The AP2 clathrin adaptor protein complex regulates the abundance of GLR-1 glutamate receptors in the ventral nerve cord of C. elegans.
ionotropic glutamate receptors (AMPARs) mediate the majority of excitatory
neurotransmission in the mammalian CNS, and their abundance at synapses can directly
alter synaptic strength. Alterations in synaptic strength are believed to underlie the
mechanism by which we learn and encode memory, while aberrant glutamatergic signaling is
thought to contribute to several neurod... read moreegenerative diseases. It is well-established that
AMPAR-containing vesicles can be transported from the cell body to the synapse by
members of the kinesin family of molecular motors that drive vesicle transport along
microtubules. While many motors have been implicated in the targeting of AMPARs to
synapses, much less is known about the mechanisms and specific adaptor proteins that
recruit AMPARs into vesicles earlier in the biosynthetic trafficking pathway. In this
thesis, I investigated the role of the AP2 clathrin adaptor protein complex in
regulating the abundance of AMPA-type glutamate receptors in the ventral nerve cord
(VNC) of C. elegans. In Chapter 2, I found that the abundance of the AMPA-type glutamate
receptor GLR-1 was reduced in the VNC and increased in the interneuron cell bodies of
multiple loss of function AP2 mutants. Defects in GLR-1 abundance in the VNC of AP2
mutants could be rescued in the mature nervous system, and do not appear to depend on
the role of AP2 in synaptic vesicle recycling. Surprisingly, genetic analysis of apm-2,
the mu2 subunit of AP2, with the clathrin adaptin unc-11/AP180 suggests that apm-2
functions upstream of endocytosis in the VNC. Preliminary evidence suggests that AP2 may
directly interact with GLR-1 via the APM-2/mu2 subunit, and mutation of a conserved
residue in GLR-1 demonstrated to be critical for the interaction of AP2 mu2 with
mammalian AMPARs results in reduced levels of GLR-1 in the VNC and increased GLR-1
levels in the cell body. Further, I found that GLR-1 accumulates in the cell bodies of
multiple loss-of-function AP2 mutants, not at the plasma membrane as might be expected
for an endocytic adaptor, but instead in syntaxin-13 positive endosomal compartments.
These results raise the intriguing possibility that AP2 may regulate the forward
trafficking of GLR-1 in the biosynthetic pathway by mediating GLR-1 transport events
between intracellular compartments of the cell body and/or GLR-1 loading into transport
vesicles for motor-driven transport to the VNC. In Chapter 3, I investigated the genetic
interaction of apm-2 with other regulators of GLR-1 including the kinesin motor
klp-4/Kif13, the AP1 unc-101/mu1 subunit, and clathrin heavy chain. The results in this
thesis uncover a novel regulation of AMPA-type glutamate receptors in C. elegans, and
set the stage for future mechanistic studies.
Thesis (Ph.D.)--Tufts University, 2014.
Submitted to the Dept. of Cellular & Molecular Physiology.
Advisors: Peter Juo, and Michael Forgac.
Committee: Jerry Faust, Daniel Jay, and Suzanne Paradis.
Keywords: Physiology, Cellular biology, and Neurosciences.read less