Methods for Cryosectioning and Mass Spectrometry Imaging of Whole-Body Zebrafish

Abstract

The zebrafish (Danio rerio) is an ideal model for whole animal studies of lipid metabolism and lipid-related disease. In this work, infrared matrix-assisted laser desorption electrospray ionization (IR-MALDESI) mass spectrometry imaging (MSI) was applied for direct visualization of lipid and metabolite distributions across various organs in whole-body zebrafish tissue sections. Detailed methods for overcoming the challenges of cryosectioning adult male zebrafish for MSI and complementary histological imaging are described. Representative two-dimensional ion maps demonstrated organ specific localization of lipid analytes allowing for visualization of areas of interest including the brain, liver, intestines, and skeletal muscle. A high resolving power mass spectrometer was utilized for accurate mass measurements, which permitted the use of open-source, web-based tools for MS¹ annotations including METASPACE and METLIN. Whole-body MSI with IR-MALDESI allowed for broad lipid coverage with high spatial resolution, illustrating the potential of this technique for studying lipid-related diseases using zebrafish as a model organism.

Keywords: IR-MALDESI; cryosectioning; lipids; mass spectrometry imaging; zebrafish.

Figure 1.

Histology (a) and colocalization maps of representative lipids and metabolites in adult male zebrafish: (b) skin/testes (blue), brain/eye/spinal cord (green), intestines (red), (c) liver/kidney/skin (blue), spinal cord (green), kidney (red), and (d) skeletal muscle (blue), brain/eye/spinal cord (green), gills/spleen (red). Phosphatidylcholines and ceramides are abbreviated PC and Cer, respectively.

Figure 2.

Ion heatmaps of deprotonated fatty acyls in adult male zebrafish. Optical images of the MSI tissue section coated with ice and serial section stained by H & E are shown for histological context.