High-frequency induction of chromosomal rearrangements in mouse germ cells by the chemotherapeutic agent chlorambucil

Genotoxic and mutagenic studies of teratogens in developing rat and mouse

In this review, genotoxic and mutagenic effects of teratogenic chemical agents in both rat and mouse have been reviewed. Of these chemicals, 97 are drugs and 33 are pesticides or belong to other groups. Large literature searches were conducted to determine the effects of chemicals on chromosome abnormalities, sister chromatid exchanges, and micronucleus formation in experimental animals such as rats and mice. In addition, studies that include unscheduled DNA synthesis, DNA adduct formations, and gene mutations, which help to determine the genotoxicity or mutagenicity of chemicals, have been reviewed. It has been estimated that 46.87% of teratogenic drugs and 48.48% of teratogenic pesticides are positive in all tests. So, all of the teratogens involved in this group have genotoxic and mutagenic effects. On the other hand, 36.45% of the drugs and 21.21% of the pesticides have been found to give negative results in at least one test, with the majority of the tests giving positive results. However, only 4.16% of the drugs and 18.18% of the pesticides were determined to give negative results in the majority of the tests. Among tests with major negative results, 12.50% of the teratogenic drugs and 12.12% of the teratogenic pesticides were negative in all conducted tests.

Mouse models of genomic syndromes as tools for understanding the basis of complex traits: an example with the smith-magenis and the potocki-lupski syndromes

Each human's genome is distinguished by extra and missing DNA that can be “benign” or powerfully impact everything from development to disease. In the case of genomic disorders DNA rearrangements, such as deletions or duplications, correlate with a clinical specific phenotype. The clinical presentations of genomic disorders were thought to result from altered gene copy number of physically linked dosage sensitive genes. Genomic disorders are frequent diseases (~1 per 1,000 births). Smith-Magenis syndrome (SMS) and Potocki-Lupski syndrome (PTLS) are genomic disorders, associated with a deletion and a duplication, of 3.7 Mb respectively, within chromosome 17 band p11.2. This region includes 23 genes. Both syndromes have complex and distinctive phenotypes including multiple congenital and neurobehavioral abnormalities. Human chromosome 17p11.2 is syntenic to the 32-34 cM region of murine chromosome 11. The number and order of the genes are highly conserved. In this review, we will exemplify how genomic disorders can be modeled in mice and the advantages that such models can give in the study of genomic disorders in particular and gene copy number variation (CNV) in general. The contributions of the SMS and PTLS animal models in several aspects ranging from more specific ones, as the definition of the clinical aspects of the human clinical spectrum, the identification of dosage sensitive genes related to the human syndromes, to the more general contributions as the definition of genetic locus impacting obesity and behavior and the elucidation of general mechanisms related to the pathogenesis of gene CNV are discussed.

New techniques to understand chromosome dosage: mouse models of aneuploidy

Aberrations in human chromosome copy number and structure are common and extremely deleterious. Their downstream effects on phenotype are caused by aberrant dosage of sequences in the affected regions. However, we know little about why the abnormal gene copy number causes disease or why specific features result from deficits in specific chromosomes. Mice are the organism of choice to help us try to tease apart the complex relationships between genotype and phenotype in aneuploidy and segmental aneusomy syndromes. As new technologies such as chromosome engineering and the creation of transchromosomic mice become routine, these will help us identify individual dosage-sensitive genes that are causative in specific syndromes and will enable us to produce mouse models to accurately recapitulate human chromosomal disorders.

The effect of chlorambucil upon lysozyme activity

Chicken egg white lysozyme is progressively inhibited by diazoacetyl-DL-norleucine methyl ester (DANME) and by chlorambucil at concentrations of 3.4 x 10(-3) M and 5 x 10(-3) M respectively over a three-hour time period. DANME inhibits lysozyme activity to the extent of 87%, and chlorambucil inhibits the enzyme to the extent of 93%. N,N',N"-triacetylchitotriose [(NAG)3], which binds to subsites A, B and C of the enzyme protects lysozyme from DANME inhibition to the extent of 40% of the total activity when added to the enzyme at a concentration of 3.6 x 10(-3) M prior to the addition of DANME. (NAG)3 protects the enzyme from inhibition by chlorambucil to the extent of 14% of the total activity when added to the enzyme at a concentration of 5.6 x 10(-3) M prior to the addition of chlorambucil. Since DANME reacts exclusively with carboxyl groups, and since aspartic acid 101 is required for binding the carbohydrate substrate at site A, it is suggested that (NAG)3 may bind reversibly to the active site of the enzyme, thereby protecting aspartic acid 101 from esterification by DANME and subsequent inactivation. Chlorambucil, which may react with carboxyl, amino, imidazole and thiol groups, more likely acts upon a larger number of susceptible sites, thereby causing irreversible alkylation and conformation changes. As a bifunctional alkylating agent, it may also cross-link with two available nucleophiles. The K(m) for lysozyme with M. lysodeikticus as a substrate in wholly aqueous medium was determined to be 0.05 mg/mL. The inhibitor exhibits a partially uncompetitive upon pre-incubation with the enzyme, and a mixed inhibition between competitive and noncompetitive when pre-incubated with the substrate.

Embryonic lethality and tumorigenesis caused by segmental aneuploidy on mouse chromosome 11

Chromosome engineering in mice enables the construction of models of human chromosomal diseases and provides key reagents for genetic studies. To begin to define functional information for a small portion of chromosome 11, deficiencies, duplications, and inversions were constructed in embryonic stem cells with sizes ranging from 1 Mb to 22 cM. Two deficiencies and three duplications were established in the mouse germline. Mice with a 1-Mb duplication developed corneal hyperplasia and thymic tumors, while two different 3- to 4-cM deficiencies were embryonically lethal in heterozygous mice. A duplication corresponding to one of these two deficiencies was able to rescue its haplolethality.

Mutations in mouse Aristaless-like4 cause Strong's luxoid polydactyly

Mutations that affect vertebrate limb development provide insight into pattern formation, evolutionary biology and human birth defects. Patterning of the limb axes depends on several interacting signaling centers; one of these, the zone of polarizing activity (ZPA), comprises a group of mesenchymal cells along the posterior aspect of the limb bud that express sonic hedgehog (Shh) and plays a key role in patterning the anterior-posterior (AP) axis. The mechanisms by which the ZPA and Shh expression are confined to the posterior aspect of the limb bud mesenchyme are not well understood. The polydactylous mouse mutant Strong's luxoid (lst) exhibits an ectopic anterior ZPA and expression of Shh that results in the formation of extra anterior digits. Here we describe a new chlorambucil-induced deletion allele, lstAlb, that uncovers the lst locus. Integration of the lst genetic and physical maps suggested the mouse Aristaless-like4 (Alx4) gene, which encodes a paired-type homeodomain protein that plays a role in limb patterning, as a strong molecular candidate for the Strong's luxoid gene. In genetic crosses, the three lst mutant alleles fail to complement an Alx4 gene-targeted allele. Molecular and biochemical characterization of the three lst alleles reveal mutations of the Alx4 gene that result in loss of function. Alx4 haploinsufficiency and the importance of strain-specific modifiers leading to polydactyly are indicative of a critical threshold requirement for Alx4 in a genetic program operating to restrict polarizing activity and Shh expression in the anterior mesenchyme of the limb bud, and suggest that mutations in Alx4 may also underlie human polydactyly.

Generation, identification, and recovery of mouse mutations

Mouse mutations can be generated by a variety of techniques including those that rely on inducing agents such as X rays or chemicals and those that involve genetic manipulations such as in transgene insertions and gene knockouts. Each technique has its advantages and disadvantages. Inducing agents are often more efficient when random mutations in as yet unknown genes are desired. In contrast, genetic manipulations are advantageous when the mutagenesis needs to be targeted to certain genes or regions. Once these mutations are produced, they must be systematically identified and characterized to confirm their distinction from other known mutations and environmental influences. Allelism and linkage tests should be performed. Finally, methods for maintaining these mutations should be applied so that studies of them can be pursued in the most efficient manner.

Reln(rl-Alb2), an allele of reeler isolated from a chlorambucil screen, is due to an IAP insertion with exon skipping

The reeler Albany2 mutation (Reln(rl-Alb2) in the mouse is an allele of reeler isolated during a chlorambucil mutagenesis screen. Homozygous animals had drastically reduced concentrations of reelin mRNA, in which an 85-nt exon was absent. At the genomic level, the mutation was shown to be due to an intracisternal A-particle insertion leading to exon skipping. This appears to be the first observation of retrotransposon insertion during chlorambucil mutagenesis.

Chlorambucil-induced structural changes in the gpt gene of AS52 cells

The bifunctional alkylating agent chlorambucil (CBC) is a chemotherapeutic agent that induces a high yield of mouse germ-line mutations, apparently due to multi-locus deletions or other chromosomal rearrangements. We investigated the mutagenicity of CBC in cultured mammalian cells by comparing its effect in the AS52/gpt and CHO/hprt gene mutation assays, which detect large and small effects, respectively. CBC significantly increased the mutant frequency in the AS52/gpt assay, but not in the CHO/hprt assay, while the cytotoxic responses to CBC were similar in the two cell lines. This indicates that CBC induced predominantly large deletions or other gross structural changes, and not point or other small mutations. The mutational responses to CBC were similar to the responses to mitomycin C comparing them based on the cytotoxic responses. Molecular analysis of the gpt gene in AS52 mutant cells by electrophoresis following PCR amplification revealed that 81% of CBC-induced mutants lost the entire gpt gene, which is caused by large deletions or interchromosomal recombinations. The loss frequency was lower in spontaneous mutants (42%) and ethylmethanesulfonate-induced mutants (29%). This supports cytogenetic data showing that CBC is a potent clastogen in cultured mammalian cells, inducing predominantly large deletions and/or other gross structural alterations.

A high-resolution genetic map around waltzer on mouse chromosome 10 and identification of a new allele of waltzer

A new autosomal recessive mouse mutation characterized by deafness and circling behavior was recovered during mutagenesis experiments with chlorambucil (CHL). On the basis of allelism tests and linkage analyses, this mutation appears to represent a new allele of waltzer (v) that maps to mouse Chromosome (Chr) 10. We have designated this new allele, Albany waltzer (vAlb). A high-resolution map of the region around v was constructed from data from two intersubspecific backcrosses involving Mus musculus castaneus. The analysis of 648 backcross mice has allowed vAlb to be localized 1.1 +/- 0.4 cM distal to D10Mit60 and 0.2 +/- 0.2 cM proximal to a cluster of four markers, D10Mit172, D10Mit112, D10Mit48, and D10Mit196. An independent backcross was used to confirm the map order and distances in the vAlb backcross. The two linkage maps were consistent, indicating that the lesion in vAlb, which is presumed to be a deletion based on the known action of CHL, is small and has not significantly altered the map at this level of detection. Additionally, three genes (Ros1, Grik2, and Zfa) were eliminated as possible candidates for vAlb, and several SSLP markers were separated genetically.

High-resolution genetic map and YAC contig around the mouse neurological locus reeler

Mutations at the recessive reeler locus (rl) on mouse Chromosome (Chr) 5 result in abnormal development of multiple central nervous system components, including the cerebral and cerebellar cortices. These abnormalities are characterized by highly disorganized laminar structures thought to have arisen from a post-migration failure of neuronal organization events that are probably mediated through cell-cell interactions. As a result of a mutagenesis scheme designed to generate visible recessive mutations induced by the drug chlorambucil, we had previously recovered a new allele of the reeler locus (rlAlb) that is likely to involve a deletion based on the known mechanisms of chlorambucil action. We have constructed a high-resolution genetic map from two intercrosses segregating this allele. Our first cross, in which the mutation was outcrossed to the 101 strain prior to intercrossing, consisted of 196 meioses and resulted in the positioning of four loci proximal to rl, with D5Mit1 being the closest (2.6 +/- 1.1 cM). The second cross consisted of intercrossing rl heterozygotes derived from an outcross to the C57BL/6 strain. A total of 318 mice (636 meioses) gave rise to a panel of 41 recombinants, which were used to map a total of 14 loci within a 6.4-cM interval bounded by D5Mit1 and the En-2 gene. A yeast artificial chromosome contig consisting of clones containing two of these loci, D5Mit72 (located 0.31 cM distal to rl), and D5Mit61 (no recombinants with rl), has been assembled and is being used to locate the rl gene.