The X-gal caution in neural transplantation studies

Grb7 knockout mice develop normally but litters born to knockout females fail to thrive

BACKGROUND

Growth factor receptor-bound 7 (Grb7) is an adaptor protein involved in signal transduction downstream of multiple receptor tyrosine kinases, including ERBB, FGFR, and PDGFR pathways. Experimental studies have implicated Grb7 in regulating cell proliferation, survival, migration, and invasion through its large repertoire of protein-protein interactions.

RESULTS

Here, we describe the generation and characterization of a Grb7 knockout mouse. These mice are viable and fertile. A lacZ knock-in reporter was used to visualize Grb7 promoter activity patterns in adult tissues, indicating widespread Grb7 expression in glandular epithelium, the central nervous system, and other tissues. The sole defect observed in these animals was a failure of Grb7 knockout females to successfully raise pups to weaning age, a phenotype that was independent of both paternal and pup genotypes.

CONCLUSIONS

These data suggest a regulatory role for Grb7 in mammary lactational physiology.

Recent Advances of Molecular Optical Probes in Imaging of β-Galactosidase

β-Galactosidase (β-Gal), as a lysosomal hydrolytic enzyme, plays an important physiological role in catalyzing the hydrolysis of glycosidic bonds which convert lactose into galactose. Moreover, upregulation of β-Gal is often correlated with the occurrence of primary ovarian cancers and cell senescence. Thereby, detection of β-Gal activity is relevant to cancer diagnosis. Optical imaging possesses high spatial and temporal resolution, high sensitivity, and real-time imaging capability. These properties are beneficial for the detection of β-Gal in living systems. This Review summarizes the recent progress in development of molecular optical probes for near-infrared fluorescence (NIRF), bioluminescence (BL), chemiluminescence (CL), or photoacoustic (PA) imaging of β-Gal in biological systems. The challenges and opportunities in the probe design for detection of β-Gal are also discussed.

Tracing Gene Expression Through Detection of β-galactosidase Activity in Whole Mouse Embryos

The Escherichia coli LacZ gene, encoding β-galactosidase, is largely used as a reporter for gene expression and as a tracer in cell lineage studies. The classical histochemical reaction is based on the hydrolysis of the substrate X-gal in combination with ferric and ferrous ions, which produces an insoluble blue precipitate that is easy to visualize. Therefore, β-galactosidase activity serves as a marker for the expression pattern of the gene of interest as the development proceeds. Here we describe the standard protocol for the detection of β-galactosidase activity in early whole mouse embryos and the subsequent method for paraffin sectioning and counterstaining. Additionally, a procedure for clarifying whole embryos is provided to better visualize X-gal staining in deeper regions of the embryo. Consistent results are obtained by performing this procedure, although optimization of reaction conditions is needed to minimize background activity. Limitations in the assay should be also considered, particularly regarding the size of the embryo in whole mount staining. Our protocol provides a sensitive and a reliable method for β-galactosidase detection during the mouse development that can be further applied to the cryostat sections as well as whole organs. Thus, the dynamic gene expression patterns throughout development can be easily analyzed by using this protocol in whole embryos, but also detailed expression at the cellular level can be assessed after paraffin sectioning.

Generation of transgenic mouse line with prostate-specific expression of codon-improved Cre recombinase

Background

Genetically engineered mouse models are useful tools to decipher molecular mechanisms of diseases. As for prostates, a rat probasin promoter has been widely used to drive prostate-specific gene expression. To optimize its codon usage to that of mammals, we used codon-improved Cre recombinase (iCre) for prostate-specific Cre-loxP recombination.

Materials and methods

We generated transgenic mice that express iCre driven by conventional probasin promoter in a prostate-specific manner (PB-iCre). Linearized PB-iCre transgene deoxyribonucleic acids (DNAs) were microinjected into pronuclei of fertilized mouse embryos. The integration of the transgene was confirmed by Southern blot analysis. A line of transgenic mice expressing a sufficient amount of iCre mRNA in its prostate was selected. To test recombinase activity of PB-iCre in vivo, its offspring was crossbred with Pten^flox/flox mice in which murine prostate adenocarcinoma is reported to occur upon excision of loxP-flanked regions.

Results

Eight founder animals were obtained, all of which showed germ line integration of PB-iCre transgene by Southern blot analysis. Among them, the prostate from only one line (line 58) expressed a sufficient amount of iCre mRNA. This line was crossbred with Pten^flox/flox mice to generate PB-iCre58/Pten^flox/flox. As a result, 12-week-old PB-iCre58/Pten^flox/flox mice presented with prostate adenocarcinoma that was histologically similar to human cribriform prostate cancer of Gleason grade 4.

Conclusions

We have successfully established a transgenic mouse line that expresses iCre in a prostate-specific manner.

Functional Stem Cell Integration into Neural Networks Assessed by Organotypic Slice Cultures

Re-formation or preservation of functional, electrically active neural networks has been proffered as one of the goals of stem cell-mediated neural therapeutics. A primary issue for a cell therapy approach is the formation of functional contacts between the implanted cells and the host tissue. Therefore, it is of fundamental interest to establish protocols that allow us to delineate a detailed time course of grafted stem cell survival, migration, differentiation, integration, and functional interaction with the host. One option for in vitro studies is to examine the integration of exogenous stem cells into an existing active neural network in ex vivo organotypic cultures. Organotypic cultures leave the structural integrity essentially intact while still allowing the microenvironment to be carefully controlled. This allows detailed studies over time of cellular responses and cell-cell interactions, which are not readily performed in vivo. This unit describes procedures for using organotypic slice cultures as ex vivo model systems for studying neural stem cell and embryonic stem cell engraftment and communication with CNS host tissue. © 2017 by John Wiley & Sons, Inc.

The Influence of Donor Age, Nerve Growth Factor, and Cografting with Drosophila Cells on Survival of Peripherally Grafted Embryonic or Fetal Rat Dorsal Root Ganglia

Previous studies have shown that embryonic rat and human dorsal root ganglion (DRG) cells survive grafting to the cavity of extirpated adult rat DRG. Furthermore, grafted human embryonic neurons were shown to send axons peripherally and into the spinal cord, where they establish functional synaptic connections. This study analyzed the survival of orthotopically allografted rat DRG cells from embryonic stages 15 (E15) and 20 (E20), and the influence on their survival of nerve growth factor (NGF). NGF was delivered to the DRG transplants either by pump infusion or by cotransplantation of cells from Drosophila melanogaster, transgenic for human NGF. Lumbar DRGs of adult rats were removed and a collection of E15 or E20 DRGs placed in the cavity. One month after grafting the total number of DRG cells in the grafts was counted. Differentiation of subpopulations of DRG cells was estimated by counting cells immunostained for calcitonin gene-related peptide (CGRP), Griffonia simplicifolia agglutinin isolectin B4 (GSA), or heavy neurofilament protein (antibody RT97). The results show: i) similar survival of E15 and E20 grafts, with great variability in the survival of different subpopulations in E15 transplants, but a more consistent distribution of different phenotypes in E20 transplants; ii) infusion of NGF for 2 weeks increases the survival of E15 transplants, but has a negative effect on E20 transplants; iii) Drosophila cells transfected with human NGF gene survive peripheral xenografting and have a positive effect on the survival of the GSA- and CGRP-positive populations in E15 and E20 transplants; iv) Drosophila cells without the human NGF gene increase cell survival in E20 transplants. These data suggest that i) the effect of NGF is dependent on the embryonic stage of the transplants, ii) age-dependent sensitivity to NGF influences graft survival, and iii) transgenic Drosophila cells can be cotransplanted with embryonic neural tissue to the mammalian peripheral nervous system with a positive effect on the survival of neural grafts.

A Comparison of Exogenous Labels for the Histological Identification of Transplanted Neural Stem Cells

The interpretation of cell transplantation experiments is often dependent on the presence of an exogenous label for the identification of implanted cells. The exogenous labels Hoechst 33342, 5-bromo-2'-deoxyuridine (BrdU), PKH26, and Qtracker were compared for their labeling efficiency, cellular effects, and reliability to identify a human neural stem cell (hNSC) line implanted intracerebrally into the rat brain. Hoechst 33342 (2 mg/ml) exhibited a delayed cytotoxicity that killed all cells within 7 days. This label was hence not progressed to in vivo studies. PKH26 (5 μM), Qtracker (15 nM), and BrdU (0.2 μM) labeled 100% of the cell population at day 1, although BrdU labeling declined by day 7. BrdU and Qtracker exerted effects on proliferation and differentiation. PKH26 reduced viability and proliferation at day 1, but this normalized by day 7. In an in vitro coculture assay, all labels transferred to unlabeled cells. After transplantation, the reliability of exogenous labels was assessed against the gold standard of a human-specific nuclear antigen (HNA) antibody. BrdU, PKH26, and Qtracker resulted in a very small proportion (<2%) of false positives, but a significant amount of false negatives (∼30%), with little change between 1 and 7 days. Exogenous labels can therefore be reliable to identify transplanted cells without exerting major cellular effects, but validation is required. The interpretation of cell transplantation experiments should be presented in the context of the label's limitations.

Overview and assessment of the histochemical methods and reagents for the detection of β-galactosidase activity in transgenic animals

Bacterial β-galactosidase is one of the most widely used reporter genes in experiments involving transgenic and knockout animals. In this review we discuss the current histochemical methods and available reagents to detect β-galactosidase activity. Different substrates are available, but the most commonly used is X-gal in combination with potassium ferri- and ferro-cyanide. The reaction produces a characteristic blue precipitate in the cells expressing β-galactosidase, and despite its efficiency in staining whole embryos, its detection on thin tissue sections is difficult. Salmon-gal is another substrate, which in combination with ferric and ferrous ions gives a reddish-pink precipitate. Its sensitivity for staining tissue sections is similar to that of X-gal. Combining X-gal or Salmon-gal with tetrazolium salts provides a faster and more sensitive reaction than traditional β-galactosidase histochemistry. Here, we compare the traditional β-galactosidase assay and the combination of X-gal or Salmon-gal with three tetrazolium salts: nitroblue tetrazolium, tetranitroblue tetrazolium and iodonitrotetrazolium. Based on an assessment of the sensitivity and specificity of the different combinations of substrates, we are proposing an optimized and enhanced method for β-galactosidase detection in histological sections of the transgenic mouse brain. Optimal staining was obtained with X-gal in combination with nitroblue tetrazolium, which provides a faster and more specific staining than the traditional X-gal combination with potassium ferri- and ferro-cyanide. We recommend the X-gal/nitroblue tetrazolium staining mixture as the first choice for the detection of β-galactosidase activity on histological sections. When faster results are needed, Salmon-gal/nitroblue tetrazolium should be considered as an alternative, while maintaining acceptable levels of noise.

Isolation and immortalization of MIP-GFP neurons from the hypothalamus

The mouse insulin I promoter (MIP) construct was developed to eliminate the promoter activity detected with the rat insulin II promoter in specific hypothalamic neurons that may have unintended effects on glucose and energy homeostasis in transgenic models. Thus, the specificity of this novel construct must be validated prior to the widespread availability of derived Cre models. Although limited validation efforts have indicated a lack of MIP activity within neuronal tissue, the global immunohistochemical methodology used may not be specific enough to rule out the possibility of specific populations of neurons with MIP activity. To investigate possible MIP activity within the hypothalamus, primary hypothalamic isolates from MIP-green fluorescent protein reporter mice were analyzed after fluorescent-activated cell sorting. Primary hypothalamic neurons isolated from the MIP-green fluorescent protein mice were immortalized. Characterization detected the presence of hypothalamic neuropeptide Y (NPY) and agouti-related peptide, involved in the control of energy homeostasis, as well as confirmed insulin responsiveness in the cell lines. Moreover, because insulin was demonstrated to differentially regulate NPY expression within these MIP neurons, the promoter construct may be active in multiple hypothalamic NPY/agouti-related peptide subpopulations with unique physiological functions. MIP transgenic animals may therefore face similar limitations seen previously with rat insulin II promoter-based models.

Functional stem cell integration assessed by organotypic slice cultures

Re-formation or preservation of functional, electrically active neural networks has been proffered as one of the goals of stem cell-mediated neural therapeutics. A primary issue for a cell therapy approach is the formation of functional contacts between the implanted cells and the host tissue. Therefore, it is of fundamental interest to establish protocols that allow us to delineate a detailed time course of grafted stem cell survival, migration, differentiation, integration, and functional interaction with the host. One option for in vitro studies is to examine the integration of exogenous stem cells into an existing active neuronal network in ex vivo organotypic cultures. Organotypic cultures leave the structural integrity essentially intact while still allowing the microenvironment to be carefully controlled. This allows detailed studies over time of cellular responses and cell-cell interactions, which are not readily performed in vivo. This unit describes procedures for using organotypic slice cultures as ex vivo model systems for studying neural stem cell and embryonic stem cell engraftment and communication with CNS host tissue.

β-Galactosidase staining of lacZ fusion proteins in whole tissue preparations

The lacZ gene product, β-galactosidase, has classically been used as a reporter of gene expression. β-Galactosidase activity can be detected using a chromogenic substrate, X-gal, which leaves an intense blue precipitate when cleaved by the enzyme. Insertion of the lacZ coding DNA targeted into a specific gene creates a β-galactosidase-tagged fusion protein that is expressed under the endogenous promoter. Analysis of the hybrid protein takes advantage of the chromogenic detection system, as the distribution and relative abundance of the expressed protein can be efficiently visualized.

What you always needed to know about electroporation based DNA vaccines

Vaccinations are increasingly used to fight infectious disease, and DNA vaccines offer considerable advantages, including broader possibilities for vaccination and lack of need for cold storage. It has been amply demonstrated, that electroporation augments uptake of DNA in both skin and muscle, and it is foreseen that future DNA vaccination may to a large extent be coupled with and dependent upon electroporation based delivery. Understanding the basic science of electroporation and exploiting knowledge obtained on optimization of DNA electrotransfer to muscle and skin, may greatly augment efforts on vaccine development. The purpose of this review is to give a succinct but comprehensive overview of electroporation as a delivery modality including electrotransfer to skin and muscle. As well, this review will speculate and discuss future uses for this powerful electrotransfer technology.

Improved methods for detection of β-galactosidase (lacZ) activity in hard tissue

The β-galactosidase gene (lacZ) of Escherichia coli is widely used as a reporter gene. The expression of lacZ can be detected by enzyme-based histochemical staining using chromogenic substrates such as 5-bromo-4-chloro-3-indolyl-β-D: -galactoside (X-gal). Because the enzymatic activity of lacZ is vulnerable to high temperatures and acid treatment for demineralization, detection of lacZ on paraffinized sections is difficult, especially for hard tissues, which require demineralization before sectioning in paraffin. To circumvent this problem, whole-mount X-gal staining before sectioning is performed. However, detection of lacZ activity in the center of larger portions of hard whole adult tissues is challenging. In this study, focusing on fixation procedures, we determined the conditions conducive to improved detection of lacZ activity in deeper areas of whole tissues. We used an annexin a5 (Anxa5)-lacZ reporter mouse model in which the Anxa5 expression in hard tissue is indicated by lacZ activity. We found that lacZ activity could be detected throughout the periodontal ligament of adult mice when fixed in 100% acetone, whereas it was not detected in the periodontal ligament around the root apex fixed in glutaraldehyde and paraformaldehyde. This staining could not be detected in wild-type mice. Acetone maintains the lacZ activity within 48 h of fixation at both 4°C and at room temperature. In conclusion, acetone is the optimal fixative to improve permeability for staining of lacZ activity in large volumes of adult hard tissues.

Smooth-muscle-specific expression of neurotrophin-3 in mouse embryonic and neonatal gastrointestinal tract

Vagal gastrointestinal (GI) afferents are essential for the regulation of eating, body weight, and digestion. However, their functional organization and the way that this develops are poorly understood. Neurotrophin-3 (NT-3) is crucial for the survival of vagal sensory neurons and is expressed in the developing GI tract, possibly contributing to their survival and to other aspects of vagal afferent development. The identification of the functions of this peripheral NT-3 thus requires a detailed understanding of the localization and timing of its expression in the developing GI tract. We have studied embryos and neonates expressing the lacZ reporter gene from the NT-3 locus and found that NT-3 is expressed predominantly in the smooth muscle of the outer GI wall of the stomach, intestines, and associated blood vessels and in the stomach lamina propria and esophageal epithelium. NT-3 expression has been detected in the mesenchyme of the GI wall by embryonic day 12.5 (E12.5) and becomes restricted to smooth muscle and lamina propria by E15.5, whereas its expression in blood vessels and esophageal epithelium is first observed at E15.5. Expression in most tissues is maintained at least until postnatal day 4. The lack of colocalization of beta-galactosidase and markers for myenteric ganglion cell types suggests that NT-3 is not expressed in these ganglia. Therefore, NT-3 expression in the GI tract is largely restricted to smooth muscle at ages when vagal axons grow into the GI tract, and when vagal mechanoreceptors form in smooth muscle, consistent with its role in these processes and in vagal sensory neuron survival.

Indigogenic substrates for detection and localization of enzymes

Indoxyl esters and glycosides are useful chromogenic substrates for detecting enzyme activities in histochemistry, biochemistry and bacteriology. The chemical reactions exploited in the laboratory are similar to those that generate indigoid dyes from indoxyl-beta-d-glucoside and isatans (in certain plants), indoxyl sulfate (in urine), and 6-bromo-2-S-methylindoxyl sulfate (in certain molluscs). Pairs of indoxyl molecules released from these precursors react rapidly with oxygen to yield insoluble blue indigo (or purple 6,6'-dibromoindigo) and smaller amounts of other indigoid dyes. Our understanding of indigogenic substrates was developed from studies of the hydrolysis of variously substituted indoxyl acetates for use in enzyme histochemistry. The smallest dye particles, with least diffusion from the sites of hydrolysis, are obtained from 5-bromo-, 5-bromo-6-chloro- and 5-bromo-4-chloroindoxyl acetates, especially the last of these three. Oxidation of the diffusible indoxyls to insoluble indigoid dyes must occur rapidly. This is achieved with atmospheric oxygen and an equimolar mixture of K(3)Fe(CN)(6) and K(4)Fe(CN)(6), which has a catalytic function. H(2)O(2) is a by-product of the oxidation of indoxyl by oxygen. In the absence of a catalyst, the indoxyl diffuses and is oxidized by H(2)O(2) (catalyzed by peroxidase-like proteins) in sites different from those of the esterase activity. The concentration of K(3)Fe(CN)(6)/K(4)Fe(CN)(6) in a histochemical medium should be as low as possible because this mixture inhibits some enzymes and also promotes parallel formation from the indoxyl of soluble yellow oxidation products. The identities and positions of halogen substituents in the indoxyl moiety of a substrate determine the color and the physical properties of the resulting indigoid dye. The principles of indigogenic histochemistry learned from the study of esterases are applicable to methods for localization of other enzymes, because all indoxyl substrates release the same type of chromogenic product. Substrates are commercially available for a wide range of carboxylic esterases, phosphatases, phosphodiesterases, aryl sulfatase and several glycosidases. Indigogenic methods for carboxylic esterases have low substrate specificity and are used in conjunction with specific inhibitors of different enzymes of the group. Indigogenic methods for acid and alkaline phosphatases, phosphodiesterases and aryl sulfatase generally have been unsatisfactory; other histochemical techniques are preferred for these enzymes. Indigogenic methods are widely used, however, for glycosidases. The technique for beta-galactosidase activity, using 5-bromo-4-chloroindoxyl-beta-galactoside (X-gal) is applied to microbial cultures, cell cultures and tissues that contain the reporter gene lac-z derived from E. coli. This bacterial enzyme has a higher pH optimum than the lysosomal beta-galactosidase of animal cells. In plants, the preferred reporter gene is gus, which encodes beta-glucuronidase activity and is also demonstrable by indigogenic histochemistry. Indoxyl substrates also are used to localize enzyme activities in non-indigogenic techniques. In indoxyl-azo methods, the released indoxyl couples with a diazonium salt to form an azo dye. In indoxyl-tetrazolium methods, the oxidizing agent is a tetrazolium salt, which is reduced by the indoxyl to an insoluble coloured formazan. Indoxyl-tetrazolium methods operate only at high pH; the method for alkaline phosphatase is used extensively to detect this enzyme as a label in immunohistochemistry and in Western blots. The insolubility of indigoid dyes in water limits the use of indigogenic substrates in biochemical assays for enzymes, but the intermediate indoxyl and leucoindigo compounds are strongly fluorescent, and this property is exploited in a variety of sensitive assays for hydrolases. The most commonly used substrates for this purpose are glycosides and carboxylic and phosphate esters of N-methylindoxyl. Indigogenic enzyme substrates are among many chromogenic reagents used to facilitate the identification of cultured bacteria. An indoxyl substrate must be transported into the organisms by a permease to detect intracellular enzymes, as in the blue/white test for recognizing E. coli colonies that do or do not express the lac-z gene. Secreted enzymes are detected by substrate-impregnated disks or strips applied to the surfaces of cultures. Such devices often include several reagents, including indigogenic substrates for esterases, glycosidases and DNAse.

Comparative characterization of mesenchymal stem cells from eGFP transgenic and non-transgenic mice

BACKGROUND

Adipose derived- and bone marrow-derived murine mesenchymal stem cells (mMSCs) may be used to study stem cell properties in an in vivo setting for the purposes of evaluating therapeutic strategies that may have clinical applications in the future. If these cells are to be used for transplantation, the question arises of how to track the administered cells. One solution to this problem is to transplant cells with an easily identifiable genetic marker such as enhanced green fluorescent protein (eGFP). This protein is fluorescent and therefore does not require a chemical substrate for identification and can be visualized in living cells. This study seeks to characterize and compare adipose derived- and bone marrow-derived stem cells from C57Bl/6 mice and eGFP transgenic C57Bl/6 mice.

RESULTS

The expression of eGFP does not appear to affect the ability to differentiate along adipogenic or osteogenic lineages; however it appears that the tissue of origin can influence differentiation capabilities. The presence of eGFP had no effect on cell surface marker expression, and mMSCs derived from both bone marrow and adipose tissue had similar surface marker profiles. There were no significant differences between transgenic and non-transgenic mMSCs.

CONCLUSION

Murine adipose derived and bone marrow derived mesenchymal stem cells from non-transgenic and eGFP transgenic C57Bl/6 mice have very similar characterization profiles. The availability of mesenchymal stem cells stably expressing a genetic reporter has important applications for the advancement of stem cell research.

A comparative analysis of constitutive and cell-specific promoters in the adult mouse hippocampus using lentivirus vector-mediated gene transfer

BACKGROUND

Viral vectors provide powerful tools for transgene delivery to the mammalian brain to assess the effects of therapeutic proteins, antisense RNAs or small interfering RNAs. A key advantage of such approaches is that specific brain regions implicated in a particular disease can be independently targeted.

METHODS

To optimize transgene expression in sub-regions of the mouse hippocampus and with a view towards devising gene therapy strategies for Alzheimer's disease, we designed lentivirus-based reporter vectors bearing various promoters, including constitutive and cell-specific promoters. Furthermore, we devised methods allowing a side-by-side comparison of transgene expression levels in neural cells both in vitro and in vivo.

RESULTS

Following stereotaxic injection into the adult mouse hippocampus, titer-adjusted lentiviral vectors bearing constitutive promoters resulted in robust and sub-region-specific transgene expression. Our results show that the human CMV-IE promoter resulted in efficient transgene expression in the entire hippocampus whereas transgene expression mediated by the hybrid hEF1alpha/HTLV promoter was limited mainly in the dentate gyrus and the CA2/3 region. Finally, the neuron-specific human synapsin I promoter was particularly effective in the dentate gyrus.

CONCLUSIONS

These findings indicate that subregion-specific transgene expression in the hippocampus can be achieved following lentivirus vector-mediated gene transfer.

Whole Mount Enzyme Histochemistry as a Rapid Screen at Necropsy for Expression of β-Galactosidase (LacZ)–Bearing Transgenes: Considerations for Separating Specific LacZ Activity from Nonspecific (Endogenous) Galactosidase Activity

Whole mount enzyme histochemistry to localize lacZ-bearing transgenes (lacZ-WMH) also detects endogenous β-galactosidases. The experiments reported here evaluated lacZ-WMH as a potential tool for transgene expression analysis during high-throughput rodent necropsies. A lacZ-WMH survey of organs from adult, wild-type, male and female mice (C57BL/6, FVB/N) and female rats (Sprague-Dawley) performed at the optimal pH (≥ 7.0) for bacterial lacZ yielded intense endogenous staining in the gonads, kidney, male accessory sex organs, salivary glands, submucosal glands in the duodenum, and thyroid. Substantial staining occurred in the adrenal cortex, lymph nodes, and linings of the gastrointestinal tract, the urinary bladder and uterus, and (for rat only) in the adenohypophysis, bone marrow, thymus, and trigeminal ganglia. Endogenous galactosidases were distributed similarly in sections of flash-frozen organs used for slide-based lacZ histochemistry (lacZ-SBH) at pH ≤ 5.0 (optimal for eukaryotic enzymes). Cerebral neurons were labeled only by lacZ-SBH. At pH 7.4, endogenous but not specific lacZ activity was abolished for lacZ-SBH, while endogenous activity was not halted without reducing specific activity for lacZ-WMH. These data demonstrate that lacZ-WMH is feasible during rodent necropsies for many but not all organs if species-, strain-, and sex-specific divergence in endogenous galactosidase activity is considered and special fixation (3% paraformaldehyde for 3 hours at 4°C) is used.

Synthesis and evaluation of 18F- and 11C-labeled phenyl-galactopyranosides as potential probes for in vivo visualization of LacZ gene expression using positron emission tomography

3-Hydroxy-2-nitrophenyl 2,3,4,6-tetra-O-acetyl-beta-D-galactopyranoside, a derivative of the chromogenic beta-galactosidase (beta-gal) substrate o-nitrophenyl beta-D-galactopyranoside (ONPG) was synthesized using a Koenigs-Knorr glycosylation reaction. It was alkylated with 2-[(18)F]fluoroethyl triflate or [(11)C]methyl triflate, followed by deacetylation of the sugar hydroxyl groups to obtain radiolabeled 3-(2'-[(18)F]fluoroethoxy)-2-nitrophenyl beta-D-galactopyranoside ([(18)F]-2c) and 3-[(11)C]methoxy-2-nitrophenyl beta- d-galactopyranoside ([(11)C]-3c), which were evaluated as potential reporter probes for in vivo visualization of LacZ gene expression with positron emission tomography (PET). In vitro, [(18)F]- 2c and [(11)C]-3c were good substrates of beta-gal and showed, respectively, a 7.5- and 2.5-fold higher uptake into beta-gal expressing cells (LacZ cells) compared to control cells. However, reversed-phase HPLC analysis of the LacZ cell lysate and supernatant showed that labeled 3-(2'-[(18)F]fluoroethoxy)-2-nitrophenol, the hydrolysis product formed by beta-gal-mediated cleavage of [(18)F]-2c, substantially leaked out of the cells, which would lead to loss of PET signal. In a microPET study of [(18)F]-2c in a mouse with a beta-gal expressing tumor, high retention was observed in liver and kidneys, but only negligible accumulation was seen in the tumor. As a general conclusion, it can be stated that the synthesized PET tracers [ (18)F]-2c and [(11)C]-3c are not suitable for use as LacZ reporter probes. Further structural modifications to improve the diffusion over the tumor cell membrane and to increase retention in beta-gal expressing cells may lead to more favorable in vivo imaging probes.

Assessment of a nuclear affinity labeling method for tracking implanted mesenchymal stem cells

Therapeutic implantation of mesenchymal stem cells (MSCs) is entering the realm of clinical trials for several human diseases, and yet much remains uncertain regarding their dynamic distribution and cell fate after in vivo application. Discrepancies in the literature can be attributed in part to the use of different cell labeling/tracking methods and cell administration protocols. To identify a stem cell detection method suitable for myocardial implantation in a large animal model, we experimented on three different MSC labeling methods: adenovirus-mediated expression of enhanced green fluorescence protein (EGFP) and beta-galactosidase (LacZ), and nuclear staining with DAPI. Intramuscular and intracoronary administrations of labeled porcine MSCs identified the nuclear affinity dye to be a reliable stem cell tracking marker. Stem cell identification is facilitated by an optimized live cell labeling condition generating bright blue fluorescence sharply confined to the nucleus. DAPI-labeled MSCs retained full viability, ceased proliferation, and exhibited an increased differentiation potential. The labeled MSCs remained fully active in expressing key growth factor and cytokine genes, and notably exhibited enhanced expression of the chemokine receptor CXCR4 and its ligand SDF1, indicating their competency in response to tissue injury. Histological analysis revealed that approximately half a million MSCs or approximately 2% of the administered MSCs remained localized in the normal pig heart 2 weeks after coronary infusion. That the vast majority of these identified MSCs were interstitial indicated the ability of MSCs to migrate across the coronary endothelium. No evidence was obtained indicating MSC differentiation to cardiomyocyte.

Proteomic analysis of protein complexes

While it sometimes does not generate the publicity that biomarker discovery does, the identification of protein complexes may be the most popular use of proteomic technology. The partners a protein interacts with is a key component that describes the function of any protein. Basic research has long appreciated the importance of identifying protein interactions through techniques such as Western blotting and colocalization studies using immunofluorescence microscopy. This appreciation has carried over into the field of proteomics and brought with it the development of tools that increase the capabilities to characterize protein complexes to a far greater scale. While advances in technology have had a huge impact, sample preparation issues related to the isolation of protein complexes remains a critical factor in determining the success of these types of studies.

Neural stem cell implantation extends life in Niemann-Pick C1 mice

In order to evaluate the phenotypic effects of implanted neural stem cells (NSCs) in the mouse model of Niemann-Pick C (NPC) disease, we injected a well-characterized clone of murine NSCs into the cerebella of neonatal Npc1(-/-) and control mice. The implanted cells survived and were abundant in some regions of the cerebellum. Life span was lengthened in NPC mice with the implanted NSCs. However, the rate of weight gain and subsequent weight loss, resulting from neurodegeneration, was not significantly different from un-injected controls. Ataxia was measured by Rota-Rod performance. The overall rate of decline in time on the Rota-Rod was not significantly slowed down. Thus, in this small group of NPC mice, a single administration in the neonatal period of the NSCs (which were not engineered to over-express the missing gene and not directed into the parenchyma) was only partially therapeutic.

Embedding of bone samples in methylmethacrylate: a suitable method for tracking LacZ mesenchymal stem cells in skeletal tissues

Considerable research has been focused on the use of bone marrow-derived mesenchymal stem cells (MSCs) for the repair of non-unions and bone defects. To date, the question of whether transplanted MSCs survive and engraft within newly formed tissue remains unresolved. The development of an easy and reliable method that would allow cell fate monitoring in transplant recipients is a pressing concern for the field of tissue engineering. To demonstrate the presence of transplanted cells in newly formed bone, we established a xenograft nude rat model allowing the detection of murine LacZ MSCs in vivo. MSCs were isolated from transgenic lacZ mice, seeded onto bioabsorbable collagen sponges, and transplanted to repair a calvarial defect in nude rats. As a preliminary step, the histological procedure was adapted to optimize the detection of LacZ cells in bone tissue embedded in methylmethacrylate (MMA). Four fixatives and four fixation times were evaluated. Among all the fixatives tested, 2% formaldehyde/0.2% glutaraldehyde at 4C for 4 days gave the best results for X-gal staining at pH 7.4 on both cell cultures and bone explants. All fixatives were effective for immunodetection of beta-gal. In the chimeric LacZ/nude rat animal model, MSCs were detected in vivo for up to 4 weeks after implantation and contributed to the repair and the neovascularization of the bone defect. LacZ is a suitable phenotypic marker to track MSCs in skeletal tissues embedded in MMA.

Analysis of neuron-like differentiation of human bone marrow mesenchymal stem cells

The objective of the study was to evaluate differentiation of human bone marrow mesenchymal stem cells into true or pseudo neurons after treating with chemical induction medium in vitro. The morphological changes were assessed using interference contrast microscopy. Immunocytochemistry and Western blotting were performed using neuronal markers. Further evaluation was conducted with proteomic profiling, DNA microarray analysis and the whole-cell patch clamp test. After three hours of treatment with chemical induction medium, nearly three-fourths of the hMSCs changed to cells with a neuronal phenotype. The results of immunocytochemistry and Western blotting showed a high expression of neuronal markers in these cells at 3 h which decreased at 24 h. The proteomics analysis showed no change of proteins related to neuronal differentiation. DNA microarray showed downregulation of neuron related genes. The patch clamp test was unable to demonstrate any similarity to true neurons. Our findings suggest that neuron-like cells derived from chemical induction of hMSCs are not the genuine neurons as they resemble true neurons phenotypically but are different in genotypic and electrophysiological characteristics.

Structure-specific patterns of neural stem cell engraftment after transplantation in the adult mouse brain

Transplantation of neural stem cells (NSCs) may be useful for delivering exogenous gene products to the diseased CNS. When NSCs are transplanted into the developing mouse brain, they can migrate extensively and differentiate into cells appropriate to the sites of engraftment, in response to the normal signals directing endogenous cells to their appropriate fates. Much of the prior work on NSC migration in the adult brain has examined directed migration within or toward focal areas of injury such as ischemia, brain tumors, or 6-hydroxydopamine (6-OHDA) lesions. However, treatment of many genetic disorders that affect the CNS will require widespread dissemination of the donor cells in the postnatal brain, because the lesions are typically distributed globally. We therefore tested the ability of NSCs to migrate in the unlesioned adult mouse brain after stereotaxic transplantation into several structures including the cortex and hippocampus. NSC engraftment was monitored in live animals by magnetic resonance imaging (MRI) after superparamagnetic iron oxide (SPIO) labeling of cells. Histological studies demonstrated that the cells engrafted in significantly different patterns within different regions of the brain. In the cerebral cortex, donor cells migrated in all directions from the injection site. The cells maintained an immature phenotype and cortical migration was enhanced by trypsin treatment of the cells, indicating a role for cell surface proteins. In the hippocampus, overall cell survival and migration were lower but there was evidence of neuronal differentiation. In the thalamus, the transplanted cells remained in a consolidated mass at the site of injection. These variations in pattern of engraftment should be taken into account when designing treatment approaches in nonlesion models of neurologic disease.

Optimizing techniques for tracking transplanted stem cells in vivo

The potential for bone marrow-derived cells (BMDCs) to contribute to nonhematopoietic tissues has generated considerable debate in recent years. Causes for the controversies include disparities in the techniques used to track engraftment of BMDCs, inappropriate tissue preparation, a lack of appropriate positive and negative controls, and basic misunderstandings about how to properly collect and interpret images from epifluorescent and confocal microscopes. Our laboratory was among the first to use bone marrow transplants from transgenic mice constitutively expressing enhanced green fluorescent protein (GFP) to study the ability of BMDCs to give rise to nonhematopoietic tissue types, a system that is now in widespread use. During our 6 years of experience using GFP, as well as beta-galactosidase and the Y chromosome, to track BMDCs in vivo, we have identified many difficulties and have developed techniques to resolve them. We discuss several of these methods, and, in particular, we describe ratiometric analysis techniques for improving detection of transplanted cells derived from genetically modified bone marrow. Finally, to help resolve reported discrepancies regarding the frequency with which BMDCs contribute to skeletal myofibers, we demonstrate that the pattern of highly autofluorescent myofibers in skeletal muscle is clearly distinct from that of GFP-expressing myofibers and describe how unambiguous conclusions can be drawn from such data.

An optimized protocol for detection of E. coli beta-galactosidase in lung tissue following gene transfer

Staining by 5-bromo-4-chloro-3-indolyl-beta-D: -galactopyranoside (X-gal) typically detects activity of E. coli beta-galactosidase (beta-gal) in transduced tissues that express the LacZ reporter gene. In lung tissue from mice that received beta-galactosidase-expressing adeno-associated virus (AAV) vectors via intranasal inhalation, we observed only a low frequency of positive cells after X-gal staining in contrast to other reporter genes, such as alkaline phosphatase or green fluorescent protein. In this study, we systematically tested a number of parameters to improve the sensitivity of X-gal staining in lungs transduced with beta-galactosidase-expressing AAV2/5 vectors. We observed that the use of nuclear-targeted LacZ instead of cytoplasmic LacZ as the reporter gene substantially increases the number of positive cells after X-gal staining. The pH of the staining solution determines staining sensitivity and background staining with pH 7.0 resulting in high sensitivity and no background levels. Glutaraldehyde at 0.2% or 0.5% in PBS as fixative provides optimal results for X-gal staining. The alternative substrate, Bluo-gal, showed no improvement compared with X-gal but instead caused nonspecific background staining. We further stained intact fixed lungs with X-gal and processed them for paraffin embedding or cryosectioning, resulting in equal staining intensities. However, en bloc staining of intact tissues resulted in the absence of positive cells within deeper-located lung areas.

Overcoming bacterial DNA contamination in real-time PCR and RT-PCR reactions for LacZ detection in cell therapy monitoring

Since the introduction of the polymerase chain reaction the presence of contaminating bacterial DNA in the Taq polymerase preparations has hampered the use of this technique in microbiology. Lately, this inconvenience has equally impeded gene quantification in the field of cell or gene therapy, where bacterial genes such as LacZ are often used as tags to detect vectors or cells after their injection in the recipient organism. Several means to overcome the DNA contamination of Taq Polymerase have been reported with variable degrees of decontamination efficiency and alteration of the PCR reaction. Here we propose two protocols to efficiently quantify DNA or RNA from the LacZ gene by real-time PCR using either decontamination by low concentrations of DNAse I prior to PCR amplification or a highly purified Taq Polymerase which is devoid of detectable contamination.

Targeted modification of atrial electrophysiology by homogeneous transmural atrial gene transfer

BACKGROUND

Safe and effective myocardial gene transfer remains elusive. Heterogeneous ventricular gene delivery has been achieved in small mammals but generally with methods not readily transferable to the clinic. Atrium-specific gene transfer has not yet been reported. We hypothesized that homogeneous atrial gene transfer could be achieved by direct application of adenoviral vectors to the epicardial surface, use of poloxamer gel to increase virus contact time, and mild trypsinization to increase virus penetration.

METHODS AND RESULTS

We "painted" recombinant adenovirus encoding the reporter gene Escherichia coli beta-galactosidase directly onto porcine atria. Investigational variables included poloxamer use, trypsin concentration, and safety. Using the painting method, we modified the atrial phenotype with an adenovirus expressing HERG-G628S, a long-QT-syndrome mutant. Our results showed that application of virus with poloxamer alone resulted in diffuse epicardial gene transfer with negligible penetration into the myocardium. Dilute trypsin concentrations allowed complete transmural gene transfer. After trypsin exposure, echocardiographic left atrial diameter did not change. Left atrial function decreased on postoperative day 3 but returned to baseline by day 7. Tissue tensile strength was affected only in the 1% trypsin group. HERG-G628S gene transfer prolonged atrial action potential duration and refractory period without affecting ventricular electrophysiology.

CONCLUSIONS

We show complete transmural atrial gene transfer by this novel painting method. Adaptation of the method could allow application to other tissue targets. Use with functional proteins in the atria could cure or even prevent diseases such as atrial fibrillation or sinus node dysfunction.

Transduction of the Choroid Plexus and Ependyma in Neonatal Mouse Brain by Vesicular Stomatitis Virus Glycoprotein-Pseudotyped Lentivirus and Adeno-Associated Virus Type 5 Vectors

Evaluation of gene transfer into the developing mouse brain has shown that when adeno-associated virus serotype 1 (AAV1) or AAV2 vectors are injected into the cerebral lateral ventricles at birth, widespread parenchymal transduction occurs. Lentiviral vectors have not been tested by this route. In this study, we found that injection of lentiviral vectors pseudotyped with vesicular stomatitis virus glycoprotein (VSV-G) resulted in targeted transduction of the ependymal cells lining the ventricular system and the choroid plexus along the entire rostrocaudal axis of the brain, whereas a Mokola pseudotype transduced only a few cells after injection into the neonatal ventricle. In contrast, when lentiviral vectors pseudotyped with either VSV-G or Mokola glycoprotein are injected into the adult mouse brain, they transduce similar patterns of cells. An Ebola-Zaire-pseudotyped vector did not transduce any neonatal CNS cells, as was also the case for adult parenchymal injections. Long-term gene expression (12 months) occurred with a constitutively active mammalian promoter and a self-inactivating long terminal repeat (LTR), whereas the cytomegalovirus promoter in a vector with an intact LTR was expressed only in short-term experiments. We found that an AAV5 vector also targeted the ependymal and choroid plexus cells throughout the ventricular system. This vector exhibited limited penetration from the ventricle to other structures, which was significantly different from the previously reported patterns of transduction after intraventricular injection of AAV1 and AAV2 vectors.

Changing intracellular compartmentalization of beta-galactosidase in the ROSA26 reporter mouse during embryonic development: a light- and electron-microscopic study

The beta-geo (LacZ) reporter gene encodes for beta-galactosidase (beta-gal) in all cells of the ROSA26 mouse during embryonic development. As such, beta-gal activity constitutes an excellent marker for in situ labeling of expressing cells. However, the intracellular distribution of beta-gal differs between cells, and changes during embryonic development. Therefore, we studied LacZ-encoded beta-gal using light and electron microscopy in the heart, lung, liver, and small intestine on days 13 and 16 of gestation, and the kidney on day 16 of gestation in ROSA26 mice. The Bluo-gal method was carried out under standardized conditions, including fixation, washing, and incubation procedures. Intracellular beta-gal staining is encountered in a combination of membranous compartments, including the nuclear envelope, the endoplasmic reticulum, and the plasma membrane. Its exact localization depends on the cell type and is regulated during development. Therefore, one must take the compartmental transition of intracellular beta-gal staining into consideration when interpreting results obtained from experiments using ROSA26 mice.

Comparison of transfection conditions for a lentivirus vector produced in large volumes

A number of different transfection reagents have been used for lentiviral vector production. We directly compared transfection buffers, DNA purification methods, chemical facilitators, and DNA concentrations to optimize production. The use of N,N-bis (2-hydroxyethyl)-2-aminoethanesulfonic acid (BES), sodium butyrate, and one fourth the total amount of DNA used in standard transient transfection protocols were the best conditions for virus production. These reagents were combined into a single protocol and scaled-up to produce liter quantities of virus in a multitray tissue culture vessel.

Survival of neuronal tissue following xenograft implantation into the adult rat inner ear

The poor regenerative capacity of the spiral ganglion neurons of the mammalian inner ear has initiated research on how to assist the functional recovery of the injured auditory system. A possible treatment is to use a biological implant with a potential to establish central or peripheral synaptic contacts to develop into a functional auditory unit. The feasibility of this approach was tested by xenograft implantation of dorsal root ganglion (DRG) neurons from embryonic days 13 to 14, mouse expressing either LacZ or enhanced green fluorescent protein (EGFP) into the scala tympani of the adult rat inner ear. Transplanted DRG neurons survived in the scala tympani for a postoperative period ranging from 3 to 10 weeks, as verified by histochemical detection of LacZ, EGFP fluorescence and immunohistochemical labeling of the neuronal markers neurofilament and Thy 1.2. DRG neurons were found close to structures near the sensory epithelium (the organ of Corti) as well as adjacent to the spiral ganglion neurons with their peripheral dendrites. These results illustrate not only the survival of xenografted DRG neurons in the adult inner ear but also the feasibility of a neuronal transplantation strategy in the degenerated auditory system, thereby creating possibilities to replace spiral ganglion neurons.

Immunohistologic labeling of murine endothelium

BACKGROUND

Reliable identification of endothelial cells is a prerequisite for understanding vascularity changes in many cardiovascular diseases and therapeutic interventions. With the rising use of mouse models of disease and genetic manipulation, a consistent system to label murine endothelial cells in normal and diseased tissues would be an invaluable tool.

METHODS

Immunohistologic and histochemical methods were used to label endothelial cells in normal and infarcted heart as well as small intestine. Isolectin B(4) or antibodies to thrombomodulin, vWF, Tie-2, VE-cadherin, CD34, and CD31 were used to immunostain tissues fixed in either 4% formaldehyde (prepared fresh from powdered paraformaldehyde, PF), methyl Carnoy's (MC), zinc (Zn) (all paraffin-embedded), or frozen sections. In addition, we used beta-galactosidase histochemistry in frozen sections from the Tie-2/beta-galactosidase transgenic mouse, in which the lacZ reporter gene is driven by the endothelial-specific Tie-2 promoter.

RESULTS AND CONCLUSIONS

Immunohistologic localization of endothelial cells was best accomplished using anti-CD31 in Zn-fixed, paraffin-embedded tissues. Antithrombomodulin staining also worked in Zn-fixed tissues as well as frozen tissues, but additional steps were required to reduce background. The beta-galactosidase reporter system also marked endothelial cells in frozen Tie-2 transgenic mouse tissues; however, this system required careful control of fixation and optimization of histochemistry and was not amenable to double labeling. Lectin staining gave complete labeling of endothelial cells but cross-reacted intensely with macrophages in the infarcted heart. We conclude that anti-CD31 immunostaining in Zn-fixed, paraffin-embedded murine tissue offered superior morphology and permitted optimal identification of proliferating endothelial cells during infarct repair.

Targeted transduction patterns in the mouse brain by lentivirus vectors pseudotyped with VSV, Ebola, Mokola, LCMV, or MuLV envelope proteins

Lentiviral vectors have proven to be promising tools for transduction of central nervous system (CNS) cells in vivo and in vitro. In this study, CNS transduction patterns of lentiviral vectors pseudotyped with envelope glycoproteins from Ebola virus, murine leukemia virus (MuLV), lymphocytic choriomeningitis virus (LCMV), or the rabies-related Mokola virus were compared to a vector pseudotyped with the vesicular stomatitis virus glycoprotein (VSV-G). Mokola-, LCMV-, and VSV-G-pseudotyped vectors transduced similar populations, including striatum, thalamus, and white matter. Mokola-pseudotyped vectors were the most efficient of the three. MuLV-pseudotyped lentivirus efficiently transduced striatum and hippocampal dentate gyrus. In contrast, no transduction resulted from injection of Ebola-pseudotyped virus in the CNS. The same pattern was observed in vitro with primary cultured oligodendrocytes. LCMV, MuLV, and Ebola pseudotypes were the most stable. These results demonstrate that targeted transduction in the CNS can be achieved using specific envelope glycoproteins to pseudotype lentiviral vectors, and support the use of Mokola-pseudotyped and MuLV-pseudotyped lentiviral vectors as efficient and stable alternatives to VSV-G-pseudotyped vectors for experiments in the mouse CNS.

New tools to trace populations of inflammatory cells in the CNS

Cells of the central nervous system (CNS) and immune system communicate regularly. There is a constant surveillance of the intact, healthy CNS by activated T-cells, and massive infiltration of the CNS by immune cells under pathological conditions such as neurodegeneration or neuroinflammation. Labeling CNS-infiltrating T-cells is an essential tool to identify the signals and mechanisms, which mediate the interaction between immune cells and cells of the CNS. In this article, we will present an overview describing currently used cellular markers and demonstrate how these markers have contributed to our current knowledge of CNS inflammation and immune surveillance.