Gene markers for alcohol-metabolizing enzymes among recombinant inbred strains of mice with differential behavioural responses towards alcohol

Alcohol dehydrogenases: gene multiplicity and differential functions of five classes of isozymes

Mammalian alcohol dehydrogenases (ADHs) constitute an enzyme family of multiple forms (isozymes) which are differentially distributed throughout the body. Subunit types alpha, beta and gamma in dimeric combinations constitute the isozymes of human liver class I ADH, and are >94% homologous in structure. Human pi and chi subunits form homodimeric Class II and III ADH isozymes. pi-ADH is liver specific whereas chi-ADH is widely distributed throughout the body. A sixth human ADH subunit (designated mu or sigma), forming a new dimeric human stomach ADH, has been recently reported as Class IV ADH. Evidence for a seventh human ADH subunit has also been described, designated as Class V, the transcripts having been reported in the stomach and liver. All five classes of ADH represent isozymes which are homologous but exhibit at least 30% sequence differences in primary srtructure. Kinetic analyses of four of these classes of ADH indicated differential functions, serving either in the oxidative or reductive mode. Studies from various laboratories indicate the following respective functions: oxidation of aliphatic and aromatic alcohols-liver Class I and Class II, and stomach Class IV ADHs; reduction of peroxidic aldehydes-Classes I, II and IV; 'biogenic' alcohol oxidation-Classes I and II; and glutathione-dependent formaldehyde dehydrogenase-Class III.

Genetic factors in neurotoxicology and neuropharmacology: a critical evaluation of the use of genetics as a research tool

Animals have evolved a detoxication system to enable them to survive in a hostile chemical environment in which foods contain many non-nutrient chemicals. Detoxication depends on enzymes which are often genetically polymorphic. As a result, inter-individual variation is common, and in humans several Mendelian loci have been identified. However, most variation in response is probably due to the action of several genes. Genetic variation in response to the neurotoxin MPTP and to chemically and physically-induced seizures is reviewed. In the former case, differences between pigmented and white mouse strains have been noted which are consistent with the hypothesis that humans are more sensitive than mice or rats because of the presence of melanin in human brains. However, variation in sensitivity probably also depends on other genes. In the case of audiogenic seizures, a single locus has been identified and mapped, but its relationship with seizures induced by other agents is not clear. Genetic variation in response to alcohol is also discussed. The failure of most toxicologists to consider genetic variation as a potentially confounding variable, and as a powerful research tool, is discussed critically in relation to non-repeatability of research on the neurotoxic effects of lead, and in relation to the genetic variation in MPTP, seizures, and alcohol response already noted. It seems clear that genetic methods provide a powerful research tool which is largely being ignored by toxicologists.

Use of recombinant inbred strains to identify quantitative trait loci in psychopharmacology

Unlike simple Mendelian characteristics, individual differences in complex quantitative phenotypes studied in psychopharmacology are generally distributed continuously and are likely to be influenced by many genes. Recombinant inbred (RI) strains are valuable not only for their traditional use of detecting major gene segregation and linkage but also for identifying associations between quantitative traits and quantitative trait loci (QTL) that account for relatively small amounts of variation in phenotypes as well as loci that account for greater amounts of variation. When applied to published data on genetic markers and on amphetamine, alcohol, and morphine responses in BXD RI strains (RI strains developed from the cross between C57BL/6J and DBA/2J progenitor inbred strains), the RI QTL approach identified several significant associations beyond known major gene effects. Together, significant associations explain more than half of the genetic variance for these measures. The RI QTL approach is especially valuable for investigating the QTL underpinnings of genetic correlations among measures. It is recommended that psychopharmacogenetic research focus on the BXD RI strains. The cumulative and integrative nature of such a program of research is the major benefit of the RI QTL association approach for molecular genetic analysis of psychopharmacological processes, their physiological infrastructure, and their interface with other behavioral and biological systems.

Mapping of mouse gamma crystallin genes on chromosome 1

Restriction fragments analysis of DNA from mouse-hamster somatic-cell hybrid clones revealed that a mouse gamma crystallin cDNA hybridized to genomic sequences located on mouse chromosome 1. Identification of restriction fragment length polymorphisms (RFLPs) in the gamma crystallin sequences of inbred strains of mice permitted the further localization of the gamma crystallin genes (Cryg) to the proximal region of chromosome 1 closely linked to the loci encoding isocitrate dehydrogenase (Idh-1), a low molecular weight (LM) crystallin protein polymorphism (Len-1), and fibronectin (Fn-1). A single recombinant was observed between Len-1 and an RFLP in the gamma crystallin gene family, consistent with the hypothesis that Len-1 is one of the several structural loci encoding gamma crystallin genes. Len-1 is probably located on the centromeric end of the Cryg gene family. Linkage of Idh-1, Cryg, and Fn-1 in mice extends the syntenic relationship of those loci to the human, bovine, and rodent genomes and may define a chromosomal region that is generally conserved among mammals. The map position of Cryg, near the eye lens obsolescence (Elo) locus, was confirmed by the discovery that the restriction fragment patterns of gamma crystallin sequences differed between strain C3H/HeJ and the congenic anophthalmic mutant strain, C3H.Elo. Therefore, the gamma crystallin genes were cotransferred with the mutant Elo gene in the derivation of C3H.Elo. The results establish that LEN-1 is a marker for the gamma crystallin gene family, position the gamma crystallin gene family relative to other markers on mouse chromosome 1, and provide additional evidence that the Elo mutation is encoded at a locus closely linked to the gamma crystallin gene cluster. This study found no evidence of recombination hot spots within the gamma crystallin gene cluster.

Liver cytosolic aldehyde dehydrogenases from "alcohol-drinking" and "alcohol-avoiding" mouse strains: purification and molecular properties

Liver cytosolic aldehyde dehydrogenases (AHD-2) have been isolated in a highly purified state from "alcohol-drinking" (C57BL/6J) and "alcohol-avoiding" (DBA/2J) strains of mice. The purified enzymes were resolved into three major and one minor form of activity by isoelectric focusing (IEF) techniques and showed similar zymogram patterns. The enzymes had identical subunit sizes on SDS-polyacrylamide gels: 53,000. Gel exclusion chromatography, using Ultrogel AcA34, indicated that the enzymes were dimers. The enzymes exhibited biphasic kinetic characteristics and were readily distinguished from each other. The purified forms of AHD-2 from C57BL/6J and DBA/2J mice exhibited two apparent Km values in each case: 10 microM/100 microM and 30 microM/330 microM respectively. AHD-2 exhibited a broad pH optimum in the range 7.0-9.0 and was very sensitive towards disulphuram inhibition, with 50% inhibition occurring at 0.17 microM. The kinetic results support proposals that AHD-2 may be the primary enzyme for oxidizing acetaldehyde during ethanol oxidation in vivo.