Molecular Mechanisms of Visual Pathway Plasticity
We use a multidisciplinary approach involving biochemistry and immunoprecipitation, immunocytochemistry and vital imaging in tissue culture to identify and study the signaling molecules that are associated with the glutamate receptors in the "eye opening interval". We have also begun to collaborate with the Broad Institute Proteomics Units headed by Dr. Steven Carr. We are using liquid chromatography and tandem mass spectroscopy (LCMs/MS) to identify the protein changes in visual cortex post-synaptic densities across the eye opening and juvenile to adult intervals and we are using lentiviral vectors to express in vivo in neonate rat visual centers short inhibitory RNA molecules (siRNA) against molecules suspected of involvement in these processes. Other experiments utilize mutant mouse strains to determine whether the trafficking of NMDA receptors and/or the specific NR2A versus NR2B subunits or the receptor scaffolds and signaling modules are requuired for the plasticity observed after eye opening. Finally we are in the middle of two large gene chip experiments with mRNAs from the visual layers of the superior collciulus before, and after, eye opening and from litter mates in which eye are never opened. This has allowed us to factor out changes in gene expression due to eye opening from changes due merely to age. The one completed analysis has suggested several very interesting molecules that are good candidates for siRNA knockdown studies, again in vivo, to test the requirement for these gene products during eye opening induced plasticity. We have an additional ongoing study in which microRNAs that change in the eye opening interval are being compared to transcripts that change in the same interval to determined if any of the synaptic plasticity events are under the control of microRNA.
Translational Research on Neurodegeneration and Psychiatric Disease:
We are also currently involved in two collaborative projects in which we are applying our knowledge of developmental synaptic plasticity. (1) One study involves electrophysiological and molecular experiments designed to identify the cellular basis of motoneuron death in a mouse model of Amyotrophic Lateral Sclerosis (ALS). These studies are undertaken in collaboration with Dr. Robert Brown Jr. at MGH and Harvard Medical a leading ALS Investigator. A second recently begun project involves genes know to be linked to schizophrenia and also known to be involved in NMDA receptor signaling. Currently these experiments use small molecules known to inhibit neuregulin signaling to understand their effect on NMDA receptor activity-dependent regulation. These studies are undertaken in collaboration with Dr. Edward Skolnick's Psychiatric Disease Research Group based in the Broad Institute.
Yoshii A, Constantine-Paton M. (2007) BDNF induces transport of PSD-95 to dendrites through PI3K-AKT signaling after NMDA receptor activation. Nat Neurosci. 6:702-11.
Zhao JP, Phillips MA, Constantine-Paton M. (2006) Long-term potentiation in the juvenile superior colliculus requires simultaneous activation of NMDA receptors and L-type Ca2+ channels and reflects addition of newly functional synapses.
J Neurosci. 49:12647-55.
Miskevich F, Doench JG, Townsend MT, Sharp PA, Constantine-Paton M. (2006)
RNA interference of Xenopus NMDAR NR1 in vitro and in vivo.
J Neurosci Methods. 1-2:65-73.
Colonnese MT, Zhao JP, Constantine-Paton M. (2005) NMDA receptor currents suppress synapse formation on sprouting axons in vivo. J Neurosci. 5:1291-303.
Townsend M, Liu Y, Constantine-Paton M. (2004) Retina-driven dephosphorylation of the NR2A subunit correlates with faster NMDA receptor kinetics at developing retinocollicular synapses. J Neurosci. 49:11098-107.
Miska EA, Alvarez-Saavedra E, Townsend M, Yoshii A, Sestan N, Rakic P, Constantine-Paton M, Horvitz HR. (2004) Microarray analysis of microRNA expression in the developing mammalian brain. Genome Biol. 9:R68.
Lu W, Constantine-Paton M. (2004) Eye opening rapidly induces synaptic potentiation and refinement. Neuron. 2:237-49.
van Zundert B, Yoshii A, Constantine-Paton M. (2004) Receptor compartmentalization and trafficking at glutamate synapses: a developmental proposal. Trends Neurosci. 7:428-37.