A Short History of Insect (Neuro)Peptidomics—A Personal Story of the Birth and Youth of an Excellent Model for Studying Peptidome Biology

Digestion-Free Analysis of Peptides from 30-year-old Formalin-Fixed, Paraffin-Embedded Tissue by Mass Spectrometry Imaging

“…Proctolin was the very first insect neuropeptide (a myotropic peptide) to be sequenced (RYLPT) after a laborious isolation effort starting from 125 kg of adult American cockroaches. 39 Ions associated with proctolin (m/z 649.3668; [M + H] + ) were found to be present exclusively in sections containing a small cross section through the insect's recurrent nerve (which was not included in the whole mount tissue preparation analyzed in our work mentioned above 18,26 ). Indeed, the nervus recurrens, part of the cockroach stomatogastric nervous system, is known to transport proctolin from the frontal ganglion further into the body.…”

“…This confirms previous immunohistochemical results as well as mass spectrometry analyses, indicating that specific nerves running through the CA contain these neuropeptides. 6,36,37 Remarkably, little if any qualitative differences can be observed between the >30 year old FFPE tissue detected peptides and those that can be imaged in freshly prepared unfixed cockroach CC/CA 18,26 or that have recently have been reported detectable in P. americana CC/CA cryosections. 38 In a few sections of the >30 years old FFPE tissue preparation, the well-known cockroach pentapeptide neurohormone, proctolin, which was not reported in our previous publication, 26 was detected.…”

“…33 These two hypertrehalosemic hormones are readily detected as Na + adducts at m/z 995.4346 and 1010.4709, respectively, an observation also made in previous studies. 18,27 As illustrated by representative on-tissue, single-pixel mass spectra of the various regions of the retrocerebral complex (Figure 1), many of the observed peaks were detected at low relative abundances, being present at tissue (sub)structures, i.e., specific neurosecretory nerve fiber bundles and neuroendocrine cell groups. The MSI data were processed using PCA to facilitate identification of low-abundance peaks originating from different tissue locations.…”

“…27 These samples were taken from an insect retrocerebral complex, a neurosecretory tissue serving as a model biological system for neuropeptide secretion of higher-order animals, such as in the mammalian pituitary. 18 We describe a novel MSI sample preparation method for the digestion-free detection of endogenous neuropeptides and its application to >30-year-old FFPE tissue of P. americana. The method is free of enzymatic digestion, antigen retrieval, or aqueous washing of the tissue, allowing the label-free detection of endogenous peptides by (MALDI) MSI.…”

Mass Spectral Analysis of Neuropeptide Expression and Distribution in the Nervous System of the Lobster Homarus americanus

“…MALDI FTICR MS has recently been reported for high-mass-accuracy and high-mass-resolution MALDI imaging; however, the data acquisition speed on the MALDI FTICR instrument is on the order of 15 s/pixel, as shown in preliminary experiments . The MALDI Orbitrap data shown in Figure was collected at rate of ∼6.6 s/pixel; however, depending on the concentration level of analytes present in the tissue, MALDI Orbitrap spectrometer can also operate at even higher speed (i.e., 1.2−1.8 s/pixel in a recent study) . In addition, the imaging data size of the same tissue section obtained on FTICR MS is usually 100 times larger compared to those from the LTQ Orbitrap spectrometer, which could cause difficulties for data analysis and storage.…”