Rapid genotyping of newborn gene mutant mice

The Potential of the FSP1cre-Pparb/d-/- Mouse Model for Studying Juvenile NAFLD

Non-alcoholic fatty liver disease (NAFLD) can progress from steatosis to non-alcoholic steatohepatitis (NASH) characterized by liver inflammation, possibly leading to cirrhosis and hepatocellular carcinoma (HCC). Mice with impaired macrophage activation, when fed a high-fat diet, develop severe NASH. Evidence is mounting that Kupffer cells are implicated. However, it is unknown whether the resident CD68⁺ or bone marrow-derived CD11b⁺ Kupffer cells are involved. Characterization of the FSP1cre-Pparb/d^-/- mouse liver revealed that FSP1 is expressed in CD11b⁺ Kupffer cells. Although these cells only constitute a minute fraction of the liver cell population, Pparb/d deletion in these cells led to remarkable hepatic phenotypic changes. We report that a higher lipid content was present in postnatal day 2 (P2) FSP1cre-Pparb/d^-/- livers, which diminished after weaning. Quantification of total lipids and triglycerides revealed that P2 and week 4 of age FSP1cre-Pparb/d^-/- livers have higher levels of both. qPCR analysis also showed upregulation of genes involved in fatty acid β-oxidation, and fatty acid and triglyceride synthesis pathways. This result is further supported by western blot analysis of proteins in these pathways. Hence, we propose that FSP1cre-Pparb/d^-/- mice, which accumulate lipids in their liver in early life, may represent a useful animal model to study juvenile NAFLD.

Sensory neuron development in mouse coccygeal vertebrae and its relationship to tail biopsies for genotyping

A common method of genotyping mice is via tissue obtained from tail biopsies. However, there is no available information on the temporal development of sensory neurons in the tail and how their presence or absence might affect the age for performing tail biopsies. The goals of this study were to determine if afferent sensory neurons, and in particular nociceptive neurons, are present in the coccygeal vertebrae at or near the time of birth and if not, when they first can be visualized on or in those vertebrae. Using toluidine blue neuronal staining, transmission electron microscopy, and calcitonin-related gene peptide immunostaining, we found proximal to distal maturation of coccygeal nerve growth in the C57BL/6J mouse. Single nerve bundles were first seen on postpartum day (PPD) 0. On PPD 3 presumptive nociceptive sensory nerve fibers were seen entering the vertebral perichondrium. Neural development continued through the last time point (PPD 7) but at no time were neural fibers seen entering the body of the vertebrae. The effect of age on the development of pain perception in the neonatal mouse is discussed.

Genetic modification of the mouse: general technology - pronuclear and blastocyst injection

Introduction of germ line mutations in mice via genetic engineering involves alterations of the structure and characteristics of genes. These alterations are mostly introduced via molecular genetic technology either in embryonal stem cells or in one-cell stage embryos. This chapter describes classic biotechnological methods used to generate mice from modified pre-implantation embryos.

Vitamin C deficiency attenuates liver fibrosis by way of up-regulated peroxisome proliferator-activated receptor-gamma expression in senescence marker protein 30 knockout mice

Senescence marker protein 30 (SMP30), an important aging marker molecule that is highly expressed in the liver, has been known to protect hepatocytes from apoptosis by the synthesis of vitamin C. To explore the function of SMP30 in liver fibrosis, the effect of SMP30 deficiency on liver fibrosis was investigated in SMP30 knockout (KO) mice. Moreover, the in vivo results were further confirmed by way of hepatic stellate cell (HSC) isolation. We demonstrated that carbon tetrachloride (CCl(4))-induced liver fibrosis and the nuclear translocation of p-Smad2/3, the immediate downstream of transforming growth factor beta (TGF-beta), were significantly inhibited in the liver of SMP30 KO mice compared with wildtype (WT) mice. We also confirmed that both WT and SMP30 KO HSCs did not express SMP30. Finally, we further confirmed that up-regulation of peroxisome proliferator-activated receptor-gamma (PPAR-gamma) caused by a lack of vitamin C was the pivotal factor in the mechanisms for attenuated liver fibrosis of SMP30 KO mice, and feeding with vitamin C restored CCl(4)-induced liver fibrosis in SMP30 KO mice.

CONCLUSION

Vitamin C deficiency by SMP30 depletion attenuated liver fibrosis by way of up-regulated PPAR-gamma expression in SMP30 KO mice. Our results provide, for the first time, the possible mechanisms underlying inhibition of HSC activation associated with vitamin C and PPAR-gamma up-regulation in liver fibrosis of SMP30 KO mice.

A simple PCR-based genotyping method for M105I mutation of alpha-SNAP enhances the study of early pathological changes in hyh phenotype

alpha-SNAP is an essential component of the protein machinery responsible for membrane fusion events in different cell types. The hyh (hydrocephalus with hop gait) mouse carries a missense mutation in Napa gene that results in a point mutation (M105I) in alpha-SNAP protein. Homozygous animals for the mutant allele have been identified by the clinical and/or neuropathological phenotype, or by direct sequencing of PCR products. The aims of the present study were (i) to develop a high-throughput technique to genotype hyh mice, (ii) to correlate genotype-phenotype, and (iii) to analyze the earliest pathological changes of hyh mutant mice. As no restriction sites are affected by the hyh mutation, we resolved this problem by creating a BspHI restriction site with a modified (mismatch) polymerase chain reaction (PCR) primer in wild-type allele. This artificially created restriction site (ACRS)-PCR technique is a simple, rapid and reliable method to genotype hyh mice in a day-work procedure. Biochemical and histological analysis of genotyped hyh embryos at different developmental stages allowed us to identify and characterize the earliest brain pathological changes of the hyh phenotype, including the first signs of neuroepithelial disruption and neuronal ectopia. In addition, genotype-phenotype analysis of 327 animals confirmed that (i) hyh is a single-gene autosomal recessive disorder, and (ii) the disorder has 100% penetrance (i.e., the mutation was only present in affected mice). The genotyping method described here enhances the potentiality of hyh mouse as a unique in vivo model to study the role of membrane trafficking in different developmental and physiological processes.

Improved embryonic stem cell technologies

Murine embryonic stem (ES) cells have become an indispensable tool for investigating genetic function both in vitro and, importantly, in vivo. Recent advances, including tetraploid aggregation, new site-specific recombinases and RNAi, have enabled more sophisticated manipulation of the ES cell genome. For instance, it is now possible to control gene expression in both a temporally and spatially restricted manner. Such new technologies are answering complex questions surrounding the function and interaction of an increasing number of genes. This chapter will review both the history and recent technological progress that has been made in mouse ES cell derivation, genetic manipulation and the generation of ES cell-derived chimaeric animals.

High-throughput fluorescent screening of transgenic animals: phenotyping and haplotyping

BACKGROUND

Methods for genotyping transgenic animals currently consist of extracting genomic DNA from blood or tissue followed by PCR or Southern blot analysis. These methods when used to screen large numbers of animals can be time consuming and expensive. Therefore, we developed a novel method that allows high-throughput screening of phenotypic changes on leukocytes, resulting from the transgenic genotype. This technique allows investigators to quickly screen a large number of animals without the need to extract DNA from each one. Moreover, since blood is collected for the initial screening, putative homozygotes can be confirmed by conventional methods using the same blood samples.

METHODS

We collected blood from wild-type alphagal positive and alphagal knockout mice and probed for the presence of Galalpha(1-->3)Gal (alphagal) epitopes. Also, alloantigen specific antibodies were used to determine the haplotype of our outbred mouse colony in order to develop an inbred line.

RESULTS

alphagal epitopes were detected in wild-type but not alphagal knock-out samples. To validate these results, PCR was used to demonstrate the native alphagal gene in wild-type and the pGKneo construct in alphagal knock-out mice. Furthermore, haplotypes were determined and mice divided for backcrosses.

CONCLUSIONS

This screening method is useful for both preliminary screening of transgenic mice and the development of an inbred mouse colony by rapid determination of MHC I haplotype. Here, we demonstrate the use of this technique and show how it can be a valuable tool, saving time and resources in both investigator effort and animal husbandry.

Altered balance of glutamatergic/GABAergic synaptic input and associated changes in dendrite morphology after BDNF expression in BDNF-deficient hippocampal neurons

Cultured neurons from bdnf-/- mice display reduced densities of synaptic terminals, although in vivo these deficits are small or absent. Here we aimed at clarifying the local responses to postsynaptic brain-derived neurotrophic factor (BDNF). To this end, solitary enhanced green fluorescent protein (EGFP)-labeled hippocampal neurons from bdnf-/- mice were compared with bdnf-/- neurons after transfection with BDNF, bdnf-/- neurons after transient exposure to exogenous BDNF, and bdnf+/+ neurons in wild-type cultures. Synapse development was evaluated on the basis of presynaptic immunofluorescence and whole-cell patch-clamp recording of miniature postsynaptic currents. It was found that neurons expressing BDNF::EGFP for at least 16 h attracted a larger number of synaptic terminals than BDNF-deficient control neurons. Transfected BDNF formed clusters in the vicinity of glutamatergic terminals and produced a stronger upregulation of synaptic terminal numbers than high levels of ambient BDNF. Glutamatergic and GABAergic synapses reacted differently to postsynaptic BDNF: glutamatergic input increased, whereas GABAergic input decreased. BDNF::EGFP-expressing neurons also differed from BDNF-deficient neurons in their dendrite morphology: they exhibited weaker dendrite elongation and stronger dendrite initiation. The upregulation of glutamatergic synaptic input and the BDNF-induced downregulation of GABAergic synaptic terminal numbers by postsynaptic BDNF depended on tyrosine receptor kinase B activity, as deduced from the blocking effects of K252a. The suppression of dendrite elongation was also prevented by block of tyrosine receptor kinase B but required, in addition, glutamate receptor activity. Dendritic length decreased with the number of glutamatergic contacts. These results illuminate the role of BDNF as a retrograde synaptic regulator of synapse development and the dependence of dendrite elongation on glutamatergic input.

Electrophysiological and behavioral phenotype of insulin receptor defective mice

The olfactory bulb expresses one of the highest levels of insulin found in the brain. A high level of expression of the concomitant insulin receptor (IR) kinase is also retained in this brain region, even in the adult. We have previously demonstrated in a heterologous system that insulin modulates the voltage-dependent potassium channel, Kv1.3, through tyrosine phosphorylation of three key residues in the amino and carboxyl terminus of the channel protein. Phosphorylation also induces current suppression of the Kv1.3-contributed current in cultured olfactory bulb neurons (OBNs) of rodents. In order to explore the behavioral importance of this kinase-induced modulation of the channel for the olfactory ability of the animal, mice with a targeted-gene deletion of the insulin receptor were electrophysiologically and behaviorally characterized. Mice heterozygous for the insulin receptor kinase (IR+/-) gene performed the same as wild-type (+/+) mice when challenged with a traditional, non-learning-based task to test gross anosmia. There was also no significant difference across the two genotypes in tests designed to measure exploratory behavior or in a battery of systems physiology experiments designed to assess metabolic energy usage (locomotion, ingestive behaviors, weight, oxygen consumption, and respiratory quotient). Object memory recognition tests suggest that IR+/- mice have an impairment in recognition of familiarized objects; IR+/- mice demonstrate poor performance for both short-term (1 h) and long-term (24 h) memory tests in comparison to that of wild-type mice. Electrophysiological experiments indicate that mitral cell neurons cultured from both heterozygous and homozygous-null mice (IR+/- and IR-/-) have an decreased peak current amplitude compared with that recorded for wild-type (+/+) animals matched for days in vitro (DIV). These data indicate that the loss of one allele of the IR kinase gene modifies the electrical phenotype of the mitral cell neurons in the olfactory bulb without a change in gross olfactory ability. Given our findings that there are no significant changes in metabolic balance of the IR (+/-) mice but some impairment in memory retention, future experiments testing for specific olfactory behaviors or functional deficits in IR-/+ mice models of diabetes will need to either be tasks that do not require learning or will require a different model (such as diet-induced diabetes) that may evoke a stronger phenotype.

Effects of brain-derived neurotrophic factor (BDNF) on glial cells and serotonergic neurones during development

Serotonergic neurones are among the first to develop in the central nervous system. Their survival and maturation is promoted by a variety of factors, including serotonin itself, brain-derived neurotrophic factor (BDNF) and S100beta, an astrocyte-specific Ca(2+) binding protein. Here, we used BDNF-deficient mice and cell cultures of embryonic raphe neurones to determine whether or not BDNF effects on developing serotonergic raphe neurones are influenced by its action on glial cells. In BDNF-/- mice, the number of serotonin-immunoreactive neuronal somata, the amount of the serotonin transporter, the serotonin content in the striatum and the hippocampus, and the content of 5-hydroxyindoleacetic acid in all brain regions analysed were increased. By contrast, reduced immunoreactivity was found for myelin basic protein (MBP) in all brain areas including the raphe and its target region, the hippocampus. Exogenously applied BDNF increased the number of MBP-immunopositive cells in the respective culture systems. The raphe area displayed selectively reduced immunoreactivity for S100beta. Accordingly, S100beta was increased in primary cultures of pure astrocytes by exogenous BDNF. In glia-free neuronal cultures prepared from the embryonic mouse raphe, addition of BDNF supported the survival of serotonergic neurones and increased the number of axon collaterals and primary dendrites. The latter effect was inhibited by the simultaneous addition of S100beta. These results suggest that the presence of BDNF is not a requirement for the survival and maturation of serotonergic neurones in vivo. BDNF is, however, required for the local expression of S100beta and production of MBP. Therefore BDNF might indirectly influence the development of the serotonergic system by stimulating the expression of S100beta in astrocytes and the production MBP in oligodendrocytes.

RNA editing produces glycine receptor alpha3(P185L), resulting in high agonist potency

The function of supramedullary glycine receptors (GlyRs) is still unclear. Using Wistar rat collicular slices, we demonstrate GlyR-mediated inhibition of spike discharge elicited by low glycine (10 microM). Searching for the molecular basis of this phenomenon, we identified a new GlyR isoform. GlyR alpha3(P185L), a result of cytidine 554 deamination, confers high glycine sensitivity (EC50 approximately 5 microM) to neurons and thereby promotes the generation of sustained chloride conductances associated with tonic inhibition. The level of GlyR alpha3-C554U RNA editing is sensitive to experimentally induced brain lesion, inhibition of cytidine deamination by zebularine and inhibition of mRNA transcription by actinomycin D, but not to blockade of protein synthesis by cycloheximide. Conditional regulation of GlyR alpha3(P185L) is thus likely to be part of a post-transcriptional adaptive mechanism in neurons with enhanced excitability.

Area-specific effects of brain-derived neurotrophic factor (BDNF) genetic ablation on various neuronal subtypes of the mouse brain

The effects of brain-derived neurotrophic factor (BDNF) on the development of presynaptic terminals and of neuronal subtypes in various brain areas were studied in BDNF-knockout (BDNF-/-) mice at postnatal days 15-17. Western analysis revealed no changes in the overall amount of a variety of synaptic proteins in BDNF-/- mice as compared to wild type mice. In addition, the complex between the vesicular proteins, synaptophysin and synaptobrevin, as well as their respective homodimers were unaltered. Moreover, no changes in the density of neurons were found in, e.g., the CA3 region of the hippocampus and the nucleus nervi facialis of BDNF-/- mice. However, cholinergic cells were reduced by 20% in the medial septum of BDNF-/- mice associated with a decrease in the activity of choline acetyltransferase and protein levels of nerve growth factor in the hippocampus by 16% and 44%, respectively. In the striatum, however, the total number of cholinergic cells were comparable in both groups, although the activity of choline acetyltransferase was decreased by 46%. In GABAergic interneurons, the expression of neuropeptides in various brain areas was differentially affected by BDNF deletion as revealed by immunohistochemistry. In the hippocampus and cortex of BDNF-/- mice, the density of neuropeptide Y-, somatostatin-, and parvalbumin-immunoreactive cells was drastically reduced, whereas the density of calretinin-positive cells was increased. The extent of these changes in neuropeptide-containing cells varied among hippocampal subregions. In the striatum, only the density of parvalbumin-immunoreactive cells was decreased by approximately 45%. In conclusion, BDNF deficiency is accompanied by a differential dysregulation in the expression of neuropeptides and calcium-binding proteins in otherwise intact GABAergic and glutamatergic neurons in a region-specific manner.

Contractile activity of skeletal musculature involved in breathing is essential for normal lung cell differentiation, as revealed inMyf5−/−:MyoD−/− embryos

In the current study, the role of contractile activity of respiratory muscles in fetal lung growth and cell differentiation was examined using Myf5-/-:MyoD-/- mouse embryos. As previously found, Myf5-/-:MyoD-/- mouse embryos had no respiratory musculature. Consequently, they suffered from pulmonary hypoplasia and died shortly after birth. The hypoplastic lung had decreased proliferation and increased apoptotic index as early as embryonic day 14.5. By contrast, only at the last gestational day, the number of lung cells expressing platelet derived growth factor B and insulin growth factor I was decreased, while the gradient of the thyroid transcription factor 1 was not maintained. Type II pneumocytes had a failure in glycogen utilization and surfactant storage and secretion but were able to synthesize the surfactant-associated proteins. Type I pneumocytes were readily detectable using an early differentiation marker (i.e., Gp38). However, the late differentiation of type I pneumocytes never occurred, as revealed by transmission electron microscopy. Together, our findings suggest that pulmonary distension due to fetal breathing-like movements plays an important role not only in lung growth but also in lung cell differentiation.

The use of real-time PCR with fluorogenic probes for the rapid selection of mutant neuroectodermal grafts

Adenosine is an efficient inhibitor of neuronal activity with the ability to suppress seizure activity in various animal models of epilepsy. In the present study adenosine-releasing neuronal cells were generated as a potential source for therapeutically active grafts. Mice with a genetic disruption of the gene encoding adenosine kinase (Adk(-/-))-the major adenosine metabolizing enzyme-were used as a source for the derivation of adenosine releasing neuronal cells. Since homozygous Adk(-/-) mice constitute a lethal phenotype, embryonic neuroectoderm was derived from intercrosses of Adk(+/-)-mice. Therefore, a rapid genotyping procedure had to be developed using a fluorescent 5'-exonuclease (TaqMan) assay, which permitted the genotyping of embryonic cell material within 3 h. During this time period the cells to be grafted displayed an unaltered viability. Cultured neuroectodermal Adk(-/-) cells released up to 2 micro g adenosine per mg protein per hour. Adk(-/-) neuroectoderm grafted into the lateral brain ventricle of adult mice was found to survive for at least 6 weeks. The method described here suggests the feasibility to graft adenosine releasing neuroectodermal cells as a potential therapeutic approach for the treatment of pharmacoresistant epilepsy.

Postsynaptic action of BDNF on GABAergic synaptic transmission in the superficial layers of the mouse superior colliculus

The neurotrophin brain-derived neurotrophic factor (BDNF) is involved in numerous aspects of synapse development and plasticity. The present study was aimed at clarifying the significance of endogenous BDNF for the synaptically driven spontaneous network activity and GABAergic inhibition in the superficial layers of the mouse superior colliculus. In this structure neuron survival is unaffected by the absence of BDNF. Two experimental approaches were used: comparison of BDNF-deficient (-/-) and wild-type (+/+) mice and blockade of BDNF receptor signaling by the tyrosine kinase inhibitor K-252a. Patch-clamp recordings were performed on horizontal slices during postnatal days 15 and 16. The lack of BDNF in -/- mice caused a significant reduction of the spontaneous action potential frequency and an increase in the pharmacologically induced disinhibition of spike discharge. This change was accompanied by an increase in the amplitudes of GABAergic evoked, spontaneous, and miniature inhibitory postsynaptic currents (IPSCs). BDNF gene inactivation had no effect on the degree of paired-pulse facilitation or the frequency of miniature IPSCs. The increase of IPSC amplitudes by chronic BDNF deprivation was completely mimicked by acute exposure to K-252a in +/+ animals. The enhancement of GABAergic IPSCs in -/- animals was reversed by acute application of 100 ng/ml BDNF, but this rescue was completely prevented by blocking postsynaptic protein kinase C (PKC) activation with the PKC inhibitor peptide 19-31. From these results we conclude that BDNF increases spontaneous network activity by suppressing GABAergic inhibition, the site of action of BDNF is predominantly postsynaptic, BDNF-induced suppression of GABAergic synaptic transmission is caused by acute downregulation of GABA(A) receptors, and BDNF effects are mediated by its TrkB receptor and require PKC activation in the postsynaptic cell.

Novel double promoter approach for identification of transgenic animals: A tool for in vivo analysis of gene function and development of gene-based therapies

Advances in vertebrate genetics have allowed studies of gene function in developing animals through gene knockout and transgenic analyses. These advances have encouraged the development of gene-based therapies through introduction of exogenous genes to enhance and/or replace dysfunctional or missing genes. However, in vertebrates, such analyses often involve tedious screening for transgenic animals, such as PCR-based genotype determinations. Here, we report the use of double-promoter plasmids carrying the transgene of interest and the crystallin-promotor-driven Green fluorescent protein (GFP) in transgenic Xenopus laevis tadpoles. This strategy allows a simple examination for the presence of GFP in the eyes to identify transgenic animals. PCR-based genotyping and functional characterization confirms that all animals expressing GFP in the eyes indeed carry the desired promoter/transgene units. Thus, the use of this and other similar vectors should dramatically improve current transgenesis protocols and reduce the time and cost for identifying transgenic animals.

The use of real-time PCR and fluorogenic probes for rapid and accurate genotyping of newborn mice

Real-time PCR and fluorogenic probes were combined in a simple, rapid and sensitive method to genotype murine breeding stocks and their progeny for a point mutation. DNA from tail biopsies of newborn mice was mixed with amplification primers and fluorogenic hybridization probes in a PCR mixture. The primers were designed to amplify a region of the Fas-Ligand gene including the site for the gld natural point mutation. The fluorogenic hybridization probes overlaid this target sequence and were used to detect amplification of the PCR fragment as well as determine the presence of the point mutation using fluorescence resonance energy transfer (FRET). Both mutated and wild-type forms of the gene fragment were amplified as detected with real-time PCR. Melting curve profiles completed on each amplified sample revealed the genotype for each mouse. These genotypes were confirmed by sequencing the amplified fragments. These results suggest real-time spectrofluorometric PCR techniques incorporating FRET-based hybridization probes may be used for rapid, sensitive, inexpensive and reliable genotyping.