A Rapid Protocol for Integrating Extrachromosomal Arrays With High Transmission Rate into the C. elegans Genome

Microinjecting DNA into the cytoplasm of the syncytial gonad of Caenorhabditis elegans is the main technique used to establish transgenic lines that exhibit partial and variable transmission rates of extrachromosomal arrays to the next generation. In addition, transgenic animals are mosaic and express the transgene in a variable number of cells. Extrachromosomal arrays can be integrated into the C. elegans genome using UV irradiation to establish nonmosaic transgenic strains with 100% transmission rate of the transgene. To that extent, F1 progenies of UV irradiated transgenic animals are screened for animals carrying a heterozygous integration of the transgene, which leads to a 75% Mendelian transmission rate to the F2 progeny. One of the challenges of this method is to distinguish between the percentage of transgene transmission in a population before (X% transgenic animals) and after integration (≥75% transgenic F2 animals). Thus, this method requires choosing a nonintegrated transgenic line with a percentage of transgenic animals that is significantly lower than the Mendelian segregation of 75%. Consequently, nonintegrated transgenic lines with an extrachromosomal array transmission rate to the next generation ≤60% are usually preferred for integration, and transgene integration in highly transmitting strains is difficult. Here we show that the efficiency of extrachromosomal arrays integration into the genome is increased when using highly transmitting transgenic lines (≥80%). The described protocol allows for easy selection of several independent lines with homozygous transgene integration into the genome after UV irradiation of transgenic worms exhibiting a high rate of extrachromosomal array transmission. Furthermore, this method is quite fast and low material consuming. The possibility of rapidly generating different lines that express a particular integrated transgene is of great interest for studies focusing on gene expression pattern and regulation, protein localization, and overexpression, as well as for the development of subcellular markers.     

Targeted Integration of Single-Copy Transgenes in Drosophila melanogaster Tissue-Culture Cells Using Recombination-Mediated Cassette Exchange

Transfection of transgenes into Drosophila cultured cells is a standard approach for studying gene function. However, the number of transgenes present in the cell following transient transfection or stable random integration varies, and the resulting differences in expression level affect interpretation. Here we developed a system for Drosophila cell lines that allows selection of cells with a single-copy transgene inserted at a specific genomic site using recombination-mediated cassette exchange (RMCE). We used the φC31 integrase and its target sites attP and attB for RMCE. Cell lines with an attP-flanked genomic cassette were transfected with donor plasmids containing a transgene of interest (UAS-x), a dihydrofolate reductase (UAS-DHFR) gene flanked by attB sequences, and a thymidine kinase (UAS-TK) gene in the plasmid backbone outside the attB sequences. In cells undergoing RMCE, UAS-x and UAS-DHFR were exchanged for the attP-flanked genomic cassette, and UAS-TK was excluded. These cells were selected using methotrexate, which requires DHFR expression, and ganciclovir, which causes death in cells expressing TK. Pure populations of cells with one copy of a stably integrated transgene were efficiently selected by cloning or mass culture in ∼6 weeks. Our results show that RMCE avoids the problems associated with current methods, where transgene number is not controlled, and facilitates the rapid generation of Drosophila cell lines in which expression from a single transgene can be studied.     

Analyzing Murine Schwann Cell Development Along Growing Axons

The development of peripheral nerves is an intriguing process. Neurons send out axons to innervate specific targets, which in humans are often more than 100 cm away from the soma of the neuron. Neuronal survival during development depends on target-derived growth factors but also on the support of Schwann cells (SCs). To this end SC ensheath axons from the region of the neuronal soma (or the transition from central to peripheral nervous system) to the synapse or neuromuscular junction. Schwann cells are derivatives of the neural crest and migrate as precursors along emerging axons until the entire axon is covered with SCs. This shows the importance of SC migration for the development of the peripheral nervous system and underlines the necessity to investigate this process. In order to analyze SC development, a setup is needed which next to the SCs also includes their physiological substrate for migration, the axon. Due to intrauterine development in vivo time-lapse imaging, however, is not feasible in placental vertebrates like mouse (mus musculus). To circumvent this, we adapted the superior cervical ganglion (SCG) explant technique. Upon treatment with nerve growth factor (NGF) SCG explants extend axons, followed by SC precursors migrating along the axons from the ganglion to the periphery. The beauty of this system is that the SC are derived from a pool of endogenous SC and that they migrate along their own physiological axons which are growing at the same time. This system is especially intriguing, because the SC development along axons can be analyzed by time-lapse imaging, opening further possibilities to gain insights into SC migration.     

Methods to Assess Subcellular Compartments of Muscle in C. elegans

Muscle is a dynamic tissue that responds to changes in nutrition, exercise, and disease state. The loss of muscle mass and function with disease and age are significant public health burdens. We currently understand little about the genetic regulation of muscle health with disease or age. The nematode C. elegans is an established model for understanding the genomic regulation of biological processes of interest. This worm’s body wall muscles display a large degree of homology with the muscles of higher metazoan species. Since C. elegans is a transparent organism, the localization of GFP to mitochondria and sarcomeres allows visualization of these structures in vivo. Similarly, feeding animals cationic dyes, which accumulate based on the existence of a mitochondrial membrane potential, allows the assessment of mitochondrial function in vivo. These methods, as well as assessment of muscle protein homeostasis, are combined with assessment of whole animal muscle function, in the form of movement assays, to allow correlation of sub-cellular defects with functional measures of muscle performance. Thus, C. elegans provides a powerful platform with which to assess the impact of mutations, gene knockdown, and/or chemical compounds upon muscle structure and function. Lastly, as GFP, cationic dyes, and movement assays are assessed non-invasively, prospective studies of muscle structure and function can be conducted across the whole life course and this at present cannot be easily investigated in vivo in any other organism.     

Transgenic Rodent Assay for Quantifying Male Germ Cell Mutant Frequency

De novo mutations arise mostly in the male germline and may contribute to adverse health outcomes in subsequent generations. Traditional methods for assessing the induction of germ cell mutations require the use of large numbers of animals, making them impractical. As such, germ cell mutagenicity is rarely assessed during chemical testing and risk assessment. Herein, we describe an in vivo male germ cell mutation assay using a transgenic rodent model that is based on a recently approved Organisation for Economic Co-operation and Development (OECD) test guideline. This method uses an in vitro positive selection assay to measure in vivo mutations induced in a transgenic λgt10 vector bearing a reporter gene directly in the germ cells of exposed males. We further describe how the detection of mutations in the transgene recovered from germ cells can be used to characterize the stage-specific sensitivity of the various spermatogenic cell types to mutagen exposure by controlling three experimental parameters: the duration of exposure (administration time), the time between exposure and sample collection (sampling time), and the cell population collected for analysis. Because a large number of germ cells can be assayed from a single male, this method has superior sensitivity compared with traditional methods, requires fewer animals and therefore much less time and resources.     

Dammaradiene synthase, a squalene cyclase, from Dryopteris crassirhizoma Nakai

Ferns produce a variety of cyclic triterpene hydrocarbons in large amount. Squalene cyclases (SCs) are responsible enzymes for formation of cyclic triterpene hydrocarbon skeletons. Although more than ten bacterial SCs have been cloned and four of them characterized for their enzymatic products, the only example of a fern SC is ACH, from Adiantum capillus-veneris, which produces hydroxyhopane. To obtain a deeper understanding of the molecular evolution of SCs and the origin of the structural diversity of fern triterpenes, further cloning and characterization of SCs have been pursued. In this study, a SC cDNA, DCD, was cloned from Dryopteris crassirhizoma by homology-based RT-PCR. DCD contains a 2058-bp open reading frame that encodes a 685 amino acid polypeptide exhibiting 66% identity to the previously identified fern SC, ACH, and 35-40% identity to bacterial SCs. Heterologous expression of DCD in yeast established it to be a dammaradiene synthase affording dammara-18(28),21-diene, a tetracyclic triterpene hydrocarbon. Although neither this compound nor any derived metabolites have been previously reported from D. crassirhizoma, re-investigation of the leaflets demonstrated the presence of dammara-18(28),21-diene. DCD represents the first SC that produces a tetracyclic triterpene hydrocarbon.     

Differentiated human adipose-derived stromal cells exhibit the phenotypic and functional characteristics of mature Schwann cells through a modified approach

Background aimsTissue engineering technology is a promising therapeutic strategy in peripheral nerve injury. Schwann cells (SCs) are deemed to be a vital component of cell-based nerve regeneration therapies. Many methods for producing SC-like cells derived from adipose-derived stromal cells (ADSCs) have been explored, but their phenotypic and functional characteristics remain unsatisfactory.MethodsWe investigated whether human ADSCs can be induced to differentiate into mature and stable SC-like cells with the addition of insulin, progestero``ne and glucocorticoids. The phenotypic and functional characteristics of new differentiated ADSCs (modified SC-like cells) were evaluated by real-time quantitative polymerase chain reaction, enzyme-linked immunosorbent assay and immunocytochemistry in vitro. Cells loaded into collagen sponge biomaterials were implanted around transected sciatic nerves with a 10-mm gap in vivo. The axon regrowth and functional recovery of the regenerated nerves were assessed by immunohistochemistry and Walking footprint analysis.ResultsAfter differentiation induction, the modified SC-like cells showed significantly up-regulated levels of S100B and P0 and enhanced proliferative and migratory capacities. In addition, the modified SC-like cells showed increased secretion of neurotrophic factors, and their functional characteristics were maintained for more than 3 weeks after removing the induction reagents. The modified SC-like cells exhibited significantly enhanced axon regrowth, myelination and functional recovery after sciatic nerve injury.ConclusionsOverall, the results suggest that this modified induction method can induce human ADSCs to differentiate into cells with the molecular and functional properties of mature SCs and increase the promotion of peripheral nerve regeneration.     

Three-Dimensional Imaging of the Intracellular Fate of Plasmid DNA and Transgene Expression: ZsGreen1 and Tissue Clearing Method CUBIC Are an Optimal Combination for Multicolor Deep Imaging in Murine Tissues

Evaluation methods for determining the distribution of transgene expression in the body and the in vivo fate of viral and non-viral vectors are necessary for successful development of in vivo gene delivery systems. Here, we evaluated the spatial distribution of transgene expression using tissue clearing methods. After hydrodynamic injection of plasmid DNA into mice, whole tissues were subjected to tissue clearing. Tissue clearing followed by confocal laser scanning microscopy enabled evaluation of the three-dimensional distribution of transgene expression without preparation of tissue sections. Among the tested clearing methods (Clear^T2, SeeDB, and CUBIC), CUBIC was the most suitable method for determining the spatial distribution of transgene expression in not only the liver but also other tissues such as the kidney and lung. In terms of the type of fluorescent protein, the observable depth for green fluorescent protein ZsGreen1 was slightly greater than that for red fluorescent protein tdTomato. We observed a depth of ~1.5 mm for the liver and 500 μm for other tissues without preparation of tissue sections. Furthermore, we succeeded in multicolor deep imaging of the intracellular fate of plasmid DNA in the murine liver. Thus, tissue clearing would be a powerful approach for determining the spatial distribution of plasmid DNA and transgene expression in various murine tissues.     

Krüppel-Like Factor 6 Rendered Rat Schwann Cell More Sensitive to Apoptosis via Upregulating FAS Expression

Krüppel-like factor 6 (KLF6) is a tumor suppressor gene and play a role in the regulation of cell proliferation and apoptosis. After the peripheral nerve injury (PNI), the microenvironment created by surrounding Schwann cells (SCs) is a critical determinant of its regenerative potential. In this study, we examined the effects of KLF6 on SCs responses during PNI. Both KLF6 mRNA and protein expression levels were upregulated in the injured sciatic nerve, and immunofluorescence results showed that many KLF6-positive cells simultaneously expressed the SC markers S-100 and p75NTR. The apoptosis inducers TNFα and cisplatin upregulated KLF6 expression in primary cultured SCs and the SC line RSC96. Although KLF6 overexpression exacerbated cisplatin- and TNFα-induced apoptosis, expression levels of the apoptosis regulators Bcl2 and Bax were not significantly affected in either KLF6-overexpressing or KLF6-depleted RSC96 cells. Realtime PCR arrays and qRT-PCR demonstrated that KLF6 overexpression upregulated four pro-apoptotic genes, FAS, TNF, TNFSF12, and PYCARD, and inhibited expression of the anti-apoptotic IL10 gene expression. Further analysis revealed that FAS protein expression was positively correlated with KLF6 expression in SCs. These data suggest that KLF6 upregulation may render SCs more vulnerable to apoptosis after injury via upregulating FAS expression.     

Three-Dimensional Ultrastructural Karyotype Analysis from the Meiotic Parthenogenetic Nematode Heterodera betulae

Meiotic chromosome structure and function are described in the plant-parasitic nematode Heterodera betulae. Twelve synaptonemal complexes (SCs) were reconstructed from pachytene nuclei; therefore, n=12 is predicted for this species. Morphologically distinct sex chromosomes were not observed. Only one end of the SC is attached to the nuclear envelope, and there is no bouquet arrangement at pachytene. The structure of the SC in this meiotic parthenogenetic nematode was different than in other nematodes that reproduce via amphimixis; a striated central element with transverse filaments was not observed. Multiple SCs, or polycomplexes, were present in the nucleus. Recombination nodules were not observed. The centrioles were comprised of nine doublet microtubules connected by a ring, which is a distinct modification from the typical nine triplet microtubules without any interconnecting structure.     

The Beneficial Effect of Ginsenoside Rg1 on Schwann Cells Subjected to Hydrogen Peroxide Induced Oxidative Injury

Ginsenoside Rg1 (GRg1) has been considered to have therapeutic potential in promoting peripheral nerve regeneration and functional recovery after sciatic nerve injuries. However, the mechanism underlying the beneficial effect of GRg1 on peripheral nerve regeneration is currently unclear. The possible effect of GRg1 on Schwann cells (SCs), which were subjected to oxidative injury after nerve injury, might contribute to the beneficial effect of GRg1 on nerve regeneration. The present study was designed to investigate the potential beneficial effect of GRg1 on SCs exposed to oxidative injury. The oxidative injury to SCs was induced by hydrogen peroxide. The effect of GRg1 (50 μM) on SCs exposed to oxidative injury was measured by the levels of malondialdehyde (MDA), superoxide dismutase (SOD), glutathione (GSH) and catalase (CAT) in SCs. The cell number and cell viability of SCs were evaluated through fluorescence observation and MTT assay. The apoptosis of SCs induced by oxidative injury was evaluated by an apoptosis assay. The expression and secretion of nerve growth factor (NGF) and brain-derived neurotrophic factor (BDNF) were evaluated using RT-PCR, Western blotting, and an ELISA method. We found that GRg1 significantly up-regulated the level of SOD, GSH and CAT, and decreased the level of MDA in SCs treated with hydrogen peroxide. In addition, GRg1 has been shown to be able to inhibit the proapoptotic effect of hydrogen peroxide, as well as inhibit the detrimental effect of hydrogen peroxide on cell number and cell viability. Furthermore, GRg1 also increased the mRNA levels, protein levels and secretion of NGF and BDNF in SCs after incubation of hydrogen peroxide. Further study showed that preincubation with H89 (a PKA inhibitor) significantly inhibited the effects induced by hydrogen peroxide, indicating that the PKA pathway might be involved in the antioxidant effect and neurotrophic factors (NTFs) promoting effect of GRg1. In addition, a short-term in vivo study was performed to confirm and validate the antioxidant effect and nerve regeneration-promoting effect of GRg1 in a sciatic crush injury model in rats. We found that GRg1 significantly increased SOD, CAT and GSH, decreased MDA, as well as promoted nerve regeneration after crush injury. In conclusion, the present study showed that GRg1 is capable of helping SCs recover from the oxidative insult induced by hydrogen peroxide, which might account, at least in part, for the beneficial effect of GRg1 on nerve regeneration.     

Generation of Topically Transgenic Rats by In utero Electroporation and In vivo Bioluminescence Screening

In utero electroporation (IUE) is a technique which allows genetic modification of cells in the brain for investigating neuronal development. So far, the use of IUE for investigating behavior or neuropathology in the adult brain has been limited by insufficient methods for monitoring of IUE transfection success by non-invasive techniques in postnatal animals. For the present study, E16 rats were used for IUE. After intraventricular injection of the nucleic acids into the embryos, positioning of the tweezer electrodes was critical for targeting either the developing cortex or the hippocampus. Ventricular co-injection and electroporation of a luciferase gene allowed monitoring of the transfected cells postnatally after intraperitoneal luciferin injection in the anesthetized live P7 pup by in vivo bioluminescence, using an IVIS Spectrum device with 3D quantification software. Area definition by bioluminescence could clearly differentiate between cortical and hippocampal electroporations and detect a signal longitudinally over time up to 5 weeks after birth. This imaging technique allowed us to select pups with a sufficient number of transfected cells assumed necessary for triggering biological effects and, subsequently, to perform behavioral investigations at 3 month of age. As an example, this study demonstrates that IUE with the human full length DISC1 gene into the rat cortex led to amphetamine hypersensitivity. Co-transfected GFP could be detected in neurons by post mortem fluorescence microscopy in cryosections indicating gene expression present at ≥6 months after birth. We conclude that postnatal bioluminescence imaging allows evaluating the success of transient transfections with IUE in rats. Investigations on the influence of topical gene manipulations during neurodevelopment on the adult brain and its connectivity are greatly facilitated. For many scientific questions, this technique can supplement or even replace the use of transgenic rats and provide a novel technology for behavioral neuroscience.     

Involvement of 9-O-Acetyl GD3 Ganglioside in Mycobacterium leprae Infection of Schwann Cells

Mycobacterium leprae (ML), the etiologic agent of leprosy, mainly affects the skin and peripheral nerves, leading to demyelization and loss of axonal conductance. Schwann cells (SCs) are the main cell population infected by ML in the nerves, and infection triggers changes in the SC phenotype from a myelinated to a nonmyelinated state. In the present study, we show that expression of 9-O-acetyl GD3, a ganglioside involved in cellular anti-apoptotic signaling and nerve regeneration, increases in SCs following infection with ML. Observation by confocal microscopy together with coimmunoprecipitation suggested that this ganglioside participates in ML attachment and internalization by SC. Immunoblockage of 9-O-acetyl GD3 in vitro significantly reduced adhesion of ML to SC surfaces. Finally, we show that activation of the MAPK (ERK 1/2) pathway and SC proliferation, two known effects of ML on SCs that result in demyelization, are significantly reduced when the 9-O-acetyl GD3 ganglioside is immunoblocked. Taken together, these data suggest the involvement of 9-O-acetyl GD3 in ML infection on SCs.     

Bioluminescence Imaging of an Immunocompetent Animal Model for Glioblastoma

In contrast to commonly reported human glioma xenograft animal models, GL261 murine glioma xenografts recapitulate nearly all relevant clinical and histopathologic features of the human disease. When GL261 cells are implanted intracranially in syngeneic C57BL/6 mice, the model has the added advantage of maintaining an intact immune microenvironment. Stable expression of luciferase in GL261 cells allows non-invasive cost effective bioluminescence monitoring of intracranial tumor growth. We have recently demonstrated that luciferase expression in GL261 cells does not affect the tumor growth properties, tumor cell immunomodulatory cytokine expression, infiltration of immune cells into the tumor, or overall survival of animals bearing the intracranial tumor. Therefore, it appears that the GL261 luciferase glioma model can be useful in the study of novel chemotherapeutic and immunotherapeutic modalities. Here we report the technique for generating stable luciferase expression in GL261 cells and how to study the in vitro and in vivo growth of the tumor cells by bioluminescence imaging.     

An improved method for isolating Schwann cells from postnatal rat sciatic nerves

The major difficulty in Schwann cell (SC) purification is contamination by fibroblasts, which usually become the predominant cell type during SC enrichment in vitro. Current reported measures are mainly limited by either high cost or complicated procedures with low cell yields or purity. Our objectives have been to develop an efficient, easily applicable, rapid method to obtain highly purified SC from the sciatic nerve of newborn rats. The method involves two rounds of purification to eliminate fibroblasts with the novel combined use of cytosine-B-arabinoside hydrochloride (Ara-C) action and differential cell detachment. Cultured cells were first treated with Ara-C for 24 h. The medium was replaced with the growth medium containing 20 ng/ml human heregulin1-β1 extracellular domain (HRG1-β1 ECD). After another 48 h in culture, the cells were treated with 0.05% trypsin, following which SCs, but not fibroblasts, were easily detached from the dishes. The advantage of this method is that the two steps can eliminate the fibroblasts complementarily. Ara-C eliminates most of the fibroblasts growing among SCs, whereas the differential cell detachment technique removes the remainder growing under or interacting with the SC layer. A purity of more than 99% SCs has been obtained, as confirmed by cell morphology and immunostaining. The purified SCs have a spindle-shaped, bipolar, and sometimes tripolar morphology, align in fascicles, and express S-100. The whole procedure takes about 10 days from primary culture to the purified SCs growing to confluence (only half the time reported previously). This protocol provides an alternative method for investigating peripheral nerve regeneration and potentially could be used to produce enough SCs to construct artificial nerve scaffolds in vitro. This work was supported by Tsinghua-Yue-Yuen Medical Sciences Fund, the National Natural Science Foundation of China (contract grant numbers: 30670528, 30700848, 30772443), Beijing Municipal Science & Technology Commission (BMSTC, contract grant number: H060920050430), National Basic Research Program of China (also called the 973 Program, contract grant number: 2005CB623905), and the National Natural Science Foundation of Beijing (contract grant number: 7082090).     

Genetic Manipulation of Cerebellar Granule Neurons In Vitro and In Vivo to Study Neuronal Morphology and Migration

Developmental events in the brain including neuronal morphogenesis and migration are highly orchestrated processes. In vitro and in vivo analyses allow for an in-depth characterization to identify pathways involved in these events. Cerebellar granule neurons (CGNs) that are derived from the developing cerebellum are an ideal model system that allows for morphological analyses. Here, we describe a method of how to genetically manipulate CGNs and how to study axono- and dendritogenesis of individual neurons. With this method the effects of RNA interference, overexpression or small molecules can be compared to control neurons. In addition, the rodent cerebellar cortex is an easily accessible in vivo system owing to its predominant postnatal development. We also present an in vivo electroporation technique to genetically manipulate the developing cerebella and describe subsequent cerebellar analyses to assess neuronal morphology and migration.