Biomedical subjects

Saori Mori

Publications and source records attributed to Saori Mori.

9 recordsLinked to original sources

PubMed2006

Perturbation of the activity of replication origin by meiosis-specific transcription.

We have determined the activity of all ARSs on the Saccharomyces cerevisiae chromosome VI as chromosomal replication origins in premeiotic S-phase by neutral/neutral two-dimensional gel electrophoresis. The comparison of origin activity of each origin in mitotic and premeiotic S-phase showed that one of the most efficient origins in mitotic S-phase, ARS605, was completely inhibited in premeiotic S-phase. ARS605 is located within the open reading frame of MSH4 gene that is transcribed specifically during an early stage of meiosis. Systematic analysis of relationships between MSH4 transcription and ARS605 origin activity revealed that transcription of MSH4 inhibited the ARS605 origin activity by removing origin recognition complex from ARS605. Deletion of UME6, a transcription factor responsible for repressing MSH4 during mitotic S-phase, resulted in inactivation of ARS605 in mitosis. Our finding is the first demonstration that the transcriptional regulation on the replication origin activity is related to changes in cell physiology. These results may provide insights into changes in replication origin activity in embryonic cell cycle during early developmental stages.

Cell Cycle Proteins↗

PubMed2006

Monopolar attachment of sister kinetochores at meiosis I requires casein kinase 1.

In meiosis, a single round of DNA replication is followed by two consecutive rounds of chromosome segregation, called meiosis I and II. Disjunction of maternal from paternal centromeres during meiosis I depends on the attachment of sister kinetochores to microtubules emanating from the same pole. In budding yeast, monopolar attachment requires recruitment to kinetochores of the monopolin complex. How monopolin promotes monopolar attachment was unclear, as its subunits are poorly conserved and lack similarities to proteins with known functions. We show here that the monopolin subunit Mam1 binds tightly to Hrr25, a highly conserved casein kinase 1 delta/epsilon (CK1delta/epsilon), and recruits it to meiosis I centromeres. Hrr25 kinase activity and Mam1 binding are both essential for monopolar attachment. Since CK1delta/epsilon activity is important for accurate chromosome segregation during meiosis I also in fission yeast, phosphorylation of kinetochore proteins by CK1delta/epsilon might be an evolutionary conserved process required for monopolar attachment.

ATP-Binding Cassette Transporters↗

PubMed2006

A starvation-specific serine protease gene, isp6+, is involved in both autophagy and sexual development in Schizosaccharomyces pombe.

Schizosaccharomyces pombe isp6(+) gene encodes a vacuolar serine protease, which is specifically induced during nitrogen starvation. An isp6-disruption mutant, isp6Delta, grew normally under normal conditions but was defective in large-scale protein degradation during nitrogen starvation, a hallmark of autophagy. Vacuoles are the organelles for such drastic protein degradation but those of isp6Delta were apparently aberrant. isp6Delta was infertile under nitrogen source-free conditions with poor expression of ste11(+), a gene critical for sexual development. A protein kinase A-disruption mutant, pka1Delta, is prone to sexual development because expression of ste11(+) is derepressed. However, isp6Deltapka1Delta still showed defects in ste11(+) expression and sexual development under nitrogen source-free conditions. isp6Delta and isp6Deltapka1Delta were able to initiate sexual development to produce spores when only a small amount of a nitrogen source was present. Pat1 protein kinase negatively controls meiosis, and a temperature-sensitive mutant of pat1, pat1-114, initiates meiosis irrespective of ploidy at the restrictive temperature. However, isp6Deltapat1-114 did not start meiosis under nitrogen source-free conditions even at the restrictive temperature. These observations suggest that isp6(+) contributes to sexual development by providing a nitrogen source through autophagy.

Autophagy↗

PubMed2006

Protein phosphatase 2A protects centromeric sister chromatid cohesion during meiosis I.

Segregation of homologous maternal and paternal centromeres to opposite poles during meiosis I depends on post-replicative crossing over between homologous non-sister chromatids, which creates chiasmata and therefore bivalent chromosomes. Destruction of sister chromatid cohesion along chromosome arms due to proteolytic cleavage of cohesin's Rec8 subunit by separase resolves chiasmata and thereby triggers the first meiotic division. This produces univalent chromosomes, the chromatids of which are held together by centromeric cohesin that has been protected from separase by shugoshin (Sgo1/MEI-S332) proteins. Here we show in both fission and budding yeast that Sgo1 recruits to centromeres a specific form of protein phosphatase 2A (PP2A). Its inactivation causes loss of centromeric cohesin at anaphase I and random segregation of sister centromeres at the second meiotic division. Artificial recruitment of PP2A to chromosome arms prevents Rec8 phosphorylation and hinders resolution of chiasmata. Our data are consistent with the notion that efficient cleavage of Rec8 requires phosphorylation of cohesin and that this is blocked by PP2A at meiosis I centromeres.

Animals↗

PubMed2004

Spo13 facilitates monopolin recruitment to kinetochores and regulates maintenance of centromeric cohesion during yeast meiosis.

BACKGROUND: Cells undergoing meiosis perform two consecutive divisions after a single round of DNA replication. During the first meiotic division, homologous chromosomes segregate to opposite poles. This is achieved by (1) the pairing of maternal and paternal chromosomes via recombination producing chiasmata, (2) coorientation of homologous chromosomes such that sister chromatids attach to the same spindle pole, and (3) resolution of chiasmata by proteolytic cleavage by separase of the meiotic-specific cohesin Rec8 along chromosome arms. Crucially, cohesin at centromeres is retained to allow sister centromeres to biorient at the second division. Little is known about how these meiosis I-specific events are regulated. RESULTS: Here, we show that Spo13, a centromere-associated protein produced exclusively during meiosis I, is required to prevent sister kinetochore biorientation by facilitating the recruitment of the monopolin complex to kinetochores. Spo13 is also required for the reaccumulation of securin, the persistence of centromeric cohesin during meiosis II, and the maintenance of a metaphase I arrest induced by downregulation of the APC/C activator CDC20. CONCLUSION: Spo13 is a key regulator of several meiosis I events. The presence of Spo13 at centromere-surrounding regions is consistent with the notion that it plays a direct role in both monopolin recruitment to centromeres during meiosis I and maintenance of centromeric cohesion between the meiotic divisions. Spo13 may also limit separase activity after the first division by ensuring securin reaccumulation and, in doing so, preventing precocious removal from chromatin of centromeric cohesin.

ATP-Binding Cassette Transporters↗

PubMed2004

Cohesin relocation from sites of chromosomal loading to places of convergent transcription.

Sister chromatids, the products of eukaryotic DNA replication, are held together by the chromosomal cohesin complex after their synthesis. This allows the spindle in mitosis to recognize pairs of replication products for segregation into opposite directions. Cohesin forms large protein rings that may bind DNA strands by encircling them, but the characterization of cohesin binding to chromosomes in vivo has remained vague. We have performed high resolution analysis of cohesin association along budding yeast chromosomes III-VI. Cohesin localizes almost exclusively between genes that are transcribed in converging directions. We find that active transcription positions cohesin at these sites, not the underlying DNA sequence. Cohesin is initially loaded onto chromosomes at separate places, marked by the Scc2/Scc4 cohesin loading complex, from where it appears to slide to its more permanent locations. But even after sister chromatid cohesion is established, changes in transcription lead to repositioning of cohesin. Thus the sites of cohesin binding and therefore probably sister chromatid cohesion, a key architectural feature of mitotic chromosomes, display surprising flexibility. Cohesin localization to places of convergent transcription is conserved in fission yeast, suggesting that it is a common feature of eukaryotic chromosomes.

Cell Cycle Proteins↗

PubMed2004

In situ intestinal absorption studies on low molecular weight heparin in rats using labrasol as absorption enhancer.

Oral absorption of low molecular weight heparin (LMWH) is limited by its molecular size and negative charge. Development of its oral formulations would allow outpatient treatment with LMWH and decrease the hospital expenses. Studies were aimed at evaluating Labrasol for improving intestinal absorption of LMWH. Formulations containing LMWH and Labrasol were administered to duodenum, jejunum, and ileum of the fasted rats. The doses of LMWH and Labrasol were 200 IU/kg and 50 mg/kg, respectively. Reversibility of absorption enhancing effect of Labrasol was assessed by administering LMWH to jejunum after 0.5 and 1 h of administration of Labrasol. The effect of different doses of Labrasol on LMWH absorption was studied by administering Labrasol at 50, 100, and 200 mg/kg doses. Administration of LMWH formulation tojejunum resulted in the highest plasma anti-Xa activity (0.50+/-0.03 IU/ml) compared to duodenum (0.19+/-0.03 IU/ml), and ileum (0.29 +/-0.06 IU/ml) and the anti-Xa levels were maintained above the therapeutic level for about 160 min. The absorption of LMWH was negligible when LMWH was administered at 0.5 and 1 h post-Labrasol administration. Increasing the dose of Labrasol has decreased the absorption of LMWH from jejunum. Labrasol increased the intestinal absorption of LMWH, and jejunum was found to be the best site of absorption. Intestinal membrane permeability changes induced by Labrasol were transient and reversible. Maintaining high drug concentration gradient across intestinal wall is important to obtain increased intestinal LMWH absorption.

Animals↗

PubMed2004

Studies on the intestinal absorption of low molecular weight heparin using saturated fatty acids and their derivatives as an absorption enhancer in rats.

Intestinal absorption of low molecular weight heparin (LMWH) as well as unfractionated heparin (UFH) is limited due to its large molecular size and extensive negative charge. Development of its oral formulations would allow outpatient treatment with LMWH and UFH, and contribute a reduction in hospital expenses. The present study was aimed at evaluating the absorption enhancers Labrasol and Gelucire 44/14, which mainly consist of glycerides and fatty acids esters, to improve the intestinal absorption of LMWH. The absorption effects of saturated fatty acids with several carbon chain lengths (C6-C14) were also investigated. LMWH formulated with or without absorption enhancer was administered to the duodenum of fasted rats. The doses of LMWH and absorption enhancer were 20 mg/kg and 30 mg/kg, respectively. Plasma anti-Xa activity was measured as a marker of the LMWH absorption. By administration of the LMWH formulation with Labrasol but not with Gelucire 44/14, the plasma anti-Xa activity was increased to a level above 0.2 IU/ml which is the critical level for elucidation of its anticoagulant activity. Saturated fatty acids also enhanced the intestinal absorption of LMWH, and the order of absorption-enhancing effect was C10=C12>C14>C16>C8> or =C6. These results suggest that the intestinal absorption of LMWH varies with carbon chain lengths of the saturated fatty acids.

Adjuvants, Pharmaceutic↗

PubMed2002

Beta-hydroxybutyrate, a cerebral function improving agent, protects rat brain against ischemic damage caused by permanent and transient focal cerebral ischemia.

In our previous study, beta-hydroxybutyrate (BHB) was found to prolong survival time and to inhibit cerebral edema by improving energy metabolism in the hypoxia, anoxia and global cerebral ischemia models. In this study, the cerebroprotective effect of BHB was examined in rats with permanent (p)-occlusion and transient (t)-occlusion of middle cerebral artery (MCA). BHB (30 mg x kg(-1) x h(-1) was continuously administered through the femoral vein. In rats with p-MCA occlusion, BHB significantly reduced infarct area at 24 h after the occlusion, but not at 72 h after the occlusion. In rats with 2-h t-MCA occlusion followed by 22-h reperfusion, BHB significantly reduced cerebral infarct area, edema formation, lipid peroxidation and neurological deficits. Moreover, in the t-MCA occlusion model, delayed administration of BHB started at 1 h after the initiation of the MCA occlusion also significantly reduced cerebral infarct area. Taking together the results obtained in our previous study into account, these results indicate that BHB decreased cerebral edema formation and infarct area by improving of the cerebral energy metabolism during ischemia and by inhibition of lipid peroxidation after reperfusion.

3-Hydroxybutyric Acid↗