基因敲除小鼠技术的研究进展

基因敲除小鼠技术的建立和发展使得人们为研究基因的功能和寻找新的治疗人类疾病的靶点提供了强有力的支持。基因打靶和基因捕获是两种通过胚胎干细胞(Embryonicstemcell,ESC)构建基因敲除小鼠的技术。基因打靶通过同源重组替换内源基因从而敲除目的基因,而基因捕获则有启动子捕获和polyA捕获两种方法对目的基因进行敲除。近年来,有许多新的基因敲除技术不断被开发出来,包括Cre/loxP系统、CRISP/Cas9系统以及最新的ZFN技术和TAILEN技术,都有望取代传统基因敲除手段。文中简要阐述了如今新出现的几种基因敲除小鼠技术。     

Chondrodysplasia of gene knockout mice for aggrecan and link protein

The proteoglycan aggregate of the cartilage is composed of aggrecan, link protein, and hyaluronan and forms a unique gel-like moiety that provides resistance to compression in joints and a foundational cartilage structure critical for growth plate formation. Aggrecan, a large chondroitin sulfate proteoglycan, is one of the major structural macromolecules in cartilage and binds both hyaluronan and link protein through its N-terminal domain G1. Link protein, a small glycoprotein, is homologous to the G1 domain of aggrecan. Mouse cartilage matrix deficiency (cmd) is caused by a functional null mutation of the aggrecan gene and is characterized by perinatal lethal dwarfism and craniofacial abnormalities. Link protein knockout mice show chondrodysplasia similar to but milder than cmd mice, suggesting a supporting role of link protein for the aggregate structure. Analysis of these mice revealed that the proteoglycan aggregate plays an important role in cartilage development and maintenance of cartilage tissue and may provide a clue to the identification of human genetic disorders caused by mutations in these genes. Published in 2003.     

In vivo effects of uncoupling protein-3 gene disruption on mitochondrial energy metabolism

To clarify the role of uncoupling protein-3 (UCP3) in skeletal muscle, we used NMR and isotopic labeling experiments to evaluate the effect of UCP3 knockout (UCP3KO) in mice on the regulation of energy metabolism in vivo. Whole body energy expenditure was determined from the turnover of doubly labeled body water. Coupling of mitochondrial oxidative phosphorylation in skeletal muscle was evaluated from measurements of rates of ATP synthesis (using (31)P NMR magnetization transfer experiments) and tricarboxylic acid (TCA) cycle flux (calculated from the time course of (13)C enrichment in C-4 and C-2 of glutamate during an infusion of [2-(13)C]acetate). At the whole body level, we observed no change in energy expenditure. However, at the cellular level, skeletal muscle UCP3KO increased the rate of ATP synthesis from P(i) more than 4-fold under fasting conditions (wild type, 2.2 +/- 0.6 versus knockout, 9.1 +/- 1.4 micromol/g of muscle/min, p < 0.001) with no change in TCA cycle flux rate (wild type, 0.74 +/- 0.04 versus knockout, 0.71 +/- 0.03 micromol/g of muscle/min). The increased efficiency of ATP production may account for the significant (p < 0.05) increase in the ratio of ATP to ADP in the muscle of UCP3KO mice (5.9 +/- 0.3) compared with controls (4.5 +/- 0.4). The data presented here provide the first evidence of uncoupling activity by UCP3 in skeletal muscle in vivo.     

The role of uncoupling protein 1 in the metabolism and adiposity of RII beta-protein kinase A-deficient mice

Mice lacking the RII beta regulatory subunit of protein kinase A exhibit a 50% reduction in white adipose tissue stores compared with wild-type littermates and are resistant to diet-induced obesity. RII beta(-/-) mice also have an increase in resting oxygen consumption along with a 4-fold increase in the brown adipose-specific mitochondrial uncoupling protein 1 (UCP1). In this study, we examined the basis for UCP1 induction and tested the hypothesis that the induced levels of UCP1 in RII beta null mice are essential for the lean phenotype. The induction of UCP1 occurred at the protein but not the mRNA level and correlated with an increase in mitochondria in brown adipose tissue. Mice lacking both RII beta and UCP1 (RII beta(-/-)/Ucp1(-/-)) were created, and the key parameters of metabolism and body composition were studied. We discovered that RII beta(-/-) mice exhibit nocturnal hyperactivity in addition to the increased oxygen consumption at rest. Disruption of UCP1 in RII beta(-/-) mice reduced basal oxygen consumption but did not prevent the nocturnal hyperactivity. The double knockout animals also retained the lean phenotype of the RII beta null mice, demonstrating that induction of UCP1 and increased resting oxygen consumption is not the cause of leanness in the RII beta mutant mice.     

Involvement of Drosophila uncoupling protein 5 in metabolism and aging

A novel uncoupling protein, UCP5, has recently been characterized as a functional mitochondrial uncoupler in Drosophila. Here we demonstrate that UCP5 knockout (UCP5KO) flies are highly sensitive to starvation stress, a phenotype that can be reversed by ectopic neuronal expression of UCP5. UCP5KO flies live longer than controls on low-calorie diets, have a decreased level of fertility, and gain less weight than controls on high-calorie diets. However, isolated mitochondria from UCP5KO flies display the same respiration patterns as controls. Furthermore, total ATP levels in both UCP5KO and control flies are comparable. UCP5KO flies have a lower body composition of sugars, and during starvation stress their triglyceride reserves are depleted more rapidly than controls. Taken together, these data indicate that UCP5 is important to maintain metabolic homeostasis in the fly. We hypothesize that UCP5 influences hormonal control of metabolism.     

Expression of an uncoupling protein gene homolog in chickens

An avian uncoupling protein (UCP) gene homolog was recently sequenced from skeletal muscle and was proposed to have a role in thermogenesis in chickens, ducks and hummingbirds. Since mammalian UCP 2 and UCP 3 also appear to have functions associated with energy and substrate partitioning and body weight regulation, the purpose of this study was to further characterize chicken UCP under conditions of nutritional stress and/or leptin administration. Male 3-week-old chickens were starved for 24 or 48 h and then half of each group was refed for an additional 24 h. In a follow-up experiment, chickens were fed or starved for 48 h with or without leptin administration. Feed deprivation increased UCP mRNA expression in skeletal muscle by up to 260% (P<0.001), and in a time-dependent manner in pectoralis muscle. Refeeding for 24 h normalized muscle UCP mRNA levels. Leptin administration had no effect on muscle UCP. Chicken muscle UCP mRNA levels were highly correlated with plasma triglyceride and non-esterified fatty acid (NEFA) concentrations, and with circulating levels of insulin, insulin-like growth factor (IGF)-I and IGF-II. These results suggest that, as in mammals, avian UCP is up-regulated during feed deprivation and is highly correlated with increased fatty acid oxidation and flux into skeletal muscle.     

Clustered gene expression changes flank targeted gene loci in knockout mice

Background

Gene expression profiling using microarrays is a powerful technology widely used to study regulatory networks. Profiling of mRNA levels in mutant organisms has the potential to identify genes regulated by the mutated protein.

Methodology/Principle Findings

Using tissues from multiple lines of knockout mice we have examined genome-wide changes in gene expression. We report that a significant proportion of changed genes were found near the targeted gene.

Conclusions/Significance

The apparent clustering of these genes was explained by the presence of flanking DNA from the parental ES cell. We provide recommendations for the analysis and reporting of microarray data from knockout mice     

Alterations in protein and gene expression within the barrel cortices of ZnT3 knockout mice: experience-independent and dependent changes

Much evidence exists for the involvement of vesicular zinc in neurotransmission and cortical plasticity. Recent studies have reported that mice deficient in zinc transporter-3 protein (ZnT3) and thus, vesicular zinc, have significant behavioural and biochemical deficits. Here, we examined whether phenotypic differences existed in the barrel cortices of ZnT3 KO mice using functional proteomics and quantitative PCR. Additionally, by manipulating whisker input, we also investigated experience-dependent changes in protein and gene expression, thereby assaying how cortical plasticity is different in the absence of vesicular zinc. The GABA metabolizing protein ABAT was observed in lower abundances consistently in KO mice. Several presynaptic proteins were identified that were abundant in differing amounts between the WT and KO groups in an experience-dependent manner. At baseline, we observed a decrease in the relative expression of Dlg4, Grin2a, Mt3, and Ntrkb genes in KO mice. The reduced expression of Nrtkb persisted with whisker plucking. These data demonstrate that fundamental changes in the expression of proteins and genes important in neurotransmission occur in the absence of vesicular zinc. Furthermore, the complement of experience-dependent changes were different between WT and KO mice, indicating that the lack of vesicular zinc affects the process of cortical plasticity.     

Proteomic analysis of parkin knockout mice: alterations in energy metabolism, protein handling and synaptic function

Parkin knockout (KO) mice show behavioural and biochemical changes that reproduce some of the presymptomatic aspects of Parkinson's disease, in the absence of neuronal degeneration. To provide insight into the pathogenic mechanisms underlying the preclinical stages of parkin-related parkinsonism, we searched for possible changes in the brain proteome of parkin KO mice by means of fluorescence two-dimensional difference gel electrophoresis and mass spectrometry. We identified 87 proteins that differed in abundance between wild-type and parkin KO mice by at least 45%. A high proportion of these proteins were related to energy metabolism. The levels of several proteins involved in detoxification, stress-related chaperones and components of the ubiquitin-proteasome pathway were also altered. These differences might reflect adaptive mechanisms aimed at compensating for the presence of reactive oxygen species and the accumulation of damaged proteins in parkin KO mice. Furthermore, the up-regulation of several members of the membrane-associated guanylate kinase family of synaptic scaffold proteins and several septins, including the Parkin substrate cell division control related protein 1 (CDCRel-1), may contribute to the abnormalities in neurotransmitter release previously observed in parkin KO mice. This study provides clues into possible compensatory mechanisms that protect dopaminergic neurones from death in parkin KO mice and may help us understand the preclinical deficits observed in parkin-related parkinsonism.     

The use of gene knockout mice in thermoregulation studies

As the use of gene knockout models in thermoregulation studies has gained popularity, the reported incidence of redundant or discrepant phenotypes between studies has also increased. Several gene knockout models mimic human processes and have provided valuable insight into the role of endogenous mediators in thermoregulatory processes. There are also many examples of mutant strains expressing virtually identical phenotypes as their wild-type controls, causing concern regarding the appropriateness of these models for the study of physiological processes. In some cases, discrepancies in results are being reported from different laboratories that are studying the same gene knockout model. While mutant strains provide a powerful tool for analysis of gene function in vivo, the breeding strategies used to generate the strain may have a profound impact on the expressed phenotype. This review examines the intricacies of working with a small rodent such as the mouse and discusses the advantages and disadvantages of using gene knockout models for thermoregulatory research. A number of experimental strategies that can be used to minimize the occurrence of redundant phenotypes are presented. The influence of background strain effects is also considered, since this may be one of the most important factors influencing a mutant phenotype. A future perspective is provided in which more advanced technologies using conditional gene inactivation and the production of rat knockout strains will improve current experimental design.     

尿素通道蛋白B基因敲除小鼠心脏电生理特性的改变

目的:研究尿素通道蛋白B(UT-B)基因敲除对小鼠心脏电生理特性的影响。方法:使用常规的心电图、心肌细胞动作电位记录方法和膜片钳实验技术。结果:①UT-B基因敲除小鼠30%发生了不同程度的心律失常,而对照组的野生C57小鼠无一例发生心律失常。②基因敲除小鼠心室肌细胞动作电位幅值(APA)及最大除极速度(Vmax)明显受到抑制(P<0.05),而心室肌细胞动作电位复极50%、90%时程(APD50、APD90)和正常对照组比明显延长(P<0.05)。③基因敲除小鼠心室肌细胞膜上钠离子通道电流幅值和对照组比明显降低(p<0.01)。结论:UT-B基因敲除可以导致小鼠心脏电生理特性发生改变。     

Differential expression of genes and changes in glucose metabolism in the liver of liver-specific glucokinase gene knockout mice

To investigate the role of liver-specific expression of glucokinase (GCK) in the pathogenesis of hyperglycemia and to identify candidate genes involved in mechanisms of the onset and progression of maturity onset diabetes of the young, type 2 (MODY-2), we examined changes in biochemical parameters and gene expression in GCK knockout (gck^w/–) and wild-type (gck^w/w) mice as they aged. Fasting blood glucose levels were found to be significantly higher in the gck^w/– mice, compared to age-matched gck^w/w mice, at all ages (P < 0.05), except at 2 weeks. GCK activity of gck^w/– mice was about 50% of that of wild type (gck^w/w) mice (P < 0.05). Glycogen content at 4 and 40 weeks of age was lower in gck^w/– mice compared to gck^w/w mice. Differentially expressed genes in the livers of 2 and 26 week-old liver-specific GCK knockout (gck^w/–) mice were identified by suppression subtractive hybridization (SSH), which resulted in the identification of phosphoenolpyruvatecarboxykinase (PEPCK, also called PCK1) and Sterol O-acyltransferase 2 (SOAT2) as candidate genes involved in pathogenesis. The expressions of PEPCK and SOAT2 along with glycogen phosphorylase (GP) and glycogen synthase (GS) were then examined in GCK knockout (gck^w/–) and wild-type (gck^w/w) mice at different ages. Changes in PEPCK mRNA levels were confirmed by real-time RT-PCR, while no differences in the levels of expression of SOAT2 or GS were observed in age-matched GCK knockout (gck^w/–) and wild-type (gck^w/w) mice. GP mRNA levels were decreased in 40-week old gck^w/– mice compared to age-matched gck^w/w mice. Changes in gluconeogenesis, delayed development of GCK and impaired hepatic glycogen synthesis in the liver potentially lead to the onset and progression of MODY2.     

Insulin control of glycogen metabolism in knockout mice lacking the muscle-specific protein phosphatase PP1G/RGL

The regulatory-targeting subunit (RGL), also called GM) of the muscle-specific glycogen-associated protein phosphatase PP1G targets the enzyme to glycogen where it modulates the activity of glycogen-metabolizing enzymes. PP1G/RGL has been postulated to play a central role in epinephrine and insulin control of glycogen metabolism via phosphorylation of RGL. To investigate the function of the phosphatase, RGL knockout mice were generated. Animals lacking RGL show no obvious defects. The RGL protein is absent from the skeletal and cardiac muscle of null mutants and present at approximately 50% of the wild-type level in heterozygotes. Both the level and activity of C1 protein are also decreased by approximately 50% in the RGL-deficient mice. In skeletal muscle, the glycogen synthase (GS) activity ratio in the absence and presence of glucose-6-phosphate is reduced from 0.3 in the wild type to 0.1 in the null mutant RGL mice, whereas the phosphorylase activity ratio in the absence and presence of AMP is increased from 0.4 to 0.7. Glycogen accumulation is decreased by approximately 90%. Despite impaired glycogen accumulation in muscle, the animals remain normoglycemic. Glucose tolerance and insulin responsiveness are identical in wild-type and knockout mice, as are basal and insulin-stimulated glucose uptakes in skeletal muscle. Most importantly, insulin activated GS in both wild-type and RGL null mutant mice and stimulated a GS-specific protein phosphatase in both groups. These results demonstrate that RGL is genetically linked to glycogen metabolism, since its loss decreases PP1 and basal GS activities and glycogen accumulation. However, PP1G/RGL is not required for insulin activation of GS in skeletal muscle, and rather another GS-specific phosphatase appears to be involved.     

Cutaneous overexpression of neurotrophin-3 (NT3) selectively restores sensory innervation in NT3 gene knockout mice

Neurotrophin-3 (NT3) is essential for development of sensory innervation to the skin. NT3 supports the postnatal survival of primary sensory neurons that mediate mechanoreception and their Merkel cell containing touch dome end organs (Airaksinen et al., 1996). In this study we determined whether NT3 overexpressed in the skin could restore innervation lost when endogenous NT3 levels were reduced. Hybrid mice that overexpress NT3 in basal keratinocytes but lack one endogenous NT3 allele (K14-NT3/NT3(+/-)) were compared to NT3 overexpresser (K14-NT3) mice, heterozygous knockout (NT3(+/-)) mice, and littermate control mice. In line with previous analyses, NT3(+/-) mice lost 63% of the Merkel cells associated with touch domes, 67% of touch dome units and the associated SAI innervation. All of these parameters were restored to overexpresser levels in K14-NT3/NT3(+/-) mice. Knockout NT3(+/-) mice also had a 31% reduction of L4/L5 dorsal root ganglion cells and a 24% reduction of myelinated axons in the saphenous cutaneous nerve. These losses were also restored in hybrid K14-NT3/NT3(+/-) mice, though only to control mouse values. These results indicate that overexpression of NT3 in skin of NT3(+/-) knockout mice rescued most cutaneous neurons lost in NT3(+/-) mice, but was unable to rescue NT3-dependent neurons that project to noncutaneous sensory targets.     

Mild mitochondrial uncoupling in mice affects energy metabolism, redox balance and longevity

Caloric restriction is the most effective non-genetic intervention to enhance lifespan known to date. A major research interest has been the development of therapeutic strategies capable of promoting the beneficial results of this dietary regimen. In this sense, we propose that compounds that decrease the efficiency of energy conversion, such as mitochondrial uncouplers, can be caloric restriction mimetics. Treatment of mice with low doses of the protonophore 2,4-dinitrophenol promotes enhanced tissue respiratory rates, improved serological glucose, triglyceride and insulin levels, decrease of reactive oxygen species levels and tissue DNA and protein oxidation, as well as reduced body weight. Importantly, 2,4-dinitrophenol-treated animals also presented enhanced longevity. Our results demonstrate that mild mitochondrial uncoupling is a highly effective in vivo antioxidant strategy, and describe the first therapeutic intervention capable of effectively reproducing the physiological, metabolic and lifespan effects of caloric restriction in healthy mammals.     

Effects of forced uncoupling protein 1 expression in 3T3-L1 cells on mitochondrial function and lipid metabolism

Obesity-related increase in body fat mass is a risk factor for many diseases, including type 2 diabetes. Controlling adiposity by targeted modulation of adipocyte enzymes could offer an attractive alternative to current dietary approaches. Brown adipose tissue, which is present in rodents but not in adult humans, expresses the mitochondrial uncoupling protein 1 (UCP1) that promotes cellular energy dissipation as heat. Here, we report on the direct metabolic effects of forced UCP1 expression in white adipocytes derived from a murine (3T3-L1) preadipocyte cell line. After stable integration, the ucp1 gene product was continuously expressed during differentiation and reduced the total lipid accumulation by approximately 30% without affecting other adipocyte markers, such as cytosolic glycerol-3-phosphate dehydrogenase activity and leptin production. The expression of UCP1 also decreased glycerol output and increased glucose uptake, lactate output, and the sensitivity of cellular ATP content to nutrient removal. However, oxygen consumption and beta-oxidation were minimally affected. Together, our results suggest that the reduction in intracellular lipid by constitutive expression of UCP1 reflects a downregulation of fat synthesis rather than an upregulation of fatty acid oxidation.     

Opposite regulation of uncoupling protein 1 and uncoupling protein 3 in vivo in brown adipose tissue of cold-exposed rats

Earlier we reported a 14-fold increase of glycogen in the brown adipose tissue (BAT) in rats when the animals were placed back from cold to neutral temperature. To elucidate the mechanism, here we compared the level of glucose transporter 4 (GLUT4) protein, uncoupling protein (UCP) 1 and UCP3 mRNA and protein expressions in the BAT under the same conditions. We found that the increased GLUT4 level in cold was maintained during the reacclimation. After 1 week cold exposure the mRNA and protein content of UCP1 increased parallel, while the protein level of UCP3 decreased, contrary to its own mRNA level.