The gene encoding proline dehydrogenase modulates sensorimotor gating in mice

The acoustic startle response as an effective model for elucidating the effect of genes on the neural mechanism of behavior in mice

One current approach in investigating the neural basis of behavior is to use mutant mice with specific genetic alterations which affect neural functions. We are convinced that this approach is only effective if a behavioral model with sufficiently known underlying neuronal mechanisms is used. We present a model system which is well-suited for the above approach. Because the neural basis is known in great detail, in the startle system behavioral results can be very well interpreted. This is demonstrated here by using footshock sensitization of the acoustic startle response (ASR) as an example. Sensitization is elicited by aversive stimuli such as electric footshocks and causes an increase in ASR amplitude. The present experiment showed that this ASR increase is not due to a drop in the startle threshold but to increased gain in the response to suprathreshold stimuli. This makes it possible to draw conclusions about the neuronal site of the startle threshold in the startle pathway and the synapse at which the gain shift during sensitization occurs. The possibility of interpreting behavioral output on a well known neural basis (as demonstrated here) makes the ASR a promising model system for investigating (neuro-) genetic influences of behavior.

Association study of a promoter polymorphism of UFD1L gene with schizophrenia

Schizophrenia or schizoaffective disorders are often found in patients affected by DiGeorge/velo-cardio-facial syndrome (DGS/VCFS) as a result of hemizygosity of chromosome 22q11.2. We evaluated the UFD1L gene, mapping within the DGS/VCFS region, as a potential candidate for schizophrenia susceptibility. UFD1L encodes for the ubiquitin fusion degradation 1 protein, which is expressed in the medial telencephalon during mouse development. Using case control, simplex families (trios), and functional studies, we provided evidence for association between schizophrenia and a single nucleotide functional polymorphism, -277A/G, located within the noncoding region upstream the first exon of the UFD1L gene. The results are supportive of UFD1L involvement in the neurodevelopmental origin of schizophrenia and contribute in delineating etiological and pathogenetic mechanism of the schizophrenia subtype related to 22q11.2 deletion syndrome.

Polymorphism in SNAP29 gene promoter region associated with schizophrenia

Linkage studies indicate that chromosome 22q contains a locus, or loci, for schizophrenia (SZ) and bipolar disorder (BPD). Furthermore, the congenital disorder velo cardio facial syndrome (VCFS), which is usually caused by a 22q11 microdeletion, is associated with an increased prevalence of psychiatric disease, including SZ and BPD. One plausible candidate gene that maps to 22q11, in a region deleted in the most common form of VCFS, is SNAP29, a member of the SNAP-25 family of SNARE proteins. To search for possible functional mutations in SNAP29 that could be analyzed as candidates for 22q11-linked psychiatric problems, exons, intron-exon junctions and the promoter region were screened. No coding variants were found, although a silent mutation at codon 6 and three single nucleotide polymorphisms (SNPs) were identified in the 5' untranslated and promoter regions. One SNP, an A-->G transition 923 [corrected] nucleotides upstream of the transcription start site, showed a moderately significant difference in the distribution of alleles and genotypes in patients with SZ compared with controls (allele frequency: chi(2) = 5.57, 1 df, P = 0.018; genotype: chi(2) = 9.49, 2 df, P = 0.009; odds ratio = 1.59, 95% Cl = 1.08--2.34). No significant difference was found in patients with BPD. Although the functional significance of this mutation is not known, the tetranucleotide core sequence of the ets and IK2 families of transcription factors is altered as a result of the SNP. These data suggest that a mutation in the SNAP29 gene promoter region, or a mutation in linkage disequilibrium with the promoter SNP, may be involved in the pathogenesis of chromosome 22-linked SZ.

Two Functional Copies of the DGCR6 Gene Are Present on Human Chromosome 22q11 Due to a Duplication of an Ancestral Locus

The DGCR6 (DiGeorge critical region) gene encodes a putative protein with sequence similarity to gonadal(gdl), a Drosophila melanogaster gene of unknown function. We mapped the DGCR6 gene to chromosome 22q11 within a low copy repeat, termed sc11.1a, and identified a second copy of the gene, DGCR6L, within the duplicate locus, termed sc11.1b. Both sc11.1 repeats are deleted in most persons with velo-cardio-facial syndrome/DiGeorge syndrome (VCFS/DGS), and they map immediately adjacent and internal to the low copy repeats, termed LCR22, that mediate the deletions associated with VCFS/DGS. We sequenced genomic clones from both loci and determined that the putative initiator methionine is located further upstream than originally described, but in a position similar to the mouse and chicken orthologs.DGCR6L encodes a highly homologous, functional copy ofDGCR6, with some base changes rendering amino acid differences. Expression studies of the two genes indicate that both genes are widely expressed in fetal and adult tissues. Evolutionary studies using FISH mapping in several different species of ape combined with sequence analysis of DGCR6 in a number of different primate species indicate that the duplication is at least 12 million years old and may date back to before the divergence of Catarrhines from Platyrrhines, 35 mya. These data suggest that there has been selective evolutionary pressure toward the functional maintenance of both paralogs. Interestingly, a full-length HERV-K provirus integrated into the sc11.1a locus after the divergence of chimpanzees and humans.

Deletion of 150 kb in the minimal DiGeorge/velocardiofacial syndrome critical region in mouse

Deletions or rearrangements of human chromosome 22q11 lead to a variety of related clinical syndromes such as DiGeorge syndrome (DGS) and velo--cardiofacial syndrome (VCFS). In addition, patients with 22q11 deletions have an increased incidence of schizophrenia and several studies have mapped susceptibility loci for schizophrenia to this region. Human molecular genetic studies have so far failed to identify the crucial genes or disruption mechanisms that result in these disorders. We have used gene targeting in the mouse to delete a defined region within the conserved DGS critical region (DGCR) on mouse chromosome 16 to prospectively investigate the role of the mouse DGCR in 22q11 syndromes. The deletion spans a conserved portion ( approximately 150 kb) of the proximal region of the DGCR, containing at least seven genes ( Znf74l, Idd, Tsk1, Tsk2, Es2, Gscl and Ctp ). Mice heterozygous for this deletion display no findings of DGS/VCFS in either inbred or mixed backgrounds. However, heterozygous mice display an increase in prepulse inhibition of the startle response, a manifestation of sensorimotor gating that is reduced in humans with schizophrenia. Homozygous deleted mice die soon after implantation, demonstrating that the deleted region contains genes essential for early post-implantation embryonic development. These results suggest that heterozygous deletion of this portion of the DGCR is sufficient for sensorimotor gating abnormalities, but not sufficient to produce the common features of DGS/VCFS in the mouse.