The mouse Pgk-1 gene promoter contains an upstream activator sequence

Synthetic enhancers including TFREs improve transgene expression in CHO cells

The human cytomegalovirus major immediate early gene (CMV) promoter is currently the most preferred promoter for recombinant therapeutic proteins (RTPs) production in CHO cells. To enhance the production of RTPs, five synthetic enhancers including multiple transcription factor regulatory elements (TFREs) were evaluated to enhance recombinant protein level in transient and stably transfected CHO cells. Compared with the control, four elements can enhance the report genes expression under both two transfected states. Further, the function of these four enhancers on human serum albumin (HSA) were investigated. We found that the transient expression can increase by up to 1.5 times, and the stably expression can maximum increase by up to 2.14 times. The enhancement of transgene expression was caused by the boost of their corresponding mRNA levels. Transcriptomics analysis was performed and found that transcriptional activation and cell cycle regulation genes were involved. In conclusion, optimization of enhancers in the CMV promoter could increase the production yield of transgene in transfected CHO cells, which has significance for developing high-yield CHO cell expression system.

Calling Cards: A Customizable Platform to Longitudinally Record Protein-DNA Interactions Over Time in Cells and Tissues

Calling Cards is a platform technology to record a cumulative history of transient protein-DNA interactions in the genome of genetically targeted cell types. The record of these interactions is recovered by next-generation sequencing. Compared with other genomic assays, readouts of which provide a snapshot at the time of harvest, Calling Cards enables correlation of historical molecular states to eventual outcomes or phenotypes. To achieve this, Calling Cards uses the piggyBac transposase to insert self-reporting transposon "Calling Cards" into the genome, leaving permanent marks at interaction sites. Calling Cards can be deployed in a variety of in vitro and in vivo biological systems to study gene regulatory networks involved in development, aging, and disease. Out of the box, it assesses enhancer usage but can be adapted to profile-specific transcription factor (TF) binding with custom TF-piggyBac fusion proteins. The Calling Cards workflow has five main stages: delivery of Calling Cards reagents, sample preparation, library preparation, sequencing, and data analysis. Here, we first present a comprehensive guide for experimental design, reagent selection, and optional customization of the platform to study additional TFs. Then, we provide an updated protocol for the five steps, using reagents that improve throughput and decrease costs, including an overview of a newly deployed computational pipeline. This protocol is designed for users with basic molecular biology experience to process samples into sequencing libraries in 2 days. Familiarity with bioinformatic analysis and command line tools is required to set up the pipeline in a high-performance computing environment and to conduct downstream analyses. © 2023 Wiley Periodicals LLC. Basic Protocol 1: Preparation and delivery of Calling Cards reagents Support Protocol 1: Next-generation sequencing quantification of barcode distribution within self-reporting transposon plasmid pool and adeno-associated virus genome Basic Protocol 2: Sample collection and RNA purification Support Protocol 2: Library density quantitative PCR Basic Protocol 3: Sequencing library preparation Basic Protocol 4: Library pooling and sequencing Basic Protocol 5: Data analysis.

Calling Cards: a customizable platform to longitudinally record protein-DNA interactions over time in cells and tissues

Calling Cards is a platform technology to record a cumulative history of transient protein-DNA interactions in the genome of genetically targeted cell types. The record of these interactions is recovered by next generation sequencing. Compared to other genomic assays, whose readout provides a snapshot at the time of harvest, Calling Cards enables correlation of historical molecular states to eventual outcomes or phenotypes. To achieve this, Calling Cards uses the piggyBac transposase to insert self-reporting transposon (SRT) "Calling Cards" into the genome, leaving permanent marks at interaction sites. Calling Cards can be deployed in a variety of in vitro and in vivo biological systems to study gene regulatory networks involved in development, aging, and disease. Out of the box, it assesses enhancer usage but can be adapted to profile specific transcription factor binding with custom transcription factor (TF)-piggyBac fusion proteins. The Calling Cards workflow has five main stages: delivery of Calling Card reagents, sample preparation, library preparation, sequencing, and data analysis. Here, we first present a comprehensive guide for experimental design, reagent selection, and optional customization of the platform to study additional TFs. Then, we provide an updated protocol for the five steps, using reagents that improve throughput and decrease costs, including an overview of a newly deployed computational pipeline. This protocol is designed for users with basic molecular biology experience to process samples into sequencing libraries in 1-2 days. Familiarity with bioinformatic analysis and command line tools is required to set up the pipeline in a high-performance computing environment and to conduct downstream analyses. Basic Protocol 1: Preparation and delivery of Calling Cards reagentsBasic Protocol 2: Sample preparationBasic Protocol 3: Sequencing library preparationBasic Protocol 4: Library pooling and sequencingBasic Protocol 5: Data analysis.

Development of a dual hybrid AAV vector for endothelial-targeted expression of von Willebrand factor

Von Willebrand disease (VWD), the most common inherited bleeding disorder in humans, is caused by quantitative or qualitative defects in von Willebrand factor (VWF). VWD represents a potential target for gene therapy applications, as a single treatment could potentially result in a long-term correction of the disease. In recent years, several liver-directed gene therapy approaches have been exploited for VWD, but their efficacy was generally limited by the large size of the VWF transgene and the reduced hemostatic activity of the protein produced from hepatocytes. In this context, we aimed at developing a gene therapy strategy for gene delivery into endothelial cells, the natural site of biosynthesis of VWF. We optimized an endothelial-specific dual hybrid AAV vector, in which the large VWF cDNA was put under the control of an endothelial promoter and correctly reconstituted upon cell transduction by a combination of trans-splicing and homologous recombination mechanisms. In addition, we modified the AAV vector capsid by introducing an endothelial-targeting peptide to improve the efficiency for endothelial-directed gene transfer. This vector platform allowed the reconstitution of full-length VWF transgene both in vitro in human umbilical vein endothelial cells and in vivo in VWD mice, resulting in long-term expression of VWF.

The Expression of the Immunoproteasome Subunit PSMB9 Is Related to Distinct Molecular Subtypes of Uterine Leiomyosarcoma

Simple Summary

Uterine leiomyosarcoma (uLMS) is a rare, aggressive, and highly heterogeneous tumor. Knockout female mice for the catalytic subunit of the immunoproteasome PSMB9 develops spontaneous uLMS. In this study, we used molecular data from 3 non-related uLMS cohorts that were integrated and analyzed by proteotranscriptomics. We observed overexpression of the immunoproteasome pathway in uLMS, and then further classified the samples as low or high PSMB9 gene expression levels and we provide evidence that; (i) in the group high there is an enrichment of pathways related to the immune system and in the group low, the ECM formation; (ii) samples with high CD8+/PSMB9 ratio shows better OS; and (iii) the main regulator in the high group is IFNγ and in the low, the proto-oncogene SRC. These findings contribute to the understanding of potential therapeutic or prognostic markers in uLMS.

Abstract

Background: Uterine leiomyosarcoma (uLMS) are rare and malignant tumors that arise in the myometrium cells and whose diagnosis is based on histopathological features. Identifying diagnostic biomarkers for uLMS is a challenge due to molecular heterogeneity and the scarcity of samples. In vivo and in vitro models for uLMS are urgently needed. Knockout female mice for the catalytic subunit of the immunoproteasome PSMB9 (MIM:177045) develop spontaneous uLMS. This study aimed to analyze the role of PSMB9 in uLMS tumorigenesis and patient outcome. Methods: Molecular data from 3 non-related uLMS cohorts were integrated and analyzed by proteotranscriptomic using gene expression and protein abundance levels in 68 normal adjacent myometrium (MM), 66 uterine leiomyoma (LM), and 67 uLMS. Results: the immunoproteasome pathway is upregulated and the gene PMSB9 shows heterogeneous expression values in uLMS. Quartile group analysis showed no significant difference between groups high and low PSMB9 expression groups at 3-years overall survival (OS). Using CYBERSORTx analysis we observed 9 out of 17 samples in the high group clustering together due to high M2 macrophages and CD4 memory resting, and high CD8+/PSMB9 ratio was associated with better OS. The main pathway regulated in the high group is IFNγ and in the low is the ECM pathway dependent on the proto-oncogene SRC. Conclusion: these findings suggest 2 subtypes of uLMS (immune-related and ECM-related) with different candidate mechanisms of malignancy.

SyNPL: Synthetic Notch pluripotent cell lines to monitor and manipulate cell interactions in vitro and in vivo

Cell-cell interactions govern differentiation and cell competition in pluripotent cells during early development, but the investigation of such processes is hindered by a lack of efficient analysis tools. Here, we introduce SyNPL: clonal pluripotent stem cell lines that employ optimised Synthetic Notch (SynNotch) technology to report cell-cell interactions between engineered ‘sender’ and ‘receiver’ cells in cultured pluripotent cells and chimaeric mouse embryos. A modular design makes it straightforward to adapt the system for programming differentiation decisions non-cell-autonomously in receiver cells in response to direct contact with sender cells. We demonstrate the utility of this system by enforcing neuronal differentiation at the boundary between two cell populations. In summary, we provide a new adaptation of SynNotch technology that could be used to identify cell interactions and to profile changes in gene or protein expression that result from direct cell-cell contact with defined cell populations in culture and in early embryos, and that can be customised to generate synthetic patterning of cell fate decisions.

Summary: Optimised Synthetic Notch circuitry in mouse pluripotent stem cells provides a modular tool with which to monitor cell-cell interactions and program synthetic patterning of cell fates in culture and in embryos.

Control of the activity of CAR-T cells within tumours via focused ultrasound

Focused ultrasound can deliver energy safely and non-invasively into tissues at depths of centimetres. Here we show that the genetics and cellular functions of chimeric antigen receptor T cells (CAR-T cells) within tumours can be reversibly controlled by the heat generated by short pulses of focused ultrasound via a CAR cassette under the control of a promoter for the heat-shock protein. In mice with subcutaneous tumours, locally injected T cells with the inducible CAR and activated via focused ultrasound guided by magnetic resonance imaging mitigated on-target off-tumour activity and enhanced the suppression of tumour growth, compared with the performance of non-inducible CAR-T cells. Acoustogenetic control of the activation of engineered T cells may facilitate the design of safer cell therapies.

Group V Secretory Phospholipase A2 Regulates Endocytosis of Acetylated LDL by Transcriptional Activation of PGK1 in RAW264.7 Macrophage Cell Line

AIMS

It was suggested that group V secretory phospholipase A₂ (sPLA2-V) existed in the nucleus. This study examined whether nuclear sPLA₂-V plays a role in endocytosis of acetylated low-density lipoprotein (AcLDL) in monocyte/macrophage-like cell line RAW264.7 cells.

METHODS

RAW264.7 cells were transfected with shRNA vector targeting sPLA₂-V (sPLA₂-V-knockdown [KD] cells) or empty vector (sPLA₂-V-wild-type [WT] cells). AcLDL endocytosis was assessed by incubation with ¹²⁵I-AcLDL or AcLDL conjugated with pHrodo. Actin polymerization was assessed by flow cytometry using Alexa Fluor 546-phalloidin.

RESULTS

In immunofluorescence microscopic studies, sPLA₂-V was detected in the nucleus. ChIP-Seq and ChIP-qPCR analyses showed binding of sPLA₂-V to the promoter region of the phosphoglycerate kinase 1 (Pgk1) gene. In the promoter assay, sPLA₂-V-KD cells had lower promoter activity of the Pgk1 gene than sPLA₂-V-WT cells, and this decrease could be reversed by transfection with a vector encoding sPLA₂-V-H48Q that lacks enzymatic activity. Compared with sPLA₂-V-WT cells, sPLA₂-V-KD cells had decreased PGK1 protein expression, beclin 1 (Beclin1) phosphorylation at S30, and class III PI3-kinase activity that could also be restored by transfection with sPLA₂-V-H48Q. sPLA₂-V-KD cells had impaired actin polymerization and endocytosis, which was reversed by introduction of sPLA₂-V-H48Q or PGK1 overexpression. In sPLA₂-V-WT cells, siRNA-mediated depletion of PGK1 suppressed Beclin1 phosphorylation and impaired actin polymerization and intracellular trafficking of pHrodo-conjugated AcLDL.

CONCLUSIONS

Nuclear sPLA₂-V binds to the Pgk1 gene promoter region and increases its transcriptional activity. sPLA₂-V regulates AcLDL endocytosis through PGK1-Beclin1 in a manner that is independent of its enzymatic activity in RAW264.7 cells.

Multiplexed Cas9 targeting reveals genomic location effects and gRNA-based staggered breaks influencing mutation efficiency

Understanding the impact of guide RNA (gRNA) and genomic locus on CRISPR-Cas9 activity is crucial to design effective gene editing assays. However, it is challenging to profile Cas9 activity in the endogenous cellular environment. Here we leverage our TRIP technology to integrate ~ 1k barcoded reporter genes in the genomes of mouse embryonic stem cells. We target the integrated reporters (IRs) using RNA-guided Cas9 and characterize induced mutations by sequencing. We report that gRNA-sequence and IR locus explain most variation in mutation efficiency. Predominant insertions of a gRNA-specific nucleotide are consistent with template-dependent repair of staggered DNA ends with 1-bp 5' overhangs. We confirm that such staggered ends are induced by Cas9 in mouse pre-B cells. To explain observed insertions, we propose a model generating primarily blunt and occasionally staggered DNA ends. Mutation patterns indicate that gRNA-sequence controls the fraction of staggered ends, which could be used to optimize Cas9-based insertion efficiency.

An upstream activator sequence regulates the murine Pgk-1 promoter and binds multiple nuclear proteins

The murine Pgk-1 gene is driven by a strong promoter that is regulated by a 304 bp upstream activator sequence (UAS). The activity of the UAS is high in undifferentiated embryonal carcinoma cells but declines when these cells are induced to differentiate with retinoic acid. The effect of the UAS on promoter activity is particularly striking when the activity of the Pgk-1 promoter is assayed following its integration into the genome, suggesting that it may function by regulating chromatin structure in the region of the core promoter. Three sites on the UAS bind nuclear proteins. Two of these sites bind factors present in both embryonal carcinoma cells and their differentiated derivatives whereas one site binds factors present only in differentiated cells. There appears to be both cooperation and antagonism in the binding of proteins to different sites in the UAS, suggesting that the activity of the Pgk-1 promoter is determined by the constellation of proteins assembled upstream of its transcription start site.

Mammalian-Specific Central Myelin Protein Opalin Is Redundant for Normal Myelination: Structural and Behavioral Assessments

Opalin, a central nervous system-specific myelin protein phylogenetically unique to mammals, has been suggested to play a role in mammalian-specific myelin. To elucidate the role of Opalin in mammalian myelin, we disrupted the Opalin gene in mice and analyzed the impacts on myelination and behavior. Opalin-knockout (Opalin^−/−) mice were born at a Mendelian ratio and had a normal body shape and weight. Interestingly, Opalin^−/− mice had no obvious abnormalities in major myelin protein compositions, expression of oligodendrocyte lineage markers, or domain organization of myelinated axons compared with WT mice (Opalin^+/+) mice. Electron microscopic observation of the optic nerves did not reveal obvious differences between Opalin^+/+ and Opalin^−/− mice in terms of fine structures of paranodal loops, transverse bands, and multi-lamellae of myelinated axons. Moreover, sensory reflex, circadian rhythm, and locomotor activity in the home cage, as well as depression-like behavior, in the Opalin^−/− mice were indistinguishable from the Opalin^+/+ mice. Nevertheless, a subtle but significant impact on exploratory activity became apparent in Opalin^−/− mice exposed to a novel environment. These results suggest that Opalin is not critical for central nervous system myelination or basic sensory and motor activities under conventional breeding conditions, although it might be required for fine-tuning of exploratory behavior.

The long terminal repeat negative control region is a critical element for insertional oncogenesis after gene transfer into hematopoietic progenitors with Moloney murine leukemia viral vectors

Integrating vectors based on γ-retroviruses and containing full-length long terminal repeats (LTRs) have been associated with activation of oncogene expression and leukemogenesis in human gene therapy trials. Identification of the specific molecular elements of the LTRs that have a role in insertional oncogenesis events is important as it can lead to the development of safer gene transfer vectors. The negative control region (NCR) of the LTR is a particularly well-conserved sequence among mammalian γ-retroviruses with demonstrated regulatory activity of gene transcription in hematopoietic cells, which led us to hypothesize that this region may have a role in insertional oncogenesis after γ-retroviral vector (GV)-mediated gene transfer into hematopoietic progenitors. We used an in vitro assay of murine bone marrow cell immortalization to compare the immortalization capabilities of a series of GVs carrying murine leukemia virus (MLV) LTR deletion mutants. Compared with GV carrying the full-length MLV LTR, deletion of the complete LTR enhancer sequence showed significant reduction of immortalization rates. However, the use of a mutant LTR deleted of the enhancer sequence, with exception of the NCR, did not affect immortalization. Importantly, the inclusion of an LTR mutant devoid only of the NCR did show significant reduction of immortalization rates compared with the full LTR sequence. Therefore, our data point to the NCR as a key element for immortalization and justify additional studies to evaluate its specific role in MLV-mediated insertional oncogenesis.

The bimodally expressed microRNA miR-142 gates exit from pluripotency

A stem cell's decision to self‐renew or differentiate is thought to critically depend on signaling cues provided by its environment. It is unclear whether stem cells have the intrinsic capacity to control their responsiveness to environmental signals that can be fluctuating and noisy. Using a novel single‐cell microRNA activity reporter, we show that miR‐142 is bimodally expressed in embryonic stem cells, creating two states indistinguishable by pluripotency markers. A combination of modeling and quantitative experimental data revealed that mESCs switch stochastically between the two miR‐142 states. We find that cells with high miR‐142 expression are irresponsive to differentiation signals while cells with low miR‐142 expression can respond to differentiation cues. We elucidate the molecular mechanism underpinning the bimodal regulation of miR‐142 as a double‐negative feedback loop between miR‐142 and KRAS/ERK signaling and derive a quantitative description of this bistable system. miR‐142 switches the activation status of key intracellular signaling pathways thereby locking cells in an undifferentiated state. This reveals a novel mechanism to maintain a stem cell reservoir buffered against fluctuating signaling environments.

MXS-Chaining: A Highly Efficient Cloning Platform for Imaging and Flow Cytometry Approaches in Mammalian Systems

The continuous improvement of imaging technologies has driven the development of sophisticated reporters to monitor biological processes. Such constructs should ideally be assembled in a flexible enough way to allow for their optimization. Here we describe a highly reliable cloning method to efficiently assemble constructs for imaging or flow cytometry applications in mammalian cell culture systems. We bioinformatically identified a list of restriction enzymes whose sites are rarely found in human and mouse cDNA libraries. From the best candidates, we chose an enzyme combination (MluI, XhoI and SalI: MXS) that enables iterative chaining of individual building blocks. The ligation scar resulting from the compatible XhoI- and SalI-sticky ends can be translated and hence enables easy in-frame cloning of coding sequences. The robustness of the MXS-chaining approach was validated by assembling constructs up to 20 kb long and comprising up to 34 individual building blocks. By assessing the success rate of 400 ligation reactions, we determined cloning efficiency to be 90% on average. Large polycistronic constructs for single-cell imaging or flow cytometry applications were generated to demonstrate the versatility of the MXS-chaining approach. We devised several constructs that fluorescently label subcellular structures, an adapted version of FUCCI (fluorescent, ubiquitination-based cell cycle indicator) optimized to visualize cell cycle progression in mouse embryonic stem cells and an array of artificial promoters enabling dosage of doxycyline-inducible transgene expression. We made publicly available through the Addgene repository a comprehensive set of MXS-building blocks comprising custom vectors, a set of fluorescent proteins, constitutive promoters, polyadenylation signals, selection cassettes and tools for inducible gene expression. Finally, detailed guidelines describe how to chain together prebuilt MXS-building blocks and how to generate new customized MXS-building blocks.

Chromatin position effects assayed by thousands of reporters integrated in parallel

Reporter genes integrated into the genome are a powerful tool to reveal effects of regulatory elements and local chromatin context on gene expression. However, so far such reporter assays have been of low throughput. Here, we describe a multiplexing approach for the parallel monitoring of transcriptional activity of thousands of randomly integrated reporters. More than 27,000 distinct reporter integrations in mouse embryonic stem cells, obtained with two different promoters, show ∼1,000-fold variation in expression levels. Data analysis indicates that lamina-associated domains act as attenuators of transcription, likely by reducing access of transcription factors to binding sites. Furthermore, chromatin compaction is predictive of reporter activity. We also found evidence for crosstalk between neighboring genes and estimate that enhancers can influence gene expression on average over ∼20 kb. The multiplexed reporter assay is highly flexible in design and can be modified to query a wide range of aspects of gene regulation.

Highly efficient, in vivo optimized, archaeal endonuclease for controlled RNA splicing in mammalian cells

ARCHAEA-ExPRESs is an mRNA modification technology that makes use of components derived from the Archaeon Methanocaldococcus jannaschii, namely the tRNA splicing endonuclease (MJ-EndA) and its natural substrate, the bulge-helix-bulge (BHB) structure (1). These components can perform both cis- and trans-splicing in cellular and animal models and may provide a convenient way to modulate gene expression using components independent of cellular regulatory networks. To use MJ-EndA in stable expression mammalian systems, we developed variants characterized by high efficiency and sustainable in vivo activity. The MJ-EndA variants were created by the introduction of proper localization signals followed by mutagenesis and direct selection in mammalian cells. Of note, enzyme selection used an in vivo selection method based on puromycin resistance conferred to cells by BHB-mediated intron splicing from an out-of-frame puromycin N-acetyl transferase (PAC) gene. This approach yielded several endonuclease variants, the best of which showed 40-fold higher activity compared to the parental enzyme and stable processing of 30% of the target mRNA. Notably, these variants showed complete compatibility with long-term expression in mammalian cells, suggesting that they may be usefully applied in functional genomics and genetically modified animal models.

Treatment of canine leukocyte adhesion deficiency by foamy virus vectors expressing CD18 from a PGK promoter

Proto-oncogene activation caused by retroviral vector integration can cause malignancies in gene therapy trials. This has led investigators to search for less genotoxic vectors with minimal enhancer activity and a decreased risk of influencing neighboring chromosomal gene expression after integration. We previously showed that foamy virus vectors expressing the canine CD18 gene from an internal murine stem cell virus promoter could cure canine leukocyte adhesion deficiency. Here we have repeated these studies using a foamy virus vector expressing canine CD18 from a phosphoglycerate kinase gene promoter. In vitro analysis showed that this vector did not contain an enhancer that activated neighboring genes, and it expressed CD18 efficiently in canine neutrophils and CD34+ cells. However, dogs that received hematopoietic stem cells transduced with the PGK-CD18 vector continued to suffer from leukocyte adhesion deficiency, and sometimes died prematurely of the disease. These studies show that the phosphoglycerate kinase promoter cannot effectively replace the murine stem cell virus promoter in CD18-expressing foamy virus vectors, and they suggest that vectors containing a strong promoter/enhancer may be necessary for the treatment of human leukocyte adhesion deficiency.

Genome-wide maps of transcription regulatory elements

Expression of eukaryotic genes with complex spatial-temporal regulation during development requires finer regulation than that of genes with simpler expression patterns. Given the high degree of conservation of the developmental gene set across distantly related phylogenetic taxa, it is argued that evolutionary variation has occurred by tweaking regulation of expression of developmental genes, rather than by changes in genes themselves. Complex regulation is often achieved through the coordinated action of transcription regulatory elements spread across the genome up to tens of kilobases from the promoters of their target genes. Disruption of regulatory elements has been implicated in several diseases and studies showing associations between disease traits and nonprotein coding variation hint for a role of regulatory elements as cause of diseases. Therefore, the identification and mapping of regulatory elements in genome scale is crucial to understand how gene expression is regulated, how organisms evolve, and to identify sequence variation causing diseases. Previously developed experimental techniques have been adapted to identify regulatory elements in genome scale and high-throughput, allowing a global view of their biological roles. We review methods as chromatin immunoprecipitation, DNase I hypersensitivity, and computational approaches and how they have been employed to generate maps of histone modifications, open chromatin, nucleosome positioning, and transcription factor binding regions in whole mammalian genomes. Given the importance of non-promoter elements in gene regulation and the recent explosion in the number of studies devoted to them, we focus on these elements and discuss the insights on gene regulation being obtained by these studies.

Stable suppression of gene expression by short interfering RNAs targeted to promoter in a mouse embryonal carcinoma stem cell line

RNA interference (RNAi) can induce gene silencing via two pathways: post-transcriptional gene silencing (PTGS) and transcriptional gene silencing (TGS). The mediators of gene inactivation in both pathways are 21-bp small interfering RNAs (siRNAs) generated from longer double-stranded RNA (dsRNA). PTGS involves siRNA-mediated targeting and degradation of mRNA. However, siRNAs induce TGS via DNA methylation at the targeted promoter. Synthetic siRNAs can induce loss of gene activity comparable to long dsRNA. The limitation of this method is that the transfected synthetic siRNA works for only a few days. In this study, we tested the RNAi response to siRNA (PTGS pathway) by using a plasmid containing an enhanced green fluorescent protein (eGFP) gene as a target as well as a plasmid creates siRNA transcript, in a form of a hairpin, against eGFP gene. To investigate TGS pathway via RNAi, we also used a plasmid creates hairpin siRNA transcript against pgk-1 promoter. The data presented here indicated long-lasting inhibition in expression of eGFP and puromycin genes, both under the control of the murine Pgk-1 promoter. However, Southern blot analysis showed no methylation in pgk-1 promoter.

GATA-1 directly regulates p21 gene expression during erythroid differentiation

Lineage-determination transcription factors coordinate cell differentiation and proliferation by controlling the synthesis of lineage-specific gene products as well as cell cycle regulators. GATA-1 is a master regulator of erythropoiesis. Its role in regulating erythroid-specific genes has been extensively studied, whereas its role in controlling genes that regulate cell proliferation is less understood. Ectopic expression of GATA-1 in erythroleukemia cells releases the block to their differentiation and leads to terminal cell division. An early event in reprogramming the erythroleukemia cells is induction of the cyclin-dependent kinase inhibitor p21. Remarkably, ectopic expression of p21 also induces the erythroleukemia cells to differentiate. We now report that GATA-1 directly regulates transcription of the p21 gene in both erythroleukemia cells and normal erythroid progenitors. Using reporter, electrophoretic mobility shift, and chromatin immunoprecipitation assays, we show that GATA-1 stimulates p21 gene transcription by binding to consensus binding sites in the upstream region of the p21 gene promoter. This activity is also dependent on a binding site for Sp1/KLF-like factors near the transcription start site. Our findings indicate that p21 is a crucial downstream gene target and effector of GATA-1 during red blood cell terminal differentiation.

Overview: generation of gene knockout mice

The technique of gene targeting allows for the introduction of engineered genetic mutations into a mouse at a determined genomic locus. The process of generating mouse models with targeted mutations was developed through both the discovery of homologous recombination and the isolation of murine embryonic stem cells (ES cells). Homologous recombination is a DNA repair mechanism that is employed in gene targeting to insert a designed mutation into the homologous genetic locus. Targeted homologous recombination can be performed in murine ES cells through electroporation of a targeting construct. These ES cells are totipotent and, when injected into a mouse blastocyst, they can differentiate into all cell types of a chimeric mouse. A chimeric mouse harboring cells derived from the targeted ES cell clone can then generate a whole mouse containing the desired targeted mutation. The initial step for the generation of a mouse with a targeted mutation is the construction of an efficient targeting vector that will be introduced into the ES cells.

Dermatan sulfate epimerase 1-deficient mice have reduced content and changed distribution of iduronic acids in dermatan sulfate and an altered collagen structure in skin

Dermatan sulfate epimerase 1 (DS-epi1) and DS-epi2 convert glucuronic acid to iduronic acid in chondroitin/dermatan sulfate biosynthesis. Here we report on the generation of DS-epi1-null mice and the resulting alterations in the chondroitin/dermatan polysaccharide chains. The numbers of long blocks of adjacent iduronic acids are greatly decreased in skin decorin and biglycan chondroitin/dermatan sulfate, along with a parallel decrease in iduronic-2-O-sulfated-galactosamine-4-O-sulfated structures. Both iduronic acid blocks and iduronic acids surrounded by glucuronic acids are also decreased in versican-derived chains. DS-epi1-deficient mice are smaller than their wild-type littermates but otherwise have no gross macroscopic alterations. The lack of DS-epi1 affects the chondroitin/dermatan sulfate in many proteoglycans, and the consequences for skin collagen structure were initially analyzed. We found that the skin collagen architecture was altered, and electron microscopy showed that the DS-epi1-null fibrils have a larger diameter than the wild-type fibrils. The altered chondroitin/dermatan sulfate chains carried by decorin in skin are likely to affect collagen fibril formation and reduce the tensile strength of DS-epi1-null skin.

Self-inactivating retroviral vector-mediated gene transfer induces oncogene activation and immortalization of primary murine bone marrow cells

Insertional mutagenesis leading to insurgence of leukemia has been shown as a consequence of retroviral (RV)-mediated gene transfer in animal models and in clinical trials of gene therapy for X-linked severe combined immunodeficiency. Aberrant expression of oncogenes neighboring the gamma-RV vector insertion site via induction by the enhancer element of the viral long terminal repeats (LTRs) is thought to have played a role in leukemogenesis. Consequently, RV vectors devoid of LTR enhancer elements could prove as safer tools for gene transfer. To test this hypothesis, we evaluated the immortalization ability of two RV vectors: one carrying the full-length Moloney leukemia virus (MLV) LTR and one with the same LTR in which the enhancer element was deleted [MLV self-inactivating (SIN)]. Unexpectedly, transduction with MLV SIN resulted in an only slightly and not significant decreased immortalization frequency of primary bone marrow (BM) cultures (about 37%) compared to transduction with MLV (about 48%). Similar to MLV, immortalization by MLV SIN is likely caused by insertional activation of oncogenes including Evi1, Mds1, Mef2c, and Hoxa7. Our results indicate that the MLV SIN, devoid of the LTR enhancer element, was still able to immortalize BM cells by activating nearby gene expression, indicating the need of an accurate selection of the internal promoter to obtain safer SIN RV vectors.

Generation of double-knockout embryonic stem cells

Gene inactivation in mouse embryonic stem (ES) cells usually affects a single allele that is subsequently transmitted to the mouse germline. Upon breeding to homozygosity the consequences of complete gene ablation can be studied in the context of the complete organism. In many cases, it can be useful to study the consequences of gene ablation already in ES cells, for example, when a cellular phenotype is expected. This requires both alleles of a gene to be disrupted. Besides consecutive targeting by using different selectable marker genes, homozygosity for gene disruption can also be obtained by selecting cells for duplication of (part of) the chromosome carrying the targeted allele with concomitant loss of the wild-type allele.

HIV-1 assembly: viral glycoproteins segregate quantally to lipid rafts that associate individually with HIV-1 capsids and virions

HIV-1 assembly depends on its structural protein, Gag, which after synthesis on ribosomes, traffics to the late endosome/plasma membrane, associates with HIV Env glycoprotein, and forms infectious virions. While Env and Gag migrate to lipid microdomains, their stoichiometry and specificity of interaction are unknown. Pseudotyped viral particles can be made with one viral core surrounded by heterologous envelope proteins. Taking advantage of this property, we analyzed the association of HIV Env and Ebola glycoprotein (GP), with HIV-1 Gag coexpressed in the same cell. Though both viral glycoproteins were expressed, each associated independently with Gag, giving rise to distinct virion populations, each with a single glycoprotein type. Confocal imaging demonstrated that Env and GP localized to distinct lipid raft microdomains within the same cell where they associated with different virions. Thus, a single Gag particle associates “quantally” with one lipid raft, containing homogeneous trimeric viral envelope proteins, to assemble functional virions.

Implication of endogenous beta-endorphin in the inhibition of the morphine-induced rewarding effect by the direct activation of spinal protein kinase C in mice

It has often been proposed that opioid addiction does not arise as a consequence of opioid treatment for pain. Recently, we demonstrated that activated protein kinase C (PKC) in the spinal cord associated with chronic pain-like hyperalgesia suppressed the morphine-induced rewarding effect in mice. In the present study, we investigated whether a gene deletion for an endogenous mu-opioid peptide beta-endorphin could affect pain-like behavior and the suppression of the morphine-induced rewarding effect by the direct activation of PKC in the spinal cord. We found that activation of spinal PKC by intrathecal (i.t.) treatment with phorbol 12,13-dibutyrate (PDBu), a specific PKC activator, caused thermal hyperalgesia, pain-like behaviors and suppression of the morphine-induced rewarding effect. This suppression of morphine reward was eliminated in mice that lacked beta-endorphin. In contrast, thermal hyperalgesia and pain-like behaviors were not affected in beta-endorphin knockout mice. These results suggest that the activation of PKC in the spinal cord may play an essential role in the suppression of the morphine-induced rewarding effect in mice with neuropathic pain through the constant release of beta-endorphin.

An oligodendrocyte enhancer in a phylogenetically conserved intron region of the mammalian myelin gene Opalin

Opalin is a transmembrane protein detected specifically in mammalian oligodendrocytes. Opalin homologs are found only in mammals and not in the genome sequences of other animal classes. We first determined the nucleotide sequences of Opalin orthologs and their flanking regions derived from four prosimians, a group of primitive primates. A global comparison revealed that an evolutionarily conserved region exists in the first intron of Opalin. When the conserved domain was assayed for its enhancer activity in transgenic mice, oligodendrocyte-directed expression was observed. In an oligodendroglial cell line, Oli-neu, the conserved domain showed oligodendrocyte-directed expression. The conserved domain is composed of eight subdomains, some of which contain binding sites for Myt1 and cAMP-response element binding protein (CREB). Deletion analysis and cotransfection experiments revealed that the subdomains have critical roles in Opalin gene expression. Over-expression of Myt1, treatment of the cell with leukemia inhibitory factor (LIF), and cAMP analog (CREB activator) enhanced the expression of endogenous Opalin in Oli-neu cells and activated the oligodendrocyte enhancer. These results suggest that LIF, cAMP signaling cascades and Myt1 play significant roles in the differentiation of oligodendrocytes through their action on the Opalin oligodendrocyte enhancer.

Positive regulation of immune cell function and inflammatory responses by phosphatase PAC-1

Mitogen-activated protein kinases facilitate many cellular processes and are essential for immune cell function. Their activity is controlled by kinases and dual-specificity phosphatases. A comprehensive microarray analysis of human leukocytes identified DUSP2 (encoding the phosphatase PAC-1) as one of the most highly induced transcripts in activated immune cells. We generated Dusp2(-/-) mice and found considerably reduced inflammatory responses in the 'K/BxN' model of rheumatoid arthritis. PAC-1 deficiency led to increased activity of Jun kinase (Jnk) but unexpected impairment of the activity of extracellular signal-regulated kinase (Erk) and the kinase p38, reduced activity of the transcription factor Elk1 and a complex of mobilized transcription factor NFAT and the AP-1 transcription factor and decreased effector immune cell function. Thus, PAC-1 is a key positive regulator of inflammatory cell signaling and effector functions, mediated through Jnk and Erk mitogen-activated protein kinase crosstalk.

Use of the hereditary persistence of fetal hemoglobin 2 enhancer to increase the expression of oncoretrovirus vectors for human gamma-globin

The development of oncoretrovirus vectors for human gamma-globin has been hampered by problems of low expression and gene silencing. In order to address these problems, we investigated an enhancer element identified from individuals with deletional hereditary persistence of fetal hemoglobin 2 (HPFH2), a genetic condition characterized by elevated levels of gamma-globin in adults. Plasmid transfection studies in erythroid MEL (murine erythroleukemia) cells demonstrated the HPFH2 element could function synergistically with the beta-globin locus control region to enhance the expression of an Agamma-globin gene with a truncated -382 bp promoter. A series of oncoretrovirus vectors were subsequently generated that contain an expression cassette for Agamma-globin linked to various combinations of the HPFH2 enhancer, the alpha-globin HS40 enhancer, and several versions of the promoter from Agamma-globin or beta-globin. Expression analysis in transduced MEL cell clones revealed very high levels of promoter-autonomous silencing that was at least partially abrogated by the HPFH2 enhancer. The vector containing a combination of a -201 bp Agamma-globin gene promoter with the Greek HPFH -117 point mutation and both the HPFH2 and HS40 enhancers exhibited no signs of vector silencing and was expressed at 248+/-99% per copy of mouse alpha-globin (62% of total alpha-globin). This represents a significant improvement over previously reported oncoretrovirus vectors for Agamma-globin, and demonstrates the capacity of the HPFH2 enhancer to abrogate sequence-autonomous silencing of the Agamma-globin promoter in the context of a gene transfer vector.

Rasgrf1 imprinting is regulated by a CTCF-dependent methylation-sensitive enhancer blocker

Imprinted methylation of the paternal Rasgrf1 allele in mice occurs at a differentially methylated domain (DMD) 30 kbp 5' of the promoter. A repeated sequence 3' of the DMD regulates imprinted methylation, which is required for imprinted expression. Here we identify the mechanism by which methylation controls imprinting. The DMD is an enhancer blocker that binds CTCF in a methylation-sensitive manner. CTCF bound to the unmethylated maternal allele silences expression. CTCF binding to the paternal allele is prevented by repeat-mediated methylation, allowing expression. Optimal in vitro enhancer-blocking activity requires CTCF binding sites. The enhancer blocker can be bypassed in vivo and imprinting abolished by placing an extra enhancer proximal to the promoter. Together, the repeats and the DMD constitute a binary switch that regulates Rasgrf1 imprinting.

Granuphilin molecularly docks insulin granules to the fusion machinery

The Rab27a effector granuphilin is specifically localized on insulin granules and is involved in their exocytosis. Here we show that the number of insulin granules morphologically docked to the plasma membrane is markedly reduced in granuphilin-deficient β cells. Surprisingly, despite the docking defect, the exocytosis of insulin granules in response to a physiological glucose stimulus is significantly augmented, which results in increased glucose tolerance in granuphilin-null mice. The enhanced secretion in mutant β cells is correlated with a decrease in the formation of the fusion-incompetent syntaxin-1a–Munc18-1 complex, with which granuphilin normally interacts. Furthermore, in contrast to wild-type granuphilin, its mutant that is defective in binding to syntaxin-1a fails to restore granule docking or the protein level of syntaxin-1a in granuphilin-null β cells. Thus, granuphilin not only is essential for the docking of insulin granules but simultaneously imposes a fusion constraint on them through an interaction with the syntaxin-1a fusion machinery. These findings provide a novel paradigm for the docking machinery in regulated exocytosis.

The human beta-globin locus control region can silence as well as activate gene expression

Using recombinase-mediated cassette exchange to test multiple transgenes at the same site of integration, we demonstrate a novel chromatin context-dependent silencer activity of the beta-globin locus control region (LCR). This silencer activity requires DNase I hypersensitive sites HS2 and HS3 but not HS4. After silencing, the silenced cassettes adopt a typical closed chromatin conformation (histone H3 and H4 deacetylation, histone H3-K4 methylation, DNA methylation, and replication in late S phase). In the absence of the LCR at the same site of integration, the chromatin remains decondensed. We demonstrate that the LCR is necessary but not sufficient to trigger these chromatin changes. We also provide evidence that this novel silencing activity is caused by transcriptional interference triggered by activation of transcription in the flanking sequences by the LCR.

Implication of cyclin-dependent kinase 5 in the development of psychological dependence on and behavioral sensitization to morphine

In the present study, we investigated the role of cyclin-dependent kinase 5 (cdk5) in the brain dynamics changed by repeated in vivo treatment with morphine. The level of phosphorylated-cdk5 was significantly increased in the cingulate cortex of mice showing the morphine-induced rewarding effect. Under these conditions, roscovitine, a cdk5 inhibitor, given intracerebroventricularly (i.c.v.) caused a dose-dependent and significant inhibition of the morphine-induced rewarding effect. In addition, the dose-response effect of the morphine-induced rewarding effect was dramatically attenuated in cdk5 heterozygous (+/-) knockout mice. Furthermore, the development of behavioral sensitization by intermittent administration of morphine was virtually abolished in cdk5 (+/-) mice. These findings suggest that the induction and/or activation of cdk5 are implicated in the development of psychological dependence on morphine.

Anatomical identification of neurons responsive to nociceptive stimuli

We describe methods for labeling and identifying neurons within the central nervous system involved in the transmission of nociceptive stimuli. The most reliable methods are physiological identification followed by intracellular injection or immunocytochemical detection of stimulus-induced markers such as Fos. These latter strategies are used with appropriate controls to distinguish neurons activated secondarily (e.g., motor response or inhibitory neurons) by the nociceptive stimuli. Other methods include location and morphology as determined by standard cytological and tracing methods and/or the presence of specific neurochemical markers such as substance P determined by immunocytochemistry.

A pro-apoptotic fragment of the p75 neurotrophin receptor is expressed in p75NTRExonIV null mice

The p75 neurotrophin receptor (p75NTR) regulates neuronal survival, apoptosis, and growth. Recent studies have reported that disruption of Exon IV produces a null mouse lacking all p75NTR gene products (p75NTRExonIV-/-), whereas mice lacking p75NTR Exon III (p75NTRExonIII-/-) maintain expression of an alternatively spliced form of p75NTR (s-p75NTR). Here, we report that p75NTRExonIV-/- mice express a p75NTR gene product that encodes a truncated protein containing the extracellular stalk region together with the entire transmembrane and intracellular domains. The gene product is initiated from a cryptic Kozak consensus/initiator ATG sequence within a region of Exon IV located 3' to the pGK-Neo insertion site. Overexpression of this fragment in heterologous cells results in activation of Jun kinase and induces Pro-caspase-3 cleavage, indicating that it activates p75NTR signaling cascades. These results indicate that aspects of the p75NTRExonIV-/- phenotype may reflect a gain-of-function mutation rather than loss of p75NTR function.

CHD1 associates with NCoR and histone deacetylase as well as with RNA splicing proteins

CHD1 is one of a family of nuclear proteins containing two chromodomains, a SWI/SNF-like helicase/ATPase domain and a DNA binding domain. We found that CHD1 co-immunoprecipitates with histone deacetylase (HDAC) activity and that CHD1 also associates with NCoR, a transcriptional corepressor, in yeast two-hybrid and in vitro pull-down assays. NCoR is known to associate with HDACs to effect its repressive activity, suggesting that the predicted chromatin remodeling activity of CHD1 plays a role in this repression. Yeast two-hybrid assays also showed that CHD1 interacts with splicing proteins mKIAA0164, Srp20, and SAF-B. Splicing assays show that CHD1 overexpression can affect alternative splicing. These results suggest that CHD1 may function in both chromatin mediated transcriptional repression and RNA splicing.

Functional domains of FOXJ2

FOXJ2 is a fork head transcriptional activator, the expression of which starts very early in embryonic development and it is distributed widely in the adult. Here, we describe the characterization of domains that are important for its function. FOXJ2 is localized constitutively at the nucleus of the cell. Two tyrosine residues and a stretch of basic amino acid residues at the N and C-terminal ends of the fork head domain, respectively, are important for its nuclear targeting. These residues are conserved strongly among all members of the fork head family, suggesting that they could be involved in the nuclear translocation mechanism of all fork head factors. In addition to the AB domain, we have found, at least, two other transactivation domains: Domain I, at the N terminus, and the H/P domain, rich in histidine and proline residues. Although the AB domain shows the strongest transactivation capacity, all three domains are required for full FOXJ2 transcriptional activity. Furthermore, a fourth region rich in proline and glutamine residues and with no intrinsic transactivation function, the P/Q domain, appears to play an important role in the FOXJ2-mediated transactivation mechanism. Although FOXJ2 can be phosphorylated in two serine residues, this post-translational modification did not appear to be essential for transactivation. Finally, we have found that the W2 wing of the fork head domain of FOXJ2 is dispensable for specific DNA binding, although it could have a weak stabilizing role for the DNA-FOXJ2 complex.

Protective role of phosphorylation in turnover of glial fibrillary acidic protein in mice

Glial fibrillary acidic protein (GFAP), the principal intermediate filament (IF) protein of mature astrocytes in the CNS, plays specific roles in astrocyte functions. GFAP has multiple phosphorylation sites at its N-terminal head domain. To examine the role of phosphorylation at these sites, we generated a series of substitution mutant mice in which phosphorylation sites (Ser/Thr) were replaced by Ala, in different combinations. Gfap(hm3/hm3) mice carrying substitutions at all five phosphorylation sites showed extensive decrease in both filament formation and amounts of GFAP. Gfap(hm1/hm1) and Gfap(hm2/hm2) mice, which carry substitutions at three of five sites and in different combinations, showed differential phenotypes. Although Gfap(hm3/hm3) mice retained GFAP filaments in Bergmann glia in the cerebellum, the (Gfap(hm3/hm3):Vim(-/-)) mice lacked GFAP filaments. Pulse-chase experiments of cultured astrocytes indicated that the Hm3-GFAP encoded by Gfap(hm3) was unstable particularly in the absence of vimentin, another IF protein. These results revealed the role of phosphorylation in turnover of GFAP and a synergistic role of GFAP and vimentin in the dynamics of glial filaments. The data further suggest that each of the phosphorylated sites has a distinct impact on the dynamics of GFAP.

Efficient marking of neural stem cell-derived neurons with a modified murine embryonic stem cell virus, MESV2

Treatments for nervous system disorders that involve transplanting genetically modified neural stem cells may ultimately be feasible. As a step towards this therapeutic approach, a novel murine embryonic stem cell gammaretroviral vector was developed with features designed to optimize transgene expression in neural stem cells and to increase vector safety. All potential start sites of translation in the 5' leader were removed. These sites may compete with an inserted transgene for translation initiation, and also produce potentially immunogenic peptides. Further, all of the gag gene sequences were replaced with a well-defined constitutive transport element from avian leukemia virus to promote nuclear export of viral RNA, and to eliminate any homology between the vector and a murine leukemia virus-derived gag-pol packaging plasmid. Two versions of the virus were made in which EGFP expression was driven either by the Rous sarcoma virus U3 enhancer or by a combination of sequences from the Syn1 and Pgk-1 promoters. Both of these viruses efficiently transduced neural stem cells isolated from embryonic rat hippocampus, and robust EGFP expression was observed in neurons derived from these cells following differentiation in vitro.

Development and optimization of a real-time quantitative PCR-based method for the titration of AAV-2 vector stocks

Despite the clinical application of adeno-associated virus (AAV) gene therapy, the titration of viral stocks has not yet been standardized. This complicates the comparison of viral stocks between laboratories. Functional titering of AAV is time-consuming, requires the manipulation of hazardous material, and often has a high degree of variability. We established an optimized real-time quantitative polymerase chain reaction (RQ-PCR) titration assay to determine viral titers and compared it with a functional green fluorescent protein (GFP)-based titration method. With a combination of improved lysis procedures and RQ-PCR protocols we could decrease the intraexperimental coefficient of variation (CV) from 0.24 +/- 0.03 to 0.042 +/- 0.004 and the interexperimental CV from 0.34 +/- 0.06 to 0.093 +/- 0.028 following functional and RQPCR-based titration, respectively. This low variability conforms to even the strictest quality standards required, for example, in clinical laboratories. The highly standardized titration by RQPCR described here will be especially advantageous for groups working on AAV-based gene therapy in a good manufacturing practice setting.

Abnormal organogenesis of Peyer's patches in mice deficient for NF-kappaB1, NF-kappaB2, and Bcl-3

BACKGROUND & AIMS

Nuclear factor (NF) kappaB1, NF-kappaB2, and Bcl-3 encode for proteins of the NF-kappaB/Rel/IkappaB families, known as regulators of innate and adoptive immune responses. Targeted disruption of these genes showed essential roles in lymphoid organ development and organization.

METHODS

NF-kappaB1-, NF-kappaB2-, and Bcl-3-deficient mouse lines were established, and their role in organogenesis of Peyer's patches (PP) was investigated.

RESULTS

Macroscopic inspection showed a reduced number and size of PP in Bcl-3(-/-) and NF-kappaB1(-/-) mice but failed to detect PP in NF-kappaB2(-/-) mice. Whole-mount in situ hybridization revealed the presence of interleukin-7 receptor-alpha spots in NF-kappaB2(-/-) mice, indicating no defect in PP organogenesis of NF-kappaB2(-/-) mice in principle. Immunostaining shows that residual lymphocytes mainly consist of T cells. B cells are substantially reduced and are accumulated as terminal extravasations. Organized follicular structures and follicular dendritic cell networks fail to form, and myeloid, but not lymphoid, dendritic cells are obviously reduced. Expression of the chemokines macrophage inflammatory protein-3alpha, B-lymphocyte chemoattractant, and thymus-expressed chemokine is impaired in epithelial cells and in the subendothelial dome area that is not well defined. A similar but less severe phenotype is seen in Bcl-3(-/-) mice, which also do not develop germinal centers. In contrast, in NF-kappaB1(-/-) mice, T-cell numbers are visibly reduced, and no alteration could be observed in the B-cell and dendritic-cell populations.

CONCLUSIONS

These data show that all 3 genes are crucial for PP development but contribute differently to PP organogenesis.

Cartilage oligomeric matrix protein-deficient mice have normal skeletal development

Cartilage oligomeric matrix protein (COMP) belongs to the thrombospondin family and is a homopentamer primarily expressed in cartilage. Mutations in the COMP gene result in the autosomal dominant chondrodysplasias pseudoachondroplasia (PSACH) and some types of multiple epiphyseal dysplasia (MED), which are characterized by mild to severe short-limb dwarfism and early-onset osteoarthritis. We have generated COMP-null mice to study the role of COMP in vivo. These mice show no anatomical, histological, or ultrastructural abnormalities and show none of the clinical signs of PSACH or MED. Northern blot analysis and immunohistochemical analysis of cartilage indicate that the lack of COMP is not compensated for by any other member of the thrombospondin family. The results also show that the phenotype in PSACH/MED cartilage disorders is not caused by the reduced amount of COMP.

Dual functions of [alpha]4[beta]1 integrin in epicardial development: initial migration and long-term attachment

The epicardium of the mammalian heart arises from progenitor cells outside the developing heart. The epicardial progenitor (EPP) cells migrate onto the heart through a cyst-mediated mechanism in which the progenitors are released from the tissue of origin as cysts; the cysts float in the fluid of the pericardial cavity and attach to the naked myocardial surface of the heart, and cells in the cysts then migrate out to form an epithelial sheet. In this paper, we show that the gene encoding the alpha4 subunit of alpha4beta1 integrin (alpha4beta1) is essential for this migratory process. We have generated a knockin mutation in mice replacing the alpha4 integrin gene with the lacZ reporter gene, placing lacZ under the control of the alpha4 integrin promoter. We show that in homozygous mutant embryos, the migration of EPP progenitor cells is impaired due to inefficient budding of the cysts and a failure of the cells in the cysts to migrate on the heart. This study provides direct genetic evidence for essential roles for alpha4beta1 integrin-mediated cell adhesion in the migration of progenitor cells to form the epicardium, in addition to a previous finding that alpha4beta1 is essential for maintaining the epicardium (Yang, J.T., H. Rayburn, and R.O. Hynes. 1995. Development. 121:549-560).

Distribution of phosphorylated glial fibrillary acidic protein in the mouse central nervous system

BACKGROUND

Glial fibrillary acidic protein (GFAP) is the principal component of intermediate filaments (IFs) in mature astrocytes in the central nervous system (CNS). Like other IF proteins, GFAP has multiple phosphorylation sites in the N-terminal head domain. The distribution of phospho-GFAP in vivo has not been elucidated.

RESULTS

We generated Gfap(hwt) knock-in mice, in which the coding region for the head domain of GFAP is replaced with the corresponding human sequence. In combination with a series of monoclonal antibodies (mAbs) reactive to human phospho-GFAP, we visualized the distribution of phospho-GFAP in vivo in mice. GFAP phosphorylated at Thr7, Ser8 and/or Ser13 increased postnatally in the CNS of these mice. Limited populations of GFAP-positive astrocytes were labelled with anti-phospho-GFAP mAbs in most brain areas, whereas almost all the astrocytes in the optic nerve and spinal cord were labelled. Astrocytes in the subventricular zone and rostral migratory stream preferentially contained phospho-GFAP. In a cold injury model of the cerebral cortex, we detected phospho-GFAP in reactive astrocytes at 2-3 weeks after the injury.

CONCLUSIONS

Phospho-GFAP provides a molecular marker indicating the heterogeneity of astrocytes, and Gfap(hwt) knock-in mice will aid in monitoring intracellular conditions of astrocytes, under various conditions. Our results suggest that the phosphorylation of GFAP plays a role in non-dividing astrocytes in vivo.

Transient disruption of autocrine TGF-beta signaling leads to enhanced survival and proliferation potential in single primitive human hemopoietic progenitor cells

Hemopoietic stem cells (HSCs) are maintained at relative quiescence by the balance between the positive and negative regulatory factors that stimulate or inhibit their proliferation. Blocking the action of negative regulatory factors may provide a new approach for inducing HSCs into proliferation. A variety of studies have suggested that TGF-beta negatively regulates cell cycle progression of HSCs. In this study, a dominant negatively acting mutant of TGF-beta type II receptor (TbetaRIIDN) was transiently expressed in HSCs by using adenoviral vector-mediated gene delivery, such that the effects of disrupting the autocrine TGF-beta signaling in HSCs can be directly examined at a single cell level. Adenoviral vectors allowing the expression of TbetaRIIDN and green fluorescence protein in the same CD34(+)CD38(-)Lin(-) cells were constructed. Overexpression of TbetaRIIDN specifically disrupted TGF-beta-mediated signaling. Autocrine TGF-beta signaling in CD34(+)CD38(-)Lin(-) cells was studied in single cell assays under serum-free conditions. Transient blockage of autocrine TGF-beta signaling in CD34(+)CD38(-)Lin(-) cells enhanced their survival. Furthermore, the overall proliferation potential and proliferation kinetics in these cells were significantly enhanced compared with the CD34(+)CD38(-)Lin(-) cells expressing green fluorescence protein alone. Therefore, we have successfully blocked the autocrine TGF-beta-negative regulatory loop of primitive hemopoietic progenitor cells.

Reexpression of a cluster of silenced transgenes is associated with their rearrangement

Irreversible inactivation or silencing of tumor suppressor genes occurs frequently in the development of cancer. A similar process of silencing can occur after the integration of transfected or microinjected genes into the genomes of recipient cells. The inactivation of transfected genes seems particularly efficient in cells with stem cell characteristics. We have been studying the inactivation of genes transfected into cultured P19 embryonal carcinoma cells and found that the CpG-rich sequence comprising the coding region of the lacZ reporter gene becomes extensively methylated after integration into the genome. 5-Aza-2'-deoxycytidine (5AdC), an inhibitor of DNA methylation, induced the reexpression of silent transgenes in one clone of P19 cells studied in detail. However, the reexpressed genes remained heavily methylated over the lacZ coding sequence. We used pulsed-field gel electrophoresis to analyze the structure of the transgenic locus in the parental and in 5AdC-treated cells and found that, in each of the cells reexpressing the transgene, the cluster of transgenes had been rearranged. Each clone had undergone a different rearrangement that appeared to involve recombination within the tandemly repeated copies of the transgene. Our data seem consistent with the idea that 5AdC induces efficient DNA recombination between tandemly repeated genes and that the reexpression of silenced genes induced by 5AdC might be triggered by the chromatin reorganization at the site of DNA recombination.

In vitro and in vivo expression of a nephritogenic Ig heavy chain determinant: pathogenic autoreactivity requires permissive light chains

Lymphocyte antigen receptors are promising targets for immune intervention strategies in disorders marked by repertoire skewing or expansion of lymphocyte subsets. Appropriate application of immune receptor modulation is predicated on understanding the role of a particular receptor in pathogenesis and disease regulation. The VHB/W16 gene, restricted to mice carrying the j haplotype for the J558 family, is overexpressed by murine lupus anti-DNA Ig. This gene is also expressed recurrently among nephritogenic anti-DNA Ig recovered from several autoimmune strains, suggesting that cells expressing this pathogenic receptor are positively selected during disease progression. To explore the extent and mechanisms by which Ig H chains expressing this gene contribute to autoimmunity, an Ig H chain gene was engineered for in vitro and in vivo recombination studies. Site-directed mutagenesis generated unique restriction sites to link PCR-amplified V region (VDJ) cDNA to previously isolated genomic fragments containing Ig regulatory and signal sequences. The new 3 kb VDJ gene was then ligated to a 9 kb fragment encoding the IgM constant region. Transfection of H chain loss variant myeloma with the complete 12 kb construct, termed 238H-Cmicro, resulted in secretion of intact Ig pairing 238H-Cmicro, with a lambda L chain; however, transfectant Ig lacked autoreactivity and pathogenicity. Introduction of the 238H-Cmicro H chain as a transgene onto the non-autoimmune C57BL/6 background resulted in abundant B cell surface expression of 238H-Cmicro, however, four transgenic Ig recovered by fusion of LPS-stimulated splenocytes and formed by combination of 238H-Cmicro, with endogenous kappa chains do not bind DNA or laminin. These results indicate that the antigen binding sites encoded by this disease-associated gene and/or H chain must associate with permissive L chains to specify autoimmunity. The 238H-Cmicro, transgenic model should prove useful in dissecting the in vivo fate of 238H-Cmicro, L combinations that produce pathogenic autoreactive receptors and in evaluating receptor-targeted interventions.