IRBIT suppresses IP3 receptor activity by competing with IP3 for the common binding site on the IP3 receptor

The inositol 1,4,5-trisphosphate (IP3) receptors (IP3Rs) are IP3-gated intracellular Ca2+ channels. We previously identified an IP3R binding protein, IRBIT, which binds to the IP3 binding domain of IP3R and is dissociated from IP3R in the presence of IP3. In the present study, we showed that IRBIT suppresses the activation of IP3R by competing with IP3 by [3H]IP3 binding assays, in vitro Ca2+ release assays, and Ca2+ imaging of intact cells. Multiserine phosphorylation of IRBIT was essential for the binding, and 10 of the 12 key amino acids in IP3R for IP3 recognition participated in binding to IRBIT. We propose a unique mode of IP3R regulation in which IP3 sensitivity is regulated by IRBIT acting as an endogenous "pseudoligand" whose inhibitory activity can be modulated by its phosphorylation status.     

Insight into the basis of root growth in Arabidopsis thaliana provided by a simple mathematical model

Plant organ growth changes under genetic and environmental influences can be observed as altered cell proliferation and volume growth. The two aspects are mutually dependent and intricately related. For comprehensive growth analysis, it is necessary to specify the relationship quantitatively. Here, we develop a simple mathematical model for this purpose. Our model assumes that the biological activity of a given organ is proportional to the cell number of the organ and is allocated into three aspects: cell proliferation, volume growth, and organ maintenance. We analyzed the growth of primary roots of Arabidopsis thaliana (L.) Heynh. in one tetraploid and four diploid strains using this model. The analysis determined various growth parameters, such as specific cost coefficients of cell proliferation and volume growth for each strain. The results provide insight into the basis of interstrain variations and ploidy effects in root growth.     

Whole-Body Water Flow Stimulation to the Lower Limbs Modulates Excitability of Primary Motor Cortical Regions Innervating the Hands: A Transcranial Magnetic Stimulation Study

Whole-body water immersion (WI) has been reported to change sensorimotor integration. However, primary motor cortical excitability is not affected by low-intensity afferent input. Here we explored the effects of whole-body WI and water flow stimulation (WF) on corticospinal excitability and intracortical circuits. Eight healthy subjects participated in this study. We measured the amplitude of motor-evoked potentials (MEPs) produced by single transcranial magnetic stimulation (TMS) pulses and examined conditioned MEP amplitudes by paired-pulse TMS. We evaluated short-interval intracortical inhibition (SICI) and intracortical facilitation (ICF) using the paired-TMS technique before and after 15-min intervention periods. Two interventions used were whole-body WI with water flow to the lower limbs (whole-body WF) and whole-body WI without water flow to the lower limbs (whole-body WI). The experimental sequence included a baseline TMS assessment (T0), intervention for 15 min, a second TMS assessment immediately after intervention (T1), a 10 min resting period, a third TMS assessment (T2), a 10 min resting period, a fourth TMS assessment (T3), a 10 min resting period, and the final TMS assessment (T4). SICI and ICF were evaluated using a conditioning stimulus of 90% active motor threshold and a test stimulus adjusted to produce MEPs of approximately 1–1.2 mV, and were tested at intrastimulus intervals of 3 and 10 ms, respectively. Whole-body WF significantly increased MEP amplitude by single-pulse TMS and led to a decrease in SICI in the contralateral motor cortex at T1, T2 and T3. Whole-body WF also induced increased corticospinal excitability and decreased SICI. In contrast, whole-body WI did not change corticospinal excitability or intracortical circuits.     

Role of Pin1 Protein in the Pathogenesis of Nonalcoholic Steatohepatitis in a Rodent Model

Nonalcoholic steatohepatitis (NASH) is a disorder characterized by simultaneous fat accumulation and chronic inflammation in the liver. In this study, Pin1 expression was revealed to be markedly increased in the livers of mice with methionine choline-deficient (MCD) diet-induced NASH, a rodent model of NASH. In addition, Pin1 KO mice were highly resistant to MCD-induced NASH, based on a series of data showing simultaneous fat accumulation, chronic inflammation, and fibrosis in the liver. In terms of Pin1-induced fat accumulation, it was revealed that the expression levels of peroxisome proliferator-activated receptor α and its target genes were higher in the livers of Pin1 KO mice than in controls. Thus, resistance of Pin1 KO mice to hepatic steatosis is partially attributable to the lack of Pin1-induced down-regulation of peroxisome proliferator-activated receptor α, although multiple other mechanisms are apparently involved. Another mechanism involves the enhancing effect of hematopoietic Pin1 on the expressions of inflammatory cytokines such as tumor necrosis factor and monocyte chemoattractant protein 1 through NF-κB activation, eventually leading to hepatic fibrosis. Finally, to distinguish the roles of hematopoietic or nonhematopoietic Pin1 in NASH development, mice lacking Pin1 in either nonhematopoietic or hematopoietic cells were produced by bone marrow transplantation between wild-type and Pin1 KO mice. The mice having nonhematopoietic Pin1 exhibited fat accumulation without liver fibrosis on the MCD diet. Thus, hepatic Pin1 appears to be directly involved in the fat accumulation in hepatocytes, whereas Pin1 in hematopoietic cells contributes to inflammation and fibrosis. In summary, this is the first study to demonstrate that Pin1 plays critical roles in NASH development. This report also raises the possibility that hepatic Pin1 inhibition to the appropriate level might provide a novel therapeutic strategy for NASH.     

The genetic population structure of lacustrine sockeye salmon, <Emphasis Type="Italic">Oncorhynchus nerka,</Emphasis> in Japan as the endangered species

Lacustrine sockeye salmon (Oncorhynchus nerka) are listed as an endangered species in Japan despite little genetic information on their population structure. In order to clarify the genetic diversity and structure of Japanese populations for evaluating on the bottleneck effect and an endangered species, we analyzed the ND5 region of mitochondrial DNA (mtDNA) and 45 single nucleotide polymorphisms (SNPs) in 640 lacustrine sockeye salmon in Japan and 80 anadromous sockeye salmon in Iliamna Lake of Alaska. The genetic diversity of the Japanese population in both mtDNA and SNPs was significantly less than that of the Iliamna Lake population. Moreover, all Japanese populations had SNP loci deviating from the HWE. In spite of low genetic diversity, the SNP analyses resulted that the Japanese population was significantly divided into three groups. These suggest that Japanese sockeye salmon populations should be protected as an endangered species and genetically disturbed by the hatchery program and transplantations.     

Aluminum-induced secretion of both citrate and malate in rye

Aluminum (Al)-resistant mechanisms responsible for Al-induced secretion of organic acids are poorly understood. In this study, we characterized the Al-induced secretion of both citrate and malate from rye (Secale cereale L. cv. King). Secretion of organic acids increased with increasing concentration (10, 30 and 50 M) and duration of Al treatments. Neither phosphorous (P) deficiency up to 15 days nor addition of 50M lanthanum, 50 M lead, 10 M cadmium, or 200 M manganese caused secretion of organic acids, suggesting that this secretion was a specific response to Al stress. Aluminum activated citrate synthase, the main enzyme for the synthesis of citrate, but its activation occurred only in the root tip. The elongation of roots of an Al-sensitive cultivar of wheat (Tritium aestivum L. cv. Scout 66) was not inhibited by 50 M Al in the presence of externally applied 50 M citrate or 400 M malate. The secretion of citrate and malate from intact rye roots exposed to 50 M Al corresponded to 31.3 ± 1.7 M and 11.5 ± 2.5 M, respectively, in the rhizosphere based on an assumption of a 2 mm thick unstirred layer around root tips. This result indicated that Al-resistance in rye was achieved by the Al-induced synthesis of citrate in root apices followed by Al-induced specific secretion of citrate from root tips.     

Deletion of a chaperonin 60 beta gene leads to cell death in the Arabidopsis lesion initiation 1 mutant

Lesion mimic mutants develop spontaneous cell death without pathogen attack. Some of the genes defined by these mutations may function as regulators of cell death, whereas others may perturb cellular metabolism in a way that leads to cell death. To understand the molecular mechanism of cell death in lesion mimic mutants, we isolated a lesion initiation 1 (len1) mutant by a T-DNA tagging method. The len1 mutant develops lesions on its leaves and expresses systemic acquired resistance (SAR). LEN1 was identified to encode a chloroplast chaperonin 60 beta (Cpn60 beta), a homologue of bacterial GroEL. The recombinant LEN1 had molecular chaperone activity for suppressing protein aggregation in vitro. Moreover, len1 plants develop accelerated cell death to heat shock stress in comparison with wild-type plants. The chlorophyll a/b binding protein (CAB) was present in len1 plants at a lower level than in the wild-type plants. These results indicate that LEN1 functions as a molecular chaperone in chloroplasts and its deletion leads to cell death in Arabidopsis.     

Mechanisms of Al‐induced iron chlorosis in wheat (Triticum aestivum). Al‐inhibited biosynthesis and secretion of phytosiderophore

Although Al‐induced iron chlorosis has been observed in many plants, the mechanisms responsible for this phenomenon are yet to be understood. We investigated the effect of Al on iron acquisition in a Strategy II plant, wheat ( Triticum aestivum L.) using both Al‐tolerant (Atlas 66) and ‐sensitive (Scout 66) cultivars. When iron was supplied as insoluble iron, ferric hydroxide, in the culture solution, both cultivars without Al treatment grew normally, while those with 100 µ M AlCl₃ developed chlorosis of the young leaves after 3 days of the treatment. A 21‐h treatment with 100 µ M AlCl₃ in 0.5 m M CaCl₂ solution (pH 4.5) decreased the amount of 2'‐deoxymugineic acid (DMA) secreted by Fe‐deficient Atlas 66 and Scout 66 plants by 85 and 90%, respectively. The amount of DMA secreted decreased with increasing external Al concentrations. Al treatment during the biosynthesis process caused the inhibition of that of DMA within 3 h. The secretion process was also found to be inhibited by Al, resulting in the biosynthesized DMA remaining in the roots. These results demonstrate the inhibition by Al of both biosynthesis and secretion of DMA attributed to Al‐induced iron chlorosis.     

Altered conditioned fear behavior in glutamate decarboxylase 65 null mutant mice

We investigated the involvement of the 65 kDa isoform of glutamic acid decarboxylase (GAD65) and GAD65-mediated γ-aminobutyric acid (GABA) synthesis in the formation and expression of Pavlovian fear memory. To this end, behavioral, endocrine and autonomic parameters were examined during conditioned fear retrieval of mice with targeted ablation of the GAD65 gene (GAD65^–/– mice). These mutant mice were found to display specific fear behavior (freezing, escape), as well as autonomic (increased defecation) and endocrine activation (increased plasma corticosterone) during fear memory retrieval. However, freezing was reduced and flight and escape behavior were increased in GAD65^–/– mice compared to their wild type and heterozygous littermates, while corticosterone levels and defecation rates did not differ between genotypes. Active defensive behavior of GAD65^–/– mice was observed during both auditory cued and contextual retrieval of fear memory, as well as immediately after conditioning. These data indicate a selectively altered behavioral fear response in GAD65^–/– mice, most likely due to deficits in threat estimation or the elicitation of appropriate conditioned fear behavior, and suggest that GAD65 is a genetic determinant of conditioned fear behavior. GAD65^–/– mice provide a valuable tool to further dissect the GABAergic mechanisms involved in fear and anxiety and to model GABA-related neurological and psychiatric disorders.