title: Molecular identification of Rab7 (ApRab7) in Aiptasia pulchella and its exclusion from phagosomes harboring zooxanthellae.
abstract: The establishment and maintenance of the intracellular association between marine cnidarians and their symbiotic microalgae is essential to the well being of coral reef ecosystems; however, little is known concerning its underlying molecular mechanisms. In light of the critical roles of the small GTPase, Rab7, as a key regulator of vesicular trafficking, we cloned and characterized the Rab7 protein in the endosymbiosis system between the sea anemone, Aiptasia pulchella and its algal symbiont, Symbiodinium spp. The Aiptasia homologue of Rab7 proteins, ApRab7 is 88% identical to human Rab7 protein and contains all Rab-specific signature motifs. Results of EGFP reporter analysis, protein fractionation, and immunocytochemistry support that ApRab7 is located in late endocytic and phagocytic compartments and is able to promote their fusion. Significantly, the majority of phagosomes containing live symbionts that either have taken long residency in, or were newly internalized by Aiptasia digestive cells did not contain detectable levels of ApRab7, while most phagosomes containing either heat-killed or photosynthesis-impaired symbionts were positive for ApRab7 staining. Overall, our data suggest that live algal symbionts persist inside their host cells by actively excluding ApRab7 from their phagosomes, and thereby, establish and/or maintain an endosymbiotic relationship with their cnidarian hosts.
authors.affiliation: Department of Planning and Research, National Museum of Marine Biology and Aquarium, Pingtung, Taiwan, ROC.
authors.forename: Ming-Chyuan
authors.initials: MC
authors.lastname: Chen
authors.forename: Ying-Min
authors.initials: YM
authors.lastname: Cheng
authors.forename: Ping-Jyun
authors.initials: PJ
authors.lastname: Sung
authors.forename: Cham-En
authors.initials: CE
authors.lastname: Kuo
authors.forename: Lee-Shing
authors.initials: LS
authors.lastname: Fang
mesh_terms: D000595:Amino Acid Sequence; D000818:Animals; D001483:Base Sequence; D019556:COS Cells; D003001:Cloning, Molecular; D003600:Cytosol / Q000201:enzymology; D004141:Dinoflagellida / Q000502:physiology; D004705:Endocytosis; D006367:HeLa Cells; D006801:Humans; D007425:Intracellular Membranes / Q000201:enzymology; D008969:Molecular Sequence Data; D010588:Phagosomes / Q000201:enzymology*; D012615:Sea Anemones / Q000166:cytology / Q000201:enzymology* / Q000502:physiology; D016415:Sequence Alignment; D013559:Symbiosis; D022161:Transport Vesicles / Q000201:enzymology; D020691:rab GTP-Binding Proteins / Q000032:analysis* / Q000235:genetics*; D000090802:rab7 GTP-Binding Proteins
chemical_list: D000090802:rab7 GTP-Binding Proteins; C000716463:rab7 GTP-binding proteins, human; D020691:rab GTP-Binding Proteins