Improving cell-specific recombination using AAV vectors in the murine CNS by capsid and expression cassette optimization

The production of cell-type- and age-specific genetically modified mice is a powerful approach for unraveling unknown gene functions. Here, we present a simple and timesaving method that enables adeno-associated virus (AAV)-mediated cell-type- and age-specific recombination in floxed mice. To achieve astrocyte-specific recombination in floxed Ai14 reporter mice, we intravenously injected blood-brain barrier-penetrating AAV-PHP.eB vectors expressing Cre recombinase (Cre) using the astrocyte-specific mouse glial fibrillary acidic protein (mGfaABC1D) promoter. However, we observed nonspecific neuron-predominant transduction despite the use of an astrocyte-specific promoter. We speculated that subtle but continuous Cre expression in nonastrocytic cells triggers recombination, and that excess production of Cre in astrocytes inhibits recombination by forming Cre-DNA aggregates. Here, we resolved this paradoxical event by dividing a single AAV into two mGfaABC1D-promoter-driven AAV vectors, one expressing codon-optimized flippase (FlpO) and another expressing flippase recognition target-flanked rapidly degrading Cre (dCre), together with switching the neuron-tropic PHP.eB capsid to astrocyte-tropic AAV-F. Moreover, we found that the FlpO-dCre system with a target cell-tropic capsid can also function in neuron-targeting recombination in floxed mice.

Association of Diabetes Mellitus With Increased Mortality in Carbapenem-Resistant Enterobacterales Infections

Introduction Carbapenem-resistant Enterobacterales (CRE) infections have high mortality. We aimed to examine the diabetes mellitus (DM) association with CRE mortality. Methodology Our study is a retrospective cohort study including patients who were admitted to the medical wards in the main district hospital (New Jahra Hospital, Kuwait) between January 1, 2022, and January 1, 2023, and diagnosed with CRE infections during hospitalization. The patients were divided into diabetic and non-diabetic groups. Clinical and laboratory data were collected. The presence of carbapenemase genes was detected. The primary outcome was 30-day hospital mortality. We assessed the effect of glycemic control on the outcomes. Results We included 47 patients in the diabetic group and 39 patients in the non-diabetic group. Females represented 54.7% of patients, and the median age was 73 and 55 years in the two groups, respectively. Klebsiella pneumonia (86%) and Escherichia coli (12.8%) were the most frequently isolated CRE. Carbapenemase genes were detected in all patients: NDM-1 in 67.4%, OXA-48 in 18.6%, and both genes coexisted in 14%. The 30-day hospital mortality was significantly higher in the diabetic group compared to the non-diabetic group (48.9% vs. 28.2%, P = 0.041). Among the diabetic patients, there was no significant difference between survivors and non-survivors regarding median glucose or glycated hemoglobin (HbA1c) levels (P = 0.465 and 0.932, respectively). Moreover, levels of glucose (odds ratio (OR) 0.928, confidence interval (CI) 0.763-1.13, P = 0.457) and HbA1c (OR 0.89, CI 0.63-1.26, P = 0.507) were not risk factors for increased mortality among diabetic patients.  Conclusion We demonstrated the association between DM and increased CRE mortality regardless of the level of glycemic control. This study demonstrates the interaction between communicable and non-communicable diseases.

A highly discriminatory RNA strand-specific assay to facilitate analysis of the role of cis-acting elements in foot-and-mouth disease virus replication

Foot-and-mouth-disease virus (FMDV), the aetiological agent responsible for foot-and-mouth disease (FMD), is a member of the genus Aphthovirus within the family Picornavirus. In common with all picornaviruses, replication of the single-stranded positive-sense RNA genome involves synthesis of a negative-sense complementary strand that serves as a template for the synthesis of multiple positive-sense progeny strands. We have previously employed FMDV replicons to examine viral RNA and protein elements essential to replication, but the factors affecting differential strand production remain unknown. Replicon-based systems require transfection of high levels of RNA, which can overload sensitive techniques such as quantitative PCR, preventing discrimination of specific strands. Here, we describe a method in which replicating RNA is labelled in vivo with 5-ethynyl uridine. The modified base is then linked to a biotin tag using click chemistry, facilitating purification of newly synthesised viral genomes or anti-genomes from input RNA. This selected RNA can then be amplified by strand-specific quantitative PCR, thus enabling investigation of the consequences of defined mutations on the relative synthesis of negative-sense intermediate and positive-strand progeny RNAs. We apply this new approach to investigate the consequence of mutation of viral cis-acting replication elements and provide direct evidence for their roles in negative-strand synthesis.

Relaxed control of sugar utilization in Parageobacillus thermoglucosidasius DSM 2542

Though carbon catabolite repression (CCR) has been intensively studied in some more characterised organisms, there is a lack of information of CCR in thermophiles. In this work, CCR in the thermophile, Parageobacillus thermoglucosidasius DSM 2542 has been studied during growth on pentose sugars in the presence of glucose. Physiological studies under fermentative conditions revealed a loosely controlled CCR when DSM 2542 was grown in minimal medium supplemented with a mixture of glucose and xylose. This atypical CCR pattern was also confirmed by studying xylose isomerase expression level by qRT-PCR. Fortuitously, the pheB gene, which encodes catechol 2, 3-dioxygenase was found to have a cre site highly similar to the consensus catabolite-responsive element (cre) at its 3' end and was used to confirm that expression of pheB from a plasmid was under stringent CCR control. Bioinformatic analysis suggested that the CCR regulation of xylose metabolism in P. thermoglucosidasius DSM 2542 might occur primarily via control of expression of pentose transporter operons. Relaxed control of sugar utilization might reflect a lower affinity of the CcpA-HPr (Ser46-P) or CcpA-Crh (Ser46-P) complexes to the cre(s) in these operons.

Emergence of a Clinical Escherichia coli Sequence Type 131 Strain Carrying a Chromosomal bla KPC-2 Gene

Objectives: Bacteria carrying the Klebsiella pneumoniae carbapenemase genes have rapidly spread worldwide and have become a great threat to public health. The bla_KPC–2 gene has been primarily located on plasmids cocirculating in various strains. However, chromosomal integration of the bla_KPC–2 gene in Escherichia coli has not been reported. In the present study, we report the detection of the first clinical strain of E. coli ST131 with a bla_KPC–2 gene, which integrated in the chromosome. E. coli strain EC3385 was identified and subjected to susceptibility testing and genotyping. The complete genome sequences of this strain and four Proteus mirabilis strains were obtained. Chromosomal integration of the bla_KPC–2 gene was confirmed using a combination of short- and long-read sequencing. Comparative genetic analyses were performed and the origin of the chromosomal location of the bla_KPC–2 gene was further analyzed. Whole-genome sequencing revealed that strain EC3385 belonged to the ST131 type and possessed various resistance and virulence genes. Sequence analysis showed that the bla_KPC–2 gene was carried in a 24-kb insertion sequence on the chromosome. This insertion sequence possessed high sequence similarity to previously reported bla_KPC–2-habouring plasmids of P. mirabilis in China. To the best of our knowledge, this is the first report of a clinical ST131 E. coli strain carrying bla_KPC–2 on the chromosome. The bla_KPC–2 gene was probably horizontally transferred from the P. mirabilis plasmid to the E. coli chromosome by the IS26 element, indicating that P. mirabilis might be an important reservoir of bla_KPC–2 gene for E. coli. Furthermore, the E. coli ST131 strain carrying the chromosomal bla_KPC–2 gene could be further spread due to its carbapenem resistance and high virulence. It is imperative to perform active surveillance to prevent further dissemination of KPC-2 type carbapenemase-producing isolates.

Optogenetic Control of Airway Cholinergic Neurons In Vivo

Dysregulation of airway nerves leads to airway hyperreactivity, a hallmark of asthma. Although changes to nerve density and phenotype have been described in asthma, the relevance of these changes to nerve function has not been investigated due to anatomical limitations where afferent and efferent nerves run in the same nerve trunk, making it difficult to assess their independent contributions. We developed a unique and accessible system to activate specific airway nerves to investigate their function in mouse models of airway disease. We describe a method to specifically activate cholinergic neurons using light, resulting in immediate, measurable increases in airway inflation pressure and decreases in heart rate. Expression of light-activated channelrhodopsin 2 in these neurons is governed by Cre expression under the endogenous choline acetyltransferase promoter, and we describe a method to decrease variability in channelrhodopsin expression in future experiments. Optogenetic activation of specific subsets of airway neurons will be useful for studying the functional relevance of other observed changes, such as changes to nerve morphology and protein expression, across many airway diseases, and may be used to study the function of subpopulations of autonomic neurons in lungs and other organs.

Efficient CD4Cre-Mediated Conditional KRas Expression in Alveolar Macrophages and Alveolar Epithelial Cells Causes Fatal Hyperproliferative Pneumonitis

The CD4Cre transgenic model has been widely used for T cell-specific gene manipulation. We report unexpected highly efficient Cre-mediated recombination in alveolar macrophages (AMFs), bronchial epithelial cells (BECs), and alveolar epithelial cells (AECs) in this strain of mice. Different from CD4 T cells, AMFs, AECs, and BECs do not express detectable Cre protein, suggesting that Cre protein is either very transiently expressed in these cells or only expressed in their precursors. Mice carrying a conditional constitutively active KRas (caKRas) allele and the CD4Cre transgene contain not only hyperactivated T cells but also develop severe AMF accumulation, AEC and BEC hyperplasia, and adenomas in the lung, leading to early lethality correlated with caKRas expression in these cells. We propose that caKRas-CD4Cre mice represent, to our knowledge, a novel model of proliferative pneumonitis involving macrophages and epithelial cells and that the CD4Cre model may offer unique usefulness for studying gene functions simultaneously in multilineages in the lung. Our observations, additionally, suggest that caution in data interpretation is warranted when using the CD4Cre transgenic model for T cell-specific gene manipulation, particularly when lung pathophysiological status is being examined.

Targeting Microglia Using Cx3cr1-Cre Lines: Revisiting the Specificity

Microglia play a pivotal role in maintaining homeostasis of the CNS. There is growing interest in understanding how microglia influence normal brain function and disease progression. Several microglia-specific Cx3cr1-Cre lines have been developed and have become indispensable tools in many investigations of microglial function. However, some recent studies have reported that these lines may have significant leakage into neurons. Other studies have reported that Cx3cr1 is expressed in non-microglial cells, including neurons and astrocytes, in vitro or in vivo either during brain development or upon neurological insult. All these reports raise serious concerns about the trustworthiness of these Cre-lines and whether the conclusions drawn from previous studies are valid. Here, we found that a floxed fluorescent reporter mouse line which has been frequently used to verify Cre lines displayed spontaneous expression of the GFP reporter, independent of Cre recombinase, thus revealing a potential caveat in assessing cre lines. We further confirmed that two Cx3cr1-Cre mouse lines can drive fluorescent reporter expression largely restrictively in microglia. Finally, we clarified that these two mouse lines maintain microglia-specific expression even following excitatory injury. Together, our findings confirm that two previously created Cx3cr1-Cre lines remain as invaluable tools for studying microglia. Moreover, to ensure the quality of data generated and the soundness of conclusions drawn from such data, it should be compulsory to thoroughly examine reporter lines for spontaneous leakiness when labeling cells to study CNS function and diseases.

Stereotaxic Surgery for Genetic Manipulation in Striatal Cells of Neonatal Mouse Brains

Many genes are expressed in embryonic brains, and some of them are continuously expressed in the brain after birth. For such persistently expressed genes, they may function to regulate the developmental process and/or physiological function in neonatal brains. To investigate neurobiological functions of specific genes in the brain, it is essential to inactivate genes in the brain. Here, we describe a simple stereotaxic method to inactivate gene expression in the striatum of transgenic mice at neonatal time windows. AAV-eGFP-Cre viruses were microinjected into the striatum of Ai14 reporter gene mice at postnatal day (P) 2 by stereotaxic brain surgery. The tdTomato reporter gene expression was detected in P14 striatum, suggesting a successful Cre-loxP mediated DNA recombination in AAV-transduced striatal cells. We further validated this technique by microinjecting AAV-eGFP-Cre viruses into P2Foxp2fl/fl mice. Double labeling of GFP and Foxp2 showed that GFP-positive cells lacked Foxp2 immunoreactivity in P9 striatum, suggesting the loss of Foxp2 protein in AAV-eGFP-Cre transduced striatal cells. Taken together, these results demonstrate an effective genetic deletion by stereotaxically microinjected AAV-eGFP-Cre viruses in specific neuronal populations in the neonatal brains of floxed transgenic mice. In conclusion, our stereotaxic technique provides an easy and simple platform for genetic manipulation in neonatal mouse brains. The technique can not only be used to delete genes in specific regions of neonatal brains, but it also can be used to inject pharmacological drugs, neuronal tracers, genetically modified optogenetics and chemogenetics proteins, neuronal activity indicators and other reagents into the striatum of neonatal mouse brains.

Atorvastatin inhibits insulin synthesis by inhibiting the Ras/Raf/ERK/CREB pathway in INS-1 cells

BACKROUND

Type 2 diabetes has become a global epidemic disease. Atorvastatin has become a cornerstone in the prevention and treatment of atherosclerosis. However, increasing evidence showed that statins can dose-dependently increase the risk of diabetes mellitus. The mechanism is not clear.

OBJECTIVE

The Ras complex pathway (Ras/Raf/extracellular signal-regulated kinase [ERK]/cAMP response element-binding protein [CREB]) is the major pathway that regulates the gene transcription. Except for the inhibition of cholesterol synthesis by inhibiting the 3-hydroxy-3-methyl glutaryl coenzyme A (HMG-COA) reductase, statins can also downregulate the phosphorylation of a series of downstream substrates including the key proteins of the Ras complex pathway, therefore may inhibit the insulin syntheses in pancreatic beta cells. In our study, we investigated the inhibitory effect and the underlying mechanism of atorvastatin on insulin synthesis in rat islets.

METHODS

Islets were isolated from Wistar rats and cultured in Roswell Park Memorial Institute (RPMI)-1640 medium. The insulin content in the medium was measured by radioimmunoassay before and after the treatment of 50 μM atorvastatin. Effect of atorvastatin on the expression of insulin message Ribonucleic acid (mRNA) in pancreatic islet beta cells was also detected using quantitative real-time polymerase chain reaction. Western blotting was used to explore the possible role of the Ras complex pathway (Ras/Raf/ERK/CREB) in atorvastatin-inhibited insulin synthesis. The effects of atorvastatin on the binding of nuclear transcription factor p-CREB with CRE in INS-1 cells were examined via chromatin immunoprecipitation assay.

RESULTS

Compared with the control group, the insulin level decreased by 27.1% at 24 hours after atorvastatin treatment. Atorvastatin inhibited insulin synthesis by decreasing insulin mRNA expression of pancreatic islet beta cells. The activities of Ras, Raf-1, and p-CREB in the Ras complex pathway were inhibited by 50 μM atorvastatin in INS-1 cells in vitro. Moreover, 50 μM atorvastatin reduced the binding of p-CREB with deoxyribonucleic acid (DNA) in INS-1 cells in vitro.

CONCLUSION

Atorvastatin inhibits insulin synthesis in beta cells by inhibiting the activation of the Ras complex pathway.

Increasing the efficiency of CRISPR/Cas9-mediated precise genome editing in rats by inhibiting NHEJ and using Cas9 protein

Precise modifications such as site mutation, codon replacement, insertion or precise targeted deletion are needed for studies of accurate gene function. The CRISPR/Cas9 system has been proved as a powerful tool to generate gene knockout and knockin animals. But the homologous recombination (HR)-directed precise genetic modification mediated by CRISPR/Cas9 is relatively lower compared with nonhomologous end-joining (NHEJ) pathway and extremely expected to be improved. Here, in this study 2 strategies were used to increase the precise genetic modification in rats. Scr7, a DNA ligase IV inhibitor, first identified as an anti-cancer compound, and considered as a potential NHEJ inhibitor, was used to increase the HR-mediated precise genetic modification. Meanwhile, the Cas9 protein instead of mRNA was used to save the mRNA to protein translation step to improve the precise modification efficiency. The Fabp2 and Dbndd1 loci were selected to knockin Cre and CreER(T2), respectively. Our result showed that both Scr7 and Cas9 protein can increase the precise modification.

Hepatic S1P deficiency lowers plasma cholesterol levels in apoB-containing lipoproteins when LDLR function is compromised

Background

Site-1 protease (S1P) is the key enzyme required for activation of the sterol regulatory element binding proteins (SREBPs) that govern lipid synthesis. While S1P has been speculated to influence plasma apoB-containing lipoprotein (Blp) metabolism, there has been little investigative work. LDL receptor (LDLR) is the major receptor for clearing plasma LDL cholesterol (LDL-c). Proprotein convertase subtilisin kexin type 9 (PCSK9) modulates LDL-c through post-translational degradation of the LDLR.

Methods

A hepatic-specific knockdown (KD) of S1P was achieved using floxed S1P mouse models (S1P^f/f and LDLR^-/-S1P^f/f) and hepatic expression of Cre recombinase. Lipids were measured in total plasma and size fractionated plasma using colorimetric assays. Realtime polymerase chain reaction, western blotting and ELISA were used to determine hepatic expression of key genes/protein. Plasmid mediated overexpression and siRNA mediated knockdown of genes were performed in mouse primary hepatocytes to determine the mechanistic basis of PCSK9 gene regulation.

Results

A hepatic-specific KD of S1P resulted in a 45 % and 38 % reduction in plasma total cholesterol and triglyceride levels, respectively. Hepatic S1P KD had a minimal effect on plasma Blp cholesterol (Blp-c) in S1P^f/f mice, despite significantly reducing VLDL secretion. Notably, hepatic S1P KD decreased the LDL receptor (LDLR) mRNA expression by 50 %. However, the reduction in LDLR protein levels was less than that of mRNA expression, especially under fed conditions. Further assessment of hepatic S1P deficiency revealed that it increased LDLR protein stability in vivo. Mechanistically, hepatic S1P KD was shown to decrease the liver and plasma levels of the protein proprotein convertase subtilisin/kexin type 9 (PCSK9), which degrades LDLR protein. This effect was more prominent in the fed condition and sufficient to account for the discordance in LDLR mRNA and protein levels. Furthermore, hepatic S1P was shown to regulate PCSK9 expression through activation of the SREBPs. In the LDLR^-/- background, hepatic S1P KD significantly reduced Blp-c levels.

Conclusion

Hepatic S1P is a physiological modulator of plasma Blp metabolism through its regulation of LDLR and PCSK9. Hepatic S1P is a valid target for lowering plasma Blp-c levels in the situation where LDLR function is compromised.

Generation of a Magoh conditional allele in mice

Magoh encodes a core component of the exon junction complex (EJC), which binds mRNA and regulates mRNA metabolism. Magoh is highly expressed in proliferative tissues during development. EJC components have been implicated in several developmental disorders including TAR syndrome, Richieri-Costa-Pereira syndrome, and intellectual disability. Existing germline null Magoh mice are embryonic lethal as homozygotes and perinatal lethal as heterozygotes, precluding detailed analysis of embryonic and postnatal functions. Here, we report the generation of a new genetic tool to dissect temporal and tissue-specific roles for Magoh in development and adult homeostasis. This Magoh conditional allele has two loxP sites flanking the second exon. Ubiquitous Cre-mediated deletion of the floxed allele in a heterozygous mouse (Magoh(del/+) ) causes 50% reduction of both Magoh mRNA and protein. Magoh(del/+) mice exhibit both microcephaly and hypopigmentation, thus phenocopying germline haploinsufficient Magoh mice. Using Emx1-Cre, we further show that conditional Magoh deletion in neural progenitors during embryonic development also causes microcephaly. We anticipate this novel conditional allele will be a valuable tool for assessing tissue-specific roles for Magoh in mammalian development and postnatal processes.

Generating tamoxifen-inducible Cre alleles to investigate myogenesis in mice

Gene inactivation has become the gold standard for determining gene function in the mouse. Many genes inactivated in the germ line cause early lethality that precludes phenotypic assessment at a later time point. Conditional gene inactivation using Cre recombinase expressed via a tissue specific promoter/enhancer allows phenotypic analyses of selected tissues, but lacks temporal control. Recent development of the tamoxifen-inducible Cre-ER (T2) offers both cell type-specific and temporal control of conditional gene inactivation. As an example, we describe the design and step-wise construction of a Cre-ER (T2) knock-in allele at the Pax7 locus using the recombineering method - Pax7 is selectively expressed in embryonic muscle progenitors and adult muscle stem cells. The resulting Pax7-Cre- ER (T2) (Pax7 (CE)) allele has been successfully applied to embryos and adults for tamoxifen-regulated myogenic lineage tracing and gene inactivation (Nature 460:627-631, 2009; Genesis 48:424-436, 2010).

Development of a simple and efficient system for excising selectable markers in Arabidopsis using a minimal promoter::Cre fusion construct

The development of rapid and efficient strategies to generate selectable marker-free transgenic plants could help increase the consumer acceptance of genetically modified (GM) plants. To produce marker-free transgenic plants without conditional treatment or the genetic crossing of offspring, we have developed a rapid and convenient DNA excision method mediated by the Cre/loxP recombination system under the control of a -46 minimal CaMV 35S promoter. The results of a transient expression assay showed that -46 minimal promoter::Cre recombinase (-46::Cre) can cause the loxP-specific excision of a selectable marker, thereby connecting the 35S promoter and β-glucuronidase (GUS) reporter gene. Analysis of stable transgenic Arabidopsis plants indicated a positive correlation between loxP-specific DNA excision and GUS expression. PCR and DNA gel-blot analysis further revealed that nine of the 10 tested T(1) transgenic lines carried both excised and nonexcised constructs in their genomes. In the subsequent T(2) generation plants, over 30% of the individuals for each line were marker-free plants harboring the excised construct only. These results demonstrate that the -46::Cre fusion construct can be efficiently and easily utilized for producing marker-free transgenic plants.

Visual tuning properties of genetically identified layer 2/3 neuronal types in the primary visual cortex of cre-transgenic mice

The putative excitatory and inhibitory cell classes within the mouse primary visual cortex V1 have different functional properties as studied using recording microelectrode. Excitatory neurons show high selectivity for the orientation angle of moving gratings while the putative inhibitory neurons show poor selectivity. However, the study of selectivity of the genetically identified interneurons and their subtypes remain controversial. Here we use novel Cre-driver and reporter mice to identify genetic subpopulations in vivo for two-photon calcium dye imaging: Wfs1(+)/Gad1(−) mice that labels layer 2/3 excitatory cell population and Pvalb(+)/Gad1(+) mice that labels a genetic subpopulation of inhibitory neurons. The cells in both mice were identically labeled with a tdTomato protein, visible in vivo, using a Cre-reporter line. We found that the Wfs1(+) cells exhibited visual tuning properties comparable to the excitatory population, i.e., high selectivity and tuning to the angle, direction, and spatial frequency of oriented moving gratings. The functional tuning of Pvalb(+) neurons was consistent with previously reported narrow-spiking interneurons in microelectrode studies, exhibiting poorer selectivity than the excitatory neurons. This study demonstrates the utility of Cre-transgenic mouse technology in selective targeting of subpopulations of neurons and makes them amenable to structural, functional, and connectivity studies.

Activation of NR2A receptors induces ischemic tolerance through CREB signaling

Previous exposure to a nonlethal ischemic insult protects the brain against subsequent harmful ischemia. N-methyl-D-aspartate (NMDA) receptors are a highly studied target of neuroprotection after ischemia. Recently, NMDA receptor subtypes were implicated in neuronal survival and death. We focused on the contribution of NR2A and cyclic-AMP response element (CRE)-binding protein (CREB) signaling to ischemic tolerance using primary cortical neurons. Ischemia in vitro was modeled by oxygen-glucose deprivation (OGD). Ischemic tolerance was induced by applying 45-mins OGD 24 h before 180-mins OGD. Sublethal OGD also induced cross-tolerance against lethal glutamate and hydrogen peroxide. After sublethal OGD, expression of phosphorylated CREB and CRE transcriptional activity were significantly increased. When CRE activity was inhibited by CREB-S133A, a mutant CREB, ischemic tolerance was abolished. Inhibiting NR2A using NVP-AAM077 attenuated preconditioning-induced neuroprotection and correlated with decreased CRE activity levels. Activating NR2A using bicuculline and 4-aminopiridine induced resistance to lethal ischemia accompanied by elevated CRE activity levels, and this effect was abolished by NVP-AAM077. Elevated brain-derived neurotrophic factor (BDNF) transcriptional activities were observed after sublethal OGD and administration of bicuculline and 4-aminopiridine. NR2A-containing NMDA receptors and CREB signaling have important functions in the induction of ischemic tolerance. This may provide potential novel therapeutic strategies to treat ischemic stroke.

Dependence of reversibility and progression of mouse neuronopathic Gaucher disease on acid beta-glucosidase residual activity levels

Genetic and chemically induced neuronopathic mouse models of Gaucher disease were developed to facilitate understanding of the reversibility and/or progression of CNS involvement. The lethality of the skin permeability barrier defect of the complete gene knock out [gba, (glucocerebrosidase) GCase] was avoided by conditional reactivation of a low activity allele (D409H) in keratinocytes (kn-9H). In kn-9H mice, progressive CNS disease and massive glucosylceramide storage in tissues led to death from CNS involvement by the age of 14 days. Conduritol B epoxide (CBE, a covalent inhibitor of GCase) treatment (for 8-12 days) of wild type, D409H, D409V or V394L homozygotes recapitulated the CNS phenotype of the kn-9H mice with seizures, tail arching, shaking, tremor, quadriparesis, extensive neuronal degeneration loss and apoptosis, and death by the age of 14 days. Minor CNS abnormalities occurred after daily CBE injections of 100 mg/kg/day for 6 doses, but neuronal degeneration was progressive and glucosylceramide storage persisted in D409V homozygotes in the 2 to 5 months after CBE cessation; wild type and D409H mice had persistent neurological damage without progression. The persistent CNS deterioration, histologic abnormalities, and glucosylceramide storage in the CBE-treated D409V mice revealed a threshold level of GCase activity necessary for the prevention of progression of CNS involvement.

Lack of the murine homeobox gene Hesx1 leads to a posterior transformation of the anterior forebrain

The homeobox gene Hesx1 is an essential repressor that is required within the anterior neural plate for normal forebrain development in mouse and humans. Combining genetic cell labelling and marker analyses, we demonstrate that the absence of Hesx1 leads to a posterior transformation of the anterior forebrain (AFB) during mouse development. Our data suggest that the mechanism underlying this transformation is the ectopic activation of Wnt/beta-catenin signalling within the Hesx1 expression domain in the AFB. When ectopically expressed in the developing mouse embryo, Hesx1 alone cannot alter the normal fate of posterior neural tissue. However, conditional expression of Hesx1 within the AFB can rescue the forebrain defects observed in the Hesx1 mutants. The results presented here provide new insights into the function of Hesx1 in forebrain formation.

Controlled expression of transgenes introduced by in vivo electroporation

In vivo electroporation is a powerful technique for the introduction of genes into organisms. Temporal and spatial regulation of expression of introduced genes, or of RNAi, would further enhance the utility of this method. Here we demonstrate conditional regulation of gene expression from electroporated plasmids in the postnatal rat retina and the embryonic mouse brain. For temporal regulation, Cre/loxP-mediated inducible expression vectors were used in combination with a vector expressing a conditionally active form of Cre recombinase, which is activated by 4-hydroxytamoxifen. Onset of gene expression was regulated by the timing of 4-hydroxytamoxifen administration. For spatial regulation, transgenes were expressed by using promoters specific for rod photoreceptors, bipolar cells, amacrine cells, Müller glia or progenitor cells. Combinations of these constructs will facilitate a variety of experiments, including cell-type-specific gene misexpression, conditional RNAi, and fate mapping of progenitor and precursor cells.

Roles of histone acetylation and chromatin remodeling factor in a meiotic recombination hotspot

Histone acetyltransferases (HATs) and ATP-dependent chromatin remodeling factors (ADCRs) are involved in selective gene regulation via modulation of local chromatin configuration. Activation of the recombination hotspot ade6-M26 of Schizosaccharomyces pombe is mediated by a cAMP responsive element (CRE)-like sequence, M26, and a heterodimeric ATF/CREB transcription factor, Atf1.Pcr1. Chromatin remodeling occurs meiotically around M26. We examined the roles of HATs and ADCRs in chromatin remodeling around M26. Histones H3 and H4 around M26 were hyperacetylated in an M26- and Atf1-dependent manner early in meiosis. SpGcn5, the S. pombe homolog of Gcn5p, was required for the majority of histone H3 acetylation around M26 in vivo. Deletion of gcn5+ caused a significant delay in chromatin remodeling but only partial reduction of M26 meiotic recombination frequency. The snf22+ (a Swi2/Snf2-ADCR homologue) deletion and snf22+ gcn5+ double deletion abolished chromatin remodeling and significant reduction of meiotic recombination around M26. These results suggest that HATs and ADCRs cooperatively alter local chromatin structure, as in selective transcription activation, to activate meiotic recombination at M26 in a site-specific manner.

Semaphorin 3F is critical for development of limbic system circuitry and is required in neurons for selective CNS axon guidance events

Little is known about the role of class 3 semaphorins in the development of CNS circuitry. Several class 3 semaphorins, including semaphorin 3F (Sema3F) bind to the receptor neuropilin-2 to confer chemorepulsive responses in vitro. To understand the role of Sema3F in the establishment of neural circuitry in vivo, we have generated sema3F null and sema3F conditional mutant mice. Inspection of the peripheral nervous system in sema3F null mice reveals that Sema3F is essential for the proper organization of specific cranial nerve projections. Analysis of the CNS in sema3F null mice reveals a crucial role for Sema3F in the rostral forebrain, midbrain, and hippocampus in establishing specific Npn-2 (neuropilin-2)-expressing limbic tracts. Furthermore, we identify Sema3F and Npn-2 as the first guidance cue-receptor pair shown to be essential for controlling the development of amygdaloid circuitry. In addition, we provide genetic evidence in vertebrates for a neuronal requirement of a soluble axon guidance cue in CNS axon guidance. Our data reveal a requirement for neuronal Sema3F in the normal development of the anterior commissure in the ventral forebrain and infrapyramidal tract in the hippocampus. Thus, our results show that Sema3F is the principal ligand for Npn-2-mediated axon guidance events in vivo and is a critical determinant of limbic and peripheral nervous system circuitry.

Downregulation of fasting-induced cAMP response element-mediated gene induction by leptin in neuropeptide Y neurons of the arcuate nucleus

States of increased metabolic demand such as fasting modulate hypothalamic neuropeptide gene expression and decrease circulating leptin levels. This study tested the hypotheses that fasting stimulates gene induction mediated by cAMP response element (CRE)-dependent increases in gene transcription and that fasting-induced decreases in leptin can regulate this CRE-mediated gene induction. Using C57BL/6J mice transgenic for a CRE-lacZ construct, an immunocytochemical study showed that fasting activated reporter gene expression in the hypothalamic arcuate nucleus (Arc) in a small subset of neurons and increased phosphorylation of CRE binding protein. The increase of beta-galactosidase expression caused by fasting was inhibited by a protein kinase A inhibitor, Rp-8-Br-cAMPS, when the compound was microinjected into the medial basal hypothalamus, and enhanced by intraperitoneal injection of selective phosphodiesterase inhibitors. In situ hybridization studies showed that neuropeptide Y (NPY) mRNA levels increased in the Arc during fasting, whereas proopiomelanocortin (POMC) mRNA levels decreased. Double labeling of mRNA and beta-galactosidase immunoreactivity in the fasted brain indicated that the subpopulation of the neurons expressing beta-galactosidase all produced NPY but not POMC. To study the possible involvement of decreased circulating leptin during starvation on CRE-mediated gene induction, leptin was administered intraperitoneally to fasted mice. Leptin significantly attenuated both beta-galactosidase expression and NPY gene expression stimulated by fasting, suggesting that leptin inhibits fasting-stimulated NPY gene expression at least in part through downregulation of CRE-mediated gene induction in the Arc. Leptin-induced modification of CRE-mediated gene induction in the Arc may play an essential role in the central regulation of feeding behavior and energy expenditure.

Differential regulation of mitogen-activated protein kinases ERK1/2 and ERK5 by neurotrophins, neuronal activity, and cAMP in neurons

Activation of the extracellular signal-regulated kinase 1 (ERK1) and ERK2 by neurotrophins, neuronal activity, or cAMP has been strongly implicated in differentiation, survival, and adaptive responses of neurons during development and in the adult brain. Recently, a new member of the mitogen-activated protein (MAP) kinase family, ERK5, was discovered. Like ERK1 and ERK2, ERK5 is expressed in neurons, and ERK5 stimulation by epidermal growth factor is blocked by the MAP kinase/ERK kinase 1 (MEK1) inhibitors PD98059 and U0126. This suggests the interesting possibility that some of the functions attributed to ERK1/2 may be mediated by ERK5. However, the regulatory properties of ERK5 in primary cultured neurons have not been reported. Here we examined the regulation of ERK5 signaling in primary cultured cortical neurons. Our data demonstrate that, similar to ERK1/2, ERK5 is activated by neurotrophins including brain-derived neurotrophic factor (BDNF), neurotrophin-3 (NT-3), and NT-4. BDNF stimulation of ERK5 required the activity of MEK5. Surprisingly, ERK5 was not stimulated by cAMP or neuronal activity induced by glutamate or membrane depolarization. In contrast to ERK1/2, ERK5 strongly activated the transcriptional activity of myocyte enhancer factor 2C (MEF2C) in pheochromocytoma 12 (PC12) cells and was required for neurotrophin stimulation of MEF2C transcription in both PC12 cells and cortical neurons. Furthermore, ERK1/2, but not ERK5, induced transcription from Elk1 and the cAMP/ Ca(2+) response element in PC12 cells. Our data suggest that mechanisms for regulation of ERK5 and downstream transcriptional pathways regulated by ERK5 are distinct from those of ERK1/2 in neurons. Furthermore, ERK5 is the first MAP kinase identified whose activity is stimulated by neurotrophins but not by neuronal activity.

X inactivation and somatic cell selection rescue female mice carrying a Piga-null mutation

A somatic mutation in the X linked PIGA gene is responsible for the deficiency of glycosyl phosphatidylinositol (GPI)-anchored proteins on blood cells from patients with paroxysmal nocturnal hemoglobinuria. No inherited form of GPI-anchor deficiency has been described. Because conventional Piga gene knockout is associated with high embryonic lethality in chimeric mice, we used the Cre/loxP system. We generated mice in which two loxP sites flank part of Piga exon 2. After crossbreeding with female mice of the EIIa-cre strain, the floxed allele undergoes Cre-mediated recombination with high efficiency during early embryonic development. Because of X chromosome inactivation, female offspring are mosaic for cells that express or lack GPI-linked proteins. Analysis of mosaic mice showed that in heart, lung, kidney, brain, and liver, mainly wild-type Piga is active, suggesting that these tissues require GPI-linked proteins. The salient exceptions were spleen, thymus, and red blood cells, which had almost equal numbers of cells expressing the wild-type or the recombined allele, implying that GPI-linked proteins are not essential for the derivation of these tissues. PIGA(-) cells had no growth advantage, suggesting that other factors are needed for their clonal dominance in patients with paroxysmal nocturnal hemoglobinuria.

A novel basal promoter element is required for expression of the rat tyrosine hydroxylase gene

Transcription of the rat tyrosine hydroxylase (TH) gene is controlled by enhancer sequences in its 5' flanking region; these enhancers include the AP1, dyad, and cAMP response element (CRE) motifs. We show that a novel basal promoter element (-17 GCCTGCCTGGCGA -5) positioned between the TATA box and +1 works in conjunction with the upstream AP1-dyad and CRE enhancers but cannot support transcription by itself. A mutation of this element, termed partial dyad, reduces basal expression of a reporter gene in TH-positive cell lines and TH-negative lines but has no effect on cAMP- or KCl-induced expression. A double mutant at positions -17 and -11 of the partial dyad reduces transcriptional activation by 80%. Conversely, insertion of this element into a heterologous promoter restores basal expression to levels mediated by the native TH promoter. The partial dyad is a novel activational element that is required for full expression of the TH gene and may assist in the function of the AP1, dyad, and CRE motifs and also other enhancers further upstream. Hence, the rat TH gene is unusual in that its enhancers will not function with a heterologous promoter but require a specific TH promoter sequence for full activation.