N-ethyl-N-nitrosourea(ENU)mutagenesis in mice can be used to study gene function in vivo and to establish genetic mouse models of human disease.In this study,a white spotted mouse(named Kit W-1Bao)was obtained by ENU-induced mutagenesis.Inheritance testing showed a single-gene dominant mutation and lethality in the Kit W-1Bao homozygous mice.The mutation was mapped to Chromosome 5 between markers D5Mit356 and D5Mit308.The region contains the Kit gene,whose mutations are known to lead to pigmentation defects in mice.Sequence analysis of the Kit cDNA from Kit W-1Bao heterozygotes revealed an A to T missense mutation resulting in an amino acid substitution of Asp(D)by Val(V)at amino acid position 849 within a highly conserved tyrosine kinase domain.The combined phenotype displayed by the Kit W-1Bao heterozygous and homozygous mutant mice demonstrates the critical function of the highly conserved aspartic acid residue at position 849 in the Kit gene product.
The scant hair mutant mouse(locus symbol:snthr1Bao) is a recessive mutation that originated in an ethylnitrosourea chemical carcinogenesis study using the DBA/2J inbred strain.The gene responsible for the mutation was previously determined to be phospholipase C,delta 1(Plcd1;mutant allele symbol Plcd1snthr1Bao).To map the modifiers of Plcd1,an intercross(DBA/2J-snthr1Bao/snthr1Bao × C57BL/6J+/+) was conducted.The F2 mutant progeny exhibited a variety of alopecia phenotypes;all F2 mutants(n=507) were classified into 3 groups(mild,moderate,and severe alopecia) and genotyped based on 96 microsatellites.A major QTL was identified on mouse chromosome(mChr) 15 at 12 cM with an LOD score greater than 7(P < 0.0001).Three minor QTLs were detected on mChr 2,5,and 7 at 40,84 and 48 cM,respectively.The QTLs on mChr 7 and 15 were associated with minor alopecia while the QTLs on mChr 2 and 5 were associated with moderate to severe alopecia.No antagonistic or synergistic effects among or between the 4 QTLs were found.Integrating the functions of the 4 potential regulatory QTLs and mutant Plcd1snthr1Bao,we found that these QTLs might contribute to variations of scant hair severity by altering the Ca2+ signal pathways in mouse skin.
KitW-2Bao mice are single-gene autosomal dominant mutation mice with a B6 background that were bred in our laboratory. Heterozygotes had morphological characteristics including albinism of the abdomen, extremities, and tail, whereas the homozygotes had albinism of the body, black eyes, and infertility. The homozygous mutants showed small, structurally abnormal gonads, and lacked germ cells. Heterozygous male mice lacked germ cells in some contorted seminiferous tubules. This mutation has been mapped at 43.8 cM from the centromere in chromosome 5 by linkage analysis and Kit has been identified as the candidate gene. After Kit full-length mRNA amplification, it was found that a G to T conversion at position 1228 in the ORF changed the 410th amino acid from V to F. This amino acid change could affect the protein’s secondary structure. Heterozygous mutant mice were intercrossed and homozygous mutant mice were bred and genotyped. We found that no primordial germ cells (PGCs) appeared in the urogenital ridge area at fetus day 11.5 in the homozygotes. The number of PGCs also significantly decreased in heterozygotes. At fetus day 15.5, the differentiation of the testis tubule structure was unclear; as well, they contained no spermatogonia. Female homozygotes contained no primordial follicles in the ovary. The numbers of PGCs and primordial follicles were significantly decreased in heterozygous mice. W-2Bao is the only mutated site in the extracellular 4th Ig-like domain and this mutant mouse model provides new material for the study of the mechanism of reproductive system development.
