Intracisternal A-particle element transposition into the murine beta-glucuronidase gene correlates with loss of enzyme activity: a new model for beta-glucuronidase deficiency in the C3H mouse

Polymer-based drug delivery systems under investigation for enzyme replacement and other therapies of lysosomal storage disorders

Lysosomes play a central role in cellular homeostasis and alterations in this compartment associate with many diseases. The most studied example is that of lysosomal storage disorders (LSDs), a group of 60 + maladies due to genetic mutations affecting lysosomal components, mostly enzymes. This leads to aberrant intracellular storage of macromolecules, altering normal cell function and causing multiorgan syndromes, often fatal within the first years of life. Several treatment modalities are available for a dozen LSDs, mostly consisting of enzyme replacement therapy (ERT) strategies. Yet, poor biodistribution to main targets such as the central nervous system, musculoskeletal tissue, and others, as well as generation of blocking antibodies and adverse effects hinder effective LSD treatment. Drug delivery systems are being studied to surmount these obstacles, including polymeric constructs and nanoparticles that constitute the focus of this article. We provide an overview of the formulations being tested, the diseases they aim to treat, and the results observed from respective in vitro and in vivo studies. We also discuss the advantages and disadvantages of these strategies, the remaining gaps of knowledge regarding their performance, and important items to consider for their clinical translation. Overall, polymeric nanoconstructs hold considerable promise to advance treatment for LSDs.

Pharmacologic characterization of TBP1901, a prodrug form of aglycone curcumin, and CRISPR-Cas9 screen for therapeutic targets of aglycone curcumin

Curcumin (aglycone curcumin) has antitumor properties in a variety of malignancies via the alteration of multiple cancer-related biological pathways; however, its clinical application has been hampered due to its poor bioavailability. To overcome this limitation, we have developed a synthesized curcumin β-D-glucuronide sodium salt (TBP1901), a prodrug form of aglycone curcumin. In this study, we aimed to clarify the pharmacologic characteristics of TBP1901. In β-glucuronidase (GUSB)-proficient mice, both curcumin β-D-glucuronide and its active metabolite, aglycone curcumin, were detected in the blood after TBP1901 injection, whereas only curcumin β-D-glucuronide was detected in GUSB-impaired mice, suggesting that GUSB plays a pivotal role in the conversion of TBP1901 into aglycone curcumin in vivo. TBP1901 itself had minimal antitumor effects in vitro, whereas it demonstrated significant antitumor effects in vivo. Genome-wide clustered regularly interspaced short palindromic repeats (CRISPR)-Cas9 screen disclosed the genes associated with NF-κB signaling pathway and mitochondria were among the highest hit. In vitro, aglycone curcumin inhibited NF-kappa B signaling pathways whereas it caused production of reactive oxygen species (ROS). ROS scavenger, N-acetyl-L-cysteine, partially reversed antitumor effects of aglycone curcumin. In summary, TBP1901 can exert antitumor effects as a prodrug of aglycone curcumin through GUSB-dependent activation.

Circulatory C-type natriuretic peptide reduces mucopolysaccharidosis-associated craniofacial hypoplasia in vivo

Skeletal alterations in the head and neck region, such as midfacial hypoplasia, foramen magnum stenosis and spinal canal stenosis, are commonly observed in patients with mucopolysaccharidosis (MPS). However, enzyme replacement therapy (ERT), one of the major treatment approaches for MPS, shows limited efficacy for skeletal conditions. In this study, we analysed the craniofacial morphology of mice with MPS type VII, and investigated the underlying mechanisms promoting jaw deformities in these animals. Furthermore, we investigated the effects of C-type natriuretic peptide (CNP), a potent endochondral ossification promoter, on growth impairment of the craniofacial region in MPS VII mice when administered alone or in combination with ERT. MPS VII mice exhibited midfacial hypoplasia caused by impaired endochondral ossification, and histological analysis revealed increased number of swelling cells in the resting zone of the spheno-occipital synchondrosis (SOS), an important growth centre for craniomaxillofacial skeletogenesis. We crossed MPS VII mice with transgenic mice in which CNP was expressed in the liver under the control of the human serum amyloid-P component promoter, resulting in elevated levels of circulatory CNP. The maxillofacial morphological abnormalities associated with MPS VII were ameliorated by CNP expression, and further prevented by a combination of CNP and ERT. Histological analysis showed that ERT decreased the swelling cell number, and CNP treatment increased the width of the proliferative and hypertrophic zones of the SOS. Furthermore, the foramen magnum and spinal stenoses observed in MPS VII mice were significantly alleviated by CNP and ERT combination. These results demonstrate the therapeutic potential of CNP, which can be used to enhance ERT outcome for MPS VII-associated head and neck abnormalities.

The beta-glucuronidase intracisternal A particle insertion model results in similar overall MPSVII phenotype as the single base deletion model when on the same C57BL/6J mouse background

Two unique gene mutations in the enzyme beta-glucuronidase (GUSB) that result in the lysosomal storage disease Mucopolysaccharidosis (MPS) type VII had previously been reported to have differing disease phenotype severities when compared on differing mouse strains. The MPSVII mouse has proven to be a highly efficacious model to study mucopolysaccharidoses and for evaluating potential gene or stem cell therapies for lysosomal storage diseases. We examined the single base pair deletion (MPSVII) and the intracisternal A particle element insertion (MPSVII2J) in GUSB compared with control animals by skeletal measures, electroretinography, auditory-evoked brainstem response and life span on a C57BL/6J background strain. In all measures, both mutations result in either a trend toward or significant changes from the background strain control. In all measures, there is no significant phenotypic difference between the two mutations. The 2J variant is a more easily genotyped and equally affected phenotype, which holds promise for further studies of chimerism and stem cell therapy approaches.

C-Type Natriuretic Peptide Restores Growth Impairment Under Enzyme Replacement in Mice With Mucopolysaccharidosis VII

Growth impairment in mucopolysaccharidoses (MPSs) is an unresolved issue as it is resistant to enzyme replacement therapy (ERT) and growth hormone therapy. C-type natriuretic peptide (CNP) is a promising agent that has growth-promoting effects. Here we investigate the effects of CNP on growth impairment of MPSs using Gusbmps-2J mice, a model for MPS type VII, with combination therapy of CNP and ERT by hydrodynamic gene delivery. Although monotherapies were not sufficient to restore short statures of treated mice, combination therapy resulted in successful restoration. The synergistic effects of CNP and ERT were not only observed in skeletal growth but also in growth plates. ERT reduced cell swelling in the resting zone and increased cell number by accelerating proliferation or inhibiting apoptosis. CNP thickened the proliferative and hypertrophic zones. Regarding changes in the bone, ERT restored bone sclerosis through decreased bone formation and increased bone resorption, and CNP did not adversely affect this process. In addition, improvement of joint deformation by ERT was suggested by analyses of joint spaces and articular cartilage. CNP additively provided restoration of the short stature of MPS VII mice in combination with ERT, which improved abnormalities of growth plates and bone metabolism.

Mouse germ line mutations due to retrotransposon insertions

Transposable element (TE) insertions are responsible for a significant fraction of spontaneous germ line mutations reported in inbred mouse strains. This major contribution of TEs to the mutational landscape in mouse contrasts with the situation in human, where their relative contribution as germ line insertional mutagens is much lower. In this focussed review, we provide comprehensive lists of TE-induced mouse mutations, discuss the different TE types involved in these insertional mutations and elaborate on particularly interesting cases. We also discuss differences and similarities between the mutational role of TEs in mice and humans.

Beta-Glucuronidase Catalyzes Deconjugation and Activation of Curcumin-Glucuronide in Bone

The biological basis for documented in vivo bone-protective effects of turmeric-derived curcumin is unclear since curcumin is barely detectable in serum, being rapidly conjugated to form what is thought to be an inactive glucuronide. Studies were therefore undertaken to test the postulate that antiresorptive effects of curcumin require deconjugation within bone to form the bioactive aglycone and that β-glucuronidase (GUSB), a deconjugating enzyme expressed by hematopoietic marrow cells, facilitates this site-specific transformation. Consistent with this postulate, aglycone, but not glucuronidated, curcumin inhibited RANKL-stimulated osteoclastogenesis, a key curcumin target in bone. Aglycone curcumin, expressed relative to total curcumin, was higher in bone marrow than in serum of curcumin-treated C57BL/6J mice, while remaining a minor component. Ex vivo, under conditions preventing further metabolism of the unstable aglycone, the majority of curcumin-glucuronide delivered to marrow in vivo was hydrolyzed to the aglycone, a process that was inhibited by treatment with saccharolactone, a GUSB inhibitor, or in mice having reduced (C3H/HeJ) or absent (mps/mps) GUSB activity. These findings suggest that curcumin, despite low systemic bioavailability, may be enzymatically activated (deconjugated) within GUSB-enriched bone to exert protective effects, a metabolic process that could also contribute to bone-protective effects of other highly glucuronidated dietary polyphenols.

Lysosomal β-glucuronidase regulates Lyme and rheumatoid arthritis severity

Lyme disease, caused by the spirochete Borrelia burgdorferi, is the most prevalent arthropod-borne illness in the United States and remains a clinical and social challenge. The spectrum of disease severity among infected patients suggests that host genetics contribute to pathogenic outcomes, particularly in patients who develop arthritis. Using a forward genetics approach, we identified the lysosomal enzyme β-glucuronidase (GUSB), a member of a large family of coregulated lysosomal enzymes, as a key regulator of Lyme-associated arthritis severity. Severely arthritic C3H mice possessed a naturally occurring hypomorphic allele, Gusbh. C57BL/6 mice congenic for the C3H Gusb allele were prone to increased Lyme-associated arthritis severity. Radiation chimera experiments revealed that resident joint cells drive arthritis susceptibility. C3H mice expressing WT Gusb as a transgene were protected from severe Lyme arthritis. Importantly, the Gusbh allele also exacerbated disease in a serum transfer model of rheumatoid arthritis. A known GUSB function is the prevention of lysosomal accumulation of glycosaminoglycans (GAGs). Development of Lyme and rheumatoid arthritis in Gusbh-expressing mice was associated with heightened accumulation of GAGs in joint tissue. We propose that GUSB modulates arthritis pathogenesis by preventing accumulation of proinflammatory GAGs within inflamed joint tissue, a trait that may be shared by other lysosomal exoglycosidases.

DNA methylation and its basic function

In the mammalian genome, DNA methylation is an epigenetic mechanism involving the transfer of a methyl group onto the C5 position of the cytosine to form 5-methylcytosine. DNA methylation regulates gene expression by recruiting proteins involved in gene repression or by inhibiting the binding of transcription factor(s) to DNA. During development, the pattern of DNA methylation in the genome changes as a result of a dynamic process involving both de novo DNA methylation and demethylation. As a consequence, differentiated cells develop a stable and unique DNA methylation pattern that regulates tissue-specific gene transcription. In this chapter, we will review the process of DNA methylation and demethylation in the nervous system. We will describe the DNA (de)methylation machinery and its association with other epigenetic mechanisms such as histone modifications and noncoding RNAs. Intriguingly, postmitotic neurons still express DNA methyltransferases and components involved in DNA demethylation. Moreover, neuronal activity can modulate their pattern of DNA methylation in response to physiological and environmental stimuli. The precise regulation of DNA methylation is essential for normal cognitive function. Indeed, when DNA methylation is altered as a result of developmental mutations or environmental risk factors, such as drug exposure and neural injury, mental impairment is a common side effect. The investigation into DNA methylation continues to show a rich and complex picture about epigenetic gene regulation in the central nervous system and provides possible therapeutic targets for the treatment of neuropsychiatric disorders.

A novel GUSB mutation in Brazilian terriers with severe skeletal abnormalities defines the disease as mucopolysaccharidosis VII

Hundreds of different human skeletal disorders have been characterized at molecular level and a growing number of resembling dysplasias with orthologous genetic defects are being reported in dogs. This study describes a novel genetic defect in the Brazilian Terrier breed causing a congenital skeletal dysplasia. Affected puppies presented severe skeletal deformities observable within the first month of life. Clinical characterization using radiographic and histological methods identified delayed ossification and spondyloepiphyseal dysplasia. Pedigree analysis suggested an autosomal recessive disorder, and we performed a genome-wide association study to map the disease locus using Illumina’s 22K SNP chip arrays in seven cases and eleven controls. A single association was observed near the centromeric end of chromosome 6 with a genome-wide significance after permutation (p_genome  = 0.033). The affected dogs shared a 13-Mb homozygous region including over 200 genes. A targeted next-generation sequencing of the entire locus revealed a fully segregating missense mutation (c.866C>T) causing a pathogenic p.P289L change in a conserved functional domain of β-glucuronidase (GUSB). The mutation was confirmed in a population of 202 Brazilian terriers (p = 7,71×10⁻²⁹). GUSB defects cause mucopolysaccharidosis VII (MPS VII) in several species and define the skeletal syndrome in Brazilian Terriers. Our results provide new information about the correlation of the GUSB genotype to phenotype and establish a novel canine model for MPS VII. Currently, MPS VII lacks an efficient treatment and this model could be utilized for the development and validation of therapeutic methods for better treatment of MPS VII patients. Finally, since almost one third of the Brazilian terrier population carries the mutation, breeders will benefit from a genetic test to eradicate the detrimental disease from the breed.

An insertion of intracisternal A-particle retrotransposon in a novel member of the phosphoglycerate mutase family in the lew allele of mutant mice

Intracisternal A-particle retrotransposons (IAPs) are known, moveable, retrovirus-like elements and are defective in envelope protein synthesis in the mouse genome. Insertion of IAP elements can either interupt or enhance gene function or expression. Using a mouse model called lethal wasting (lew), we recently identified the insertion of an IAP sequence in a gene, 9630033F20Rik, that contains domains involved in glycolysis. The expression pattern of the 9630033F20Rik gene between various normal and diseased tissues was determined by semi-quantitative RT-PCR. The effect of the insertion mutation in 9630033F20Rik on glycolysis in heart, muscle, and brain tissues was further investigated using oligonuleotide microarray analysis. Results indicated that the expression of 9630033F20Rik is ubiquitous and its signal is relatively higher in heart and brain tissues. The insertion caused the deletion of exon 5 and decreased expression of this gene in all the tissues studied in the lew mice. Changes in the expression levels of glycolytic genes mainly occured in muscle tissue, raising a possibility that 9630033F20Rik may function as one of the transcriptional regulators of glycolytic genes in skeletal muscle. However, considering the fact that a single nucleotide mutation in vesicle-associated membrane protein 1 (VAMP1) has been reported as the causal gene for the lew mouse, how much of an impact the IAP insertion in the lew mouse phenotype has on glycolytic genes compared to the effect from the VAMP1 mutation responsible for the lew mouse phenotype should be further investigated.

Mutations and polymorphisms in GUSB gene in mucopolysaccharidosis VII (Sly Syndrome)

Mucopolysaccharidosis VII (MPS VII; Sly syndrome) is an autosomal recessive disorder caused by a deficiency of beta-glucuronidase (GUS, EC 3.2.1.31; GUSB). GUS is required to degrade glycosaminoglycans (GAGs), including heparan sulfate (HS), dermatan sulfate (DS), and chondroitin-4,6-sulfate (CS). Accumulation of undegraded GAGs in lysosomes of affected tissues leads to mental retardation, short stature, hepatosplenomegaly, bone dysplasia, and hydrops fetalis. We summarize information on the 49 unique, disease-causing mutations determined so far in the GUS gene, including nine novel mutations (eight missense and one splice-site). This heterogeneity in GUS gene mutations contributes to the extensive clinical variability among patients with MPS VII. One pseudodeficiency allele, one polymorphism causing an amino acid change, and one silent variant in the coding region are also described. Among the 103 analyzed mutant alleles, missense mutations accounted for 78.6%; nonsense mutations, 12.6%; deletions, 5.8%; and splice-site mutations, 2.9%. Transitional mutations at CpG dinucleotides made up 40.8% of all the described mutations. The five most frequent mutations (accounting for 44/103 alleles) were exonic point mutations, p.L176F, p.R357X, p.P408S, p.P415L, and p.A619 V. Genotype/phenotype correlation was attempted by correlating the effects of certain missense mutations or enzyme activity and stability within phenotypes. These were in turn correlated with the location of the mutation in the tertiary structure of GUS. A total of seven murine, one feline, and one canine model of MPS VII have been characterized for phenotype and genotype.

Notch signalling in the paraxial mesoderm is most sensitive to reduced Pofut1 levels during early mouse development

Background

The evolutionarily conserved Notch signalling pathway regulates multiple developmental processes in a wide variety of organisms. One critical posttranslational modification of Notch for its function in vivo is the addition of O-linked fucose residues by protein O-fucosyltransferase 1 (POFUT1). In addition, POFUT1 acts as a chaperone and is required for Notch trafficking. Mouse embryos lacking POFUT1 function die with a phenotype indicative of global inactivation of Notch signalling. O-linked fucose residues on Notch can serve as substrates for further sugar modification by Fringe (FNG) proteins. Notch modification by Fringe differently affects the ability of ligands to activate Notch receptors in a context-dependent manner indicating a complex modulation of Notch activity by differential glycosylation. Whether the context-dependent effects of Notch receptor glycosylation by FNG reflect different requirements of distinct developmental processes for O-fucosylation by POFUT1 is unclear.

Results

We have identified and characterized a spontaneous mutation in the mouse Pofut1 gene, referred to as "compact axial skeleton" (cax). Cax carries an insertion of an intracisternal A particle retrotransposon into the fourth intron of the Pofut1 gene and represents a hypomorphic Pofut1 allele that reduces transcription and leads to reduced Notch signalling. Cax mutant embryos have somites of variable size, showed partly abnormal Lfng expression and, consistently defective anterior-posterior somite patterning and axial skeleton development but had virtually no defects in several other Notch-regulated early developmental processes outside the paraxial mesoderm that we analyzed.

Conclusion

Notch-dependent processes apparently differ with respect to their requirement for levels of POFUT1. Normal Lfng expression and anterior-posterior somite patterning is highly sensitive to reduced POFUT1 levels in early mammalian embryos, whereas other early Notch-dependent processes such as establishment of left-right asymmetry or neurogenesis are not. Thus, it appears that in the presomitic mesoderm (PSM) Notch signalling is particularly sensitive to POFUT1 levels. Reduced POFUT1 levels might affect Notch trafficking or overall O-fucosylation. Alternatively, reduced O-fucosylation might preferentially affect sites that are substrates for LFNG and thus important for somite formation and patterning.

DNA hypomethylation caused by Lsh deletion promotes erythroleukemia development

Hematopoietic malignancies are frequently associated with DNA hypomethylation but the molecular mechanisms involved in tumor formation remain poorly understood. Here we report that mice lacking Lsh develop leukemia associated with DNA hypomethylation and oncogene activation. Lsh is a member of the SNF2 chromatin remodeling family and is required for de novo methylation of genomic DNA. Mice that received Lsh deficient hematopoietic progenitors showed severe impairment of hematopoiesis, suggesting that Lsh is necessary for normal hematopoiesis. A subset of mice developed erythroleukemia, a tumor that does not spontaneously occur in mice. Tumor tissues were CpG hypomethylated and showed a modest elevation of the transcription factor PU.1, an oncogene that is crucial for Friend virus induced erythroleukemia. Analysis of Lsh(-/-) hematopoietic progenitors revealed widespread DNA hypomethylation at repetitive sequences and hypomethylation at specific retroviral elements within the PU.1 gene. Wild type cells showed Lsh and Dnmt3b binding at the retroviral elements located within the PU.1 gene. On the other hand, Lsh deficient cells had no detectable Dnmt3b association suggesting that Lsh is necessary for recruitment of Dnmt3b to its target. Furthermore, Lsh(-/-) hematopoietic precursors showed impaired suppression of retroviral elements in the PU.1 gene, an increase of PU.1 transcripts and protein levels. Thus DNA hypomethylation caused by Lsh depletion is linked to transcriptional upregulation of retroviral elements and oncogenes such as PU.1 which in turn may promote the development of erythroleukemia in mice.

An IAP retrotransposon in the mouse ADAMTS13 gene creates ADAMTS13 variant proteins that are less effective in cleaving von Willebrand factor multimers

Severe deficiency of ADAMTS13, a von Willebrand factor (VWF)-cleaving metalloprotease, causes thrombotic thrombocytopenic purpura. When analyzed with VWF multimers, but not with an abbreviated VWF peptide (VWF73) as the substrate, the plasma ADAMTS13 activity levels of mouse strains segregated into a high and a low group that differed by approximately 10 fold. Low ADAMTS13 activity was detected in mice containing 2 alleles of intracisternal A-type particle (IAP) retrotransposon sequence in the ADAMTS13 gene. Molecular cloning of mouse ADAMTS13 identified 2 truncated variants (IAP-a and IAP-b) in the low-activity mice. Both of the IAP variants lacked the 2 carboxyl terminus thrombospondin type 1 repeat (TSR) and CUB domains of full-length ADAMTS13. The IAP-b variant also had splicing abnormalities affecting the spacer domain sequence and had miniscule enzymatic activity. Compared with full-length ADAMTS13, the IAP-a variant was approximately one ninth as active in cleaving VWF multimers but was only slightly less active in cleaving VWF73 peptide. Recombinant human ADAMTS13 was also less effective in cleaving VWF multimers than VWF73 when the C-terminal TSR sequence was deleted. In summary, the carboxyl terminus TSR sequence is important for cleaving VWF multimers. Assay results should be interpreted with caution when peptide substrates are used for analysis of variant ADAMTS13 proteins.

Evidence that the mouse osteocalcin-related gene does not encode nephrocalcin

BACKGROUND/AIMS

The osteocalcin-related gene (ORG) is a mouse-specific member of the osteocalcin gene cluster predicted to encode a gamma-carboxyglutamic acid-rich protein. ORG mRNA has been predicted to encode nephrocalcin and shown to be expressed in the kidney where it could serve as an important crystallization inhibitor. To determine whether ORG encodes mouse nephrocalcin, we investigated its in vivo and in vitro expression.

METHODS

We expressed fluorescent fusion ORG proteins in kidney cell lines and generated transgenic mice expressing enhanced green fluorescent protein under the control of the ORG promoter.

RESULTS

ORG mRNA was shown to be expressed in mouse kidneys and in a variety of other tissues. Fusion constructs transfected in opossum kidney cells demonstrated integrity of the open reading frame with the presence of a protein of the expected molecular weight. However, kidneys from transgenic mice carrying the enhanced green fluorescent protein gene under the control of the ORG promoter (5.8 kb fragment) demonstrated no expression of the transgene in kidneys or other tissues.

CONCLUSION

We conclude that ORG, the third gene of the mouse osteocalcin gene cluster is silent and unlikely to play a major role in mouse renal physiology.

A mouse TRAPP-related protein is involved in pigmentation

We identified a new spontaneous recessive mutation in the mouse, mhyp (mosaic hypopigmentation), in a screen for novel proviral integration sites in a multiple ecotropic provirus mapping stock. Integration of an 8.4-kb retrovirus results in mosaic loss of coat pigment in mhyp homozygotes. Patchy loss of pigmentation in the retinal pigmented epithelial layer of the eye with abnormal melanosomes is also evident. We mapped mhyp to mouse chromosome 7 and cloned the underlying gene. mhyp is a defect in the Trappc6a gene. Expression of Trappc6a is markedly diminished in mhyp homozygotes. The normal protein, TRAPPC6A, is a subunit of the TRAPP (transport protein particle) I and II complexes. While TRAPP complexes are essential for ER-to-Golgi and intra-Golgi vesicle trafficking in yeast, TRAPP subunits participate in additional, including post-Golgi, transport events in mammals. The data implicate mammalian TRAPPC6A in vesicle trafficking during melanosome biogenesis.

Widespread Correction of Lysosomal Storage in the Mucopolysaccharidosis Type VII Mouse Brain with a Herpes Simplex Virus Type 1 Vector Expressing β-Glucuronidase

We have inoculated a herpes simplex virus type 1 (HSV-1) vector into a variety of sites in the mouse brain and assayed the regions of latency and expression of a beta-glucuronidase (GUSB) cDNA from the latency-associated transcript promoter. Injection sites used were somatosensory cortex, visual cortex, striatum, dorsal hippocampus, and CSF spaces. Latent vector was detected in regions at a distance from the respective injection sites, consistent with axonal transport of vector. Regions of GUSB activity varied by injection site and included cerebral cortex, striatum, thalamus, hypothalamus, substantia nigra, hippocampus, midbrain, pons, medulla, cerebellum, and spinal cord. After a single injection, GUSB enzymatic activity reached wild-type levels in several brain regions. GUSB was found in some areas without any detectable vector, indicative of axonal transport of GUSB enzyme. GUSB-deficient mice, which have the lysosomal storage disease mucopolysaccharidosis (MPS) VII, have lysosomal storage lesions in cells throughout the brain. Adult MPS VII mice treated by injection of vector into a single site on each side of the brain had correction of storage lesions in a large volume of brain. The potential for long-term, widespread correction of lysosomal storage diseases with HSV-1 vectors is discussed.

Histopathological and Behavioral Improvement of Murine Mucopolysaccharidosis Type VII by Intracerebral Transplantation of Neural Stem Cells

The therapeutic efficacy of neural stem cell transplantation for central nervous system (CNS) lesions in lysosomal storage disorders was explored using a murine model of mucopolysaccharidosis type VII (MPS VII). We used fetal neural stem cells derived from embryonic mouse striata and expanded in vitro by neurosphere formation as the source of graft materials. We transplanted neurospheres into the lateral ventricles of newborn MPS VII mice and found that donor cells migrated far beyond the site of injection within 24 h, and some of them could reach the olfactory bulb. A quantitative measurement indicated that the GUSB activity in the brain was 12.5 to 42.3% and 5.5 to 6.3% of normal activity at 24 h and 3 weeks after transplantation. In addition, histological analysis revealed a widespread decrease in lysosomal storage in the recipient's hippocampus, cortex, and ependyma. A functional assessment with novel-object recognition tests confirmed improvements in behavioral patterns. These results suggest that intracerebral transplantation of neural stem cells is feasible for treatment of CNS lesions associated with lysosomal storage disorders.

Caytaxin deficiency causes generalized dystonia in rats

The genetically dystonic rat (SD-dt:JFL) is an autosomal recessive model of generalized dystonia. Without cerebellectomy, the dt rat dies prior to Postnatal Day 40. The dt locus was mapped to a 4.2 Mb region on Chr 7q11 and candidate genes were screened with semi-quantitative RT-PCR. Then, Southern blotting and genomic DNA sequencing identified the 3'-long terminal repeat portion of an intracisternal A particle element inserted into Intron 1 of Atcay, the gene which encodes caytaxin. Northern and Western blotting and quantitative real-time RT-PCR defined the Atcay allele in dt rats (Atcay(dt)) as hypomorphic. To establish a framework for functional studies of caytaxin, the developmental expression of rat Atcay transcript was analyzed with Northern blotting, relative quantitative multiplex real-time RT-PCR (QRT-PCR) and in situ hybridization. With a multiple tissue Northern blot, three Atcay transcripts were identified in brain but none were present in heart, spleen, lung, liver, muscle, kidney or testis. With a multiple time-point Northern blot, the same three transcripts were present in cerebellum at Embryonic Day (E15), Postnatal Day 1 (P1), P7, P14, P36 and 8 months. During early development (E15 to P14), the relative proportion of the smallest transcript was increased. QRT-PCR was performed with total RNA from cerebral cortex, striatum, thalamus, hippocampus and cerebellum. Transcript levels peaked at P7 in hippocampus, increased linearly from P1 to P36 in cerebellum, and showed minimal developmental regulation in cerebral cortex. Radioactive in situ hybridization localized Atcay transcript to seemingly all neuronal populations in brain. In cerebellum, Atcay transcript was present in the molecular, Purkinje and granular layers; transcript density in the molecular layer peaked at P14. In the background of previous biochemical, behavioral and electrophysiological studies in the dt rat, our data are compatible with a vital role for caytaxin in the development and neurophysiology of cerebellar cortex.

Meiotic and epigenetic aberrations inDnmt3L-deficient male germ cells

The DNA methyltransferase-like protein Dnmt3L is necessary for the establishment of genomic imprints in oogenesis and for normal spermatogenesis (Bourc'his et al., 2001; Hata et al., 2002). Also, a paternally imprinted gene, H19, loses DNA methylation in Dnmt3L-/- spermatogonia (Bourc'his and Bestor, 2004; Kaneda et al., 2004). To determine the reason for the impaired spermatogenesis in the Dnmt3L-/- testes, we have carried out a series of histological and molecular studies. We show here that Dnmt3L-/- germ cells were arrested and died around the early meiotic stage. A microarray-based gene expression-profiling analysis revealed that various gonad-specific and/or sex-chromosome-linked genes were downregulated in the Dnmt3L-/- testes. In contrast, expression of retrovirus-like intracisternal A-particle (IAP) sequences was upregulated; consistent with this observation, a specific IAP copy showed complete loss of DNA methylation. These findings indicate that Dnmt3L regulates germ cell-specific gene expression and IAP suppression, which are critical for male germ cell proliferation and meiosis.

Negative and positive effects of an IAP-LTR on nearby Pcdaα gene expression in the central nervous system and neuroblastoma cell lines

Intracisternal A-particles (IAPs) are defective retrovirions encoded by members of a large family of endogenous proviral elements in the murine genome. An intact IAP element was found in the protocadherin alpha (Pcdhalpha) gene cluster of five laboratory mouse strains. However, IAP insertion was not detected in three wild mouse strains we investigated. This IAP insertion caused the disruption of one variable exon of laboratory mouse and down-regulated expression of the Pcdhalpha v8 exon, which is located just downstream of the IAP in the brain following the methylation of 5' regulatory region of Pcdhalpha v8. In contrast, the Pcdhalpha v8 exon was highly expressed in mouse neuroblastoma cell lines. This suggested that the IAP insertion activates the expression of the nearby Pcdhalpha v8 exon in these cell lines. In fact, the Pcdhalpha v8 exon expression was driven by the IAP-long terminal repeat (LTR) following the de-methylation of 5' regulatory region of Pcdhalpha v8. To investigate the promoter activity of the IAP, we constructed an IAP-LTR-ECFP reporter gene and introduced it into neuroblastoma, melanoma, lymphoma, and plasmacytoma cell lines. Interestingly, ECFP-positive cells were observed only in the neuroblastoma cell lines. Moreover, there were no differences in the promoter activities of the IAP-LTR whether it was in the sense or complimentary orientation. Thus, this IAP-LTR has negative and positive regulation on near by gene expression in the brain and neuroblastoma cell lines.

Identification of Strain-specific Variants of Mouse Adamts13 Gene Encoding von Willebrand Factor-cleaving Protease

Human ADAMTS13 was recently identified as a gene encoding von Willebrand factor-cleaving protease, hADAMTS13. Both congenital and acquired defects in this enzyme can cause thrombotic thrombocytopenic purpura. hADAMTS13 consists of 1,427 amino acid residues and is composed of multiple structural domains including thrombospondin type 1 motifs and CUB domains. To analyze the functional roles of these domains in vivo, we determined the cDNA sequence of the mouse ortholog, mADAMTS13. Unexpectedly, two forms of the mouse Adamts13 gene were isolated that differed in the insertion of an intracisternal A particle (IAP) retrotransposon including a premature stop codon. The IAP insertion was found in BALB/c, C3H/He, C57BL/6, and DBA/2 strains but not in the 129/Sv strain. The outbred ICR strain had either the IAP-free or IAP-inserted allele or both. IAP-free Adamts13 encoded mADAMTS13L, a protein of 1,426 amino acid residues with the same domain organization as hADAMTS13. In contrast, IAP-inserted Adamts13 encoded a C-terminally truncated enzyme, mADAMTS13S, that is comprised of only 1,037 amino acid residues and lacking the C-terminal two thrombospondin type 1 motifs and two CUB domains. Strain specificity was also confirmed by reverse transcription-PCR and Northern blot analyses. Both recombinant mADAMTS13L and mADAMTS13S exhibited von Willebrand factor cleaving activities in vitro. The natural variation in mouse ADAMTS13 should allow for the determination of hitherto unknown functions of its C-terminal domains in vivo.

Dnmt1 expression in pre- and postimplantation embryogenesis and the maintenance of IAP silencing

The methylation of intracisternal A-type particle (IAP) sequences is maintained during mouse embryogenesis. Methylation suppresses IAP expression and the potential for mutagenesis by retrotransposition, but it is not clear how methylation of these elements is maintained during the embryonic stages when the bulk of the genome is being demethylated. It has been suggested that the high levels of DNA methyltransferase-1 (Dnmt1) present during cleavage could be important for keeping IAPs methylated. To test this hypothesis, we combined mutant alleles of Dnmt1 with an agouti allele (A(iapy)), which provided a coat color readout for the methylation status of the IAP insertion in the agouti locus. We found that reduction in Dnmt1 levels directly impacted methylation at this locus, leading to stable transcriptional activation of the agouti gene in the adult. Specifically, the short maternal Dnmt1 protein was important in maintaining methylation at the A(iapy) locus in cleavage embryos, whereas the longer Dnmt1 isoform found in somatic cells was important in maintaining IAP methylation during the postimplantation stage. These results underscore the importance of maintaining proper maintenance of methylation patterns during gestation and suggest that interference with this process may stably affect gene expression patterns in the adult and may have profound phenotypic consequences.

A murine gene with circadian expression revealed by transposon insertion: self-sustained rhythmicity in the liver and the photoreceptors

We have previously identified in some mouse strains (e.g. BALB/c, DBA/2) a murine Intracisternal A-particle (IAP) transposable element specifically expressed in the liver. This IAP sequence is inserted within a gene, mCCR4/m. nocturnin, the sequence of which is related to the circadian Xenopus nocturnin gene. Here we show, using real-time quantitative RT-PCR, that both the IAP sequence and the m. nocturnin gene display strong circadian expression in the liver, with peak abundance after dusk. Circadian oscillations of m. nocturnin RNA are maintained in mice without the IAP insertion (e.g. CBA/J, 129/sv), are free-running under constant light and dark conditions, and persist upon food and water privation, demonstrating that m. nocturnin is a circadian gene. In situ hybridization analyses (in 129/sv mice) further show circadian expression of m. nocturnin also in the retina, precisely at the level of the photoreceptors, a result consistent with the previously described circadian expression of the Xenopus gene. These results strengthen the strong conservation of the nocturnin gene with the identification of a functional mouse ortholog of the Xenopus gene, and demonstrate the reciprocal influence of nearby genes on the expression of transposable elements via "position effects".

Genes differentially expressed in the kindled mouse brain

Kindling involves long-term changes in brain excitability and is considered a model of epilepsy and neuroplasticity. Differentially expressed genes in the kindled mouse brain were screened using an reverse transcription-polymerase chain reaction (RT-PCR) differential display (DD) method. C3H male mice were kindled with 40 stimuli in the hippocampus at 5-min intervals. Hippocampal RNA was isolated for DD from mice at 0.5 h, 1 day, 1 week, and 1 month after kindling and from sham-operated controls. About 30,000 bands were screened and of these, 50 were displayed differentially. Northern blot analysis confirmed that 26 of the 50 bands were differentially expressed following rapid kindling. Further sequence analysis revealed that 14 of the genes were previously identified and 12 were novel. The novel genes are referred to as King (1-12) genes because of their association with kindling. According to their temporal and quantitative pattern of expression in forebrain, the 26 genes were grouped into five types. Expression of five of the DD genes, one from each expression type, was further analyzed in hippocampus, forebrain, brainstem, and cerebellum of the kindled mice. Differential expression of these genes was observed in hippocampus and forebrain, but not in brainstem or cerebellum. Only one gene, a regulator of G-protein signaling 4 (RGS4), showed prolonged changes in expression in response to kindling. Our results show that rapid kindling produces spatial and temporal changes in gene expression that may influence kindling-associated neuroplasticity.

In utero transplantation of fetal liver cells in the mucopolysaccharidosis type VII mouse results in low-level chimerism, but overexpression of beta-glucuronidase can delay onset of clinical signs

Mice with the lysosomal storage disease mucopolysaccharidosis (MPS) VII, caused by a deficiency of beta-glucuronidase (GUSB), have signs of disease present at birth. Bone marrow transplantation (BMT) or retroviral vector-mediated gene transfer into hematopoietic stem cells can partially correct the disease in adult mice, and BMT performed at birth results in a better clinical outcome. Thus, treatment in utero may result in further improvement. However, this must be done without cyto-ablation, and the donor cells do not have a competitive repopulating advantage over host cells. Transplantation in utero of either syngeneic fetal liver hematopoietic stem cells marked with a retroviral vector, or allogeneic donor cells that constitutively express high levels of human GUSB from a transgene, resulted in only about 0.1% engraftment in the adult. Immuno-affinity enrichment of stem and progenitor cells of 5- to 10-fold resulted in significantly higher GUSB activities at 2 months of age, but by 6 months engraftment was about 0.1%. Attempts to further increase the number of stem and progenitor cells were deleterious to the recipients. Nevertheless, GUSB expressed during the first 2 months of life in MPS VII fetuses could delay the onset of overt signs of disease. This suggests that the expression of some normal enzyme activity beginning in fetal life may offer the possibility of slowing the progression of the disease until more definitive postnatal transplantation or gene transfer to stem cells could be accomplished.

A novel model of murine mucopolysaccharidosis type VII due to an intracisternal a particle element transposition into the beta-glucuronidase gene: clinical and pathologic findings

We describe the clinical and pathologic findings in a murine model of mucopolysaccharidosis VII (Sly disease) that arose spontaneously in the C3H/HeOuJ mouse strain. Affected gus(mps2J)/gus(mps2J) mice are deficient in beta-glucuronidase because of insertion of an intracisternal A particle element into intron 8 of the gus structural gene. This is the first model of a human lysosomal storage disease caused by an intracisternal A particle element insertion. Mice with the gus(mps2J)/gus(mps2J) genotype have < 1% of normal beta-glucuronidase activity and secondary elevations of other lysosomal enzymes. The phenotype includes shortened life-span, dysmorphic features, and skeletal dysplasia. Lysosomal storage of glycosaminoglycans is widespread and affects the brain, skeleton, eye, ear, heart valves, aorta, and the fixed tissue macrophage system. Thus the phenotypic and pathologic alterations in gus(mps2J)/gus(mps2J) mice are similar to those in patients with mucopolysaccharidosis VII. The finding of antibodies to beta-glucuronidase in some older gus(mps2J)/gus(mps2J) mice suggests the mice produce sufficient enzyme to elicit an immune response. The gus(mps2J)/gus(mps2J) model provides another well-defined genetic system for the study of the pathophysiology of mucopolysaccharidosis and for evaluation of experimental therapies for lysosomal storage diseases. The disease in gus(mps2J)/gus(mps2J) mice is less severe than that seen in the previously characterized B6.C-H2(bm1)/ByBir-gus(mps)/gus(mps) mouse model. Furthermore, unlike gus(mps)/gus(mps) mice, gus(mps2J)/gus(mps2J) mice are fertile and breed to produce litters, all of which are mucopolysaccharidosis VII pups. This feature makes them extremely useful for testing intrauterine therapies.

Defective spectrin integrity and neonatal thrombosis in the first mouse model for severe hereditary elliptocytosis

Mutations affecting the conversion of spectrin dimers to tetramers result in hereditary elliptocytosis (HE), whereas a deficiency of human erythroid alpha- or beta-spectrin results in hereditary spherocytosis (HS). All spontaneous mutant mice with cytoskeletal deficiencies of spectrin reported to date have HS. Here, the first spontaneous mouse mutant, sph(Dem)/ sph(Dem), with severe HE is described. The sph(Dem) mutation is the insertion of an intracisternal A particle element in intron 10 of the erythroid alpha-spectrin gene. This causes exon skipping, the in-frame deletion of 46 amino acids from repeat 5 of alpha-spectrin and alters spectrin dimer/tetramer stability and osmotic fragility. The disease is more severe in sph(Dem)/sph(Dem) neonates than in alpha-spectrin-deficient mice with HS. Thrombosis and infarction are not, as in the HS mice, limited to adults but occur soon after birth. Genetic background differences that exist between HE and HS mice are suspect, along with red blood cell morphology differences, as modifiers of thrombosis timing. sph(Dem)/sph(Dem) mice provide a unique model for analyzing spectrin dimer- to-tetramer conversion and identifying factors that influence thrombosis.

Accumulation of abnormal amounts of glycosaminoglycans in murine mucopolysaccharidosis type VII neural progenitor cells does not alter the growth rate or efficiency of differentiation into neurons

Mucopolysaccharidosis type VII (MPS VII) results from deficiencies in the gene encoding the lysosomal enzyme beta-glucuronidase (GUSB). To study how the genetic and biochemical defects of MPS disease affect neural cell populations, neural progenitor cells (NPCs) were isolated from MPS VII mice and normal littermates. After growth in culture, approximately 90% of cells from both genotypes were nestin positive, a marker for NPCs, and lacked markers associated with lineage commitment. The mutant NPCs contained elevated levels of undegraded glycosaminoglycans (GAGs), the substrate for GUSB. Transduction with a retrovirus-vector expressing normal GUSB resulted in correction of the biochemical defects. Because of the demonstrated roles that GAGs and proteoglycans have in NPC biology and neural development, we tested whether the alterations in GAG metabolism affected MPS VII NPC properties regulated by GAG-containing molecules. MPS VII NPC cultures had growth rates in response to FGF-2 that were similar to normal cultures and the efficiency of differentiation into neurons was the same as with normal cells. Thus, even though isolated NPCs accumulate abnormally high levels of GAGs, these two key developmental properties were not altered when the cells were examined outside the milieu of the diseased brain.

Gene transfer of low levels of beta-glucuronidase corrects hepatic lysosomal storage in a large animal model of mucopolysaccharidosis VII

Gene therapy has been at least partially effective in several mouse disease models, but treatment of large mammals has been more difficult to achieve. One major limitation is that only low levels of expression of the corrective gene are often maintained in vivo. In a mouse model of the lysosomal storage disease mucopolysaccharidosis (MPS) type VII (Sly disease) with a null mutation in beta-glucuronidase, gene transfer experiments have shown that only 1-2% of normal beta-glucuronidase can correct the storage in some major organs. In contrast, MPS VII dogs, cats, and humans that have residual beta-glucuronidase activity levels in this range are affected. Thus, higher levels of transferred gene expression may be needed to achieve a therapeutic effect in large animals and humans. We tested this by examining liver pathology in MPS VII dogs after intraperitoneal transplantation of neo-organs containing retrovirus vector-corrected autologous fibroblasts that expressed low levels of beta-glucuronidase. The enzyme secreted from the neo-organs was taken up by the liver and significantly reduced the substrate content compared with untreated dogs. This suggests that small amounts of normal enzyme, when delivered to target tissues, may be therapeutically effective in human MPS VII patients.

Mucopolysaccharidosis type VII in the developing mouse fetus

Mucopolysaccharidosis type VII (MPS VII) is a lysosomal storage disease caused by a deficiency of beta-glucuronidase (1). MPS VII is a fatal, progressive degenerative disorder, and a number of patients die of hydrops fetalis. Thus an approach to treating this disease may be by transplantation or gene therapy in utero. A mouse model of MPS VII has been studied extensively but the disease in affected fetal mice has not been characterized, which is essential for evaluation of therapeutic efficacy. Fetal and newborn mice affected with MPS VII were examined for lysosomal enzyme activities and for the presence of typical storage lesions in comparison to normal and carrier littermates. No beta-glucuronidase enzymatic activity was detected in any of the tissues of affected mice, indicating that transplacental transfer of beta-glucuronidase from the dam did not occur. Lesions were not detected in affected fetuses of 13.5 d gestational age on light or electron microscopy. Vacuolation in cells, typical of lysosomal accumulation of substrate, was first seen in a small number of cells of the reticulo-endothelial system in 15.5 d gestational age livers and in 18.5 d gestational age brains. Storage lesions were not seen consistently in endothelial and Kupffer cells of fetal livers until 18.5 d gestational age and in brains until birth. The results suggest that treatment of affected mice performed at 13.5 d gestational age may be effective in forestalling disease manifestations.

Gene therapy/cell therapy for lysosomal storage disease

Lysosomal storage diseases (LSD) are considered to be appropriate disorders for gene therapy/cell therapy. We are attempting to treat one of these disorders using a mouse model, the Sly mouse. This is an authentic model for human beta-glucuronidase deficiency, MPS VII. We have carried out two types of experimental protocols; in vivo gene therapy and ex vivo gene therapy using Sly mice. For in vivo gene therapy, we produced a recombinant adenovirus that expresses human beta-glucuronidase and administered this to Sly mice intravenously. The beta-glucuronidase activities in liver and spleen were elevated to 40% and 20%, respectively, of the heterozygote enzyme level at day 16. Expression persisted for at least 35 days. Pathological abnormalities improved in these tissues and urinary glycosaminoglycan excretion was reduced in treated animals. Ex vivo gene therapy/cell therapy was carried out using macrophages obtained by cultivation of bone marrow cells. Non-myeloablated macrophages from normal mice were transplanted into Sly mice, and after 7 days donor cells had populated the liver and spleen. The human beta-glucuronidase (HBG) activity was increased in liver and spleen, although these enzyme activities subsequently fell by 38 days. The pathological improvement in Sly mice was evident at day 38 post transplantation. Furthermore, the macrophages from Sly mice were treated with retrovirus/adenovirus vector expressing HBG activity and the glycosaminoglycan accumulation was markedly decreased after 5 weeks. These data suggest that genetically engineered macrophage transplantation may be a very useful form of ex vivo gene therapy for lysosomal storage diseases. We also discuss the possible treatment of the CNS involvement in lysosomal storage diseases by gene therapy/cell therapy.

Characterization of a mammalian gene related to the yeast CCR4 general transcription factor and revealed by transposon insertion

Murine intracisternal A-particles (IAPs) are reiterated retrovirus-like transposable elements that can act as insertional mutagens. Accordingly, we previously identified a chimeric transcript initiated at an IAP promoter and extending through a 3'-located open reading frame with significant similarity to the C-terminal domain of the yeast CCR4 general transcription factor. In this report, we characterize the corresponding murine gene, mCCR4, and its human homologue, thus providing the first description of CCR4-like factors in mammals. cDNA cloning revealed two mCCR4 mRNAs of 2.7 and 3.1 kilobases, differing by their transcription start sites within the native mCCR4 gene promoter, and encoding a putative 430-amino acid protein. The mCCR4 gene contains three exons and two introns spanning almost 27 kilobases. The IAP insertion, detected only in some laboratory mouse strains, is recent and lies within the first intron. The 5'-region of the gene has features of housekeeping gene promoters. It lacks a TATA box but contains a CpG island and Sp1 sites. This region discloses strong promoter activity in transient transfection assays and also stimulates transcription in the reverse orientation, a feature common to other CpG island-containing promoters. Transcripts were detected in all the organs tested, although at a variable level, and displayed no strain-dependent differences relative to the IAP insertion, suggesting the existence of mechanisms preserving mCCR4 transcription from the usually deleterious effects of intronic transposition. The strong amino acid conservation between the human, murine, and the previously identified Xenopus CCR4-like proteins, is consistent with an important and conserved role for this protein in vertebrates.

Inner ear and kidney anomalies caused by IAP insertion in an intron of the Eya1 gene in a mouse model of BOR syndrome

A spontaneous mutation causing deafness and circling behavior was discovered in a C3H/HeJ colony of mice at the Jackson Laboratory. Pathological analysis of mutant mice revealed gross morphological abnormalities of the inner ear, and also dysmorphic or missing kidneys. The deafness and abnormal behavior were shown to be inherited as an autosomal recessive trait and mapped to mouse chromosome 1 near the position of the Eya1 gene. The human homolog of this gene, EYA1, has been shown to underly branchio-oto-renal (BOR) syndrome, an autosomal dominant disorder characterized by hearing loss with associated branchial and renal anomalies. Molecular analysis of the Eya1 gene in mutant mice revealed the insertion of an intracisternal A particle (IAP) element in intron 7. The presence of the IAP insertion was associated with reduced expression of the normal Eya1 message and formation of additional aberrant transcripts. The hypomorphic nature of the mutation may explain its recessive inheritance, if protein levels in homozygotes, but not heterozygotes, are below a critical threshold needed for normal developmental function. The new mouse mutation is designated Eya1(bor) to denote its similarity to human BOR syndrome, and will provide a valuable model for studying mutant gene expression and etiology.