Subcellular metabolite and lipid analysis of Xenopus laevis eggs by LAESI mass spectrometry

• Published in: PloS one 2014-12, Vol.9 (12), p.e115173-e115173
• Main Authors: Shrestha, Bindesh, Sripadi, Prabhakar, Reschke, Brent R, Henderson, Holly D, Powell, Matthew J, Moody, Sally A, Vertes, Akos
• Format: Article
• Language: English
• Subjects: Ablation; Acids; Amino acids; Amino Acids - analysis; Animals; Biochemistry; Biological models (mathematics); Biology; Biology and Life Sciences; Cell cycle; Chemistry; Chromatography; Cytoplasm; Data bases; Eggs; Embryogenesis; Embryonic Development; Embryonic growth stage; Embryos; Fatty acids; Fertilization; gamma-Aminobutyric Acid - analysis; Glutathione; Glutathione - analysis; Ionization; Laboratories; Laser ablation; Lasers; Lipids; Lipids - analysis; Localization; Mass spectrometry; Mass spectroscopy; Metabolism; Metabolites; Methods; Molecular chains; Ovum - chemistry; Ovum - metabolism; Physical Sciences; Poles; Proteins; Proteomics; Research and Analysis Methods; Sample preparation; Scientific imaging; Spectrometry, Mass, Electrospray Ionization; Sperm; Subcellular Fractions - chemistry; Thymosin; Triglycerides; Vertebrates; Xenopus; Xenopus laevis; γ-Aminobutyric acid
• ISSN: 1932-6203; 1932-6203
• DOI: 10.1371/journal.pone.0115173

Xenopus laevis eggs are used as a biological model system for studying fertilization and early embryonic development in vertebrates. Most methods used for their molecular analysis require elaborate sample preparation including separate protocols for the water soluble and lipid components. In this study, laser ablation electrospray ionization (LAESI), an ambient ionization technique, was used for direct mass spectrometric analysis of X. laevis eggs and early stage embryos up to five cleavage cycles. Single unfertilized and fertilized eggs, their animal and vegetal poles, and embryos through the 32-cell stage were analyzed. Fifty two small metabolite ions, including glutathione, GABA and amino acids, as well as numerous lipids including 14 fatty acids, 13 lysophosphatidylcholines, 36 phosphatidylcholines and 29 triacylglycerols were putatively identified. Additionally, some proteins, for example thymosin β4 (Xen), were also detected. On the subcellular level, the lipid profiles were found to differ between the animal and vegetal poles of the eggs. Radial profiling revealed profound compositional differences between the jelly coat vitelline/plasma membrane and egg cytoplasm. Changes in the metabolic profile of the egg following fertilization, e.g., the decline of polyamine content with the development of the embryo were observed using LAESI-MS. This approach enables the exploration of metabolic and lipid changes during the early stages of embryogenesis.