Early life sensory experience remodels brain circuitry to optimize behavioral output. This competitive renewal
continues our genetic dissection of the molecular mechanisms through which synaptic connections are refined
based on sensory experience. We use different odorant cues to activate different classes of odorant receptor
neurons, downstream projection neurons, and brain learning/memory center Kenyon cells to test the directional
remodeling of connectivity and function. In three parallel circuit channels, we use in vivo CRISPR knockout,
conditional gene manipulations and transgenic trans-synaptic connectivity mapping to test both neuron and glia
class-specific roles in activity-dependent remodeling. These mechanisms go awry in numerous disease states
of cognitive and autism spectrum disorders. We directly test here genetic models of Fragile X syndrome (FXS),
Noonan syndrome (NS), Noonan syndrome with Multiple Lentigines (NSML) and Neurobeachin (NBEA) autism
spectrum disorder (ASD). In Aim 1, we test neuron-specific Fragile X Mental Retardation Protein (FMRP) roles
in odorant sensory experience-dependent critical period brain circuit remodeling in 3 distinct circuit channels.
We target tetanus toxin light chain (TeTXLC) and excitatory (CsChrimson)/inhibitory (GtAcR) optogenetic tools
to odorant sensory neurons, projection neurons, and Kenyon cells to dissect activity-dependent mechanisms.
Based on a preliminary screen, we identify channel-selective chloride transporters and Wnt signaling ligands to
test their critical period roles. In Aim 2, we test glia-specific FMRP roles in experience-dependent critical period
synaptic remodeling by blocking phagocytic pruning at three different levels. We test neuron-to-glia signaling
mechanisms in the FXS disease model, including both synapse-secreted insulin like peptide (ILP) “find me”
signals and surface phosphatidylserine (PS) “eat me” signals. We test the roles of direct FMRP mRNA targets
1) ESCRT-III Shrub and 2) glial-secreted matrix metalloproteinase 1 (MMP1) in glial synapse phagocytosis and
critical period synaptic remodeling. We use single neuron labeling (miniSOG) to visualize glial phagocytosis via
transmission electron microscopy (TEM). In Aim 3, we test FMRP translation regulation of PKA/ERK signaling
pathways in sensory experience-dependent circuit remodeling. We use new transgenic cAMP reporter (cAMPr)
and separation of phases-based activity reporter of kinase (SPARK) to visualize signaling in vivo in response
to experience during the critical period; compartmentalized within odorant sensory neurons, projection neurons
and Kenyon cells in our 3 parallel circuit channels. We test roles of direct FMRP mRNA target Rugose/NBEA
acting as a PKA anchor, with downstream PKA pathway kinase Meng-Po. Using an ERK-SPARK reporter and
whole-cell patch-clamp recording to monitor functional remodeling, we test roles of direct FMRP mRNA target
Corkscrew/SHP2 acting as an ERK pathway phosphatase. Our ongoing program orders molecular mechanism
intersections between Fragile X syndrome (FXS), Noonan syndrome (NS), Noonan syndrome with Multiple
Lentigines (NSML), and NBEA-associated autism spectrum disorder in critical period brain circuit remodeling.