Proteins associated with migratory preparation-
Unlike the neuroendocrine system that regulates reproduction, no specific neural center has yet been localized that controls the migratory process. Migratory preparedness is characterized by increased food intake, fat deposition, and locomotion (nighttime restlessness in captivity; aka Zugunruhe , Trivedi et al., 2014; Singh et al., 2015). We found several DEPs that have been studied in the control of food intake and energy balance. Among the most relevant proteins that were more abundant in migrants than residents were monocarboxylate transport protein (MCT2) and apoptosis-inducing factor (AIF). MCT2 is involved in the transport of short-chain monocarboxylates such as pyruvate, ketone bodies, lactate and a-hydroxybutyrate, which play an essential role in energy balance (Elizondo-Vegal, Salgado, & Gracía-Robles, 2016). Studies of MCT2 protein in the regulation of food intake have located it in both orexigenic and anorexigenic neurons (Cortés-Campos et al. 2013). Specifically, projections from tanycyte specialized ependymal cells found on the lining of third ventricle of the brain communicate directly with MCT2 positive neurons that synthesize and release key neuropeptides such as proopiomelanocortin (POMC), agouti related protein (AgRP), and neuropeptide Y (NPY) that control food intake (Elizondo-Vega et al., 2015). Similarly, AIF protein is known for facilitating utilization of fatty acids for mitochondrial respiration specific to hypothalamic POMC neurons involved in regulation of glucose sensing and energy metabolism (Timper et al., 2018).
Locomotion and navigation are two other important behavioral features that differentiate the migratory junco population from the earlier reproducing resident population. During enhanced locomotor activity, one would expect sustained stimulation of nerve synapses, synaptogenesis, synaptic plasticity, and dendritic spine morphogenesis. We found greater abundance of Stonin 2, NCK2, Septin 7, Dock 7 in migratory juncos, all proteins that have been studied in relation to increased synaptogenesis, synaptic plasticity, dendritic spine morphogenesis, and neurogenesis (Jung et al., 2007; Thévenot et al., 2011; Wang et al., 2018). In addition to proteins that are involved in neuronal plasticity, we also found a member of a high mobility protein family (HMGN5) known to regulate gene expression by modulating chromatin structure (Rochman, Malicet, & Bustin, 2010). Other proteins present in high abundance in migratory juncos were RSG7 regulators for G protein signaling (RGS) in paraventricular neurons (PVN) (Gold, Ni, Dohlman, & Nestler et al., 1997), LYRIC known to regulate inflammation, immune response, and angiogenesis (Emdad et al., 2013), and SIK3 known to be associated with regulation of corticotropin releasing hormone transcription in rat hypothalamic neurons (Liu et al., 2012).