title: Imaging and identification of endogenous peptides from rat pituitary embedded in egg yolk.
abstract: BACKGROUND
  Mass spectrometry imaging (MSI) can provide accurate data containing the spatial distribution of endogenous peptides in tissue sections without previous treatment. One of the key issues in analyzing small samples is establishing a proper technique for mounting and manipulating collected tissue in order to avoid contamination of the sample with optimal cutting temperature (OCT) resin.
  
  
  METHODS
  We present a method for embedding rat pituitary tissue in a frozen egg yolk block, which enables its further imaging in experiments on a matrix-assisted laser desorption/ionization (MALDI) mass spectrometer with time-of-flight (TOF) analyzer. Embedding the sample in the egg yolk prevents contamination from the OCT resin, which decreases MALDI signal quality.
  
  
  RESULTS
  In the present study we detected numerous m/z peaks related to endogenous peptides. We identified fifteen peptides and their post-translational modifications by tandem mass spectrometry (MS/MS) directly on tissue sections of the hypophysis posterior and intermediate lobes; among these peptides were vasopressin, oxytocin, copeptin, melanocyte-stimulating hormones and beta-endorphin. We also showed that egg yolk itself does not affect localization of peptides in the pituitary.
  
  
  CONCLUSIONS
  Egg yolk embedding enables preparation of tissue sections from small tissue fragments to organs such as the pituitary gland, which is suitable for localization and identification of endogenous peptides by the MALDI-MSI and MALDI-MS/MS techniques.
authors.affiliation: Faculty of Chemistry, Biological and Chemical Research Centre, University of Warsaw, Pasteura 1, 02-093, Warsaw, Poland.
authors.forename: Piotr
authors.initials: P
authors.lastname: Sosnowski
authors.affiliation: Department of Experimental and Clinical Physiology, Laboratory of Centre for Preclinical Research, The Medical University of Warsaw, Banacha 1B, 02-097, Warsaw, Poland.
authors.forename: Tymoteusz
authors.initials: T
authors.lastname: Zera
authors.affiliation: Faculty of Chemistry, Biological and Chemical Research Centre, University of Warsaw, Pasteura 1, 02-093, Warsaw, Poland.
authors.forename: Beata
authors.initials: B
authors.lastname: Wilenska
authors.affiliation: Department of Experimental and Clinical Physiology, Laboratory of Centre for Preclinical Research, The Medical University of Warsaw, Banacha 1B, 02-097, Warsaw, Poland.
authors.forename: Ewa
authors.initials: E
authors.lastname: Szczepanska-Sadowska
authors.affiliation: Faculty of Chemistry, Biological and Chemical Research Centre, University of Warsaw, Pasteura 1, 02-093, Warsaw, Poland.|Mossakowski Medical Research Centre, Polish Academy of Sciences, Pawinskiego 5, 02-106, Warsaw, Poland.
authors.forename: Aleksandra
authors.initials: A
authors.lastname: Misicka
mesh_terms: D000595:Amino Acid Sequence; D000818:Animals; D004530:Egg Yolk / Q000737:chemistry*; D005615:Freezing; D008297:Male; D008969:Molecular Sequence Data; D010455:Peptides / Q000032:analysis*; D010902:Pituitary Gland / Q000737:chemistry*; D051381:Rats; D017207:Rats, Sprague-Dawley; D019032:Spectrometry, Mass, Matrix-Assisted Laser Desorption-Ionization / Q000379:methods*; D016610:Tissue Embedding / Q000379:methods*; D001615:beta-Endorphin / Q000032:analysis; D053500:gamma-Lipotropin / Q000032:analysis
chemical_list: D010455:Peptides; D053500:gamma-Lipotropin; D001615:beta-Endorphin