Mouse aldehyde dehydrogenase genetics: Positioning of Ahd‐1 on chromosome 4

Summary Electrophoretic variants of mitochondrial aldehyde dehydrogenase (AHD‐A 2 ) are widely distributed among inbred strains of Mus musculus and have been used to localize the gene encoding AHD‐A 2 (Ahd‐1) at the non‐centromeric end of chromosome 4. In the mouse (Mus musculus), aldehyde dehydrogenase (AHD; E.C.1.2.1.3) exists as at least three isozymes which are differentially distributed in liver subcellular fractions (designated A 2 , B 4 and Cy* for the mitochondrial, soluble and microsomal isozymes respectively) and in various tissues of this animal (Holmes, 1978a; 1978b; Timms & Holmes, 1981). Electrophoretic variants have been previously reported for the A 2 and B 4 isozymes among inbred strains of mice, and the genetic loci (designated Ahd‐1 and Ahd‐2 ) have been localized on chromosomes 4 and 19 respectively (Holmes, 1978b; Timms & Holmes, 1980). This paper describes further genetic analyses of AHD‐A 2 enabling Ahd‐1 to be positioned at the non‐centromeric end of chromosome 4. Forty‐three inbred strains of Mus musculus were used in these studies (Table 1). Two series of matings were carried out. 1) Female SM/J mice and male NZC/B1 mice were mated to obtain F, female offspring which were backcrossed to male NZC/B1 mice. These progeny were used to examine the segregation and linkage relationship of b (brown), Pgm‐2 (encoding phosphoglucomutase B) and Ahd‐1 (Table 2). 2) Female C57BL/6J mice and male SM/J. mice were mated to obtain F, female offspring which were backcrossed to male SM/J mice. The segregation and linkage relationship of Pgm‐2, Gpd‐1 (encoding the liver and kidney isozyme of hexose‐6 phosphate dehydrogenase) and Ahd‐1 were examined for these backcross progeny (Table 3). Methods for preparing liver and kidney extracts and the cellulose acetate electrophoresis procedure for typing Ahd‐1, Pgm‐2 and Gpd‐1 have been previously described (Holmes, 1978b). A previous study has described the electrophoretic patterns for allelic variants for mitochondria1 AHD and of the hybrid phenotype for this enzyme (Holmes, 1978b). The three‐allelic isozyme pattern for hybrid animals was consistent with a dimeric subunit structure: AHD‐A 1 A 2 , AHD‐A 1 A 2 and AHD‐3, with the A1 and A2 subunits being encoded by separate alleles at a single locus, designated Ahd‐1 (Ahd‐1 o and Ahd‐1 b respectively). The distribution of these alleles among 43 inbred strains of mice is given in Table 1. The allelic variants were approximately equally distributed among the inbred strains examined and no divergence of phenotype was observed among the 6 substrains of C57BL mice (Ahd‐1 a allele) and 5 substrains of BALB/c (Ahd‐1 b allele) mice examined. Genetic variants for phosphoglucomutase‐B (PGM‐B) have been reported by Shows, Ruddle and Roderick (1969) and the gene ( Pgm‐2 ) was subsequently localized on chromosome 4 near b (brown) by Chapman, Ruddle and Roderick (1970). Table 2 illustrates the results of a three‐point cross between b, Pgm‐2 and Ahd‐1. Variation from the expected 1:1:1:1:1:1 ratio for unlinked loci was significant(x 2 = 73.15; 7 df; P < 1 × 10 ‐5 ), indicating that the three loci are linked. Recombination frequency data are consistent with the gene order: b ‐ Pgm‐2 ‐ Ahd‐1 The second cross examined the segregation of Pgm‐2, Ahd‐1 and Gpd‐1 loci (Table 3). The latter locus has been previously positioned on chromosome 4 (linkage group VIII) by Hutton & Roderick (1970) and Chapman (1975), and has been used to localize Ahd‐1 in this region (Ahd‐1 and Gpd‐1 exhibit a recombination frequency of 10.3 ± 3.7 %) (Holmes, 1978b). The data from Table 3 is consistent with a gene order of Pgm‐2 ‐ Ahd‐1 ‐ Gpd‐1. The recombination frequency data of Ahd‐1 with Gpd‐1, Pgm‐2 and b also supports the proposal that Ahd‐1 is localized between Pgm‐2 and Gpd‐1 (Tables 2 and 3; Holmes, 1978b). Recent metabolic studies have indicated that mitochondria1 aldehyde dehydrogenase (AHD) plays a very important role in the metabolism of acetaldehyde derived from ethanol, ensuring a low concentration of acetaldehyde in the blood leaving the liver (Grunnet, 1973; Parilla et al., 1974; Corral1 et al., 1976). Moreover, genetic variation of this isozyme in human livers has been recently reported (Harada et al., 1978), and this polymorphism has been proposed as the molecular basis for individual and racial differences in alcohol sensitivity (Goedde et al., 1979). Consequently, genetic analyses of mitochondria1 AHD are of particular significance to studies on the genetic control of alcohol metabolism in mammals. In summary, this report confirms previous studies which demonstrated that the genetic locus encoding mitochondrial aldehyde dehydrogenase in the mouse (Ahd‐1) is on chromosome 4 (Holmes, 1978b), and positions the gene with respect to b (brown), Pgrn‐2 (encoding phosphoglucomutase B) and Gpd‐ 1 (encoding the liver and kidney isozyme of hexose‐6‐phosphate dehydrogenase). In addition, the distribution of the 2‐allelic phenotypes for this isozyme has been examined among 43 in‐ bred strains of mice.