MSI is often based on matrix-assisted laser desorption ionisation (MALDI) 15, 16, a soft ionisation technique that relies on aromatic molecules (the matrix) for energy transfer from a UV laser to the analyte. Reproducible methodologies that can spatially and temporally detect secondary metabolites in situ will significantly advance the field of chemical ecology 13.Ĭurrent advances in mass spectrometry imaging (MSI) provide a sophisticated platform to spatially map the distribution of biologically-relevant molecules or mixtures by detection of their molecular mass and characteristic fragment ions in tissues 11, 14. To place secondary metabolites in an ecological context, their biodistribution and abundance should be examined on a temporal scale relevant to the biological phenomena which they mediate. The initial step in understanding the function and therefore relevance of secondary metabolites to the producing organism, is to understand the in situ synthesis, storage and deployment 11, 12. Advantageous secondary metabolites have been known to have community wide effects across multiple trophic levels, termed “keystone” molecules 9, 10. The importance of understanding the mechanisms behind these chemical interactions within a species cannot be underestimated, particularly when specific secondary metabolites impart a competitive advantage. In molluscs, secondary metabolites have been detected and identified during mate attraction 2, defence 3, 4, predatory behaviour 5, anti-fouling 6, 7 and reproduction 8. Secondary metabolites are known to chemically mediate intra- and interspecies interactions between organisms 1. This study shows that DIOS-MSI is a powerful tool that can provide new insights into marine chemo-ecology.
Murexine was found to tranquilise the larvae and may relax the reproductive tract. But during egg-laying, murexine was transferred to the capsule gland and then to the egg capsules, where chemical ripening resulted in Tyrian purple formation. DIOS-MSI showed muscle-relaxing choline ester murexine to co-localise with tyrindoxyl sulfate in the biosynthetic hypobranchial glands. Here we applied desorption-ionisation on porous silicon (DIOS) to examine in situ changes in biodistribution over the reproductive cycle. Mass spectrometry imaging (MSI) on nano-structured surfaces has emerged as a sophisticated platform for spatial analysis of low molecular mass metabolites in heterogeneous tissues, ideal for low abundant secondary metabolites. One such example is the association between choline esters and Tyrian purple precursors in muricid molluscs.
Despite significant advances in chemical ecology, the biodistribution, temporal changes and ecological function of most marine secondary metabolites remain unknown.
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