Visualization of the localization of phospholipids in developing rat teeth by matrix-assisted laser desorption/ionization imaging mass spectrometry.

Matrix-assisted laser desorption/ionization imaging mass spectrometry (IMS) is used to comprehensively visualize the spatial distribution of numerous biomolecules. The present study was designed to investigate the distribution of phospholipids in developing rat teeth by IMS to identify the characteristic phospholipid molecules for tooth development, and to evaluate the suitability of tissue preparation methods. Rats at postnatal day 3 were euthanized, and the resected head specimens were either fixed or not fixed with 4% paraformaldehyde (PFA), and decalcified or not decalcified in 10% ethylenediaminetetraacetic acid (EDTA) before being frozen. Subsequently, sections were prepared and mounted on glass slides coated with indium tin oxide, and analyzed by IMS. The mass spectra showed the highest peaks around m/z 706, 732, and 734 in the region of interest. Characteristic localization of signals in the tooth buds was seen around m/z 706 and 732, and a database search indicated that the corresponding molecules were phosphatidylcholines. The signals were localized to the dental papillae and enamel epithelia in the tooth buds. The PFA-fixed specimens with or without EDTA decalcification showed preserved IMS signals, while the non-fixed specimens showed fewer signals. Thus, PFA fixation with EDTA decalcification appears to be suitable for IMS analysis of calcified tissues.