Characterization, evolutionary relationships, and chromosome location of processed mouse HPRT pseudogene

Quantitative trait loci affecting methamphetamine responses in BXD recombinant inbred mouse strains

Individual differences in most behavioral and pharmacological responses to abused drugs are dependent on both genetic and environmental factors. The genetic influences on the complex phenotypes related to drug abuse have been difficult to study using classical genetic analyses. Quantitative trait locus (QTL) mapping is a method that has been used successfully to examine genetic contributions to some of these traits by correlating allelic variation in polymorphic genetic markers of known chromosomal location with variation in drug-response phenotypes. We evaluated several behavioral responses to multiple doses of methamphetamine (METH) in C57BL/6J (B6), DBA/2J (D2), and 25 of their recombinant inbred (BXD RI) strains. Stereotyped chewing, horizontal home cage activity, and changes in body temperature after 0, 4, 8, or 16 mg/kg METH, as well as stereotyped climbing behavior after 16 mg/kg METH, were examined. Associations (p < 0.01) between METH sensitivity and allelic status at multiple microsatellite genetic markers were subsequently determined for each response. QTLs were provisionally identified for each phenotype, some unique to a particular behavior and others that appeared to influence multiple phenotypes. Candidate genes suggested by these analyses included several that mapped near genes relevant for the neurotransmitters acetylcholine and glutamate. The locations of QTLs provisionally identified by this analysis were compared with QTLs hypothesized in other studies to influence methamphetamine- and cocaine-related phenotypes. In several instances, QTLs appeared to overlap, which is consistent with idea that common neural substrates underlie some responses to psychostimulants.

Isolation of a potentially functional HPRT processed pseudogene from the hill kangaroo Macropus robustus

A highly conserved hypoxanthine phosphoribosyltransferase processed pseudogene (KPH) has been isolated from a female kangaroo (Macropus robustus) lambda EMBL3 genomic library. The pseudogene contains only transcribed material with all of the introns precisely removed and has possible direct repeats at either end of the message. It has a 654-nucleotide open reading frame (ORF) from the Met start codon to the stop codon that contains no additions, deletions or premature stops relative to expressed HPRT genes and, therefore, the possibility exists that it is expressed in vivo. Possible CAAT and GC boxes are present in the region 5' to the ORF and a polyadenylation signal is present in the region 3' to the ORF. If not expressed, the age of the pseudogene is estimated to be 10.7 million years. We propose that integration into the genome occurred specifically in a homocopolymeric region within a highly repeated region unique to the kangaroo genome.

The gene encoding hypoxanthine-guanine phosphoribosyltransferase as target for mutational analysis: PCR cloning and sequencing of the cDNA from the rat

In this paper, the cloning and nucleotide sequence of the cDNA of the rat gene coding for hypoxanthine-guanine phosphoribosyltransferase (hprt) is reported. Knowledge of the cDNA sequence is needed, among other reasons, for the molecular analysis of hprt mutations occurring in rat cells, such as skin fibroblasts isolated according to the granuloma pouch assay. The rat hprt cDNA was synthesized and used as a template for in vitro amplification by PCR. For this purpose, oligonucleotide primers were used, the nucleotide sequences of which were based on mouse and hamster hprt cDNA sequences. Sequence analysis of 1146 bp of the amplified rat hprt cDNA showed a single open reading frame of 654 bp, encoding a protein of 218 amino acids. In the predicted rat hprt amino acid sequence, the proposed functional domains for 5'-phosphoribosyl-1-pyrophosphate (PRPP) and nucleotide binding in phosphoribosylating enzymes as well as a region near the carboxyl terminal part were highly conserved when compared with amino acid sequences of other mammalian hprt proteins. Analysis of hprt amino acid sequences of 727 independent hprt mutants from human, mouse, hamster and rat cells bearing single amino acid substitutions revealed that a large variety of amino acid changes were located in these highly conserved regions, suggesting that all 3 domains are important for proper catalytic activity. The suitability of the hprt gene as target for mutational analysis is demonstrated by the fact that amino acid changes in at least 151 of the 218 amino acid residues of the hprt protein result in a 6-thioguanine-resistant phenotype.

The Chinese hamster HPRT gene: restriction map, sequence analysis, and multiplex PCR deletion screen

The fine structure of the Chinese hamster hypoxanthine guanine phosphoribosyltransferase (HPRT) gene has been determined; the gene has nine exons and is dispersed over 36 kb DNA. Exons 2-9 are contained within overlapping lambda bacteriophage clones and exon 1 was obtained by an inverse polymerase chain reaction (PCR). All the exons have been sequenced, together with their immediate flanking regions, and these sequences compared to those of the mouse and human HPRT genes. Sequences immediately flanking all exons but the first show considerable homology between the different species but the region around exon 1 is less conserved, apart from the preserved location of putative functional elements. Oligonucleotide primers derived from sequences flanking the HPRT gene exons were used to amplify simultaneously seven exon-containing fragments in a multiplex PCR. This simple procedure was used to identify total and partial gene deletions among Chinese hamster HPRT-deficient mutants. The multiplex PCR is quicker to perform than Southern analysis, traditionally used to study such mutants, and also provides specific exon-containing fragments for further analysis. The Chinese hamster HPRT gene is often used as a target for mutation studies in vitro because of the ease of selection of forward and reverse mutants; the information presented here will enhance the means of investigating molecular defects within this gene.

Genetic maps of mouse chromosome 17 including 12 new anonymous DNA loci and 25 anchor loci

An interspecific backcross between lab mice and Mus spretus was used to construct a multilocus map of Chromosome 17 consisting of 12 new anonymous loci and 9 anchor loci. In addition, 7 anonymous DNA loci were added to the Chr 17 map for the BXD strains. Although we were able to identify readily the most likely gene order in the interspecific backcross, we found no evidence for an unambiguous gene order using the BXD recombinant inbred strains. Comparison of the interspecific backcross map and the BXD RI strain map revealed evidence in the interspecific backcross for a longer total genetic length, enhanced recombination distal to H-2, a segment showing suppressed recombination, and strong interference.

Linkage map of mouse chromosome 17: localization of 27 new DNA markers

Chromosome 17 of the laboratory variant of the house mouse (Mus musculus L.), MMU17, has been studied extensively, largely because of its involvement in the control of immune response and embryonic as well as male germ cell differentiation. A detailed linkage map of this chromosome is therefore a highly desired goal. As the first step toward achieving this goal, we have isolated, using a LINE 1 repetitive sequence as a probe, 52 anonymous DNA clones from MMU17. Twenty-seven repetitive sequence-free probes isolated from these clones displayed restriction fragment length variation among common inbred strains and could be mapped with the help of recombinant inbred strains, congenic strains, F2 segregants, or intra-t recombinants. Together with markers identified previously, the new markers can be used to construct a map of MMU17 that contains 125 DNA loci. The markers are distributed over a length of approximately 71 cM, which probably represents the entire length of MMU17. Most of the markers reside in the proximal portion of the chromosome, which contains the t and H-2 complexes; this chromosomal region is now fairly well mapped. The distal region of MMU17, on the other hand, is populated by only a few, rather imprecisely mapped markers. Molecular maps are available for most of the H-2 complex and for parts of the t complex.

Germ line transmission and expression of a corrected HPRT gene produced by gene targeting in embryonic stem cells

The deletion mutation in the HPRT-deficient mouse embryonic stem (ES) cell line E14TG2a has been corrected by gene targeting. The presence of plasmid sequences in the correcting vector DNA did not affect the frequency of correction. We have characterized three different HPRT gene structures in correctants. Cells from one corrected clone have been introduced into mouse blastocysts, and germ line transmission of the ES cell-derived corrected gene has been achieved. The corrected gene has the same pattern of expression as the wild-type gene, with the characteristic elevated level of expression in brain tissue. Hence, we have demonstrated the feasibility of introducing targeted modifications into the mouse germ line by homologous recombination in ES cells.