Neuronal co-expression of EGFP and beta-galactosidase in mice causes neuropathology and premature death

GFP Transfection Alters Protein Expression Patterns in Prostate Cancer Cells: A Proteomic Study

PURPOSE

Green Fluorescent Protein is widely used as a cellular marker tool, but its potential influence on cells has been questioned. Although the potential off-target effects of GFP on tumor cells have been studied to some extent, the findings at the molecular level are insufficient to explain the effect of GFP expression on the tumorigenic capacity of cancer cells. Here, we aimed to investigate the effect of GFP expression on the tumorigenicity of PC3 prostate cancer cells.

METHODS

Using GFP-expressing and wild-type PC-3 cells, xenograft models were generated in athymic BALB/C mice. To identify differentially expressed proteins, the change in cells proteome was investigated by label-free quantification with nano-high performance liquid chromatography to tandem mass spectrometry (nHPLC-MS/MS). Proteins that showed significantly altered expression levels were evaluated using the bioinformatics tools.

RESULTS

Unlike the wild-type PC-3 cells, GFP-expressing cells failed to develop tumor. Comparative proteome analysis of GFP-expressing cells with WT PC-3 cells revealed a total of 216 differentially regulated proteins, of which 98 were upregulated and 117 were downregulated.

CONCLUSION

Upon GFP expression, differential changes in several pathways including the immune system, translational machinery, energy metabolism, elements of cytoskeletal and VEGF signaling pathway were observed. Therefore, care should be taken into account to prevent reporting deceitful mechanisms generated from studies utilizing GFP.

ESIPT Nano-Emitter to Probe Lysosome Biogenesis in Live Cells

Endosome-lysosome fusion and endo-lysosome fission-mediated lysosome biogenesis are crucial in regulating cellular health, and their dysregulation signifies disease. Tracking such intricate events with minimal disturbance remains elusive due to the scarcity of single-component synthetic probes capable of distinctly and simultaneously labeling both endosomes and lysosomes. Here, an amphiphilic π-conjugated imine probe is designed that forms micellar self-assemblies in water, called Nano-emitter, which distinctly and simultaneously labels endosomes and lysosomes upon monochromatic-wavelength excitation. ESIPT (Excited State Intramolecular Proton Transfer) active Nano-emitter shows red fluorescence at endosomal pH. Its hydrolysis to fluorescent amine, PEG-Naph at lysosomal pH illuminated lysosomes fluorescent green, with both imine and amine forms excitable using a 405 nm confocal laser. The two-color labeling of endosomes and lysosomes enabled tracking of their fusion and lysosome-biogenesis processes in living cells. Using multiplexed time-lapse imaging with Nano-emitter and anti-cancer drug doxorubicin, the role of these processes is investigated in lysosome-mediated doxorubicin sequestration in MCF-7 cells. The results show that endosomes as well as endo-lysosomes also sequestered doxorubicin apart from lysosomes. Interestingly, doxorubicin-sequestered endo-lysosomes underwent fission and generated more doxorubicin-sequestered lysosomes, preventing the drug's nuclear localization. Such versatile probes can enhance the understanding of drug sequestration and foster therapeutic strategies.

Toxicity of nuclear-localized GFP in reporter mice

Various techniques using fluorescent reporter probes have been developed, such as GFP transgenic mouse lines that are used to detect spatial-temporal expression levels of genes. Although GFP expression is largely considered non-toxic, recent reports have indicated that under certain conditions GFP can display cellular toxicity. We hereby report the nuclear toxicity of H2B-GFP using a K14 specific Tet-on reporter mouse system. Using this system, GFP accumulates in the nucleus of all K14 expressing cells, such as the ocular surface epithelia and ocular adnexa. Expression of high levels of nuclear GFP during embryonic stages led to an eye open-at-birth (EOB) phenotype and abnormal ocular adnexa development and during adult and aging stages showed notable toxicity to ocular tissues. Other tissues, such as skin, also presented multiple defects associated with H2B-GFP expression. This toxicity was found to be concentration dependent, with homozygous mice presenting extremely high toxicity, while heterozygous mice presented limited toxicity. Upon induction, the accumulation of H2B-GFP in the nucleus of homozygous mice led to apoptosis within 2 weeks. This study therefore shows that although the use of nuclear GFP reporter mice is a valuable tool, at high levels, nuclear GFP can be toxic, leading to cell death and affecting tissue function.

Transduction Efficiency of Zika Virus E Protein Pseudotyped HIV-1gfp and Its Oncolytic Activity Tested in Primary Glioblastoma Cell Cultures

The development of new tools against glioblastoma multiforme (GBM), the most aggressive and common cancer originating in the brain, remains of utmost importance. Lentiviral vectors (LVs) are among the tools of future concepts, and pseudotyping offers the possibility of tailoring LVs to efficiently transduce and inactivate GBM tumor cells. Zika virus (ZIKV) has a specificity for GBM cells, leaving healthy brain cells unharmed, which makes it a prime candidate for the development of LVs with a ZIKV coat. Here, primary GBM cell cultures were transduced with different LVs encased with ZIKV envelope variants. LVs were generated by using the pNLgfpAM plasmid, which produces the lentiviral, HIV-1-based, core particle with GFP (green fluorescent protein) as a reporter (HIVgfp). Using five different GBM primary cell cultures and three laboratory-adapted GBM cell lines, we showed that ZIKV/HIVgfp achieved a 4-6 times higher transduction efficiency compared to the commonly used VSV/HIVgfp. Transduced GBM cell cultures were monitored over a period of 9 days to identify GFP+ cells to study the oncolytic effect due to ZIKV/HIVgfp entry. Tests of GBM tumor specificity by transduction of GBM tumor and normal brain cells showed a high specificity for GBM cells.

EYFP fusions to HD-Zip IV transcription factors enhance their stability and lead to phenotypic changes in Arabidopsis

Green fluorescent protein (GFP) and its derivatives are extensively used for labeling cells, monitoring gene expression and/or tracking the localization or interactions of proteins. Previous reports of detrimental effects of fluorescent protein (FP) expression include cytotoxicity and interference with fusion protein function or localization. Only a few studies have documented the fluorescent tag-specific effects in plants. Here, we show that placing an enhanced yellow FP (EYFP) tag on the amino-terminus of GLABRA2 (GL2) and PROTODERMAL FACTOR2 (PDF2), two developmentally important HD-Zip IV transcription factors from Arabidopsis, enhances their protein stability. Additionally, expression of EYFP:GL2 not only rescued the gl2 null mutant but also resulted in the abnormal development of abaxially curled leaves associated with EYFP-tag induced GL2 overexpression. Our study raises concerns on the use of FPs regarding their effects on the native properties of target proteins as well as biological consequences of fusion protein expression on morphology.

ASD/OCD-Linked Protocadherin-10 Regulates Synapse, But Not Axon, Development in the Amygdala and Contributes to Fear- and Anxiety-Related Behaviors

The Protocadherin-10 (PCDH10) gene is associated with autism spectrum disorder (ASD), obsessive-compulsive disorder (OCD), and major depression (MD). The PCDH10 protein is a homophilic cell adhesion molecule that belongs to the δ2-protocadherin family. PCDH10 is highly expressed in the developing brain, especially in the basolateral nucleus of the amygdala (BLA). However, the role of PCDH10 in vivo has been debatable: one paper reported that a Pcdh10 mutant mouse line showed changes in axonal projections; however, another Pcdh10 mutant mouse line was reported to have failed to detect axonal phenotypes. Therefore, the actual roles of PCDH10 in the brain remain to be elucidated. We established a new Pcdh10 KO mouse line using the CRISPR/Cas9 system, without inserting gene cassettes to avoid nonspecific effects, examined the roles of PCDH10 in the brain, and studied the behavioral consequences of Pcdh10 inactivation. Here, we show that Pcdh10 KO mice do not show defects in axonal development. Instead, we find that Pcdh10 KO mice exhibit impaired development of excitatory synapses in the dorsal BLA. We further demonstrate that male Pcdh10 KO mice exhibit reduced anxiety-related behaviors, impaired fear conditioning, decreased stress-coping responses, and mildly impaired social recognition and communication. These results indicate that PCDH10 plays a critical role in excitatory synapse development, but not axon development, in the dorsal BLA and that PCDH10 regulates anxiety-related, fear-related, and stress-related behaviors. Our results reveal the roles of PCDH10 in the brain and its relationship to relevant psychiatric disorders such as ASD, OCD, and MD.SIGNIFICANCE STATEMENTProtocadherin-10 (PCDH10) encodes a cell adhesion molecule and is implicated in autism spectrum disorder (ASD), obsessive-compulsive disorder (OCD), and major depression (MD). PCDH10 is highly expressed in the basolateral nucleus of the amygdala (BLA). However, the phenotypes of previously published Pcdh10 mutant mice are debatable, and some are possibly because of the nonspecific effects of the LacZ/Neo cassette inserted in the mice. We have generated a new Pcdh10 mutant mouse line without the LacZ/Neo cassette. Using our new mouse line, we reveal the roles of PCDH10 for excitatory synapse development in the BLA. The mutant mice exhibit anxiety-related, fear-related, and stress-related behaviors, which are relevant to ASD, OCD, and MD, suggesting a possible treatment strategy for such psychiatric disorders.

GFP transgenic animals in biomedical research: a review of potential disadvantages

Green Fluorescent protein (GFP) transgenic animals are accepted tools for studying various physiological processes, including organ development and cell migration. However, several in vivo studies claimed that GFP may impair transgenic animals' health. Glomerulosclerosis was observed in transgenic mice and rabbits with ubiquitous reporter protein expression. Heart-specific GFP expression evoked dilated cardiomyopathy and altered cardiac function in transgenic mouse and zebrafish lines, respectively. Moreover, growth retardation and increased axon swelling were observed in GFP and yellow fluorescent protein (YFP) transgenic mice, respectively. This review will focus on the potential drawbacks of the applications of GFP transgenic animals in biomedical research.

Autophagy Caught in the Act: A Supramolecular FRET Pair Based on an Ultrastable Synthetic Host-Guest Complex Visualizes Autophagosome-Lysosome Fusion

A supramolecular FRET pair based on the ultrahigh binding affinity between cyanine 3 conjugated cucurbit[7]uril (CB[7]-Cy3) and cyanine 5 conjugated adamantylamine (AdA-Cy5) was exploited as a new synthetic tool for imaging cellular processes in live cells. Confocal laser scanning microscopy revealed that CB[7]-Cy3 and AdA-Cy5 were intracellularly translocated and accumulated in lysosomes and mitochondria, respectively. CB[7]-Cy3 and AdA-Cy5 then formed a host-guest complex, reported by a FRET signal, as a result of the fusion of lysosomes and mitochondria. This observation not only indicated that CB[7] forms a stable complex with AdA in a live cell, but also suggested that this FRET pair can visualize dynamic organelle fusion processes, such as those involved in the degradation of mitochondria through autophagy (mitophagy), by virtue of its small size, chemical stability, and ease of use.

Cellular GFP Toxicity and Immunogenicity: Potential Confounders in in Vivo Cell Tracking Experiments

Green Fluorescent protein (GFP), used as a cellular tag, provides researchers with a valuable method of measuring gene expression and cell tracking. However, there is evidence to suggest that the immunogenicity and cytotoxicity of GFP potentially confounds the interpretation of in vivo experimental data. Studies have shown that GFP expression can deteriorate over time as GFP tagged cells are prone to death. Therefore, the cells that were originally marked with GFP do not survive and cannot be accurately traced over time. This review will present current evidence for the immunogenicity and cytotoxicity of GFP in in vivo studies by characterizing these responses.

Placental-Specific Overexpression of sFlt-1 Alters Trophoblast Differentiation and Nutrient Transporter Expression in an IUGR Mouse Model

Since it is known that placental overexpression of the human anti-angiogenic molecule sFlt-1, the main candidate in the progression of preeclampsia, lead to intrauterine growth restriction (IUGR) in mice by lentiviral transduction of mouse blastocysts, we hypothesize that sFlt-1 influence placental morphology and physiology resulting in fetal IUGR. We therefore examined the effect of sFlt-1 on placental morphology and physiology at embryonic day 18.5 with histologic and morphometric analyses, transcript analyses, immunoblotting, and methylation studies. Interestingly, placental overexpression of sFlt-1 leads to IUGR in the fetus and results in lower placental weights. Moreover, we observed altered trophoblast differentiation with reduced expression of IGF2, resulting in a smaller placenta, a smaller labyrinth, and the loss of glycogen cells in the junctional zone. Changes in IGF2 are accompanied by small changes in its DNA methylation, whereas overall DNA methylation is unaffected. In addition, the expression of placental nutrient transporters, such as the glucose diffusion channel Cx26, is decreased. In contrast, the expression of the fatty acid transporter CD36 and the cholesterol transporter ABCA1 is significantly increased. In conclusion, placental sFlt-1 overexpression resulted in a reduction in the differentiation of the spongiotrophoblast into glycogen cells. These findings of a reduced exchange area of the labyrinth and glycogen stores, as well as decreased expression of glucose transporter, could contribute to the intrauterine growth restriction phenotype. All of these factors change the intrauterine availability of nutrients. Thus, we speculate that the alterations triggered by increased anti-angiogenesis strongly affect fetal outcome and programming. J. Cell. Biochem. 118: 1316-1329, 2017. © 2016 Wiley Periodicals, Inc.

Comparative assessment of fluorescent proteins for in vivo imaging in an animal model system

Fluorescent protein tags are fundamental tools used to visualize gene products and analyze their dynamics in vivo. Recent advances in genome editing have expedited the precise insertion of fluorescent protein tags into the genomes of diverse organisms. These advances expand the potential of in vivo imaging experiments and facilitate experimentation with new, bright, photostable fluorescent proteins. Most quantitative comparisons of the brightness and photostability of different fluorescent proteins have been made in vitro, removed from biological variables that govern their performance in cells or organisms. To address the gap, we quantitatively assessed fluorescent protein properties in vivo in an animal model system. We generated transgenic Caenorhabditis elegans strains expressing green, yellow, or red fluorescent proteins in embryos and imaged embryos expressing different fluorescent proteins under the same conditions for direct comparison. We found that mNeonGreen was not as bright in vivo as predicted based on in vitro data but is a better tag than GFP for specific kinds of experiments, and we report on optimal red fluorescent proteins. These results identify ideal fluorescent proteins for imaging in vivo in C. elegans embryos and suggest good candidate fluorescent proteins to test in other animal model systems for in vivo imaging experiments.

Hearing sensitivity differs between zebrafish lines used in auditory research

Zebrafish are increasingly used in auditory studies, in part due to the development of several transgenic lines that express hair cell-specific fluorescent proteins. However, it is largely unknown how transgene expression influences auditory phenotype. We previously observed reduced auditory sensitivity in adult Brn3c:mGFP transgenic zebrafish, which express membrane-bound green fluorescent protein (GFP) in sensory hair cells. Here, we examine the auditory sensitivity of zebrafish from multiple transgenic and background strains. We recorded auditory evoked potentials in adult animals and observed significantly higher auditory thresholds in three lines that express hair cell-specific GFP. There was no obvious correlation between hair cell density and auditory thresholds, suggesting that reduced sensitivity was not due to a reduction in hair cell density. FM1-43 uptake was reduced in Brn3c:mGFP fish but not in other lines, suggesting that a mechanotransduction defect may be responsible for the auditory phenotype in Brn3c animals, but that alternate mechanisms underlie the increased AEP thresholds in other lines. We found reduced prepulse inhibition (a measure of auditory-evoked behavior) in larval Brn3c animals, suggesting that auditory defects develop early in this line. We also found significant differences in auditory sensitivity between adults of different background strains, akin to strain differences observed in mouse models of auditory function. Our results suggest that researchers should exercise caution when selecting an appropriate zebrafish transgenic or background strain for auditory studies.

Sequential Adeno-Associated Viral Vector Serotype 9-Green Fluorescent Protein Gene Transfer Causes Massive Inflammation and Intense Immune Response in Rat Striatum

Green fluorescent protein (GFP) is a broadly used live cell reporter for gene transduction although side effects associated with GFP in gene transfer are reported. The present study was designed to systematically examine host responses, including inflammatory and immune responses, induced by persistent overexpression of the GFP gene mediated by adeno-associated viral vector serotype 9 (AAV9), and their effects on GFP gene transduction in rat striatum. Our results show that host responses against AAV9-GFP transduction, and GFP transgene expression in the striatum exhibited a temporal and dose-dependent pattern. Both muscular and striatal delivery of AAV9-GFP increased levels of inflammation and immune reactions against sequential AAV9-GFP transduction in the striatum, leading to reduced levels of GFP expression. We also observed that rat sera from sequential administrations of AAV9-GFP group had significantly higher levels of neutralizing antibody against AAV9 vectors when compared with the age-matched rats. As excessive GFP can trigger vigorous inflammation and intense immune response after GFP gene transduction, the use of GFP as a live cell marker protein should be deliberated, especially in repeated administration studies.

Immunohistochemical toolkit for tracking and quantifying xenotransplanted human stem cells

AIM

Biomarker-based tracking of human stem cells xenotransplanted into animal models is crucial for studying their fate in the field of cell therapy or tumor xenografting.

MATERIALS & METHODS

Using immunohistochemistry and in situ hybridization, we analyzed the expression of three human-specific biomarkers: Ku80, human mitochondria (hMito) and Alu.

RESULTS

We showed that Ku80, hMito and Alu biomarkers are broadly expressed in human tissues with no or low cross-reactivity toward rat, mouse or pig tissues. In vitro, we demonstrated that their expression is stable over time and does not change along the differentiation of human-derived induced pluripotent stem cells or human glial-restricted precursors. We tracked in vivo these cell populations after transplantation in rodent spinal cords using aforementioned biomarkers and human-specific antibodies detecting apoptotic, proliferating or neural-committed cells.

CONCLUSION

This study assesses the human-species specificity of Ku80, hMito and Alu, and proposes useful biomarkers for characterizing human stem cells in xenotransplantation paradigms.

Adenoviral overexpression of Lhx2 attenuates cell viability but does not preserve the stem cell like phenotype of hepatic stellate cells

Hepatic stellate cells (HSC) are well known initiators of hepatic fibrosis. After liver cell damage, HSC transdifferentiate into proliferative myofibroblasts, representing the major source of extracellular matrix in the fibrotic organ. Recent studies also demonstrate a role of HSC as progenitor or stem cell like cells in liver regeneration. Lhx2 is described as stem cell maintaining factor in different organs and as an inhibitory transcription factor in HSC activation. Here we examined whether a continuous expression of Lhx2 in HSC could attenuate their activation and whether Lhx2 could serve as a potential target for antifibrotic gene therapy. Therefore, we evaluated an adenoviral mediated overexpression of Lhx2 in primary HSC and investigated mRNA expression patterns by qRT-PCR as well as the activation status by different in vitro assays. HSC revealed a marked increase in activation markers like smooth muscle actin alpha (αSMA) and collagen 1α independent from adenoviral transduction. Lhx2 overexpression resulted in attenuated cell viability as shown by a slightly hampered migratory and contractile phenotype of HSC. Expression of stem cell factors or signaling components was also unaffected by Lhx2. Summarizing these results, we found no antifibrotic or stem cell maintaining effect of Lhx2 overexpression in primary HSC.

Probing the impact of GFP tagging on Robo1-heparin interaction

Green fluorescent proteins (GFPs) and their derivatives are widely used as markers to visualize cells, protein localizations in in vitro and in vivo studies. The use of GFP fusion protein for visualization is generally thought to have negligible effects on cellular function. However, a number of reports suggest that the use of GFP may impact the biological activity of these proteins. Heparin is a glycosaminoglycan (GAG) that interacts with a number of proteins mediating diverse patho-physiological processes. In the heparin-based interactome studies, heparin-binding proteins are often prepared as GFP fusion proteins. In this report, we use surface plasmon resonance (SPR) spectroscopy to study the impact of the GFP tagging on the binding interaction between heparin and a heparin-binding protein, the Roundabout homolog 1 (Robo1). SPR reveals that heparin binds with higher affinity to Robo1 than GFP-tagged Robo1 and through a different kinetic mechanism. A conformational change is observed in the heparin-Robo1 interaction, but not in the heparin-Robo1-GFP interaction. Furthermore the GFP-tagged Robo1 requires a shorter (hexasaccharide) than the tag-free Robo1 (octadecasaccharide). These data demonstrate that GFP tagging can reduce the binding affinity of Robo1 to heparin and hinder heparin binding-induced Robo1 conformation change.

Cellular therapeutics delivery to the spinal cord: technical considerations for clinical application

Current literature demonstrates the efficacy of cell-based therapeutics in small animal models of varied spinal cord diseases. However, logistic challenges remain towards development of an optimized delivery approach to the human spinal cord. Clinical trials utilize a variety of methods to achieve this aim. In this article, the authors review currently employed delivery methods, compare the merits of alternate delivery paradigms, introduce their implementation in completed and ongoing clinical trials, and discuss promising near-term advances in image-guided delivery and in vivo graft tracking.

Green fluorescent protein expression triggers proteome changes in breast cancer cells

Green fluorescent protein (GFP) is the most commonly used reporter of expression in cell biology despite evidence that it affects the cell physiology. The molecular mechanism of GFP-associated modifications has been largely unexplored. In this paper we investigated the proteome modifications following stable expression of GFP in breast cancer cells (MDA-MB-231). A combination of three different proteome analysis methods (2-DE, iTRAQ, label-free) was used to maximise proteome coverage. We found that GFP expression induces changes in expression of proteins that are associated with protein folding, cytoskeletal organisation and cellular immune response. In view of these findings, the use of GFP as a cell reporter should be carefully monitored.

Enhanced green fluorescent protein transgenic expression in vivo is not biologically inert

Enhanced green fluorescent protein (EGFP) is a widely used biological reporter. However, the effects of EGFP expression in vivo are still unclear. To investigate the effects of EGFP transgenic expression in vivo, we employed an NMR-based metabonomics method to analyze the metabonome of EGFP transgenic mice. The results show that the metabonomes of urine, liver, and kidney of the EGFP transgenic mice are different from their wild-type counterparts. The EGFP mice expressed high levels of urinary 3-ureidopropionate, which is due to the down-regulated transcriptional level of β-ureidopropionase. The expression of EGFP in vivo also affects other metabolic pathways, including nucleic acid metabolism, energy utilization, and amino acids catabolism. These findings indicate that EGFP transgenic expression is not as inert as has been considered. Our investigation provides a holistic view on the effect of EGFP expression in vivo, which is useful when EGFP is employed as a functional biological indicator. Our work also highlights the potential of a metabonomics strategy in studying the association between molecular phenotypes and gene function.

Dose-dependent Toxicity of Humanized Renilla reniformis GFP (hrGFP) Limits Its Utility as a Reporter Gene in Mouse Muscle

Gene therapy has historically focused on delivering protein-coding genes to target cells or tissues using a variety of vectors. In recent years, the field has expanded to include gene-silencing strategies involving delivery of noncoding inhibitory RNAs, such as short hairpin RNAs or microRNAs (miRNAs). Often called RNA interference (RNAi) triggers, these small inhibitory RNAs are difficult or impossible to visualize in living cells or tissues. To circumvent this detection problem and ensure efficient delivery in preclinical studies, vectors can be engineered to coexpress a fluorescent reporter gene to serve as a marker of transduction. In this study, we set out to optimize adeno-associated viral (AAV) vectors capable of delivering engineered miRNAs and green fluorescent protein (GFP) reporter genes to skeletal muscle. Although the more broadly utilized enhanced GFP (eGFP) gene derived from the jellyfish, Aequorea victoria was a conventional choice, we were concerned about some previous studies suggesting this protein was myotoxic. We thus opted to test vectors carrying the humanized Renilla reniformis-derived GFP (hrGFP) gene, which has not seen as extensive usage as eGFP but was purported to be a safer and less cytotoxic alternative. Employing AAV6 vector dosages typically used in preclinical gene transfer studies (3×10¹⁰ –1 × 10¹¹ particles), we found that hrGFP caused dose-dependent myopathy when delivered to wild-type (wt) mouse muscle, whereas identical titers of AAV6 carrying eGFP were relatively benign. Dose de-escalation at or below 8 × 10⁹ AAV particles effectively reduced or eliminated hrGFP-associated myotoxicity, but also had dampening effects on green fluorescence and miRNA-mediated gene silencing in whole muscles. We conclude that hrGFP is impractical for use as a transduction marker in preclinical, AAV-based RNA interference therapy studies where adult mouse muscle is the target organ. Moreover, our data support that eGFP is superior to hrGFP as a reporter gene in mouse muscle. These results may impact the design of future preclinical gene therapy studies targeting muscles and non-muscle tissues alike.

Construction of multiple shRNAs expression vector that inhibits FUT1 gene expression and production of the transgenic SCNT embryos in vitro

Enterotoxigenic Escherichia coli F18 is a major pathogen that causes postweaning diarrhoea and edema disease in piglets. The alpha(1,2)-fucosyltransferase (FUT1) gene has been identified as an ideal candidate gene for controlling the expression of the receptor for ECF18 bacteria. Therefore, the use of RNA interference (RNAi) to study the function of the FUT1 gene and to produce FUT1 knockdown transgenic pig would be highly beneficial. We developed an effective strategy for the expression of multiple small hairpin RNA simultaneously using multiple RNA polymerase III (hU6, hH1, mU6 and h7SK) promoters in a single vector to knockdown the FUT1 gene. Stable FUT1 knockdown transgenic fibroblast lines were generated by transfecting porcine fetal fibroblasts with the constructed vectors. Real-time RT-PCR indicated that the mRNA level of FUT1 in the transgenic fibroblast lines was significantly lower than that in the control, as much as 29 %. Finally, we successfully obtained transgenic SCNT porcine embryos. Overall, the results demonstrated that this vector-based RNAi expression system is an efficient approach to knockdown FUT1 gene expression in porcine fetal fibroblast cells, which could thereby provide donor cells for somatic cell nuclear cloning and the potential production of a marker-free transgenic pig resistant to F18 related diseases. Furthermore, it also provides strong evidence that this approach could be useful both in the production of transgenic livestock resistant to disease, and in the development of effective strategies for the suppression of gene expression in clinical gene therapy.

Long-distance axonal regeneration induced by CNTF gene transfer is impaired by axonal misguidance in the injured adult optic nerve

The optic nerve crush injury is a well-accepted model to study the mechanisms of axonal regeneration after trauma in the CNS. The infection of retinal ganglion cells (RGCs) with an adeno-associated virus serotype 2 - ciliary neurotrophic factor (AAV2.CNTF) was previously shown to stimulate axonal regeneration. However, the transfection of axotomized neurons themselves may not be optimal to promote full axonal regeneration in the visual system. Here, we show that the release of CNTF by glial cells is a very powerful stimulus for optic fiber regeneration and RGC survival after optic nerve crush. After 8 weeks, long-distance regeneration of severed optic axons was induced by CNTF until and beyond the optic chiasm. Regenerated axons stayed for at least 6 months in the damaged optic nerve. Strikingly, however, many regenerated axons showed one or several sharp U-turns along their course, suggesting that guidance cues are missing and that long-distance axonal regeneration is limited by the return of the growing axons toward the retina. Even more surprisingly, massive axonal sprouting was observed within the eye, forming a dense plexus of neurites at the inner surface of the retina. These results indicate that massive stimulation of the neuronal growth program can lead to aberrant growth; the absence of local regulatory and guidance factors in the adult, injured optic nerve may therefore represent a major, so far underestimated obstacle to successful axon regeneration.

Redifferentiation of expanded human pancreatic β-cell-derived cells by inhibition of the NOTCH pathway

In vitro expansion of β-cells from adult human pancreatic islets would overcome donor β-cell shortage for cell replacement therapy for diabetes. Using a β-cell-specific labeling system we have shown that β-cell expansion is accompanied by dedifferentiation resembling epithelial-mesenchymal transition and loss of insulin expression. Epigenetic analyses indicate that key β-cell genes maintain open chromatin structure in expanded β-cell-derived (BCD) cells, although they are not transcribed. In the developing pancreas important cell-fate decisions are regulated by NOTCH receptors, which signal through the Hairy and Enhancer of Split 1 (HES1) transcription regulator. We have reported that BCD cell dedifferentiation and proliferation in vitro correlate with reactivation of the NOTCH pathway. Inhibition of HES1 expression using shRNA during culture initiation results in reduced β-cell replication and dedifferentiation, suggesting that HES1 inhibition may also affect BCD cell redifferentiation following expansion. Here, we used HES1 shRNA to down-regulate HES1 expression in expanded human BCD cells, showing that HES1 inhibition is sufficient to induce BCD cell redifferentiation, as manifested by a significant increase in insulin expression. Combined treatment with HES1 shRNA, cell aggregation in serum-free medium, and a mixture of soluble factors further stimulated the redifferentiation of BCD cells. In vivo analyses demonstrated the ability of the redifferentiated cells to replace β-cell function in hyperglycemic immunodeficient mice. These findings demonstrate the redifferentiation potential of ex vivo expanded BCD cells and the reproducible differentiating effect of HES1 inhibition in these cells.

Optogenetic reporters: Fluorescent protein-based genetically encoded indicators of signaling and metabolism in the brain

Fluorescent protein technology has evolved to include genetically encoded biosensors that can monitor levels of ions, metabolites, and enzyme activities as well as protein conformation and even membrane voltage. They are well suited to live-cell microscopy and quantitative analysis, and they can be used in multiple imaging modes, including one- or two-photon fluorescence intensity or lifetime microscopy. Although not nearly complete, there now exists a substantial set of genetically encoded reporters that can be used to monitor many aspects of neuronal and glial biology, and these biosensors can be used to visualize synaptic transmission and activity-dependent signaling in vitro and in vivo. In this review, we present an overview of design strategies for engineering biosensors, including sensor designs using circularly permuted fluorescent proteins and using fluorescence resonance energy transfer between fluorescent proteins. We also provide examples of indicators that sense small ions (e.g., pH, chloride, zinc), metabolites (e.g., glutamate, glucose, ATP, cAMP, lipid metabolites), signaling pathways (e.g., G protein-coupled receptors, Rho GTPases), enzyme activities (e.g., protein kinase A, caspases), and reactive species. We focus on examples where these genetically encoded indicators have been applied to brain-related studies and used with live-cell fluorescence microscopy.

Unilateral entorhinal denervation leads to long-lasting dendritic alterations of mouse hippocampal granule cells

Following brain injury, neurons efferently connected from the lesion site are denervated and remodel their dendritic tree. Denervation-induced dendritic reorganization of granule cells was investigated in the dentate gyrus of the Thy1-GFP mouse. After mechanical transection of the perforant path, single granule cells were 3D-reconstructed at different time points post-lesion (3d, 7d, 10d, 30 d, 90 d and 180 d) and their soma size, total dendritic length, number of dendritic segments and dendritic branch orders were studied. Changes in spine densities were determined using 3D-analysis of individual dendritic segments. Following entorhinal denervation the granule cell arbor progressively atrophied until 90 d post-lesion (reduction of total dendritic length to ~50% of control). Dendritic alterations occurred selectively in the denervated outer molecular layer, where a loss of distal dendritic segments and a reduction of mean segment length were seen. At 180 d post-lesion total dendritic length partially recovered (~70% of control). This recovery appeared to be the result of a re-elongation of surviving dendrites rather than dendritic re-branching, since the number of dendritic segments did not recover. In contrast to the protracted dendritic changes, spine density changes followed a faster time course. In the denervated layer spine densities dropped to ~65% of control values and fully recovered by 30 d post-lesion. We conclude that entorhinal denervation in mouse causes protracted and long-term structural alterations of the granule cell dendritic tree. Spontaneously occurring reinnervation processes, such as the sprouting of surviving afferent fibers, are insufficient to maintain the granule cell dendritic arbor.

Degenerative abnormalities in transgenic neocortical neuropeptide Y interneurons expressing tau-green fluorescent protein

The introduction of a reporter gene into bacterial artificial chromosome (BAC) constructs allows a rapid identification of the cell type expressing the gene of interest. Here we used BAC transgenic mice expressing a tau-sapphire green fluorescent protein (GFP) under the transcriptional control of the neuropeptide Y (NPY) genomic sequence to characterize morphological and electrophysiological properties of NPY-GFP interneurons of the mouse juvenile primary somatosensory cortex. Electrophysiological whole-cell recordings and biocytin injections were performed to allow the morphological reconstruction of the recorded neurons in three dimensions. Ninety-six recorded NPY-GFP interneurons were compared with 39 wild-type (WT) NPY interneurons, from which 23 and 19 were reconstructed, respectively. We observed that 91% of the reconstructed NPY-GFP interneurons had developed an atypical axonal swelling from which emerge numerous ramifications. These abnormalities were very heterogeneous in shape and size. They were immunoreactive for the microtubule-associated protein tau and the lysosomal-associated membrane protein 1 (LAMP1). Moreover, an electron microscopic analysis revealed the accumulation of numerous autophagic and lysosomal vacuoles in swollen axons. Morphological analyses of NPY-GFP interneurons also indicated that their somata were smaller, their entire dendritic tree was thickened and presented a restricted spatial distribution in comparison with WT NPY interneurons. Finally, the morphological defects observed in NPY-GFP interneurons appeared to be associated with alterations of their electrophysiological intrinsic properties. Altogether, these results demonstrate that NPY-GFP interneurons developed dystrophic axonal swellings and severe morphological and electrophysiological defects that could be due to the overexpression of tau-coupled reporter constructs.

3D-reconstruction and functional properties of GFP-positive and GFP-negative granule cells in the fascia dentata of the Thy1-GFP mouse

Granule cells of the mouse fascia dentata are widely used in studies on neuronal development and plasticity. In contrast to the rat, however, high-resolution morphometric data on these cells are scarce. Thus, we have analyzed granule cells in the fascia dentata of the adult Thy1-GFP mouse (C57BL/6 background). In this mouse line, single neurons in the granule cell layer are GFP-labeled, making them amenable to high-resolution 3D-reconstruction. First, calbindin or parvalbumin-immunofluorescence was used to identify GFP-positive cells as granule cells. Second, the dorsal-ventral distribution of GFP-positive granule cells was studied: In the dorsal part of the fascia dentata 11% and in the ventral part 15% of all granule cells were GFP-positive. Third, GFP-positive and GFP-negative granule cells were compared using intracellular dye-filling (fixed slice technique) and patch-clamp recordings; no differences were observed between the cells. Finally, GFP-positive granule cells (dorsal and ventral fascia dentata) were imaged at high resolution with a confocal microscope, 3D-reconstructed in their entirety and analyzed for soma size, total dendritic length, number of segments, total number of spines and spine density. Sholl analysis revealed that dendritic complexity of granule cells is maximal 150-200 mum from the soma. Granule cells located in the ventral part of the hippocampus revealed a greater degree of dendritic complexity compared to cells in the dorsal part. Taken together, this study provides morphometric data on granule cells of mice bred on a C57BL/6 background and establishes the Thy1-GFP mouse as a tool to study granule cell neurobiology.

Late onset distal axonal swelling in YFP-H transgenic mice

Axonal swellings, or spheroids, are a feature of central nervous system (CNS) axon degeneration during normal aging and in many disorders. The direct cause and mechanism are unknown. The use of transgenic mouse line YFP-H, which expresses yellow-fluorescent protein (YFP) in a subset of neurons, greatly facilitates longitudinal imaging and live imaging of axonal swellings, but it has not been established whether long-term expression of YFP itself contributes to axonal swelling. Using conventional methods to compare YFP-H mice with their YFP negative littermates, we found an age-related increase in swellings in discrete CNS regions in both genotypes, but the presence of YFP caused significantly more swellings in mice aged 8 months or over. Increased swelling was found in gracile tract, gracile nucleus and dorsal roots but not in lateral columns, olfactory bulb, motor cortex, ventral roots or peripheral nerve. Thus, long-term expression of YFP accelerates age-related axonal swelling in some axons and data reliant on the presence of YFP in these CNS regions in older animals needs to be interpreted carefully. The ability of a foreign protein to exacerbate age-related axon pathology is an important clue to the mechanisms by which such pathology can arise.

Green fluorescent protein impairs actin-myosin interactions by binding to the actin-binding site of myosin

Green fluorescent proteins (GFP) are widely used in biology for tracking purposes. Although expression of GFP is considered to be innocuous for the cells, deleterious effects have been reported. We recently demonstrated that expression of eGFP in muscle impairs its contractile properties (Agbulut, O., Coirault, C., Niederlander, N., Huet, A., Vicart, P., Hagege, A., Puceat, M., and Menasche, P. (2006) Nat. Meth. 3, 331). This prompted us to identify the molecular mechanisms linking eGFP expression to contractile dysfunction and, particularly, to test the hypothesis that eGFP could inhibit actin-myosin interactions. Therefore, we assessed the cellular, mechanical, enzymatic, biochemical, and structural properties of myosin in the presence of eGFP and F-actin. In vitro motility assays, the maximum actin-activated ATPase rate (V(max)) and the associated constant of myosin for actin (K(m)) were determined at 1:0.5, 1:1, and 1:3 myosin:eGFP molar ratios. At a myosin:eGFP ratio of 1:0.5, there was a nearly 10-fold elevation of K(m). As eGFP concentration increased relative to myosin, the percentage of moving filaments, the myosin-based velocity, and V(max) significantly decreased compared with controls. Moreover, myosin co-precipitated with eGFP. Crystal structures of myosin, actin, and GFP indicated that GFP and actin exhibited similar electrostatic surface patterns and the ClusPro docking model showed that GFP bound preferentially to the myosin head and especially to the actin-binding site. In conclusion, our data demonstrate that expression of eGFP in muscle resulted in the binding of eGFP to myosin, thereby disturbing the actin-myosin interaction and in turn the contractile function of the transduced cells. This potential adverse effect of eGFP should be kept in mind when using this marker to track cells following transplantation.

The dark side of EGFP: defective polyubiquitination

Enhanced Green Fluorescent Protein (EGFP) is the most commonly used live cell reporter despite a number of conflicting reports that it can affect cell physiology. Thus far, the precise mechanism of GFP-associated defects remained unclear. Here we demonstrate that EGFP and EGFP fusion proteins inhibit polyubiquitination, a posttranslational modification that controls a wide variety of cellular processes, like activation of kinase signalling or protein degradation by the proteasome. As a consequence, the NF-kappaB and JNK signalling pathways are less responsive to activation, and the stability of the p53 tumour suppressor is enhanced in cell lines and in vivo. In view of the emerging role of polyubiquitination in the regulation of numerous cellular processes, the use of EGFP as a live cell reporter should be carefully considered.

Efficient neuronal gene transfer with AAV8 leads to neurotoxic levels of tau or green fluorescent proteins

Adeno-associated virus (AAV) serotype 8 appears to be the strongest of the natural serotypes reported to date for gene transfer in liver and muscle. In this study, we evaluated AAV8 in the brain by several methods, including biophotonic imaging of green fluorescent protein (GFP). In the adult rat hippocampus, levels of GFP expressed were clearly greater with AAV8 than with AAV2 or AAV5 by Western blot and biophotonic imaging and slightly but significantly greater than AAV1 by Western blot. In the substantia nigra, the GFP expression conferred by AAV8 was toxic to dopamine neurons, although toxicity could be avoided with dose titration. At the low dose at which there was no GFP toxicity from the GFP vector, another AAV8 vector for a disease-related (P301L) form of the microtubule-associated protein tau caused a 78% loss of dopamine neurons and significant amphetamine-stimulated rotational behavior. The AAV8 tau vector-induced cell loss was greater than that from AAV2 or AAV5 tau vectors, demonstrating that the increased gene transfer was functional. While the toxicity observed with GFP expression warrants great caution, the efficient AAV8 is promising for animal models of neurodegenerative diseases and potentially as well for gene therapy of brain diseases.