PCR-analyzed microsatellites for the inbred mouse strain 129/Sv, the strain most commonly used in gene knockout technology

Contribution of Mouse Embryonic Stem Cells and Induced Pluripotent Stem Cells to Chimeras through Injection and Coculture of Embryos

Blastocyst injection and morula aggregation are commonly used to evaluate stem cell pluripotency based on chimeric contribution of the stem cells. To assess the protocols for generating chimeras from stem cells, 8-cell mouse embryos were either injected or cocultured with mouse embryonic stem cells and induced pluripotent stem cells, respectively. Although a significantly higher chimera rate resulted from blastocyst injection, the highest germline contribution resulted from injection of 8-cell embryos with embryonic stem cells. The fully agouti colored chimeras were generated from both injection and coculture of 8-cell embryos with embryonic stem cells. Additionally, microsatellite DNA screening showed that the fully agouti colored chimeras were fully embryonic stem cell derived mice. Unlike embryonic stem cells, the mouse chimeras were only generated from injection of 8-cell embryos with induced pluripotent stem cells and none of these showed germline transmission. The results indicated that injection of 8-cell embryos is the most efficient method for assessing stem cell pluripotency and generating induced pluripotent stem cell chimeras, embryonic stem cell chimeras with germline transmission, and fully mouse embryonic stem cell derived mice.

The p75 neurotrophin receptor has nonapoptotic antineurotrophic actions in the basal forebrain

Because of controversy about the role of the p75 neurotrophin receptor (p75(NTR) ) in the cholinergic basal forebrain (CBF), we investigated this region in p75(NTR) third exon knockout mice that were congenic with 129/Sv controls. They express a shortened intracellular form of p75(NTR) , permitting detection of p75(NTR) -expressing cells. We performed separate counts of choline acetyltransferase (ChAT)-expressing and p75(NTR) -expressing neurons. In agreement with past reports, the number of ChAT-immunoreactive neurons in knockout mice was greater than in wild-type mice, and this was evident in each of the main anatomical divisions of the CBF. In contrast, the number of p75(NTR) -immunoreactive neurons did not differ between genotypes. The biggest increase in ChAT neurons (27%) was in the horizontal limb of the diagonal band of Broca (HDB), in which region the number of p75(NTR) -positive neurons was unchanged. Double staining revealed that some neurons in wild-type mice expressed p75(NTR) but not ChAT. In the knockout mice, all p75(NTR) -expressing neurons expressed ChAT. The increase in cholinergic neurons, therefore, was at least partially attributable to a higher proportion of ChAT immunoreactivity within the population of p75(NTR) -expressing neurons. Cholinergic neurons were also larger in knockout mice than in controls. In the hippocampal CA1 region, knockout mice had a greater number of cholinergic fibers. There was a 77% increase in hippocampal ChAT activity in knockout mice and a 38% increase in heterozygotes. The data do not support an apoptotic role but indicate a broad antineurotrophic role of p75(NTR) in the cholinergic basal forebrain.

Enhanced spatial memory and hippocampal long-term potentiation in p75 neurotrophin receptor knockout mice

Previous reports have described increases in the size and number of cholinergic neurons in the basal forebrain in p75 neurotrophin receptor (p75(NTR)) knockout mice. In an earlier study, we also found improved spatial memory in these mice, raising the possibility that p75(NTR) regulates hippocampal function by its effects on the cholinergic basal forebrain. We therefore investigated hippocampal long-term potentiation in p75(NTR) knockout mice that shared the same genetic background as control 129/Sv mice. We also investigated heterozygous mice, carrying just one functional p75(NTR) allele. The p75(NTR) knockout mice had enhanced long-term potentiation in the Schafer collateral fiber synapses of the hippocampus. Heterozygous mice had an intermediate level, greater than controls but less than knockout mice. Hippocampal choline acetyltransferase activity was also markedly elevated in p75(NTR) knockout mice, with a smaller increase in heterozygous mice. In the Barnes maze, p75(NTR) knockout mice displayed markedly superior learning to controls, and this was evident over the three age brackets tested. At each age, the performance of heterozygous mice was intermediate to the other groups. In the open field test, p75(NTR) knockout mice exhibited greater stress-related behavioral responses, including freezing, than did control animals. There were no differences between the three groups in a test of olfactory function. The dose-dependent effects of p75(NTR) gene copy number on hippocampal plasticity and spatial memory indicate that p75(NTR) has profound effects on hippocampal function. Bearing in mind that p75(NTR) is very sparsely expressed in the adult hippocampus and has a potent effect on hippocampal choline acetyltransferase activity, the effects of p75(NTR) on hippocampal function are likely to be mediated indirectly, by its actions on basal forebrain cholinergic neurons.

Generation of gene knockout mice by ES cell microinjection

This unit describes protocols used in the production of chimeric mice that are then used for the generation of gene knockout mice. These protocols include the collection of blastocyst embryos, ES cell injection, and uterine transfer of injected blastocysts. Support protocols for the superovulation of blastocyst donor mice, generation of pseudopregnant recipients, fabrication of glass pipets for embryo and cell manipulations, and generation of germline mice are also included. Practical tips and solutions are mentioned to help troubleshoot problems that may occur.

Microsatellite genotyping for four expected inbred mouse strains from KM mice

Chinese Kun Ming (KM) mouse, an outbreed strain of laboratory animal, has been widely utilized in related pharmaceutical and genetic studies throughout China. However, the value of KM mice to the research community has been severely limited, partially due to the fact that well-characterized inbred strain of KM mice is not available. Several expected inbred strains from KM mice have been bred, but their genetic purity remains uncertain. In this study, four expected inbred strains of KM mice (A1, T2, N2, and N4) were chosen and their inbred degree were compared with two classical inbred mouse lines (BALB/c and C57BL/6) by analyzing the genotypes of about 30 microsatellite markers. In the four strains, A1 and N4 were homozygous at all genotyped loci, but N2 and T2 were only heterozygous at locus D15Mit16. These results indicate that the level of genetic purity/homozygousity of A1, N4, N2, and T2 inbred line is comparable to those of BALB/c and C57BL/6. This study provided the first and solid evidence for genetic purity of four expected inbred strains of KM mice. These 4 inbred mice strains should be well maintained for further characterization and utilization in genetic studies.

A marker assisted selection protocol (MASP) to generate C57BL/6J or 129S6/SvEvTac speed congenic or consomic strains

A marker assisted selection protocol is presented that allows for the generation of congenic or consomic strains derived from a C57BL/6J:129S6/SvEvTac mixed strain background. The protocol uses defined primer pairs to generate amplicons that can be distinguished by non-denaturing agarose electrophoresis. Use of this application should result in substantial savings in time, effort, and cost for investigators in all areas of transgenic mouse research.

Genealogies of mouse inbred strains

The mouse is a prime organism of choice for modelling human disease. Over 450 inbred strains of mice have been described, providing a wealth of different genotypes and phenotypes for genetic and other studies. As new strains are generated and others become extinct, it is useful to review periodically what strains are available and how they are related to each other, particularly in the light of available DNA polymorphism data from microsatellite and other markers. We describe the origins and relationships of inbred mouse strains, 90 years after the generation of the first inbred strain. Given the large collection of inbred strains available, and that published information on these strains is incomplete, we propose that all genealogical and genetic data on inbred strains be submitted to a common electronic database to ensure this valuable information resource is preserved and used efficiently.

Ten years of gene targeting: targeted mouse mutants, from vector design to phenotype analysis

Gene targeting, defined as the introduction of site-specific modifications into the genome by homologous recombination, has revolutionarized the field of mouse genetics and allowed the analysis of diverse aspects of gene function in vivo. It is now possible to engineer specific genetic alterations ranging from subtle mutations to chromosomal rearrangements and more recently, even tissue-specific inducible gene targeting with temporo-spatial control has become feasible. This review tries to recapitulate what we have learned in this extremely rapidly expanding field during the past decade. Diverse aspects of the technique will be discussed starting from basic construct design to the analysis of complex phenotypes, including recent advances on inducible expression system. Many examples from different areas of biomedical research are given to illustrate the purpose and limitations of the employed experimental approaches.

Impaired ability of Cftr knockout mice to control lung infection with Pseudomonas aeruginosa

The present study was aimed at investigating the innate susceptibility of C57BL/6-Cftrunc/Cftrunc knockout [B6-Cftr (-/-)] mice to pulmonary infection with Pseudomonas aeruginosa. Our results indicate that 58.4% of B6-Cftr (-/-) mice died within 6 d following lung infection with 10(5) P. aeruginosa entrapped in agar beads, whereas only 12.1% of B6-Cftr (+/+) mice died over the same period of time. Moreover, the number of bacteria recovered from the lungs of B6-Cftr (-/-) mice 3 and 6 d after infection was significantly higher than that observed in their littermate controls. No correlation was found between the weight or age of the animals and the number of viable bacteria recovered from the lungs of mice. Histopathological examination of lung sections from P. aeruginosa-infected mice revealed that the infection results in a severe bronchopneumonia. Both B6-Cftr (-/-) knockout mice and their littermate controls developed similar lung pathology during the course of infection. Overall, results reported in the present study suggest that a defect at the Cftr locus leads to an exacerbation of P. aeruginosa lung infection resulting in a dramatically increased mortality rate and higher bacterial load.

Genetic variation among 129 substrains and its importance for targeted mutagenesis in mice

Targeted mutagenesis in mice, a powerful tool for the analysis of gene function and human disease, makes extensive use of 129 mouse substrains. Although all are named 129, we document that outcrossing of these substrains, both deliberate and accidental, has lead to extensive genetic variability among substrains and embryonic stem cells derived from them. This clearer understanding of 129 substrain variability allows consideration of its negative impact on targeting technology, including: homologous recombination frequencies, preparation of inbred animals, and availability of appropriate controls. Based on these considerations we suggest a number of recommendations for future experimental design.