Reduced Chrna7 expression in mice is associated with decreases in hippocampal markers of inhibitory function: implications for neuropsychiatric diseases.

The α7* nicotinic acetylcholine receptor encoded by CHRNA7 (human)/Chrna7 (mice) regulates the release of both the inhibitory neurotransmitter GABA and the excitatory neurotransmitter glutamate in the hippocampal formation. A heterozygous (Het) deletion at 15q13.3 containing CHRNA7 is associated with increased risk for schizophrenia, autism, and epilepsy. Each of these diseases are characterized by abnormalities in excitatory and inhibitory hippocampal circuit function. Reduced Chrna7 expression results in decreased hippocampal α7* receptor density, abnormal hippocampal auditory sensory processing, and increased hippocampal CA3 pyramidal neuron activity in C3H mice Het for a null mutation in Chrna7. These abnormalities demonstrate that decreased Chrna7 expression alters hippocampal inhibitory circuit function. The current study examined the specific impact of reduced Chrna7 expression on hippocampal inhibitory circuits by measuring the levels of GABA, GABA(A) receptors, the GABA synthetic enzyme l-glutamic acid decarboxylase-65 (GAD-65), and the vesicular GABA transporter 1 (GAT-1) in wild-type (Chrna7 +/+) and Het (Chrna7 +/-) C3H α7 mice of both genders. GAD-65 levels were significantly decreased in male and female Het C3H α7 mice, whereas GABA(A) receptors were significantly reduced only in male Het C3H α7 mice. No changes in GABA and GAT-1 levels were detected. These data suggest that reduced CHRNA7 expression may contribute to the abnormalities in hippocampal inhibitory circuits observed in schizophrenia, autism, and/or epilepsy.

Deletion of a 5-cM region at chromosome 8p23 is associated with a spectrum of congenital heart defects.

BACKGROUND: Cytogenetic evidence suggests that the haploinsufficiency of > or =1 gene located in 8p23 behaves as a dominant mutation, impairing heart differentiation and leading to a wide spectrum of congenital heart defects (CHDs), including conotruncal lesions, atrial septal defects, atrioventricular canal defects, and pulmonary valve stenosis. An 8p heart-defect-critical region was delineated, and the zinc finger transcription factor GATA4 was considered a likely candidate for these defects. We narrowed this region and excluded a major role of GATA4 in these CHDs. METHODS AND RESULTS: We studied 12 patients (7 had CHD and 5 did not) with distal 8p deletions from 9 families by defining their chromosome rearrangements at the molecular level by fluorescent in situ hybridization and short-tandem repeat analysis. Subjects with 8p deletions distal to D8S1706, at approximately 10 cM from the 8p telomere, did not have CHD, whereas subjects with a deletion that included the more proximal region suffered from the spectrum of heart defects reported in patients with 8p distal deletions. The 5-cM critical region is flanked distally by D8S1706 and WI-8327, both at approximately 10 cM, and proximally by D8S1825, at 15 cM. Neither GATA4 nor angiopoietin-2 (ANGPT2; a gene in 8p23 involved in blood vessel formation) were found to be deleted in some of the critical patients. We also found that CHDs are not related to the parental origin of deletion. CONCLUSIONS: Haploinsufficiency for a gene between WI-8327 and D8S1825 is critical for heart development. A causal relationship does not seem to exist between GATA4 and ANGPT2 haploinsufficiency and CHDs.

Cloning, sequencing, and analysis of inv8 chromosome breakpoints associated with recombinant 8 syndrome.

Rec8 syndrome (also known as "recombinant 8 syndrome" and "San Luis Valley syndrome") is a chromosomal disorder found in individuals of Hispanic descent with ancestry from the San Luis Valley of southern Colorado and northern New Mexico. Affected individuals typically have mental retardation, congenital heart defects, seizures, a characteristic facial appearance, and other manifestations. The recombinant chromosome is rec(8)dup(8q)inv(8)(p23.1q22.1), and is derived from a parental pericentric inversion, inv(8)(p23.1q22.1). Here we report on the cloning, sequencing, and characterization of the 8p23.1 and 8q22 breakpoints from the inversion 8 chromosome associated with Rec8 syndrome. Analysis of the breakpoint regions indicates that they are highly repetitive. Of 6 kb surrounding the 8p23.1 breakpoint, 75% consists of repetitive gene family members-including Alu, LINE, and LTR elements-and the inversion took place in a small single-copy region flanked by repetitive elements. Analysis of 3.7 kb surrounding the 8q22 breakpoint region reveals that it is 99% repetitive and contains multiple LTR elements, and that the 8q inversion site is within one of the LTR elements.

Molecular analysis and breakpoint definition of a set of human chromosome 21 somatic cell hybrids.

Rodent-human somatic cell hybrids containing single human chromosomes or chromosome fragments are extremely valuable in physical mapping, marker analysis, and disease mapping. Chromosome 21 has been extensively studied in this fashion, and a single set of hybrids has been utilized in mapping the majority of chromosome 21 markers. The utility of a set of hybrids depends upon the definition of the human chromosome content. Recently, Chumakov and coworkers (1) utilized 198 chromosome 21 markers in the preliminary analysis of YACs spanning chromosome 21q. We have used these same markers to evaluate the STS content of a set of 27 chromosome 21 somatic cell hybrids, resulting in the description of the breakpoints at the molecular level, as well as the definition of 35 "bins. " The detailed molecular definition of chromosome 21 content of the hybrids, in combination with the further analysis of chromosome 21 YACs (2), has resulted in the most detailed picture of chromosome 21 to date.

Identification of human chromosome 9 specific genes using exon amplification.

We have recently developed a method, exon amplification, that is designed for isolation of exon sequences from genomic DNA. To assess the efficacy of this method we have analyzed cosmid genomic clones derived from human chromosome 9, and have cloned several products from this analysis. Approximately 63% of cosmids produced at least one product derived from functioning splice sites within the target genomic fragment, and in many cases multiple products were isolated. In addition, an easily identifiable class of false positives was produced from 56% of cosmids analyzed; these are readily eliminated from subsequent study. Sequence analysis and database searches revealed that the majority (87%) of the putative exon clones were unique, the remainder being derived from repetitive sequences. Analysis of sequence conservation by Southern blotting in addition to cDNA screening experiments suggested that most, if not all, of these unique sequences represent true exons. The results of these studies indicate that exon amplification is a rapid and reliable approach for isolation of exon sequences from mammalian genomic DNA.

Genetic and physical map of the interferon region on chromosome 9p.

A region of chromosome 9, surrounding the interferon-beta (IFNB1) locus and the interferon-alpha (IFNA) gene cluster on 9p13-p22, has been shown to be frequently deleted or rearranged in a number of human cancers, including leukemia, glioma, non-small-cell lung carcinoma, and melanoma. To assist in better defining the precise region(s) of 9p implicated in each of these malignancies, a combined genetic and physical map of this region was generated using the available 9p markers IFNB1, IFNA, D9S3, and D9S19, along with a newly described locus, D9S126. The relative order and distances between these loci were determined by multipoint linkage analysis of CEPH (Centre d'Etude du Polymorphisme Humain) pedigree DNAs, pulsed-field gel electrophoresis, and fluorescence in situ hybridization. All three mapping approaches gave concordant results and, in the case of multipoint linkage analysis, the following gene order was supported for these and other closely linked chromosome 9 markers present in the CEPH database: pter-D9S33-IFNB1/IFNA-D9S126-D9S3-D9S19 -D9S9/D9S15-ASSP3-qter. This map serves to extend preexisting chromosome 9 maps (which focus primarily on 9q) and also reassigns D9S3 and D9S19 to more proximal locations on 9p.

Generation and characterization of a human chromosome 9 cosmid library.

A cosmid library has been constructed from the hamster-human hybrid cell line PK-87-9, which contains chromosome 9 as its sole known human component. Ten thousand colonies were produced, of which approximately 200, or 2%, contain human material. Fifty of these 200 were regionally mapped by an Alu-primed PCR product hybridization procedure. These cosmids were localized to all regions of chromosome 9, but were especially concentrated in the distal portion of 9q. The map location derived by the Alu-primed PCR product hybridization procedure was compared to the map location derived by fluorescent in situ hybridization. Assignment of chromosomal location by the two methods was correspondent in all but a few cases. The presumptive presence of HTF islands was investigated for 130 cosmids by digestion with the restriction enzyme NotI. Twenty percent of cosmids contained at least one NotI site. A number of simple sequence repeat polymorphisms identified from the cosmid set were characterized and will provide a link between the genetic and physical maps for this chromosome.

Construction and characterization of radiation hybrids for chromosome 9, and their use in mapping cosmid probes on the chromosome.

Radiation hybrids were produced from a monochromosomal microcell hybrid (PK87-9) which contains only human chromosome 9 with an inserted marker on 9p. Doses of radiation ranging from 1000 to 8000 rads were used to produce a series of hybrids with different size fragments of human chromosome 9. The inserted dominant selectable marker was used to select for hybrids that preferentially maintain fragments of 9p. A panel of 53 radiation hybrids were characterized for 17 chromosome 9 markers. In addition, 17 hybrids were analyzed by fluorescent in situ hybridization (FISH). Hybrids were produced with breaks on both 9p and 9q, many of which appear to contain a single fragment of human chromosome 9. These hybrid cell lines were used to regionally localize 31 cosmids isolated from a chromosome 9 cosmid library. Six cosmids were mapped to intervals on 9p, six cosmids mapped to the centromeric region of the chromosome, and 19 mapped to 9q.

Exon amplification: a strategy to isolate mammalian genes based on RNA splicing.

We have developed a method, exon amplification, for fast and efficient isolation of coding sequences from complex mammalian genomic DNA. This method is based on the selection of RNA sequences, exons, which are flanked by functional 5' and 3' splice sites. Fragments of cloned genomic DNA are inserted into an intron, which is flanked by 5' and 3' splice sites of the human immunodeficiency virus 1 tat gene contained within the plasmid pSPL1. COS-7 cells are transfected with these constructs, and the resulting RNA transcripts are processed in vivo. Splice sites of exons contained within the inserted genomic fragment are paired with splice sites of the flanking tat intron. The resulting mature RNA contains the previously unidentified exons, which can then be amplified via RNA-based PCR and cloned. Using this method, we have isolated exon sequences from cloned genomic fragments of the murine Na,K-ATPase alpha 1-subunit gene. We have also screened randomly selected genomic clones known to be derived from a segment of human chromosome 19 and have isolated exon sequences of the DNA repair gene ERCC1. The sensitivity and ease of the exon amplification method permit screening of 20-40 kilobase pairs of genomic DNA in a single transfection. This approach will be extremely useful for rapid identification of mammalian exons and the genes from which they are derived as well as for the generation of chromosomal transcription maps.

Functional expression of the genomic DNA sequences encoding mouse Na,K-ATPase alpha 1 gene by cotransfection of overlapping genomic DNA segments.

The entire 33-kb coding region of the mouse Na,K-ATPase alpha 1 subunit gene was cloned in two overlapping cosmids which contain inserts of 40 kb. To assess the functional expression of the mouse alpha 1 gene, the two cosmids were cotransfected into ouabain-sensitive CV-1 monkey cells yielding an average of 64 resistant colonies per 10(6) cells per microgram of DNA. Analysis of the DNA transferred to the ouabain-resistant transformants by the two cosmids suggests that the generation of a functional gene can occur by homologous recombination between the two introduced segments, as demonstrated by generation of a novel diagnostic restriction fragment. The ability to reconstruct the intact mouse alpha 1 gene in a heterologous host cell and to monitor its functional expression with a selection protocol permits direct identification and isolation of regulatory sequences for the gene.

Assignment of a third purine biosynthetic gene (glycinamide ribonucleotide transformylase) to human chromosome 21.

Using a series of human-hamster hybrid cell lines, a gene coding for glycinamide ribonucleotide transformylase was mapped to human chromosome 21. The availability of hybrids containing only portions of chromosome 21 allowed the gene to be assigned to the region between the q11.2 and the q22.2 bands, inclusive. Differentiation of human and hamster glycinamide ribonucleotide transformylase was accomplished via an immunoprecipitation assay that employed a polyclonal antibody raised against the human enzyme.