Neuropeptidomics Across Metazoan Life

Abstract

Every neuron in our brain is bathed in a sea of diverse signaling molecules, including peptides. It is well known that neuropeptides, acting as neurotransmitters, neuromodulators and peptide hormones, play pivotal roles in a variety of physiological processes, such as learning and memory, sleeping, pain, and anxiety. To understand how neuropeptides work in the human brain can be extremely challenge; fortunately, most neurochemical pathways are well conserved across metazoa, and thus working with simpler model organisms can provide valuable insights into the fundamental principles in the human brain. Several animal models have been commonly used in neuroscience studies, with each having specific advantages for particular research areas. For example, the sea hare (Aplysia californica) is an excellent model to understand the formation, function and plasticity of neuronal networks, while the honey bee (Apis mellifera) is important for uncovering the mechanisms and evolution of social behavior. As studies in these model organisms are undertaken, knowledge of the complement of neuropeptides used by and released from specific neuronal systems will increase our understanding of how complex suites of neuropeptides modulate neuronal network function to generate such complex behaviors. In this dissertation, several projects are presented with the goal of unraveling the functions of neuropeptides in cell-to-cell communication.

Mass spectrometry (MS) is a powerful tool to unambiguously characterize the amino acid sequences and post-translational modifications of peptides. Several MS platforms, coupled with liquid chromatography (LC), have been employed to explore the neuropeptidome of the central nervous system in different animal models. Additionally, novel putative neuropeptide genes have been identified based on the MS-derived data via de novo sequencing with the assistance of bioinformatic tools. The concurrent neuropeptidomic studies, as part of genome sequencing consortia for these animals, have significantly aided gene annotation efforts as well as future studies of peptide functions in these models.

To elucidate the biological functions of hundreds of peptides can be a daunting task. One way to shorten the candidate list is to perform the relative quantitation of samples under different biological conditions. In particular, stable isotopic labeling, followed by LC-MS analysis, has been used to identify peptide signatures that are involved in different aspects of the honey bee foraging behavior.