Cornelia I. Bargmann

Genes that act downstream of DAF-16 to influence the lifespan of Caenorhabditis elegans

Ageing is a fundamental, unsolved mystery in biology. DAF-16, a FOXO-family transcription factor, influences the rate of ageing of Caenorhabditis elegans in response to insulin/insulin-like growth factor 1 (IGF-I) signalling. Using DNA microarray analysis, we have found that DAF-16 affects expression of a set of genes during early adulthood, the time at which this pathway is known to control ageing. Here we find that many of these genes influence the ageing process. The insulin/IGF-I pathway functions cell non-autonomously to regulate lifespan, and our findings suggest that it signals other cells, at least in part, by feedback regulation of an insulin/IGF-I homologue. Furthermore, our findings suggest that the insulin/IGF-I pathway ultimately exerts its effect on lifespan by upregulating a wide variety of genes, including cellular stress-response, antimicrobial and metabolic genes, and by downregulating specific life-shortening genes.

Multiple independent activations of the neu oncogene by a point mutation altering the transmembrane domain of p185

The neu oncogene, which is frequently activated in neuro- and glioblastomas of BDIX rats, was originally identified in the NIH 3T3 focus-forming assay. cDNA clones of the normal and transforming alleles of neu have been isolated. When these clones are inserted into the expression vector pSV2, they direct the synthesis of p185, the neu gene product. The transforming cDNA clone yields foci when transfected onto a NIH 3T3 monolayer, but the normal cDNA does not. The construction of in vitro recombinants between the normal and transforming cDNAs has allowed the determination of the mutation responsible for the activation of the neu proto-oncogene. A single point mutation changes a valine in the transmembrane domain of the predicted protein product insert to a glutamic acid. The DNAs from four independent cell lines containing activated neu oncogenes contain the identical mutation at this position.

Odorant-selective genes and neurons mediate olfaction in C. elegans

Olfaction is a versatile and sensitive mechanism for detecting volatile odorants. We show that the nematode C. elegans detects many volatile chemicals, which can be attractants, repellents, or attractants at low concentrations and repellents at high concentrations. Through laser ablation, we have identified chemosensory neurons that detect volatile odorants. Chemotaxis to volatile odorants requires different sensory neurons from chemotaxis to water-soluble attractants, indicating that C. elegans might have senses that correspond to smell and taste, respectively. Single neurons have complex sensory properties, since six distinguishable volatile odorants are sensed by only two types of sensory neurons. Chemotaxis to subsets of volatile odorants is disrupted by mutations in the odr genes, which might be involved in odorant sensation or signal transduction.

Natural Variation in a Neuropeptide Y Receptor Homolog Modifies Social Behavior and Food Response in C. elegans

Natural isolates of C. elegans exhibit either solitary or social feeding behavior. Solitary foragers move slowly on a bacterial lawn and disperse across it, while social foragers move rapidly on bacteria and aggregate together. A loss-of-function mutation in the npr-1 gene, which encodes a predicted G protein-coupled receptor similar to neuropeptide Y receptors, causes a solitary strain to take on social behavior. Two isoforms of NPR-1 that differ at a single residue occur in the wild. One isoform, NPR-1 215F, is found exclusively in social strains, while the other isoform, NPR-1 215V, is found exclusively in solitary strains. An NPR-1 215V transgene can induce solitary feeding behavior in a wild social strain. Thus, isoforms of a putative neuropeptide receptor generate natural variation in C. elegans feeding behavior.

Divergent seven transmembrane receptors are candidate chemosensory receptors in C. elegans

Using their senses of taste and smell, animals recognize a wide variety of chemicals. The nematode C. elegans has only fourteen types of chemosensory neurons, but it responds to dozens of chemicals, because each chemosensory neuron detects several stimuli. Here we describe over 40 highly divergent members of the G protein-coupled receptor family that could contribute to this functional diversity. Most of these candidate receptor genes are in clusters of two to nine similar genes. Eleven of fourteen tested genes appear to be expressed in small subsets of chemosensory neurons. A single type of chemosensory neuron can potentially express at least four different receptor genes. Some of these genes might encode receptors for water-soluble attractants, repellents, and pheromones.

Chemosensory neurons with overlapping functions direct chemotaxis to multiple chemicals in C. elegans

The functions of the 11 classes of exposed chemosensory neurons of C. elegans were tested by killing cells with a laser microbeam. One pair of neurons, the ASE neurons, is uniquely important for chemotaxis: killing the ASE neurons greatly reduced chemotaxis to cAMP, biotin, Cl-, and Na+. Additional chemosensory function is distributed among several other cell types. Thus, 3 pairs of chemosensory neurons (ADF, ASG, and ASI) contribute to a residual response to cAMP, biotin, Cl-, and Na+ after ASE is killed. Chemotaxis to lysine similarly depends on the partly redundant functions of 4 pairs of chemosensory neurons (ASE, ASG, ASI, and ASK). The combined activity of several neuron types that act in parallel might increase the fidelity of chemotaxis.

OSM-9, A Novel Protein with Structural Similarity to Channels, Is Required for Olfaction, Mechanosensation, and Olfactory Adaptation inCaenorhabditis elegans

Although cyclic nucleotide-gated channels mediate sensory transduction in olfaction and vision, other forms of sensory transduction are independent of these channels. Caenorhabditis elegans cyclic nucleotide-gated channel mutants respond normally to some olfactory stimuli and to osmotic stimuli, suggesting that these chemosensory responses use an alternative sensory transduction pathway. One gene that may act in this pathway isosm-9, which is required for each of these responses as well as a mechanosensory response to nose touch. osm-9encodes a protein with ankyrin repeats and multiple predicted transmembrane domains that has limited similarity to theDrosophila phototransduction channels transient receptor potential (TRP) and TRP-like (TRPL). The sequence of OSM-9 and other TRP-like genes reveals a previously unsuspected diversity of mammalian and invertebrate genes in this family. osm-9 is required for the activity of the predicted G-protein-coupled odorant receptor ODR-10, which acts in the AWA olfactory neurons; its similarity to other G-protein-regulated transduction channels suggests that OSM-9 is involved in AWA signaling. osm-9:: GFP fusion genes are expressed in a subset of chemosensory, mechanosensory, and osmosensory neurons. osm-9 also affects olfactory adaptation within neurons that require the cyclic nucleotide-gated channel for olfaction; in these neurons, the gene has a regulatory function and not a primary role in sensory transduction.

odr-10 encodes a seven transmembrane domain olfactory receptor required for responses to the odorant diacetyl.

Olfactory signaling is initiated by interactions between odorants and olfactory receptors. We show that the C. elegans odr-10 gene is likely to encode a receptor for the odorant diacetyl. odr-10 mutants have a specific defect in chemotaxis to diacetyl, one of several odorants detected by the AWA olfactory neurons. odr-10 encodes a predicted seven transmembrane domain receptor; a green fluorescent protein-tagged Odr-10 protein is localized to the AWA sensory cilia. odr-10 expression is regulated by odr-7, a transcription factor implicated in AWA sensory specification. Expression of odr-10 from a heterologous promoter directs behavioral responses to diacetyl, but not to another odorant detected by the AWA neurons. These results provide functional evidence for a specific interaction between an olfactory receptor protein and its odorant ligand.

Comparing genomic expression patterns across species identifies shared transcriptional profile in aging

We developed a method for systematically comparing gene expression patterns across organisms using genome-wide comparative analysis of DNA microarray experiments. We identified analogous gene expression programs comprising shared patterns of regulation across orthologous genes. Biological features of these patterns could be identified as highly conserved subpatterns that correspond to Gene Ontology categories. Here, we demonstrate these methods by analyzing a specific biological process, aging, and show that similar analysis can be applied to a range of biological processes. We found that two highly diverged animals, the nematode Caenorhabditis elegans and the fruit fly Drosophila melanogaster, implement a shared adult-onset expression program of genes involved in mitochondrial metabolism, DNA repair, catabolism, peptidolysis and cellular transport. Most of these changes were implemented early in adulthood. Using this approach to search databases of gene expression data, we found conserved transcriptional signatures in larval development, embryogenesis, gametogenesis and mRNA degradation.

A Putative Cyclic Nucleotide–Gated Channel Is Required for Sensory Development and Function in C. elegans

In vertebrate visual and olfactory systems, a cyclic nucleotide-gated channel couples receptor activation to electrical activity of the sensory neurons. The Caenorhabditis elegans tax-2 gene is required for some forms of olfaction, for chemosensation of salts, and for thermosensation. We show here that tax-2 encodes a predicted subunit of a cyclic nucleotide-gated channel that is expressed in olfactory, gustatory, and thermosensory neurons, implicating this channel in multiple sensory modalities. Some sensory neurons display axon outgrowth defects in tax-2 mutants. Thus, the channel has an unexpected role in sensory neuron development in addition to its role in sensation. Consistent with this proposed dual function, a Tax-2::GFP fusion protein is present both in sensory cilia and in sensory axons.