Journal of Neuroscience, Vol 16, 1460-1469, Copyright © 1996 by Society for Neuroscience
NMDA receptor activation-responsive phosphoproteins in the developing optic tectum
AJ Scheetz and M Constantine-Paton
Department of Biology, Yale University, New Haven, Connecticut 06520, USA.
A front phosphorylation assay followed by two-dimensional gel
electrophoresis was used to detect proteins in the tadpole optic tectum,
the phosphorylation state of which is regulated by NMDA receptor
activation. Five proteins with isoelectric points between 4 and 7 displayed
marked increases in their phosphorylation state in response to application
of 10 microM glutamate and 50 microM NMDA. This response was inhibited by
60 microM 2-amino-5-phosphopentanoic acid. These proteins are termed NMDA
receptor activation-responsive phosphoproteins (NARPPs). Two NARPPs were
identified as both in vitro and in vivo substrates for protein kinase C. Of
these two NARPPs, one was located in the postsynaptic density (NARPP-50),
and one was located in the nuclear fraction (NARPP-21). Phosphorylation of
NARPP-21 was also induced by application of the metabotropic glutamate
receptor agonist trans-(+/-)-1-amino-1,3-cyclopentanedicarboxylic acid
(trans- ACPD) (100 microM). Phosphorylation of all NARPPs was eliminated by
dantrolene, which inhibits release of calcium from intracellular stores. In
adult tecta, only NARPP-21 and -50 were phosphorylation. Thus the
phosphorylation state of most NARPPs is regulated differently when synaptic
plasticity is low. Further characterization of NARPPs should lead to
identification of second messenger systems involved in NMDA receptor
signaling and developmental synaptic plasticity.