Novel regional and developmental NMDA receptor expression patterns uncovered in NR2C subunit-β-galactosidase knock-in mice

Abstract

NMDA receptor "knock-in" mice were generated by inserting the nuclear β-galactosidase reporter at the NR2C subunit translation initiation site. Novel cell-types and dynamic patterns of NR2C expression were identified using these mice, which were unnoticed before because reagents that specifically recognize NR2C-containing receptors are non-existent. We identified a transition zone from NR2C-expressing neurons to astrocytes in an area connecting the retrosplenial cortex and hippocampus. We demonstrate that NR2C is expressed in a subset of S100β-positve/GFAP-negative glial cells in the striatum, olfactory bulb and cerebral cortex. We also demonstrate novel areas of neuronal expression such as retrosplenial cortex, thalamus, pontine and vestibular nuclei. In addition, we show that during cerebellar development NR2C is expressed in transient caudalrostral gradients and parasagittal bands in subsets of granule cells residing in the internal granular layer, further demonstrating heterogeneity of granule neurons. These results point to novel functions of NR2C-containing NMDA receptors.

Long-Lasting NMDA Receptor-Mediated EPSCs in Mouse Striatal Medium Spiny Neurons

“…The generation of NR2A Ϫ/Ϫ (1) mice is reported in Sakimura et al (1995) and that of NR2C Ϫ/Ϫ (3) mice is in Lu et al (2006) and Karavanova et al (2007). Mouse pups were killed by decapitation in agreement with the guidelines of the AVMA Panel on Euthanasia and the Georgetown University Animal Care and Use Committee.…”

Neuregulin Signaling Is Dispensable for NMDA- and GABAA-Receptor Expression in the CerebellumIn Vivo

“…Thus, the onset of erbb2/erbb4 inactivation (P6) (Fig. 1 B) may appear too close to the induction of NR2C expression (P6) (Karavanova et al, 2007) to fully exclude a role of NRG/ErbB-dependent signaling in this process in the erbb2/erbb4 dKO mice. It should be noted, however, that both the degree of recombination and the normal development of NR2C mRNA levels in erbb2/erbb4-deficient mice are averaged over the entire cerebellum.…”

“…One example in the CNS is the developmental switch in neurotransmitter receptor expression in postmigratory cerebellar granule neurons that is thought to be induced by the mossy fibers innervating them. These cells express the NR2B receptor subunit at late embryonic and early postnatal stages, but switch to the NR2C subunit beginning in the second postnatal week and extending to the end of the first month (Monyer et al 1994, Karavanova et al 2007. Assaying individual granule neurons by single-cell PCR showed that NR2C was expressed specifically in postmigratory granule cells starting at the end of the first postnatal week and continuing until the end of the first postnatal month when all granule cells have completed migration (Durand et al 2006).…”

“…In contrast, the levels of NR2A and NR2C mRNAs are low at early postnatal stages and increase after the first postnatal week. Inserting a lacZ reporter at the NR2C translation initiation site, under the control of the endogenous NR2C promoter, showed that beginning at P5-P6 of cerebellar development, NR2C is expressed in a caudo-rostral sequence in granule cells of the internal granular layer, to reach a final value in the entire layer around P30 (Karavanova et al, 2007). To see whether NR2C expression is regulated by NRGs, we inactivated its receptors, ErbB2 and ErbB4, in granule cells by crossing mice doubly homozygous for loxP-flanked exons of erbb2 and erbb4 alleles with a mouse line that begins to express Cre recombinase under the control of the GABA A -R ␣6 subunit gene promoter in postmigratory granule cells of the emerging internal granule layer at P5-P6, i.e., at a stage when the NR2C and ␣6 genes are first expressed (Mellor et al, 1998;Laurie et al, 1992b;Karavanova et al, 2007).…”

“…Specifically, certain NRG-1 isoforms are thought to induce AChRs in sympathetic ganglion cells (Yang et al, 1998) and the switch in NMDA receptor (NMDA-R) subunit expression from NR2B to NR2C (Ozaki et al, 1997) observed in postnatal cerebellar granule cells Cull-Candy and Leszkiewicz, 2004;Karavanova and Buonanno, 2007). In support of this idea, granule cells maturing in the internal granule layer express NRG receptors (Rieff et al, 1999), and mossy fibers (MFs) and Golgi cells innervating them (Corfas et al, 1995) express NRG1.…”