Abstract
A protocol for the direct analysis of the phospholipid composition in the whole body of adult soil nematode, Caenorhabditis elegans (C. elegans), was developed, which combined freeze-cracking of the exoskeletal cuticle and matrix-assisted laser desorption/ionization-imaging mass spectrometry (MALDI-IMS). Biomolecules in the m/z range from 700 to 900 were more effectively detected in the freeze-cracked than from simple frozen adult nematode bodies. Different distribution of biomolecules was observed in a nematode body when the matrix was applied with a sublimation deposition method. The whole-body IMS technique was applied on genetically deficient mutant C. elegans to combine whole-body lipidomics and genetics, by comparing the fatty acid compositions, especially of the phosphatidylcholine (PC) species, between the wild-type and fat-1 mutants, which lack the gene encoding an n-3 fatty acid desaturase. A significant reduction of PC(20:5/20:5) and PC(20:4/20:5) and a marked increase of PC(20:4/20:4), PC(20:3/20:4), and PC(20:3/20:3) were detected in the fat-1 mutants in positive ion mode. In addition, phospholipid compositions other than PCs were analyzed in negative ion mode. A loss of a possible phosphatidylinositol (PI) with 18:0/20:5 and a compensative accumulation of putative PI(18:0/20:4) were detected in the fat-1 mutants. In conclusion, the whole-body MALDI-IMS technique is useful for the profiling of multiple biomolecules in C. elegans in both intra- and inter-individual levels.Electronic supplementary materialThe online version of this article (doi:10.1007/s00216-015-8932-7) contains supplementary material, which is available to authorized users.
Highlights
Recent advances in mass spectrometry have enabled the direct analyses of biomolecules in tissue samples without any targetspecific labeling [1, 2]
To evaluate the effectiveness of the exoskeleton removal, we performed the comparative analyses of the two procedures, simple freezing and freeze-cracking, in parallel on a glass slide (Fig. 1)
The surface of the freeze-cracked nematode bodies looked highly scabrous with multiple wrinkles (Fig. 2a; right), whereas the simple frozen nematodes had a highly smooth surface, which appeared to retain an intact exoskeletal cuticle (Fig. 2a; left)
Summary
Recent advances in mass spectrometry have enabled the direct analyses of biomolecules in tissue samples without any targetspecific labeling [1, 2]. The state of the art MALDI-IMS technique has been used for the investigation of molecular distributions in mammalian tissues [7], including samples of diseased human tissues [8,9,10] It has been used for label-free non-targeted analyses of biomolecules in various species [11], such as microbes [12], plants [13], parasites [14], arthropods, including crustaceans such as the giant tiger prawn (Penaeus monodon) [15], and insects such as the fruit fly (Drosophila melanogaster) [16, 17]. The body structure with multiple organs composed of the fixed number of cells (~1000 somatic cells) [18], with well-characterized cell fate is highly powerful to developmental biology Given these advantages in multiple directions, C. elegans has a big potential to provide a powerful platform for “Integrating-Omics,” in which genetics, transcriptomics, proteomics, lipidomics, and metabolomics are combined to find new insights [21], opening a new era of life sciences. C. elegans begins to be used in applied sciences, such as drug discovery or screening [22]
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