title: Localization of secondary metabolites in marine invertebrates: contribution of MALDI MSI for the study of saponins in Cuvierian tubules of H. forskali.
abstract: BACKGROUND
  Several species of sea cucumbers of the family Holothuriidae possess a particular mechanical defense system called the Cuvierian tubules (Ct). It is also a chemical defense system as triterpene glycosides (saponins) appear to be particularly concentrated in Ct. In the present study, the precise localization of saponins in the Ct of Holothuria forskali is investigated. Classical histochemical labeling using lectin was firstly performed but did not generate any conclusive results. Thus, MALDI mass spectrometry Imaging (MALDI-MSI) was directly applied and completed by statistical multivariate tests. A comparison between the tubules of relaxed and stressed animals was realized.
  
  
  RESULTS
  These analyses allowed the detection of three groups of ions, corresponding to the isomeric saponins of the tubules. Saponins detected at m/z 1287 and 1303 were the most abundant and were apparently localized in the connective tissue of the tubules of both relaxed and stressed individuals. Saponins at m/z 1125 and 1141 were detected in lower amount and were present in tissues of relaxed animals. Finally, saponin ions at 1433, 1449, 1463 and 1479 were observed in some Ct of stressed holothuroids in the outer part of the connective tissue. The saponin group m/z 14xx seems therefore to be stress-specific and could originate from modifications of the saponins with m/z of 11xx.
  
  
  CONCLUSIONS
  All the results taken together indicate a complex chemical defense mechanism with, for a single organ, different sets of saponins originating from different cell populations and presenting different responses to stress. The present study also reflects that MALDI-MSI is a valuable tool for chemical ecology studies in which specific chemical signalling molecules like allelochemicals or pheromones have to be tracked. This report represents one of the very first studies using these tools to provide a functional and ecological understanding of the role of natural products from marine invertebrates.
authors.affiliation: Laboratoire de Biologie marine, Université de Mons, Mons, Belgium.
authors.forename: Séverine
authors.initials: S
authors.lastname: Van Dyck
authors.forename: Patrick
authors.initials: P
authors.lastname: Flammang
authors.forename: Céline
authors.initials: C
authors.lastname: Meriaux
authors.forename: David
authors.initials: D
authors.lastname: Bonnel
authors.forename: Michel
authors.initials: M
authors.lastname: Salzet
authors.forename: Isabelle
authors.initials: I
authors.lastname: Fournier
authors.forename: Maxence
authors.initials: M
authors.lastname: Wisztorski
mesh_terms: D000818:Animals; D047332:Holothuria / Q000033:anatomy & histology / Q000378:metabolism*; D007150:Immunohistochemistry; D007448:Invertebrates / Q000033:anatomy & histology / Q000378:metabolism*; D037102:Lectins / Q000032:analysis / Q000378:metabolism; D008386:Marine Biology; D015394:Molecular Structure; D025341:Principal Component Analysis; D012503:Saponins / Q000032:analysis* / Q000737:chemistry / Q000378:metabolism; D012623:Seawater; D019032:Spectrometry, Mass, Matrix-Assisted Laser Desorption-Ionization / Q000379:methods*; D013312:Stress, Physiological
chemical_list: D037102:Lectins; D012503:Saponins