Speed and precise regulation of synaptic transmission are critical for complex brain functions such as cognition and learning. Release of neurotransmitters from a presynaptic nerve terminal is often impaired in neurological disorders, including autism, schizophrenia, addiction and neurodegeneration. Exact knowledge of the molecular mechanisms for neurotransmitter release is thus critical for understanding brain disease. The active zone of a presynaptic nerve terminal is the site of neurotransmitter release. An active zone consists of a highly specialized network of proteins that organizes synaptic vesicles for fast Ca2+-triggering of release, a central requirement for speed and precision of synaptic transmission. It is our over-arching goal to understand how the protein machinery at the active zone operates. We approach this goal by dissecting the molecular functions of active zone components. ELKS proteins are highly enriched at active zones, indicating that ELKS functions in neuronal exocytosis at the active zone. Before release, active zones dock and prime synaptic vesicles for exocytosis close to presynaptic Ca2+-channels. How ELKS operates during these processes to control release is not understood, maybe in part because no systematic genetic approach has been taken in vertebrates to address ELKS function. We have now generated conditional knockout mice for both mammalian ELKS genes, ELKS1 and ELKS2. Ample preliminary data lead to our central hypothesis: ELKS proteins increase release probability though controlling presynaptic Ca2+-influx, and they modulate the size of the pool of readily releasable vesicles. We address separate components of this hypothesis in three specific aims, and we dissect the underlying molecular mechanisms.
In aim 1, we hypothesize that ELKS1 and ELKS2 proteins have both shared and distinct functions. We determine how each ELKS gene contributes to the functions of active zones in neurotransmitter release by systematically studying presynaptic phenotypes in the newly generated conditional single knockout mice for ELKS1 and ELKS2, and in the ELKS1/2 double knockout mice. In preliminary experiments we find that ELKS proteins enhance presynaptic Ca2+-influx, and that individual and double ELKS deletions differentially affect the pool of readily releasable vesicles.
In aim 2, we determine the mechanisms by which ELKS controls presynaptic Ca2+-influx.
In aim 3, we propose a specific hypothesis that unifies effects on vesicle pools observed in ELKS mutants. We examine this hypothesis, determine the underlying molecular mechanisms and consider numerous alternative explanations. Our research is innovative because it addresses a novel hypothesis by a combination of genetic, biochemical and functional experiments of unique depth. Ultimately, this approach will lead to precise insights into the molecular control of neurotransmitter release, a key neuronal process that fails during various brain diseases.

Public Health Relevance

Pathological alterations in neuronal signal transmission are a hallmark of many neurological disorders, including neurodegeneration, autism, schizophrenia and addiction. In the present project, we are dissecting molecular mechanisms that underlie the release of chemical signals from neurons. Our results will provide detailed molecular insights into neuronal communication and how such communication fails in brain disorders.

Agency
National Institute of Health (NIH)
Type
Research Project (R01)
Project #
1R01NS083898-01A1
Application #
8759245
Study Section
Synapses, Cytoskeleton and Trafficking Study Section (SYN)
Program Officer
Talley, Edmund M
Project Start
Project End
Budget Start
Budget End
Support Year
1
Fiscal Year
2014
Total Cost
Indirect Cost
Name
Harvard Medical School
Department
Biology
Type
Schools of Medicine
DUNS #
City
Boston
State
MA
Country
United States
Zip Code
02115
Liu, Changliang; Bickford, Lydia S; Held, Richard G et al. (2014) The active zone protein family ELKS supports Ca2+ influx at nerve terminals of inhibitory hippocampal neurons. J Neurosci 34:12289-303