Linking the molecular logic of sensory neuron diversity and somatosensory circuitry in mouse spinal cord: development of novel tools for viral tracing and 3D analysis - Project Summary/Abstract
Sensory neurons in the dorsal spinal cord (dINs) represent the first site in the CNS to receive somatosensory
information from the periphery and are a crucial component in sensorimotor circuits that control posture and
behavior. Defining the developmental principles of somatosensory circuit formation and the molecular identity of
neurons that serve specific sensory functions is key to our understanding of the logic of sensorimotor integration
and for strategic interventions following injury or disease. All dINs arise from a small array of molecularly defined
embryonic cell populations, but markers are expressed only transiently and how these early neurons diversify
and integrate into sensory circuits serving distinct sensory modalities in the mature animal remains largely
unknown. There is an urgent need for genetic access to express tracers and to manipulate individual classes of
developing dINs as they emerge during the embryonic period but establish circuits postnatally. Here, we will
generate for the first time, mice that bridge the gap between early identity and mature function by providing
access selectively to one population of dINs, called dI1s, throughout development. We will create mouse lines
to introduce anterograde and retrograde viral tracers to reveal and map the synaptic targets of dI1s in brain and
spinal cord, and to identify input neurons to dI1s, in DRG, brain and spinal cord. These lines will extend temporal
genetic access selectively to developing dI1s into postnatal stages, by, first, a Cre-dependent Cre approach,
permitting access by Cre-dependent axonal and synaptic tracers, and second, mice that express the proteins
required for transsynaptic tracing using rabies virus. We will also develop platforms to analyze efficiently the
anatomy and connectivity of the circuitry. Furthermore, we will create a widely needed 3D spinal cord atlas for
assessment of neuronal identity and mapping circuitry. To understand the programs that regulate dI1
development, we will also identify and follow dynamic changes of transcriptional signatures in dI1s throughout
embryonic and postnatal ontogeny by single cell RNA sequencing. The tools established in the proposed
experiments and analyses will be applicable to all dIN subsets and will contribute both resources and information
to the field, and provide a template for manipulation and functional analysis of somatosensory pathways in health
and in disease.
