title: Mannosomes: a molluscan intracellular tubular membrane system related to heavy metal stress?
abstract: Amongst animals, several hydrogen peroxide-generating oxidases are apparently restricted to molluscs. One of these, D-mannitol oxidase, is concentrated in the alimentary system, where it is associated with its own subcellular membrane system of unique tubular morphology, most likely representing a structural modification of the ER. These structures can be purified by subcellular fractionation and have been termed 'mannosomes'. Little is known about the functions of mannitol oxidase or of mannosomes, but the previously reported molluscicide-induced increase in mannosomes implies their involvement in a general stress reaction. In this study, we examined the effects of heavy metal stress in the terrestrial gastropod Arion lusitanicus. The activity of mannitol oxidase and mannosome abundance were monitored, together with metal effects on heat-shock protein level, and these parameters were compared to heavy metal accumulation in the digestive gland. We found that mannitol oxidase is inhibited by heavy metals more than other oxidases. On the other hand, hsp70 levels and mannosomal protein were increased with enhanced heavy metal stress, the latter indicating a probable increase in the number of mannosome organelles. Thus, stress protein (hsp70) and mannosomal protein were positively correlated with heavy metal accumulation, whereas the enzyme activity showed a negative correlation with increasing heavy metal content of the slugs.
authors.affiliation: Cell Biology, Zoological Institute, University of Tübingen, Auf der Morgenstelle 28, D-72076 Tübingen, Germany. thomas.knigge@uni-tuebingen.de
authors.forename: Thomas
authors.initials: T
authors.lastname: Knigge
authors.forename: Neelam
authors.initials: N
authors.lastname: Mann
authors.forename: Zahida
authors.initials: Z
authors.lastname: Parveen
authors.forename: Christopher
authors.initials: C
authors.lastname: Perry
authors.forename: Maike
authors.initials: M
authors.lastname: Gernhöfer
authors.forename: Rita
authors.initials: R
authors.lastname: Triebskorn
authors.forename: Heinz R
authors.initials: HR
authors.lastname: Köhler
authors.forename: Martin
authors.initials: M
authors.lastname: Connock
mesh_terms: D000284:Administration, Oral; D000818:Animals; D015153:Blotting, Western; D002104:Cadmium / Q000008:administration & dosage / Q000032:analysis; D004064:Digestive System / Q000737:chemistry / Q000378:metabolism; D004305:Dose-Response Relationship, Drug; D004591:Electrophoresis, Polyacrylamide Gel; D007425:Intracellular Membranes / Q000378:metabolism*; D007854:Lead / Q000008:administration & dosage / Q000032:analysis; D019216:Metals, Heavy / Q000008:administration & dosage* / Q000032:analysis; D008974:Mollusca / Q000737:chemistry / Q000187:drug effects / Q000378:metabolism*; D015388:Organelles / Q000187:drug effects / Q000378:metabolism* / Q000648:ultrastructure; D010088:Oxidoreductases / Q000378:metabolism; D013312:Stress, Physiological / Q000139:chemically induced / Q000378:metabolism*; D013347:Subcellular Fractions / Q000737:chemistry; D013997:Time Factors; D015032:Zinc / Q000008:administration & dosage / Q000032:analysis
chemical_list: D019216:Metals, Heavy; D002104:Cadmium; D007854:Lead; D010088:Oxidoreductases; D015032:Zinc