Glycine receptors are anchored at inhibitory chemical synapses by a cytoplasmic protein, gephyrin. Molecular cloning revealed the similarity of gephyrin to prokaryotic and invertebrate proteins essential for synthesizing a cofactor required for activity of molybdoenzymes. Gene targeting in mice showed that gephyrin is required both for synaptic clustering of glycine receptors in spinal cord and for molybdoenzyme activity in nonneural tissues. The mutant phenotype resembled that of humans with hereditary molybdenum cofactor deficiency and hyperekplexia (a failure of inhibitory neurotransmission), suggesting that gephyrin function may be impaired in both diseases.

Clustering of neurotransmitter receptors in postsynaptic densities involves proteins that aggregate the receptors and link them to the cytoskeleton. In the case of glycine and GABA(A) receptors, gephyrin has been shown to serve this function. However, it is unknown whether gephyrin is involved in the clustering of all glycine and GABA(A) receptors or whether it interacts only with specific isoforms. This was studied in the retinae of mice, whose gephyrin gene was disrupted, with immunocytochemistry and antibodies that recognize specific subunits of glycine and GABA(A) receptors. Because homozygous (geph -/-) mutants die around birth, an organotypic culture system of the mouse retina was established to study the clustering of gephyrin and the receptors in vitro. We found that all gephyrin and all glycine receptor clusters (hot spots) were abolished in the geph (-/-) mouse retina. In the case of GABA(A) receptors, there was a significant reduction of clusters incorporating the gamma2, alpha2, and alpha3 subunits; however, a substantial number of hot spots was still present in geph (-/-) mutant retinae. This shows that gephyrin interacts with all glycine receptor isoforms but with only certain forms of GABA(A) receptors. In heterozygous geph (+/-) mutants, no reduction of hot spots was observed in the retina in vivo, but a significant reduction was found in the organotypic cultures. This suggests that mechanisms may exist in vivo that allow for the compensation of a partial gephyrin deficit.

We have devised a general strategy for producing female mice from 39,X0 embryonic stem (ES) cells derived from male cell lines carrying a targeted mutation of interest. We show that the Y chromosome is lost in 2% of subclones from 40,XY ES cell lines, making the identification of targeted 39,X0 subclones a routine procedure. After gene targeting, male and female mice carrying the mutation can be generated by tetraploid embryo complementation from the 40,XY ES cell line and its 39,X0 derivatives. A single intercross then produces homozygous mutant offspring. Because this strategy avoids outcrossing and therefore segregation of mutant alleles introduced into the ES cells, the time and expense required for production of experimental mutant animals from a targeted ES cell clone are substantially reduced. Our data also indicate that ES cells have inherently unstable karyotypes, but this instability does not interfere with production of adult ES cell tetraploid mice.

BackgroundTransgenic mice expressing mutated amyloid precursor protein (APP) and presenilin (PS)-1 or -2 have been successfully used to model cerebral β-amyloidosis, one of the characteristic hallmarks of Alzheimer's disease (AD) pathology. However, the use of many transgenic lines is limited by premature death, low breeding efficiencies and late onset and high inter-animal variability of the pathology, creating a need for improved animal models. Here we describe the detailed characterization of a new homozygous double-transgenic mouse line that addresses most of these issues.Methodology/Principal FindingsThe transgenic mouse line (ARTE10) was generated by co-integration of two transgenes carrying the K670N/M671L mutated amyloid precursor protein (APPswe) and the M146V mutated presenilin 1 (PS1) both under control of a neuron-specific promoter. Mice, hemi- as well as homozygous for both transgenes, are viable and fertile with good breeding capabilities and a low rate of premature death. They develop robust AD-like cerebral β-amyloid plaque pathology with glial inflammation, signs of neuritic dystrophy and cerebral amyloid angiopathy. Using our novel image analysis algorithm for semi-automatic quantification of plaque burden, we demonstrate an early onset and progressive plaque deposition starting at 3 months of age in homozygous mice with low inter-animal variability and 100%-penetrance of the phenotype. The plaques are readily detected in vivo by PiB, the standard human PET tracer for AD. In addition, ARTE10 mice display early loss of synaptic markers and age-related cognitive deficits. By applying a γ-secretase inhibitor we show a dose dependent reduction of soluble amyloid β levels in the brain.ConclusionsARTE10 mice develop a cerebral β-amyloidosis closely resembling the β-amyloid-related aspects of human AD neuropathology. Unifying several advantages of previous transgenic models, this line particularly qualifies for the use in target validation and for evaluating potential diagnostic or therapeutic agents targeting the amyloid pathology of AD.

The gene encoding the beta subunit of the inhibitory glycine receptor (GlyR) is widely expressed throughout the mammalian central nervous system. To unravel the elements regulating its transcription, we isolated its 5' non-coding and upstream flanking regions from mouse. Sequence analysis revealed significant differences between the 5' region of the beta subunit gene and the corresponding regions of the homologous GlyR alpha subunit genes; it also identified a novel exon (exon 0) that encodes most of the 5'-untranslated portion of the GlyR beta mRNA. Primer extension experiments disclosed multiple transcriptional start sites. Transfection experiments with luciferase reporter gene constructs showed that sequences encompassing 1.58 kb of upstream flanking region and 180 bp of exon 0 displayed high promoter activity in two neuroblastoma cell lines but not in non-neural cells. Analysis of various deletion constructs showed that the 5' flanking region preceding the transcriptional start sites silences expression in non-neural cells but is not essential for general promoter activity. In contrast, the deletion of sequences within exon 0 drastically decreased or abolished transcription; the removal of sequences harbouring Sp1 consensus sequences within exon 0 decreased expression specifically in a neuroblastoma cell line. Band-shift assays confirmed the binding of Sp1 to sites within the deleted sequence. Our results indicate that neural-specific expression of the GlyR beta subunit gene might depend on a direct interaction of Sp1 transcription factors with cis elements located downstream from transcription initiation sites.