Neural cells without functional N-Methyl- d-Aspartate (NMDA) receptors contribute extensively to normal postnatal brain development in efficiently generated chimaeric NMDA R1 −/− → +/+ mice

Abstract

Embryonic stem (ES) cells have revolutionised our understanding of animal physiology. Analysis of chimaeric mice generated from these cells allows us to study the role of genes in development and function of the nervous system. The NMDA receptor, one of the two major ionotropic glutamate receptors, has been proposed to play fundamental roles in the survival, migration, differentiation, and activity-dependent maturation of neural cells. The NMDA receptor subunit 1 (NR1) gene is indispensable for receptor function, and knock-out mice die at birth, inhibiting the study of glutamate signalling in postnatal neurons. Homozygous NR1−/− ES cells were derived from matings of heterozygous mice under feeder-free conditions. Chimaeras were made by incorporating these ES cells into wild-type blastocysts and by the classical aggregation of morulae between wild-type and NR1−/− embryos. The resulting chimaeras survive and develop normally. NR1−/− neurons, identified by their lacZ label, were analysed and quantified in developing and adult brains with varying knock-out contributions in every single brain region. Specifically, postnatal ontogenesis of cerebellum and hippocampus was normal. Accordingly, in chimaeric mice, NMDA receptor-initiated signals are not required for the migration, differentiation, and survival of most types of neurons in the central nervous system, in a cell-autonomous way.