title: Copine A is expressed in prestalk cells and regulates slug phototaxis and thermotaxis in developing Dictyostelium.
abstract: Copines are calcium-dependent membrane-binding proteins found in many eukaryotic organisms. We are studying the function of copines using the model organism, Dictyostelium discoideum. When under starvation conditions, Dictyostelium cells aggregate into mounds that become migrating slugs, which can move toward light and heat before culminating into a fruiting body. Previously, we showed that Dictyostelium cells lacking the copine A (cpnA) gene are not able to form fruiting bodies and instead arrest at the slug stage. In this study, we compared the slug behavior of cells lacking the cpnA gene to the slug behavior of wild-type cells. The slugs formed by cpnA- cells were much larger than wild-type slugs and exhibited no phototaxis and negative thermotaxis in the same conditions that wild-type slugs exhibited positive phototaxis and thermotaxis. Mixing as little as 5% wild-type cells with cpnA- cells rescued the phototaxis and thermotaxis defects, suggesting that CpnA plays a specific role in the regulation of the production and/or release of a signaling molecule. Reducing extracellular levels of ammonia also partially rescued the phototaxis and thermotaxis defects of cpnA- slugs, suggesting that CpnA may have a specific role in regulating ammonia signaling. Expressing the lacZ gene under the cpnA promoter in wild-type cells indicated cpnA is preferentially expressed in the prestalk cells found in the anterior part of the slug, which include the cells at the tip of the slug that regulate phototaxis, thermotaxis, and the initiation of culmination into fruiting bodies. Our results suggest that CpnA plays a role in the regulation of the signaling pathways, including ammonia signaling, necessary for sensing and/or orienting toward light and heat in the prestalk cells of the Dictyostelium slug.
authors.affiliation: Biology Department, Central Michigan University, Mount Pleasant, Michigan 48859, USA.
authors.forename: Kerry A
authors.initials: KA
authors.lastname: Flegel
authors.forename: Jaimie M
authors.initials: JM
authors.lastname: Pineda
authors.forename: Tasha S
authors.initials: TS
authors.lastname: Smith
authors.forename: Ann M
authors.initials: AM
authors.lastname: Laszczyk
authors.forename: Janet M
authors.initials: JM
authors.lastname: Price
authors.forename: Kristen M
authors.initials: KM
authors.lastname: Karasiewicz
authors.forename: Cynthia K
authors.initials: CK
authors.lastname: Damer
mesh_terms: D000818:Animals; D002352:Carrier Proteins / Q000235:genetics* / Q000378:metabolism / Q000502:physiology*; D002478:Cells, Cultured; D004023:Dictyostelium / Q000166:cytology / Q000235:genetics / Q000254:growth & development* / Q000502:physiology; D018507:Gene Expression Regulation, Developmental; D007763:Lac Operon; D008018:Life Cycle Stages / Q000235:genetics*; D008027:Light; D009068:Movement / Q000502:physiology / Q000528:radiation effects; D030781:Organisms, Genetically Modified; D011401:Promoter Regions, Genetic; D013696:Temperature; D014018:Tissue Distribution
chemical_list: D002352:Carrier Proteins; C110203:copine