of them for each crossing combination. Chromosome affinity expressed by pairing was certainly a factor affecting the pollen fertility or seed set in F1 hybrids, but it was not the most important. The positive correlation was generally found between pollen fertility and seed set of F1 hybrids. The L. persicum accession with relatively high interfertility with L. temulentum was supposed to be derived from natural hybridization between L. temulentum and L. persicum. The degree of cytogenetic differentiation between L. temulentum and L. persicum existed because of lower chromosomal pairing, pollen fertility and seed set, but their F1 hybrids were partially fertile.     

Lysosomal phospholipase A2 is selectively expressed in alveolar macrophages

Lung surfactant is the surface-active agent comprised of phospholipids and proteins that lines pulmonary alveoli. Surfactant stabilizes the alveolar volume by reducing surface tension. Previously, we identified a lysosomal phospholipase A2, termed LPLA2, with specificity toward phosphatidylcholine and phosphatidylethanolamine. The phospholipase is localized to lysosomes, is calcium-independent, has an acidic pH optimum, and transacylates ceramide. Here, we demonstrate that LPLA2 is selectively expressed in alveolar macrophages but not in peritoneal macrophages, peripheral blood monocytes, or other tissues. Other macrophage-associated phospholipase A2s do not show a comparable distribution. LPLA2 is of high specific activity and recognizes disaturated phosphatidylcholine as a substrate. The lysosomal phospholipase A2 activity is six times lower in alveolar macrophages from mice with a targeted deletion of the granulocyte macrophage colony-stimulating factor (GM-CSF), a model of impaired surfactant catabolism, compared with those from wild-type mice. However, LPLA2 activity and protein levels are measured in GM-CSF null mice in which GM-CSF is expressed as a transgene under the control of the surfactant protein C promoter. Thus LPLA2 may be a major enzyme of pulmonary surfactant phospholipid degradation by alveolar macrophages and may be deficient in disorders of surfactant metabolism.     

Cellular stresses induce the nuclear accumulation of importin alpha and cause a conventional nuclear import block

We report here that importin alpha accumulates reversibly in the nucleus in response to cellular stresses including UV irradiation, oxidative stress, and heat shock. The nuclear accumulation of importin alpha appears to be triggered by a collapse in the Ran gradient, resulting in the suppression of the nuclear export of importin alpha. In addition, nuclear retention and the importin beta/Ran-independent import of importin alpha also facilitate its rapid nuclear accumulation. The findings herein show that the classical nuclear import pathway is down-regulated via the removal of importin alpha from the cytoplasm in response to stress. Moreover, whereas the nuclear accumulation of heat shock cognate 70 is more sensitive to heat shock than the other stresses, importin alpha is able to accumulate in the nucleus at all the stress conditions tested. These findings suggest that the stress-induced nuclear accumulation of importin alpha can be involved in a common physiological response to various stress conditions.     

Induction of tumor regression by administration of B7-Ig fusion proteins: mediation by type 2 CD8+ T cells and dependence on IL-4 production

CD28 signals contribute to either type 1 or type 2 T cell differentiation. Here, we show that administration of B7.2-Ig fusion proteins to tumor-bearing mice induces tumor regression by promoting the differentiation of antitumor type 2 CD8(+) effector T cells along with IL-4 production. B7.2-Ig-mediated regression was not induced in IL-4(-/-) and STAT6(-/-) mice. However, it was elicited in IFN-gamma(-/-) and STAT4(-/-) mice. By contrast, IL-12-induced tumor regression occurred in IL-4(-/-) and STAT6(-/-) mice, but not in IFN-gamma(-/-) and STAT4(-/-) mice. Moreover, B7.2-Ig treatment was effective in a tumor model not responsive to IL-12. B7.2-Ig administration elicited elevated levels of IL-4 production. Tumor regression was predominantly mediated by CD8(+) T cells, although the induction of these effector cells required CD4(+) T cells. Tumor regression induced by CD8(+) T cells alone was inhibited by neutralizing the IL-4 produced during B7.2-Ig treatment. Thus, these results indicate that stimulation in vivo of CD28 with B7.2-Ig in tumor-bearing mice results in enhanced induction of antitumor type 2 CD8(+) T cells (Tc2) leading to Tc2-mediated tumor regression.     

Functional expression of Ca2+ signaling pathways in mouse embryonic stem cells

Mouse embryonic stem (mES) cells have the potential to differentiate into all types of cells, but the physiological properties of undifferentiated mES cells, including Ca2+ signaling systems, are not fully understood. In this study, we investigated Ca2+ signaling pathways in mES cells by using confocal Ca2+ imaging systems, patch clamp techniques and RT-PCR. The stimulations with ATP and histamine (His) induced a transient increase of intracellular Ca2+ concentration ([Ca2+]i), which were prevented by the pretreatment of 2-amino-ethoxydiphenyl borate (2-APB), a blocker for inositol-1,4,5-triphosphate receptors (InsP3Rs). The application of caffeine (Caff) or ryanodine (Ry) did not change [Ca2+]i. When stores were depleted with Ca2+ -ATPase blocker, thapsigargin (TG), or histamine, the capacitative Ca2+ entry (CCE) was observed. In whole cell patch clamp mode, store-operated Ca2+ currents could be recorded in cells treated with histamine and thapsigargin. On the other hand, voltage-operated Ca2+ channels (VOCCs) could not be elicited. The application of blockers for plasma membrane Ca2+ pump (PMCAs) (carboxeosin or caloxin2A1) induced a large increase of [Ca2+]i. When the Na+/Ca2+ exchangers (NCXs) were blocked by Na+ free solution or KBR7943, [Ca2+]i was also elevated. Using RT-PCR, mRNAs for InsP3Rs type-1, -2, and -3, PMCA-1 and -4, NCX-1, -2, and -3 could be detected. From these results, we conclude that Ca2+ release from ER is mediated by InsP3Rs in mES cells before differentiation and Ca2+ entry through plasma membrane is mainly mediated by the store-operated Ca2+ channels (SOCs). For the Ca2+ extrusion systems, both NCXs and PMCAs play important roles for maintaining the low level of [Ca2+]i.