Ohta T et al. (2004) Oncogene "Ubiquitin and breast cancer."

Fukuda M, Ohta T

[Oncogene, 2004]

The regulation of protein stability by the ubiquitin-proteasome pathway is a critical issue central to the comprehension of the molecular basis of carcinogenesis. However, ubiquitin modification of target substrates signals many cellular processes other than proteolysis that are also important for the development of cancer. It is noteworthy that many proteins studied by clinical breast cancer researchers are involved in these ubiquitin pathways. This review summarizes recent works on such proteins including cyclins, CDK inhibitors, and the SCF in cell cycle control; the breast and ovarian cancer suppressor BRCA1-BARD1; ErbB2/HER2/Neu and its ubiquitin ligase c-Cbl or CHIP; and the estrogen receptor and its downstream target Efp. Understanding these pathways may provide some hints toward developing diagnostic tools and treatments for breast cancer patients.

Ohta M et al. (2017) Elife "How centrioles acquire the ability to reproduce."

Oegema K, Ohta M, Desai A

[Elife, 2017]

A protein called SAS-7 is required for daughter centrioles to become mothers in C. elegans.

Ohta A et al. (2014) Nat Commun "Light and pheromone-sensing neurons regulates cold habituation through insulin signalling in Caenorhabditis elegans."

Kuhara A, Ohta A, Sonoda S, Ujisawa T

[Nat Commun, 2014]

Temperature is a critical environmental stimulus that has a strong impact on an organism's biochemistry. Animals can respond to changes in ambient temperature through behaviour or altered physiology. However, how animals habituate to temperature is poorly understood. The nematode C. elegans stores temperature experiences and can induce temperature habituation-linked cold tolerance. Here we show that light and pheromone-sensing neurons (ASJ) regulate cold habituation through insulin signalling. Calcium imaging reveals that ASJ neurons respond to temperature. Cold habituation is abnormal in a mutant with impaired cGMP signalling in ASJ neurons. Insulin released from ASJ neurons is received by the intestine and neurons regulating gene expression for cold habituation. Thus, temperature sensation in a light and pheromone-sensing neuron produces a robust effect on insulin signalling that controls experience-dependent temperature habituation.

Ohta A et al. (2013) Neurosci Res "Molecular mechanism for trimetric G protein-coupled thermosensation and synaptic regulation in the temperature response circuit of Caenorhabditis elegans."

Kuhara A, Ohta A

[Neurosci Res, 2013]

How the nervous system controls the sensation and memory of information from the environment is an essential question. The nematode Caenorhabditis elegans is a useful model for elucidating neural information processing that mediates sensation and memory. The entire nervous system of C. elegans consists of only 302 neurons, and their wiring diagram has been revealed by electron microscopy analysis. Here, we review the molecular and physiological mechanisms responsible for the neural circuit-mediated temperature-seeking behavior (thermotaxis) in C. elegans. Recent molecular biology studies and optogenetic analyses, such as the optical manipulation of neural activity, and neural imaging have revealed the novel concept of neural calculation. Most significantly, trimetric G proteincoupled thermosensation, single sensory neuron-based memory, and the orchestrated synaptic transmission system have been elucidated.

Ohta, Akane et al. (2015) International Worm Meeting "CREB facilitates a replacement of temperature experience-linked cold tolerance."

Ohta, Akane, Kuhara, Atsushi, Ioroi, Makoto, Takagaki, Natsune

[International Worm Meeting, 2015]

Environmental situation can be changed continuously, therefore animals adapt to environment such as high or cold temperature, humidity and smell. One of environment adaptabilities is cold tolerance. C. elegans stores temperature experiences and can induce temperature memory-linked cold tolerance, which is a phenomenon that 15degC -cultivated animals can survive at 2iotadegC, however, 20degC- or 25degC-cultivated animals can not survive after cold shock. We have recently reported that one pair of sensory neuron ASJ, which is known as a pheromone and light-sensing neuron, causes cold tolerance by sensing temperature (1). Temperature signals from ASJ are transmitted to downstream neurons of ASJ and intestine through insulin (1).We show here that cAMP response element binding protein (CREB) is required for building a new memory of the cold tolerance. Almost wild-type animals lost cold tolerance within three hours after temperature shift from 15 to 25 degree. However, a half of crh-1/CREB mutants kept cold tolerant even three hours after temperature shift from 15degC to 25degC. This abnormality of crh-1 mutant was rescued by the expression of CREB in neurons. We are going to determine a set of neurons, in which CREB contributes to make memory for cold tolerance.Our recent Ca2+-imaging analysis for monitoring ASJ activities revealed that Ca2+ concentrations of ASJ were changed at around cultivated temperature when wild-type animals were cultivated 20 or 25 degree. Similar phenomenon was found in snb-1 mutant, that is a mutant defective in synaptic connection between neurons. In addition, the ratio changes of Ca2+ concentrations of ASJ in crh-1/CREB mutant cultivated at 20degC were smaller than wild-type animals. This abnormality of crh-1 mutant was rescued by the expression of crh-1 cDNA in ASJ specifically, suggesting that ASJ sensory neuron can memorize cultivated-temperature cell-autonomously that could be modified by CRH-1/CREB.In order to identify the downstream molecules of CREB, we performed DNA microarray analysis comparing between before and after temperature shift in wild-type animals. The expression levels of 112 genes were changed thee hours after temperature shift from 15 to 25 degree. The mutants of 19 genes were existed in stock center. Some mutants of the genes such as MAP kinase activated kinase, transmembrane glycoprotein, hypersensitive to pore forming toxin protein, and sphingomyelin synthetase showed abnormal phenotypes in speed of cold tolerance. We are analyzing whether these molecules are controlled by CREB in modulating the pathways on forming cold tolerance memory. (1) Ohta, Ujisawa et al., Nature commun., 2014.

Ohta A et al. (2024) PNAS Nexus "The intron binding protein EMB-4 is an opposite regulator of cold and high temperature tolerance in Caenorhabditis elegans."

Ohta A, Kajino T, Tanaka K, Isono K, Sato Y, Taji T, Kuhara A

[PNAS Nexus, 2024]

Adaptation and tolerance to changes in heat and cold temperature are essential for survival and proliferation in plants and animals. However, there is no clear information regarding the common molecules between animals and plants. In this study, we found that heat, and cold tolerance of the nematode <i>Caenorhabditis elegans</i> is oppositely regulated by the RNA-binding protein EMB-4, whose plant homolog contains polymorphism causing heat tolerance diversity. <i>Caenorhabditis elegans</i> alters its cold and heat tolerance depending on the previous cultivation temperature, wherein EMB-4 respectively acts as a positive and negative controller of heat and cold tolerance by altering gene expression. Among the genes whose expression is regulated by EMB-4, a phospholipid scramblase, and an acid sphingomyelinase, which are involved in membrane lipid metabolism, were found to play essential roles in the negative regulation of heat tolerance.

Ohta, Akane et al. (2013) International Worm Meeting "Temperature experience-inducing cold tolerance is regulated by insulin signaling in intestine and neuron."

Ohta, Akane, Kobayashi, Yuko, Nakamoto, Hayato, Ujisawa, Tomoyo, Sonoda, Satoru, Kuhara, Atsushi

[International Worm Meeting, 2013]

Temperature is critical environmental stimuli and cause biochemical changes. Animals therefore can respond and habituate to the changes in ambient temperature. We are studying about molecular mechanism underlying temperature experience-dependent cold tolerance in C. elegans. 20 deg C-cultivated animals were died by cold stimuli 2 deg C, whereas 15 deg C-cultivated animals can survive at 2 deg C. Mutants defective in DAF-2/insulin receptor and its downstream molecules showed abnormal cold tolerance. DAF-2 is the sole insulin receptor in C. elegans, while there are about 40 ligands for insulin receptor. We have found that at least three insulin, DAF-28, INS-6 and INS-1, are essential for cold tolerance. Two insulin, DAF-28 and INS-6, are both positive agonists and work redundantly for DAF-2/insulin receptor in cold tolerance. Genetic epistasis analysis indicated that INS-1/insulin genetically inhibits DAF-2/insulin receptor through negative regulation of DAF-6/insulin. Abnormal cold tolerance in daf-28 mutant was strongly rescued by specific expression of daf-28 cDNA in ASJ sensoryneuron that is known as a light and pheromone-sensing neuron. By contrast, abnormality of daf-28 mutant was partially rescued by expressing daf-28 cDNA in other sensoryneurons. These suggest that DAF-28/insulin functions cell non-autonomously, but releasing DAF-28 from ASJ is essential for temperature experience-dependent cold tolerance. Unexpectedly, cell specific rescue experiments revealed that DAF-2/insulin receptor in both intestine and neuron is required for cold tolerance. These results suggest that a single sensoryneuron ASJ regulates temperature experience-dependent cold tolerance through insulin signaling in the intestine and neuron. Since abnormal cold tolerance of daf-2 mutant was suppressed by mutation in transcriptional factor FOXO/DAF-16, we are investigating downstream molecules of insulin signaling for cold tolerance by DNA microarray analysis.

Akane Ohta et al. (2002) Japanese Worm Meeting "More on thermotaxis-defective mutants: dgk-1 affects thermotaxis but not other amphid-related sensory behaviors"

Ikue Mori, Akane Ohta, Yoshifumi Okochi, Masatoshi Okumura, Kotaro Kimura

[Japanese Worm Meeting, 2002]

Sensory neurons are critical in responding to the environment by transducing external stimuli into patterned electrical activity. Themotaxis reflects the response to food and temperature stimuli. To reveal molecular mechanisms involved in thermotaxis, we conducted a screen for thermotaxis-defective mutants (see abstract by Okumura et.al ., IWM 2001). Through screening about 6,000 genomes, over twenty thermotaxis-defective mutants were isolated, including nj20, nj21, nj44, nj45 and nj46 mutants. nj20 and nj21 mutants show cryophilic phenotype, independently of cultivation temperature. nj44, nj45 and nj46 mutants also show cryophilic phenotype, but in cultivation temperature-dependent manner. nj20 mutants have only defect in thermotaxis: they showed normal chemotaxis and osmotic avoidance. These results suggest that nj20 mutation affects thermotactic behavior specifically. The other mutants, nj21, nj44, nj45 and nj46 , showed partial defects in chemotaxis to water-soluble attractant NaCl or volatile chemicals and in osmotic avoidance. We have mapped nj20 and nj21 mutations using snip-SNPs methods. nj21 mutation maps to the region between -6.15 and +4.78 on the chromosome I. We have isolated recombinant lines between two SNPs that covers the -6.15 - +4.78 interval and are now evaluating the thermotactic phenotype of the recombinant lines. After narrowing down the region for nj21through these mapping procedures, we will attempt to rescue the nj21 phenotype with the respective cosmid. nj20 maps to the region around +18.6 on the chromosome X. The complementation test revealed that nj20 did not complement dgk-1(nu62) and thermotactic defect of nj20 mutants was rescued by the genomic dgk-1 gene. DGK-1 has been studied for its function at neuromuscular junction, where it acts as the inhibitor of acetylcholine release. Like dgk-1 (nu62) mutants, nj20 animals showed hyperactive locomotion and Egl-c phenotype. Conversely, dgk-1 (nu62) mutants exhibited cryophilic phenotype. We also found that some of the mutants affecting locomotion and egg-laying showed thermotactic defects (see abstract by Okumura et.al ., this meeting). We are now investigating the role of dgk-1 in sensory signaling pathways of thermotaxis.

Hiromitsu Ohta et al. (2007) International Worm Meeting "ADBP-1, a novel protein interacting with an RNA editing-enzyme ADR-2, modulates the somatic expression of transgenes."

Manabi Fujiwara, Takeshi Ishihara, Hiromitsu Ohta

[International Worm Meeting, 2007]

The RNA editing-enzymes, ADARs, catalyze the hydrolytic deamination of adenosines in dsRNA to form inosines, which is read as guanosines during trnslation. In C. elegans, two ADAR genes, adr-1 and adr-2, are reported to exist. The null alleles of adr-1 and adr-2 cause reduced and eliminated adenosine-deaminase activities, respectively. Although several ADAR substrates are identified in C. elegans, all of the editing sites are in untraslated regions, and the biological functions have remained unclear (1). Interestingly both of adr-1 and adr-2 null mutants exhibit a transgene-silencing phenotype, which is dependent on a RNAi machinery gene, rde-1 (2). Here we report a new gene, adbp-1 (ADR-2 binding protein), whose product interacts with ADR-2 and has a crucial function for ADR-2 activity. Originally we isolated adbp-1 (qj1) as a mutant with a transgene-silencing phenotype in somatic cells, which is indicated by the decreased expression of several transgenes including Ex[lon-1p::gfp] and Ex[vha-7p::gfp]. The transgene silencing is observed in hypodermis and intestine but not in neurons and pharynx, indicating that the transgene silencing in qj1 mutant occurs in a tissue specific manner. We found that a rde-1 mutation can suppress the transgene silencing in qj1 as well as that in adr-2 and that the transgene-silencing phenotype in adr-2 shows the same tissue specificity as qj1. Positional cloning and rescuing experiment of qj1 revealed that the corresponding gene is VW02B12L.4, which encodes a protein with no homologue in other species except in C. briggsae. Expression studies using a functional gfp translational fusion suggest that VW02B12L.4 is expressed in hypodermis, pharynx, seam cells and some neurons. The GFP fusion protein is localized in nuclei of these tissues. By yeast two-hybrid screening of C. elegans cDNA library using VW02B12L.4 as bait, we obtained multiple adr-2 clones. The interaction between ADR-2 and VW02B12L.4 was verified by a coimmunoprecipitation analysis. Therefore, we named the VW02B12L.4 gene as adbp-1 for ADR-2 binding protein. To know further the role of ADBP-1 in ADR-2 function, we analyzed the ADR-2 substrates in adbp-1 animals and found no RNA editing occurs in the mutant. Our results suggest that a novel protein, ADBP-1 is required for adenosine-deaminase activity of ADR-2 and modulates the somatic expression of transgenes by interacting with ADR-2. 1. Tonkin et al. (2002). EMBO J. 21: 6025-35. 2. Knight S. W. and Bass B.L. (2002). Molecular Cell 10: 809-917.

Ohta T et al. (1999) Mol Cell "ROC1, a homolog of APC11, represents a family of cullin partners with an associated ubiquitin ligase activity."

Ohta T, Xiong Y, Michel JJ, Schottelius AJ

[Mol Cell, 1999]

We have identified two highly conserved RING finger proteins, ROC1 and ROC2, that are homologous to APC11, a subunit of the anaphase-promoting complex. ROC1 and ROC2 commonly interact with all cullins while APC11 specifically interacts with APC2, a cullin-related APC subunit. YeastROC1 encodes an essential gene whose reduced expression resulted in multiple, elongated buds and accumulation of Sic1p and Cln2p. ROC1 and APC11 immunocomplexes can catalyze isopeptide ligations to form polyubiquitin chains in an E1- and E2-dependent manner. ROC1 mutations completely abolished their ligase activity without noticeable changes in associated proteins. Ubiquitination of phosphorylated I kappa B alpha can be catalyzed by the ROC1 immunocomplex in vitro. Hence, combinations of ROC/APC11 and cullin proteins proteins potentially constitute a wide variety of ubiquitin ligases.