The Nature and Function of Genomic Imprinting in Monoaminergic Neurons

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Mental illnesses are complex, affected by stressors and metabolic factors and involve changes to multiple behavioral components and decision-making processes. Thousands of genetic variants with small effects are typically involved. Thus, we lack a coherent genetic, cellular and evolutionary model for understanding and modifying important behavioral components affecting decision-making, activity and stress. If such a fundamental model of control could be uncovered for conserved, naturalistic behavior, our capabilities for understanding and therapeutically modifying behavioral disorders would be improved. Foraging has been studied for decades to uncover the basic principles and mechanisms of decision-making. Studies typically use simplified binary choice tests. However, we recently published a naturalistic foraging assay and unsupervised machine-learning methods to study complex, naturalistic decision patterns in mice. We discovered that foraging is composed of reproducible, genetically controlled behavioral sequences that we call “modules”. Using these methods, we investigated roles for maternally and paternally imprinted genes in controlling naturalistic decision patterns in males and females. Canonical imprinting involves complete silencing of one parent’s allele; however, we previously described genes with “noncanonical imprinting effects” that involve parental allele expression biases at the tissue level. We now have evidence that noncanonical imprinting effects at the tissue level involve allele silencing in subpopulations of cells. Moreover, we uncovered important roles for noncanonical imprinting effects in controlling naturalistic foraging and risk-reward-effort decision patterns. Currently, we do not fully understand the behavioral roles for different noncanonical imprinted genes. MEGs (maternally expressed genes) and PEGs (paternally expressed genes) are postulated to have opposing functional roles, suggesting an enticing genetic and evolutionary model of mammalian decision control. Imprinting effects in different cell populations could regulate the form, expression, timing and/or sequential order of different behavioral components of foraging. Therefore, our proposed study tests the hypothesis that noncanonical MEGs and PEGs have opposing effects on discrete behavioral components of naturalistic foraging and their cell-type specific imprinting effects reveal cell populations controlling discrete behaviors. In Aim 1, we will determine how MEGs and PEGs co-expressed with Th (tyrosine hydroxylase) and Ddc (dopa decarboxylase) in monoaminergic brain cells affect naturalistic decisions. In Aim 2, we will define functional links between discrete cell populations with imprinting effects for particular genes and discrete behavioral components of naturalistic foraging and decision patterns. Our proposed study is significant because it will help define an important genetic, cellular and evolutionary model of behavioral and decision control. Our long-term objective is to define a new conserved mechanistic model of control over decision patterns that helps delineate targets for therapeutically modifying human behavior.