Molecular mechanisms of motor skill stabilization - PROJECT SUMMARY Successful motor skill learning is marked by decreased performance variability over time. For motor skills learned during early developmental time periods, such as walking and talking, performance remains highly stable and precise throughout life, suggesting that associated motor circuits exist in a stable state that is tuned to performance. Motor skill stabilization has been studied in terms of changes to neural population coding, neurophysiology, and synaptic plasticity, yet the molecular mechanisms that transition motor circuits to a state that supports stable motor performance are unknown. Like developmental motor skills in humans, the song of the Bengalese finch, an established animal model for the neural mechanisms supporting skill learning, is learned over the first few months of life, becomes less variable and plastic over time, and remains highly stable throughout a bird’s life. Birdsong is controlled by a dedicated neural circuit whose connectivity, neuronal composition, and molecular properties are similar to those of cortical motor circuits in mammals. The objective of this project is to leverage the experimental accessibility of the birdsong neural circuit and the highly quantifiable nature of birdsong to define the molecular mechanisms that regulate the transition from variable to stable motor skill performance. Recent advances in genomics and single-cell molecular assays have enabled genome-wide, cell-resolved analyses of how the molecular attributes of the birdsong neural circuit change during song learning and performance. Our preliminary data indicate that birdsong stabilization is associated with a suite of transcriptional changes in the birdsong neural circuit. In the proposed research, we will test the hypothesis that song stabilization is associated with closure of neuronal epigenetic state in song motor regions using single-nucleus gene expression and chromatin accessibility assays combined with histone modification profiling (Aim 1). We will then characterize the roles of two candidate molecular systems, one governed by a transcription factor and the other a neuropeptide pathway, in regulating the maturation of song circuitry and the stabilization of song (Aims 2 and 3). First, we will characterize the role of the homeodomain transcription factor SIX2, whose expression is dynamically regulated during song stabilization, in establishing projection neuron identity in a cortical song motor region using gene expression manipulations, transcriptomics assays, and sensitive analyses of birdsong variability (Aim 2). Finally, we will determine the role of the corticotropin releasing hormone (CRH) neuropeptide system in regulating the developmental balance between song stability and variability (Aim 3). Together, the proposed research will shed light on the molecular mechanisms that regulate motor stabilization and reveal candidate factors whose dysfunction underlie developmental motor disorders.
