Behavioral choice between conflicting alternatives is regulated by a receptor guanylyl cyclase, GCY-28, and a receptor tyrosine kinase, SCD-2, in AIA interneurons of Caenorhabditis elegans.

Animals facing conflicting sensory cues make a behavioral choice between competing alternatives through integration of the sensory cues. Here, we performed a genetic screen to identify genes important for the sensory integration of two conflicting cues, the attractive odorant diacetyl and the aversive stimulus Cu(2+), and found that the membrane-bound guanylyl cyclase GCY-28 and the receptor tyrosine kinase SCD-2 regulate the behavioral choice between these alternatives in Caenorhabditis elegans. The gcy-28 mutants and scd-2 mutants show an abnormal bias in the behavioral choice between the cues, although their responses to each individual cue are similar to those in wild-type animals. Mutants in a gene encoding a cyclic nucleotide gated ion channel, cng-1, also exhibit the defect in sensory integration. Molecular genetic analyses suggested that GCY-28 and SCD-2 regulate sensory integration in AIA interneurons, where the conflicting sensory cues may converge. Genetic ablation or hyperpolarization of AIA interneurons showed nearly the same phenotype as gcy-28 or scd-2 mutants in the sensory integration, although this did not affect the sensory response to each individual cue. In gcy-28 or scd-2 mutants, activation of AIA interneurons is sufficient to restore normal sensory integration. These results suggest that the activity of AIA interneurons regulates the behavioral choice between the alternatives. We propose that GCY-28 and SCD-2 regulate sensory integration by modulating the activity of AIA interneurons.

CASY-1, an ortholog of calsyntenins/alcadeins, is essential for learning in Caenorhabditis elegans.

Calsyntenins/alcadeins are type I transmembrane proteins with two extracellular cadherin domains highly expressed in mammalian brain. They form a tripartite complex with X11/X11L and APP (amyloid precursor protein) and are proteolytically processed in a similar fashion to APP. Although a genetic association of calsyntenin-2 with human memory performance has recently been reported, physiological roles and molecular functions of the protein in the nervous system are poorly understood. Here, we show that CASY-1, the Caenorhabditis elegans ortholog of calsyntenins/alcadeins, is essential for multiple types of learning. Through a genetic screen, we found that casy-1 mutants show defects in salt chemotaxis learning. casy-1 mutants also show defects in temperature learning, olfactory adaptation, and integration of two sensory signals. casy-1 is widely expressed in the nervous system. Expression of casy-1 in a single sensory neuron and at the postdevelopmental stage is sufficient for its function in salt chemotaxis learning. The fluorescent protein-tagged ectodomain of CASY-1 is released from neurons. Moreover, functional domain analyses revealed that both cytoplasmic and transmembrane domains of this protein are dispensable, whereas the ectodomain, which contains the LG/LNS-like domain, is critically required for learning. These results suggest that learning is modulated by the released ectodomain of CASY-1.

Modulatory effect of ionizing radiation on food-NaCl associative learning: the role of gamma subunit of G protein in Caenorhabditis elegans.

Ionizing radiation (IR) is known to impair learning by suppressing adult neurogenesis in the hippocampus. However, in a mature nervous system, IR-induced functional alterations that are independent of neurogenesis remain largely unknown. In the present study, we analyzed the effects of IR on a food-NaCl associative learning paradigm of adult Caenorhabditis elegans that does not undergo neurogenesis. We observed that a decrease in chemotaxis toward NaCl occurs only after combined starvation and exposure to NaCl. Exposure to IR induced an additional decrease in chemotaxis immediately after an acute dose in the transition stage of the food-NaCl associative learning. Strikingly, chronic irradiation induced negative chemotaxis in the exposed animals, i.e., the primary avoidance response. IR-induced additional decreases in chemotaxis after acute and chronic irradiation were significantly suppressed in the gpc-1 mutant, which was defective in GPC-1 (one of the two gamma subunits of the heterotrimeric G-protein). Chemotaxis to cAMP, but not to lysine and benzaldehyde, was influenced by IR during the food-NaCl associative learning. Our novel findings suggest that IR behaves as a modulator in the food-NaCl associative learning via C. elegans GPC-1 and a specific neuronal network and may shed light on the modulatory effect of IR on learning.

Locomotion-learning behavior relationship in Caenorhabditis elegans following gamma-ray irradiation.

Learning impairment following ionizing radiation (IR) exposure is an important potential risk in manned space missions. We previously reported the modulatory effects of IR on salt chemotaxis learning in Caenorhabditis elegans. However, little is known about the effects of IR on the functional relationship in the nervous system. In the present study, we investigated the effects of gamma-ray exposure on the relationship between locomotion and salt chemotaxis learning behavior. We found that effects of pre-learning irradiation on locomotion were significantly correlated with the salt chemotaxis learning performance, whereas locomotion was not directly related to chemotaxis to NaCl. On the other hand, locomotion was positively correlated with salt chemotaxis of animals which were irradiated during learning, and the correlation disappeared with increasing doses. These results suggest an indirect relationship between locomotion and salt chemotaxis learning in C. elegans, and that IR inhibits the innate relationship between locomotion and chemotaxis, which is related to salt chemotaxis learning conditioning of C. elegans.

Interaction of genetic markers associated with serum alkaline phosphatase levels in the Japanese population.

In the present genome-wide association study of 2,994 Japanese subjects, rs2071699 (35C>T) in the fucosyltransferase 1 (FUT1) gene was identified as a marker associated with serum alkaline phosphatase (ALP) levels. This gene encodes α(1,2)-fucosyltransferase, which is responsible for the synthesis of H antigens. In a linear regression model incorporating genetic markers, rs550057 (C>T), which is located within an intron of the ABO blood group (ABO) locus, rs2071699 in FUT1 and a gene-gene interaction between these loci accounted for 12.4, 0.9 and 0.3% of the total variability in the serum ALP level, respectively. Further association analysis using imputed genotypes detected rs1047781 in FUT2. rs1047781 is well known in this association with serum ALP levels and showed a moderate linkage with rs2071699 in FUT1. An interaction analysis using rs1047781 in FUT2 also suggested that the interaction with rs550057 in ABO is significant and contributes to the interindividual variance of serum ALP levels as well as rs2071699 in the FUT1 gene. Thus, there is evidence of interactions between ABO and FUT1/FUT2 on serum ALP levels, regardless of the possibility that rs2071699 in FUT1 is a proxy of rs1047781 in FUT2 in the Japanese population.

NIRF/UHRF2 occupies a central position in the cell cycle network and allows coupling with the epigenetic landscape.

As predicted by systems biology, a paradigm shift will emerge through the integration of information about different layers of cellular processes. The cell cycle network is at the heart of the cellular computing system, and orchestrates versatile cellular functions. The NIRF/UHRF2 ubiquitin ligase is an "intermodular hub" that occupies a central position in the network, and facilitates coordination among the cell cycle machinery, the ubiquitin-proteasome system, and the epigenetic system. NIRF interacts with cyclins, CDKs, p53, pRB, PCNA, HDAC1, DNMTs, G9a, methylated histone H3 lysine 9, and methylated DNA. NIRF ubiquitinates cyclins D1 and E1, and induces G1 arrest. The NIRF gene is frequently lost in tumors and is a candidate tumor suppressor, while its paralog, the UHRF1 gene, is hardly altered. Thus, investigations of NIRF are essential to understand the entire biological systems. Through integration of the enormous information flows, NIRF may contribute to the coupling between the cell cycle network and the epigenetic landscape. We propose the new paradigm that NIRF produces the extreme diversity in the network wiring that helps the diversity of Waddington's canals.

NIRF constitutes a nodal point in the cell cycle network and is a candidate tumor suppressor.

In biological networks, a small number of "hub" proteins play critical roles in the network integrity and functions. The cell cycle network orchestrates versatile cellular functions through interactions between many signaling modules, whose defects impair diverse cellular processes, often leading to cancer. However, the network architecture and molecular basis that ensure proper coordination between distinct modules are unclear. Here, we show that the ubiquitin ligase NIRF (also known as UHRF2), which induces G1 arrest, interacts with multiple cell cycle proteins including cyclins (A2, B1, D1 and E1), p53 and pRB, and ubiquitinates cyclins D1 and E1. Consistent with its versatility, a bioinformatic network analysis demonstrated that NIRF is an intermodular hub protein that is responsible for the coordination of multiple network modules. Notably, intermodular hubs are frequently associated with oncogenesis. Indeed, we detected loss of heterozygosity of the NIRF gene in several kinds of tumors. When a cancer outlier profile analysis was applied to the Oncomine database, loss of the NIRF gene was found at statistically significant levels in diverse tumors. Importantly, a recurrent microdeletion targeting NIRF was observed in non-small cell lung carcinoma. Furthermore, NIRF is immediately adjacent to the single nucleotide polymorphism rs719725, which is reportedly associated with the risk of colorectal cancer. These observations suggest that NIRF occupies a prominent position within the cell cycle network, and is a strong candidate for a tumor suppressor whose aberration contributes to the pathogenesis of diverse malignancies.