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Analysis combined with fragment intensity predictions results in improved identification of classical bioactive peptides and sORF-encoded peptides

ABSTRACT: Bioactive peptides exhibit key roles in a wide variety of complex processes, such as regulation of body weight, learning, aging and innate immune response. Next to the classical bioactive peptides, emerging from larger precursor proteins by specific proteolytic processing, a new class of bio-active peptides originating from small open reading frames (sORFs) have been recognized as important biological regulators. But their intrinsic properties, specific expression pattern and location on presumed non-coding regions have hindered the full characterization of the repertoire of bioactive peptides, despite their predominant role in various pathways. Although the development of peptidomics has offered the opportunity to study these peptides in vivo, it remains challenging to identify the full peptidome as the lack of cleavage enzyme specification complicates conventional database search approaches. In this study, we introduce a proteogenomics methodology using a new type of mass spectrometry instrument and the implementation of machine learning tools towards improved identification of bioactive peptides in the mouse brain. The application of trapped ion mobility spectrometry (tims) coupled to a time-of-flight mass analyzer (TOF) offers improved sensitivity, an enhanced peptide coverage, reduction in chemical noise and the occurrence of chimeric spectra. Subsequent machine learning tools MS2PIP, predicting fragment ion intensities and DeepLC, predicting retention times, improve the database searching based on a large and comprehensive custom database containing both sORFs and alternative ORFs. Finally, the identification of peptides is further enhanced by applying the post-processing semi-supervised learning tool Percolator. Applying this workflow, we identified 48 sORF-encoded peptides originating from presumed non-coding locations, next to identifying 66 known neuropeptides from within 22 different families. Altogether, this robust pipeline fuses technological advancements from different fields ensuring an improved coverage of the neuropeptidome in the mouse brain.

INSTRUMENT(S): timsTOF Pro

ORGANISM(S): Mus Musculus (mouse)

TISSUE(S): Brain

SUBMITTER: Kurt Boonen

LAB HEAD: Kurt Boonen

PROVIDER: PXD026584 | Pride | 2021-10-11

REPOSITORIES: Pride

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Project description:Despite many improvements with in vitro culture systems, the quality and developmental ability of mammalian embryos produced in vitro is still lower than their in vivo counterparts. To bring knowledge to answer this question, we used a mass spectrometry (MS) approach to compare the protein content of bovine embryos that were conceived in vivo or produced in vitro. A total of 38 pools of grade-1 quality bovine embryos at the 4-6 cell, 8-12 cell, morula, compact morula and blastocyst stages developed either in vivo or in vitro were analyzed by nano-liquid chromatography coupled with label-free quantitative mass spectrometry, allowing the identification of 3,028 proteins. Multivariate analysis of quantified proteins showed a clear separation of embryo pools according to their in vivo or in vitro origin at all stages. Three clusters of differentially abundant proteins (DAPs) according to embryo origin were evidenced, including 463 proteins more abundant in vivo than in vitro across development, and 314 and 222 proteins more abundant in vitro than in vivo before and after the morula stage, respectively. The functional analysis of proteins found more abundant in vivo showed an enrichment in carbohydrate metabolism and cytoplasmic cellular components. Proteins found more abundant in vitro before the morula stage were mostly localized in mitochondrial matrix and involved in ATP-dependent activity while those overabundant after morula stage were mostly localized in the ribonucleoprotein complex and involved in protein synthesis. Oviductin and other proteins previously shown to interact with early embryos in vitro were among the most overabundant proteins after in vivo development. In conclusion, the maternal environment led to faster degradation of mitochondrial proteins at early embryo developmental stages, lower abundance of proteins involved in protein synthesis at the time of embryonic genome activation and a global upregulation of carbohydrate and small molecule metabolic pathways compared to in vitro produced embryos. Furthermore, our data confirm that embryos developed in vivo uptake large amounts of oviduct fluid-derived proteins as soon as the 4-6 cell stage. These data provide new insight into the molecular contribution of the mother to the developmental ability of early embryos and will help designing better in vitro culture systems.

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Analysis combined with fragment intensity predictions results in improved identification of classical bioactive peptides and sORF-encoded peptides

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