The use of interspecific mouse crosses for gene localization: present status and future perspectives

Genetic mapping and developmental timing of transmission ratio distortion in a mouse interspecific backcross

BACKGROUND

Transmission ratio distortion (TRD), defined as statistically significant deviation from expected 1:1 Mendelian ratios of allele inheritance, results in a reduction of the expected progeny of a given genotype. Since TRD is a common occurrence within interspecific crosses, a mouse interspecific backcross was used to genetically map regions showing TRD, and a developmental analysis was performed to identify the timing of allele loss.

RESULTS

Three independent events of statistically significant deviation from the expected 50:50 Mendelian inheritance ratios were observed in an interspecific backcross between the Mus musculus A/J and the Mus spretus SPRET/EiJ inbred strains. At weaning M. musculus alleles are preferentially inherited on Chromosome (Chr) 7, while M. spretus alleles are preferentially inherited on Chrs 10 and 11. Furthermore, alleles on Chr 3 modify the TRD on Chr 11. All TRD loci detected at weaning were present in Mendelian ratios at mid-gestation and at birth.

CONCLUSIONS

Given that Mendelian ratios of inheritance are observed for Chr 7, 10 and 11 during development and at birth, the underlying causes for the interspecific TRD events are the differential post-natal survival of pups with specific genotypes. These results are consistent with the TRD mechanism being deviation from Mendelian inheritance rather than meiotic drive or segregation distortion.

Re-localization of Actsk-1 to mouse chromosome 8, a new region of homology with human chromosome 1

We present here the genetic mapping of the alpha-skeletal actin locus (Actsk-1) on mouse Chromosome (Chr) 8, on the basis of the PCR analysis of a microsatellite in an interspecific backcross. Linkage and genetic distances were established for four loci by analysis of 192 (or 222) meiotic events and indicated the following gene order: (centromere)-Es-1-11.7 cM-Tat-8.3 cM-Actsk-1-0.5 cM-Aprt. Mapping of ACTSK to human Chr 1 and of TAT and APRT to human Chr 16 demonstrates the existence of a new short region of homology between mouse Chr 8 and human Chr 1. Intermingling on this scale between human and mouse chromosomal homologies that occurred during evolution creates disorders in comparative linkage studies.

Genomic analysis using a yeast artificial chromosome library with mouse DNA inserts

A yeast artificial chromosome library with mouse genomic DNA inserts has been constructed. The library encompasses a 2.5-fold coverage of the mouse genome, with an average insert size of 250 kilobases. The screening strategy uses the polymerase chain reaction on pooled DNAs prepared from individually stored clones. The usefulness of the library for chromosome walking was illustrated by constructing a 600-kilobase-long contig of DNA surrounding Hba-ps4, a DNA marker that is tightly linked to the fused (Fu) locus on chromosome 17.

Random sequence oligonucleotide primers detect polymorphic DNA products which segregate in inbred strains of mice

The random amplification of polymorphic DNA (RAPD) using primers of arbitrary nucleotide sequence has been extremely valuable in identifying heritable markers in a variety of systems. The present studies examined whether the RAPD technique can identify large numbers of polymorphisms that can be used to construct genetic maps in inbred strains of mice. By screening the inbred mouse strains C57BL/6J and DBA/2J with 481 random 10-mer oligonucleotide primers, we identified 95 polymorphisms and mapped 76 of these by use of the BXD series of recombinant inbred (RI) strains. The results clearly demonstrate that the RAPD technique allows for the identification of large numbers of DNA-based polymorphisms that distinguish these two inbred strains of mice, and that such markers can readily be used to construct molecular genetic linkage maps.

Tg (9 HSA-MYC), a homozygous lethal insertion in the mouse

Transgenic mice generated with different DNA sequences were surveyed for possible homozygous mutant phenotypes. We found an embryonic lethal mutation in the transgenic mouse strain (MT-MYC12.4) containing the human c-myc gene. Embryos homozygous for the transgene die shortly after implantation. The strain MT-MYC12.4 carries approximately 50 tandem copies of the recombinant plasmid sequence. The 3' flanking sequence has been cloned and analyzed. It contains a unique sequence that has been conserved during evolution and maps to Chromosome (Chr) 9. This mutant has been designated Tg 9 (HSA-MYC).

Minisatellite linkage maps in the mouse by cross-hybridization with human probes containing tandem repeats

Tests of 29 human variable number of tandem repeat probes in inbred mouse lines showed that 80% (23/29) cross-hybridize, and 48% (14/29) produce multiple band, minisatellite polymorphisms (fingerprint patterns). Mini-satellite-type polymorphisms detected by 11 probes were characterized in eight different strains; on average, 240 polymorphic differences were detected between pairs of strains. Reproducible fingerprint patterns permit the study of the segregation of the minisatellite polymorphisms in experimentally designed crosses. As an example, we constructed primary minisatellite genetic linkage maps containing 346 polymorphic bands, distributed in 101 groups of closely linked systems, from genotypes on a recombinant inbred panel (C57BL/6J X DBA/2J); 38 of the groups were assigned by linkage to 15 autosomal chromosomes. The minisatellite genetic maps of C57BL/6J and DBA/2J can be applied in other linkage studies involving these strains.