# Function and Structure Adaptations in Forebrain Development

> **NIH NIH R01** · CHILDREN'S HOSPITAL OF LOS ANGELES · 2020 · $779,796

## Abstract

Circuit development relies on genes and experience for proper assembly and maturation. Defining the
mechanisms that drive circuit-specific adaptations during heightened periods of plasticity are key for
understanding typical and atypical development. We hypothesize that molecules that regulate timing of
maturation modulate experience-dependent development and differential circuit vulnerabilities in neuro-
developmental disorders (NDDs). Advanced molecular and connectomics technologies have provided a more
complete perspective on the extent of neuronal and circuit diversity in the mature brain, but there is a
knowledge gap for the plastic periods of growth and refinement. Insight into this gap has emerged from studies
during the current grant period showing that 1) the c-MET receptor tyrosine kinase (MET) regulates timing of
excitatory synapse maturation; 2) MET is expressed in discrete subpopulations of intra-telencephalic (IT) and
cortico-thalamic (CT) neurons; and 3) dysregulated MET signaling alters the timing of critical period (CP)
plasticity for binocularity and disrupts fear learning. Foundational studies of developing molecular and
connectivity subtypes and their function in the cortex comprise three specific aims. In Aim 1, developing medial
prefrontal cortex (mPFC) and primary visual cortex (V1) MET+ neurons will be profiled using connectomics and
transcriptomics methods. A newly derived transgenic mouse line, MetGFP, will be combined with specific tracing
of MET+ connectivity using virally-transduced split-Cre technology that produces Cre-mediated, temporally
stable labeling of GFP+ (MET+) neurons and their axonal projections. Injections of fluorescent retrograde
tracers in mPFC and V1 targets will label IT or CT neurons. Labeled neurons will be FACS-sorted and profiled
by single cell RNA sequencing. Transcriptome data analysis will delineate subtypes of Met+ and Met-neurons,
with additional methods used to validate discoveries and determine whether sex and developmental timing are
variables for the subtypes. Aim 2 will test the hypothesis that Met down-regulation is required for structural and
functional plasticity during the CP in V1. A new, controllable transgenic mouse (ctg-Met) that sustains MET
signaling beyond its endogenous expression period will be used in combination with two-photon dendritic spine
imaging to quantify spine genesis and pruning during the V1 CP. Functional circuit connectivity will be
assessed by laser scanning photostimulation combined with glutamate uncaging. V1 plasticity will be
measured using a classic paradigm of monocular deprivation-induced ocular dominance plasticity. In Aim 3,
the role of MET+ mPFC neurons in mediating the CP for contextual fear memory persistence will be
determined using selective expression of DREADDs in GFP+ neurons using the split-Cre approach. The impact
of Met deletion or ctg-Met-mediated extended expression will be examined for the developmental emergence
of conditioned fear m...

## Key facts

- **NIH application ID:** 9925833
- **Project number:** 5R01MH067842-17
- **Recipient organization:** CHILDREN'S HOSPITAL OF LOS ANGELES
- **Principal Investigator:** PAT LEVITT
- **Activity code:** R01 (R01, R21, SBIR, etc.)
- **Funding institute:** NIH
- **Fiscal year:** 2020
- **Award amount:** $779,796
- **Award type:** 5
- **Project period:** 2002-07-01 → 2024-03-31

## Primary source

NIH RePORTER: https://reporter.nih.gov/project-details/9925833

## Citation

> US National Institutes of Health, RePORTER application 9925833, Function and Structure Adaptations in Forebrain Development (5R01MH067842-17). Retrieved via AI Analytics 2026-05-24 from https://api.ai-analytics.org/grant/nih/9925833. Licensed CC0.

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