Generating transgenic mice from bacterial artificial chromosomes: transgenesis efficiency, integration and expression outcomes

Protein family FAM241 in human and mouse

FAM241B was isolated in a genome-wide inactivation screen for generation of enlarged lysosomes. FAM241B and FAM241A comprise protein family FAM241 encoding proteins of 121 and 132 amino acid residues, respectively. The proteins exhibit 25% amino acid sequence identity and contain a domain of unknown function (DUF4605; pfam15378) that is conserved from primitive multicellular eukaryotes through vertebrates. Phylogenetic comparison indicates that duplication of the ancestral FAM241B gene occurred prior to the origin of fish. FAM241B has been deleted from the avian lineage. Fam241a and Fam241b are widely expressed in mouse tissues. Experimental knockout of mouse Fam241a, Fam241b, and the double knockout, did not generate a visible phenotype. Knockout of Fam241A and Fam241B did not exacerbate the phenotype of FIG4 null mice. RNAseq of brain RNA from double knockout mice detected reduced expression of several genes including Arke1e1 and RnaseL. The human variant p.Val115Gly in FAM241B was identified in a patient with developmental delay. Lysosome morphology in patient-derived fibroblasts was normal. In previous studies, FAM241A and FAM241B appeared to co-localize with proteins of the endoplasmic reticulum. The molecular function of this ancient protein family remains to be determined.

Advances in bacterial artificial chromosome (BAC) transgenic mice for gene analysis and disease research

Transgenic mice, including those created using Bacterial Artificial Chromosomes (BACs), are artificial manipulations that have become critical tools for studying gene function. While conventional transgenic techniques face challenges in achieving precise expression of foreign genes in specific cells and tissues, BAC transgenic mice offer a solution by incorporating large DNA segments that can include entire expression units with tissue-specific enhancers. This review provides a thorough examination of BAC transgenic mouse technology, encompassing both traditional and humanized models. We explore the benefits and drawbacks of BAC transgenesis compared to other techniques such as knock-in and CRISPR/Cas9 technologies. The review emphasizes the applications of BAC transgenic mice in various disciplines, including neuroscience, immunology, drug metabolism, and disease modeling. Additionally, we address crucial aspects of generating and analyzing BAC transgenic mice, such as position effects, copy number variations, and strategies to mitigate these challenges. Despite certain limitations, humanized BAC transgenic mice have proven to be invaluable tools for studying the pathogenesis of human diseases, drug development, and understanding intricate gene regulatory mechanisms. This review discusses current topics on BAC transgenic mice and their evolving significance in biomedical research.

NEK7 phosphorylation amplifies NLRP3 inflammasome activation downstream of potassium efflux and gasdermin D

The NLRP3 inflammasome plays a critical role in innate immunity and inflammatory diseases. NIMA-related kinase 7 (NEK7) is essential for inflammasome activation, and its interaction with NLRP3 is enhanced by K+ efflux. However, the mechanism by which K+ efflux promotes this interaction remains unknown. Here, we show that NEK7 is rapidly phosphorylated at threonine-190/191 by JNK1 downstream of K+ efflux and gasdermin D (GSDMD) after NLRP3 activation. NEK7 phosphorylation enhances the binding between NEK7 and NLRP3, which further promotes inflammasome assembly and activation. Mutant mice and macrophages in which Thr190 and Thr191 of Nek7 were replaced by valine exhibited impaired NEK7 phosphorylation, NLRP3 inflammasome activation, and IL-1β secretion. Thus, NEK7 phosphorylation is an important event that acts downstream of K+ efflux and GSDMD to further enhance NLRP3 inflammasome activation.

Neuronal splicing of the unmethylated histone H3K4 reader, PHF21A, prevents excessive synaptogenesis

PHF21A is a histone-binding protein that recognizes unmethylated histone H3K4, the reaction product of LSD1 histone demethylase. PHF21A and LSD1 form a complex, and both undergo neuron-specific microexon splicing. The PHF21A neuronal microexon interferes with nucleosome binding, whereas the LSD1 neuronal microexon weakens H3K4 demethylation activity and can alter the substrate specificity to H3K9 or H4K20. However, the temporal expression patterns of PHF21A and LSD1 splicing isoforms during brain development and their biological roles remain unknown. In this work, we report that neuronal PHF21A isoform expression precedes neuronal LSD1 expression during human neuron differentiation and mouse brain development. The asynchronous splicing events resulted in stepwise deactivation of the LSD1-PHF21A complex in reversing H3K4 methylation. An unbiased proteomics survey revealed that the enzymatically inactive LSD1-PHF21A complex interacts with neuron-specific binding partners, including MYT1-family transcription factors and post-transcriptional mRNA processing proteins such as VIRMA. The interaction with the neuron-specific components, however, did not require the PHF21A microexon, indicating that the neuronal proteomic milieu, rather than the microexon-encoded PHF21A segment, is responsible for neuron-specific complex formation. Finally, by using two Phf21a mutant mouse models, we found that Phf21a neuronal splicing prevents excess synapse formation that otherwise would occur when canonical PHF21A is expressed in neurons. These results suggest that the role of the PHF21A microexon is to dampen LSD1-mediated H3K4 demethylation, thereby containing aberrant synaptogenesis.

Regulation of Sex-biased Gene Expression by the Ancestral X-Y Chromosomal Gene Pair Kdm5c-Kdm5d

Conventionally, Y-linked Sry is thought to drive sex differences by triggering differential hormone production. Ancestral X-Y gene pairs, however, are hypothesized to drive hormone-independent sex differences. Here, we show that the X-Y gene pair Kdm5c-Kdm5d regulates sex-biased gene expression in pluripotent mouse embryonic stem cells (ESCs). Wild-type (WT) XX female ESCs exhibit >2-fold higher expression of 409 genes relative to WT XY male ESCs. Conversely, WT XY male ESCs exhibit >2-fold higher expression of 126 genes compared to WT XX female ESCs. Loss of Kdm5c in female ESCs downregulates female-biased genes. In contrast, loss of either Kdm5c or Kdm5d in male ESCs upregulates female-biased genes and downregulates male-biased genes, effectively neutralizing sex-biased gene expression. KDM5C promotes the expression of Kdm5d and several other Y-linked genes in male ESCs. Moreover, ectopic Kdm5d expression in female ESCs is sufficient to drive male-biased gene expression. These results establish Kdm5c-Kdm5d as critical regulators of sex-biased gene expression.

Preclinical evaluation of stereopure antisense oligonucleotides for allele-selective lowering of mutant HTT

Huntington's disease (HD) is an autosomal dominant disease caused by the expansion of cytosine-adenine-guanine (CAG) repeats in one copy of the HTT gene (mutant HTT, mHTT). The unaffected HTT gene encodes wild-type HTT (wtHTT) protein, which supports processes important for the health and function of the central nervous system. Selective lowering of mHTT for the treatment of HD may provide a benefit over nonselective HTT-lowering approaches, as it aims to preserve the beneficial activities of wtHTT. Targeting a heterozygous single-nucleotide polymorphism (SNP) where the targeted variant is on the mHTT gene is one strategy for achieving allele-selective activity. Herein, we investigated whether stereopure phosphorothioate (PS)- and phosphoryl guanidine (PN)-containing oligonucleotides can direct allele-selective mHTT lowering by targeting rs362273 (SNP3). We demonstrate that our SNP3-targeting molecules are potent, durable, and selective for mHTT in vitro and in vivo in mouse models. Through comparisons with a surrogate for the nonselective investigational compound tominersen, we also demonstrate that allele-selective molecules display equivalent potency toward mHTT with improved durability while sparing wtHTT. Our preclinical findings support the advancement of WVE-003, an investigational allele-selective compound currently in clinical testing (NCT05032196) for the treatment of patients with HD.

Patterns of connexin36 and eGFP reporter expression among motoneurons in spinal sexually dimorphic motor nuclei in mouse

BACKGROUND

Sexually dimorphic spinal motoneurons (MNs) in the dorsomedial nucleus (DMN) and dorsolateral nucleus (DLN) as well as those in the cremaster nucleus are involved in reproductive behaviours, and the cremaster nucleus additionally contributes to testicular thermoregulation. It has been reported that MNs in DMN and DLN are extensively linked by gap junctions forming electrical synapses composed of connexin36 (Cx36) and there is evidence that subpopulation of MNs in the cremaster nucleus are also electrically coupled by these synapses.

METHODOLOGY

We used immunofluorescence methods to detect enhanced green fluorescent protein (eGFP) reporter for Cx36 expression in these motor nuclei.

RESULTS

We document in male mice that about half the MNs in each of DMN and DLN express eGFP, while the remaining half do not. Further, we found that the eGFP+ vs. eGFP- subsets of MNs in each of these motor nuclei innervate different target muscles; eGFP+ MNs in DMN and DLN project to sexually dimorphic bulbocavernosus and ischiocavernosus muscles, while the eGFP- subsets project to sexually non-dimorphic anal and external urethral sphincter muscles. Similarly, eGFP+ vs. eGFP- cremaster MNs were found to project to anatomically distinct portions of the cremaster muscle. By immunofluorescence, nearly all motoneurons in both DMN and DLN displayed punctate labelling for Cx36, including at eGFP+/eGFP+, eGFP+/eGFP- and eGFP-/eGFP- cell appositions.

CONCLUSIONS

Most if not all motoneurons in DMN and DLN are electrically coupled, including sexually dimorphic and non-dimorphic motoneurons with each other, despite absence of eGFP reporter in the non-dimorphic populations in these nuclei that have selective projections to sexually non-dimorphic target muscles.

Genetic ablation of Immt induces a lethal disruption of the MICOS complex

The mitochondrial contact site and cristae organizing system (MICOS) is important for crista junction formation and for maintaining inner mitochondrial membrane architecture. A key component of the MICOS complex is MIC60, which has been well studied in yeast and cell culture models. However, only one recent study has demonstrated the embryonic lethality of losing Immt (the gene encoding MIC60) expression. Tamoxifen-inducible ROSA-CreERT2-mediated deletion of Immt in adult mice disrupted the MICOS complex, increased mitochondria size, altered cristae morphology, and was lethal within 12 d. Pathologically, these mice displayed defective intestinal muscle function (paralytic ileus) culminating in dehydration. We also identified bone marrow (BM) hypocellularity in Immt-deleted mice, although BM transplants from wild-type mice did not improve survival. Altogether, this inducible mouse model demonstrates the importance of MIC60 in vivo, in both hematopoietic and non-hematopoietic tissues, and provides a valuable resource for future mechanistic investigations into the MICOS complex.

Asynchronous microexon splicing of LSD1 and PHF21A during neurodevelopment

LSD1 histone H3K4 demethylase and its binding partner PHF21A, a reader protein for unmethylated H3K4, both undergo neuron-specific microexon splicing. The LSD1 neuronal microexon weakens H3K4 demethylation activity and can alter the substrate specificity to H3K9 or H4K20. Meanwhile, the PHF21A neuronal microexon interferes with nucleosome binding. However, the temporal expression patterns of LSD1 and PHF21A splicing isoforms during brain development remain unknown. In this work, we report that neuronal PHF21A isoform expression precedes neuronal LSD1 isoform expression during human neuron differentiation and mouse brain development. The asynchronous splicing events resulted in stepwise deactivation of the LSD1-PHF21A complex in reversing H3K4 methylation. We further show that the enzymatically inactive LSD1-PHF21A complex interacts with neuron-specific binding partners, including MYT1-family transcription factors and post-transcriptional mRNA processing proteins such as VIRMA. The interaction with the neuron-specific components, however, did not require the PHF21A microexon, indicating that the neuronal proteomic milieu, rather than the microexon-encoded PHF21A segment, is responsible for neuron-specific complex formation. These results indicate that the PHF21A microexon is dispensable for neuron-specific protein-protein interactions, yet the enzymatically inactive LSD1-PHF21A complex might have unique gene-regulatory roles in neurons.

Epilepsy and sudden unexpected death in epilepsy in a mouse model of human SCN1B-linked developmental and epileptic encephalopathy

Voltage-gated sodium channel β1 subunits are essential proteins that regulate excitability. They modulate sodium and potassium currents, function as cell adhesion molecules and regulate gene transcription following regulated intramembrane proteolysis. Biallelic pathogenic variants in SCN1B, encoding β1, are linked to developmental and epileptic encephalopathy 52, with clinical features overlapping Dravet syndrome. A recessive variant, SCN1B-c.265C>T, predicting SCN1B-p.R89C, was homozygous in two children of a non-consanguineous family. One child was diagnosed with Dravet syndrome, while the other had a milder phenotype. We identified an unrelated biallelic SCN1B-c.265C>T patient with a clinically more severe phenotype than Dravet syndrome. We used CRISPR/Cas9 to knock-in SCN1B-p.R89C to the mouse Scn1b locus (Scn1bR89/C89). We then rederived the line on the C57BL/6J background to allow comparisons between Scn1bR89/R89 and Scn1bC89/C89 littermates with Scn1b+/+ and Scn1b-/- mice, which are congenic on C57BL/6J, to determine whether the SCN1B-c.265C>T variant results in loss-of-function. Scn1bC89/C89 mice have normal body weights and ∼20% premature mortality, compared with severely reduced body weight and 100% mortality in Scn1b-/- mice. β1-p.R89C polypeptides are expressed in brain at comparable levels to wild type. In heterologous cells, β1-p.R89C localizes to the plasma membrane and undergoes regulated intramembrane proteolysis similar to wild type. Heterologous expression of β1-p.R89C results in sodium channel α subunit subtype specific effects on sodium current. mRNA abundance of Scn2a, Scn3a, Scn5a and Scn1b was increased in Scn1bC89/C89 somatosensory cortex, with no changes in Scn1a. In contrast, Scn1b-/- mouse somatosensory cortex is haploinsufficient for Scn1a, suggesting an additive mechanism for the severity of the null model via disrupted regulation of another Dravet syndrome gene. Scn1bC89/C89 mice are more susceptible to hyperthermia-induced seizures at post-natal Day 15 compared with Scn1bR89/R89 littermates. EEG recordings detected epileptic discharges in young adult Scn1bC89/C89 mice that coincided with convulsive seizures and myoclonic jerks. We compared seizure frequency and duration in a subset of adult Scn1bC89/C89 mice that had been exposed to hyperthermia at post-natal Day 15 versus a subset that were not hyperthermia exposed. No differences in spontaneous seizures were detected between groups. For both groups, the spontaneous seizure pattern was diurnal, occurring with higher frequency during the dark cycle. This work suggests that the SCN1B-c.265C>T variant does not result in complete loss-of-function. Scn1bC89/C89 mice more accurately model SCN1B-linked variants with incomplete loss-of-function compared with Scn1b-/- mice, which model complete loss-of-function, and thus add to our understanding of disease mechanisms as well as our ability to develop new therapeutic strategies.

LncRNAs as Regulators of Atherosclerotic Plaque Stability

Current clinical data show that, despite constant efforts to develop novel therapies and clinical approaches, atherosclerotic cardiovascular diseases (ASCVD) are still one of the leading causes of death worldwide. Advanced and unstable atherosclerotic plaques most often trigger acute coronary events that can lead to fatal outcomes. However, despite the fact that different plaque phenotypes may require different treatments, current approaches to prognosis, diagnosis, and classification of acute coronary syndrome do not consider the diversity of plaque phenotypes. Long non-coding RNAs (lncRNAs) represent an important class of molecules that are implicated in epigenetic control of numerous cellular processes. Here we review the latest knowledge about lncRNAs' influence on plaque development and stability through regulation of immune response, lipid metabolism, extracellular matrix remodelling, endothelial cell function, and vascular smooth muscle function, with special emphasis on pro-atherogenic and anti-atherogenic lncRNA functions. In addition, we present current challenges in the research of lncRNAs' role in atherosclerosis and translation of the findings from animal models to humans. Finally, we present the directions for future lncRNA-oriented research, which may ultimately result in patient-oriented therapeutic strategies for ASCVD.

Transgenesis and Genome Engineering: A Historical Review

Our ability to modify DNA molecules and to introduce them into mammalian cells or embryos almost appears in parallel, starting from the 1970s of the last century. Genetic engineering techniques rapidly developed between 1970 and 1980. In contrast, robust procedures to microinject or introduce DNA constructs into individuals did not take off until 1980 and evolved during the following two decades. For some years, it was only possible to add transgenes, de novo, of different formats, including artificial chromosomes, in a variety of vertebrate species or to introduce specific mutations essentially in mice, thanks to the gene-targeting methods by homologous recombination approaches using mouse embryonic stem (ES) cells. Eventually, genome-editing tools brought the possibility to add or inactivate DNA sequences, at specific sites, at will, irrespective of the animal species involved. Together with a variety of additional techniques, this chapter will summarize the milestones in the transgenesis and genome engineering fields from the 1970s to date.

3R measures in facilities for the production of genetically modified rodents

Sociocultural changes in the human-animal relationship have led to increasing demands for animal welfare in biomedical research. The 3R concept is the basis for bringing this demand into practice: Replace animal experiments with alternatives where possible, Reduce the number of animals used to a scientifically justified minimum and Refine the procedure to minimize animal harm. The generation of gene-modified sentient animals such as mice and rats involves many steps that include various forms of manipulation. So far, no coherent analysis of the application of the 3Rs to gene manipulation has been performed. Here we provide guidelines from the Committee on Genetics and Breeding of Laboratory Animals of the German Society for Laboratory Animal Science to implement the 3Rs in every step during the generation of genetically modified animals. We provide recommendations for applying the 3Rs as well as success/intervention parameters for each step of the process, from experiment planning to choice of technology, harm-benefit analysis, husbandry conditions, management of genetically modified lines and actual procedures. We also discuss future challenges for animal welfare in the context of developing technologies. Taken together, we expect that our comprehensive analysis and our recommendations for the appropriate implementation of the 3Rs to technologies for genetic modifications of rodents will benefit scientists from a wide range of disciplines and will help to improve the welfare of a large number of laboratory animals worldwide.

Transgenic mouse models to study the physiological and pathophysiological roles of human Siglecs

Sialic acid-binding immunoglobulin-like lectins (Siglecs) are important immunomodulatory receptors. Due to differences between human and mouse Siglecs, defining the in vivo roles for human Siglecs (hSiglecs) can be challenging. One solution is the development and use of hSiglec transgenic mice to assess the physiological roles of hSiglecs in health and disease. These transgenic mice can also serve as important models for the pre-clinical testing of immunomodulatory approaches that are based on targeting hSiglecs. Four general methods have been used to create hSiglec-expressing transgenic mice, each with associated advantages and disadvantages. To date, transgenic mouse models expressing hSiglec-2 (CD22), -3 (CD33), -7, -8, -9, -11, and -16 have been created. This review focuses on both the generation of these hSiglec transgenic mice, along with the important findings that have been made through their study. Cumulatively, hSiglec transgenic mouse models are providing a deeper understanding of the differences between human and mice orthologs/paralogs, mechanisms by which Siglecs regulate immune cell signaling, physiological roles of Siglecs in disease, and different paradigms where targeting Siglecs may be therapeutically advantageous.

Angiogenesis depends upon EPHB4-mediated export of collagen IV from vascular endothelial cells

Capillary malformation-arteriovenous malformation (CM-AVM) is a blood vascular anomaly caused by inherited loss of function mutations in RASA1 or EPHB4 genes that encode p120 Ras GTPase-activating protein (p120 RasGAP/RASA1) and Ephrin receptor B4 (EPHB4) respectively. However, whether RASA1 and EPHB4 function in the same molecular signaling pathway to regulate the blood vasculature is uncertain. Here, we show that induced endothelial cell (EC)-specific disruption of Ephb4 in mice results in accumulation of collagen IV in the EC endoplasmic reticulum leading to EC apoptotic death and defective developmental, neonatal and pathological angiogenesis, as reported previously in induced EC-specific RASA1-deficient mice. Moreover, defects in angiogenic responses in EPHB4-deficient mice can be rescued by drugs that inhibit signaling through the Ras pathway and drugs that promote collagen IV export from the ER. However, EPHB4 mutant mice that express a form of EPHB4 that is unable to physically engage RASA1 but retains protein tyrosine kinase activity show normal angiogenic responses. These findings provide strong evidence that RASA1 and EPHB4 function in the same signaling pathway to protect against the development of CM-AVM independent of physical interaction and have important implications with regards possible means of treatment of this disease.

Historical DNA Manipulation Overview

The history of DNA manipulation for the creation of genetically modified animals began in the 1970s, using viruses as the first DNA molecules microinjected into mouse embryos at different preimplantation stages. Subsequently, simple DNA plasmids were used to microinject into the pronuclei of fertilized mouse oocytes and that method became the reference for many years. The isolation of embryonic stem cells together with advances in genetics allowed the generation of gene-specific knockout mice, later on improved with conditional mutations. Cloning procedures expanded the gene inactivation to livestock and other non-model mammalian species. Lentiviruses, artificial chromosomes, and intracytoplasmic sperm injections expanded the toolbox for DNA manipulation. The last chapter of this short but intense history belongs to programmable nucleases, particularly CRISPR-Cas systems, triggering the development of genomic-editing techniques, the current revolution we are living in.

Perspective of the GEMSTONE Consortium on Current and Future Approaches to Functional Validation for Skeletal Genetic Disease Using Cellular, Molecular and Animal-Modeling Techniques

The availability of large human datasets for genome-wide association studies (GWAS) and the advancement of sequencing technologies have boosted the identification of genetic variants in complex and rare diseases in the skeletal field. Yet, interpreting results from human association studies remains a challenge. To bridge the gap between genetic association and causality, a systematic functional investigation is necessary. Multiple unknowns exist for putative causal genes, including cellular localization of the molecular function. Intermediate traits ("endophenotypes"), e.g. molecular quantitative trait loci (molQTLs), are needed to identify mechanisms of underlying associations. Furthermore, index variants often reside in non-coding regions of the genome, therefore challenging for interpretation. Knowledge of non-coding variance (e.g. ncRNAs), repetitive sequences, and regulatory interactions between enhancers and their target genes is central for understanding causal genes in skeletal conditions. Animal models with deep skeletal phenotyping and cell culture models have already facilitated fine mapping of some association signals, elucidated gene mechanisms, and revealed disease-relevant biology. However, to accelerate research towards bridging the current gap between association and causality in skeletal diseases, alternative in vivo platforms need to be used and developed in parallel with the current -omics and traditional in vivo resources. Therefore, we argue that as a field we need to establish resource-sharing standards to collectively address complex research questions. These standards will promote data integration from various -omics technologies and functional dissection of human complex traits. In this mission statement, we review the current available resources and as a group propose a consensus to facilitate resource sharing using existing and future resources. Such coordination efforts will maximize the acquisition of knowledge from different approaches and thus reduce redundancy and duplication of resources. These measures will help to understand the pathogenesis of osteoporosis and other skeletal diseases towards defining new and more efficient therapeutic targets.

DSPP dosage affects tooth development and dentin mineralization

Dentin Sialoprotein (DSP) and phosphophoryn (PP) are two most dominant non-collagenous proteins in dentin, which are the cleavage products of the DSPP (dentin sialophosphoprotein) precursor protein. The absence of the DSPP gene in DSPP knock-out (KO) mice results in characteristics that are consistent with dentinogenesis imperfecta type III in humans. Symptoms include thin dentin, bigger pulp chamber with frequent pulp exposure as well as abnormal epithelial-mesenchymal interactions, and the appearance of chondrocyte-like cells in dental pulp. To better understand how DSPP influences tooth development and dentin formation, we used a bacterial artificial chromosome transgene construct (BAC-DSPP) that contained the complete DSPP gene and promoter to generate BAC-DSPP transgenic mice directly in a mouse DSPP KO background. Two BAC-DSPP transgenic mouse strains were generated and characterized. DSPP mRNA expression in BAC-DSPP Strain A incisors was similar to that from wild-type (wt) mice. DSPP mRNA expression in BAC-DSPP Strain B animals was only 10% that of wt mice. PP protein content in Strain A incisors was 25% of that found in wt mice, which was sufficient to completely rescue the DSPP KO defect in mineral density, since microCT dentin mineral density analysis in 21-day postnatal animal molars showed essentially identical mineral density in both strain A and wt mice. Strain B mouse incisors, with 5% PP expression, only partially rescued the DSPP KO defect in mineral density, as microCT scans of 21-day postnatal animal molars indicated a reduced dentin mineral density compared to wt mice, though the mineral density was still increased over that of DSPP KO. Furthermore, our findings showed that DSPP dosage in Strain A was sufficient to rescue the DSPP KO defect in terms of epithelial-mesenchymal interactions, odontoblast lineage maintenance, along with normal dentin thickness and normal mineral density while DSPP gene dosage in Strain B only partially rescued the aforementioned DSPP KO defect.

Overexpression of schizophrenia susceptibility factor human complement C4A promotes excessive synaptic loss and behavioral changes in mice

The complement component 4 (C4) gene is linked to schizophrenia and synaptic refinement. In humans, greater expression of C4A in the brain is associated with an increased risk of schizophrenia. To investigate this genetic finding and address how C4A shapes brain circuits in vivo, here, we generated a mouse model with primate-lineage-specific isoforms of C4, human C4A and/or C4B. Human C4A bound synapses more efficiently than C4B. C4A (but not C4B) rescued the visual system synaptic refinement deficits of C4 knockout mice. Intriguingly, mice without C4 had normal numbers of cortical synapses, which suggests that complement is not required for normal developmental synaptic pruning. However, overexpressing C4A in mice reduced cortical synapse density, increased microglial engulfment of synapses and altered mouse behavior. These results suggest that increased C4A-mediated synaptic elimination results in abnormal brain circuits and behavior. Understanding pathological overpruning mechanisms has important therapeutic implications in disease conditions such as schizophrenia.

Expression pattern of the V5-Ostm1 protein in bacterial artificial chromosome transgenic mice

Mutations in the osteopetrotic transmembrane protein 1 (Ostm1) gene are responsible for the most severe form of autosomal recessive osteopetrosis both in humans and in the gray lethal (gl/gl) mouse. This defect leads to increased bone mass with bone marrow occlusion and hematopoietic defects. To establish the expression profile of the mouse Ostm1 protein in vivo, homologous recombination in bacteria was designed to generate a V5-Ostm1 bacterial artificial chromosome (BAC) that was subsequently integrated in the mouse genome. Tissue expression of the transgene V5-Ostm1 RNA and protein in transgenic mice follow the endogenous expression profile. Immunohistochemistry analysis demonstrated expression in neuronal populations from central and peripheral nervous system and defined a unique cellular expression pattern. Importantly, together with appropriate protein post-translational modification, in vivo rescue of the osteopetrotic bone gl/gl phenotype in BAC V5-Ostm1 gl/gl mice is consistent with the expression of a fully functional and active protein. These mice represent a unique tool to unravel novel Ostm1 functions in individual tissue and neuronal cell populations and the V5-Ostm1 transgene represents an easy visual marker to monitor the expression of Ostm1 in vitro and in vivo.

Phenotypic Characterization of Transgenic Mice Expressing Human IGFBP-5

Pulmonary fibrosis is one of the important causes of morbidity and mortality in fibroproliferative disorders such as systemic sclerosis (SSc) and idiopathic pulmonary fibrosis (IPF). Insulin-like growth factor binding protein-5 (IGFBP-5) is a conserved member of the IGFBP family of proteins that is overexpressed in SSc and IPF lung tissues. In this study, we investigated the functional role of IGFBP-5 in the development of fibrosis in vivo using a transgenic model. We generated transgenic mice ubiquitously expressing human IGFBP-5 using CRISPR/Cas9 knock-in. Our data show that the heterozygous and homozygous mice are viable and express human IGFBP-5 (hIGFBP-5). Transgenic mice had increased expression of extracellular matrix (ECM) genes, especially Col3a1, Fn, and Lox in lung and skin tissues of mice expressing higher transgene levels. Histologic analysis of the skin tissues showed increased dermal thickness, and the lung histology showed subtle changes in the heterozygous and homozygous mice as compared with the wild-type mice. These changes were more pronounced in animals expressing higher levels of hIGFBP-5. Bleomycin increased ECM gene expression in wild-type mice and accentuated an increase in ECM gene expression in transgenic mice, suggesting that transgene expression exacerbated bleomycin-induced pulmonary fibrosis. Primary lung fibroblasts cultured from lung tissues of homozygous transgenic mice showed significant increases in ECM gene expression and protein levels, further supporting the observation that IGFBP-5 resulted in a fibrotic phenotype in fibroblasts. In summary, transgenic mice expressing human IGFBP-5 could serve as a useful animal model for examining the function of IGFBP-5 in vivo.

Nonconserved Long Intergenic Noncoding RNAs Associate With Complex Cardiometabolic Disease Traits

OBJECTIVE

Transcriptome profiling of human tissues has revealed thousands of long intergenic noncoding RNAs (lincRNAs) at loci identified through large-scale genome-wide studies for complex cardiometabolic traits. This raises the question of whether genetic variation at nonconserved lincRNAs has any systematic association with complex disease, and if so, how different this pattern is from conserved lincRNAs. We evaluated whether the associations between nonconserved lincRNAs and 8 complex cardiometabolic traits resemble or differ from the pattern of association for conserved lincRNAs. Approach and Results: Our investigation of over 7000 lincRNA annotations from GENCODE Release 33-GRCh38.p13 for complex trait genetic associations leveraged several large, established meta-analyses genome-wide association study summary data resources, including GIANT (Genetic Investigation of Anthropometric Traits), UK Biobank, GLGC (Global Lipids Genetics Consortium), Cardiogram (Coronary Artery Disease Genome Wide Replication and Meta-Analysis), and DIAGRAM (Diabetes Genetics Replication and Meta-Analysis)/DIAMANTE (Diabetes Meta-Analysis of Trans-Ethnic Association Studies). These analyses revealed that (1) nonconserved lincRNAs associate with a range of cardiometabolic traits at a rate that is generally consistent with conserved lincRNAs; (2) these findings persist across different definitions of conservation; and (3) overall across all cardiometabolic traits, approximately one-third of genome-wide association study-associated lincRNAs are nonconserved, and this increases to about two-thirds using a more stringent definition of conservation.

CONCLUSIONS

These findings suggest that the traditional notion of conservation driving prioritization for functional and translational follow-up of complex cardiometabolic genomic discoveries may need to be revised in the context of the abundance of nonconserved long noncoding RNAs in the human genome and their apparent predilection to associate with complex cardiometabolic traits.

MLL1 Inhibition and Vitamin D Signaling Cooperate to Facilitate the Expanded Pluripotency State

Dynamic establishment of histone modifications in early development coincides with programed cell fate restriction and loss of totipotency beyond the early blastocyst stage. Causal function of histone-modifying enzymes in this process remains to be defined. Here we show that inhibiting histone methyltransferase MLL1 reprograms naive embryonic stem cells (ESCs) to expanded pluripotent stem cells (EPSCs), with differentiation potential toward both embryonic and extraembryonic lineages in vitro and in vivo. MLL1 inhibition or deletion upregulates gene signatures of early blastomere development. The function of MLL1 in restricting induction of EPSCs is mediated partly by Gc, which regulates cellular response to vitamin D signaling. Combined treatment of MLL1 inhibitor and 1α,25-dihydroxyvitamin D₃ (1,25-(OH)₂D₃) cooperatively enhanced functionality of EPSCs, triggering an extended 2C-like state in vitro and robust totipotent-like property in vivo. Our study sheds light on interplay between epigenetics and vitamin D pathway in cell fate determination.

Histone Acetyltransferase MOF Blocks Acquisition of Quiescence in Ground-State ESCs through Activating Fatty Acid Oxidation

Self-renewing embryonic stem cells (ESCs) respond to environmental cues by exiting pluripotency or entering a quiescent state. The molecular basis underlying this fate choice remains unclear. Here, we show that histone acetyltransferase MOF plays a critical role in this process through directly activating fatty acid oxidation (FAO) in the ground-state ESCs. We further show that the ground-state ESCs particularly rely on elevated FAO for oxidative phosphorylation (OXPHOS) and energy production. Mof deletion or FAO inhibition induces bona fide quiescent ground-state ESCs with an intact core pluripotency network and transcriptome signatures akin to the diapaused epiblasts in vivo. Mechanistically, MOF/FAO inhibition acts through reducing mitochondrial respiration (i.e., OXPHOS), which in turn triggers reversible pluripotent quiescence specifically in the ground-state ESCs. The inhibition of FAO/OXPHOS also induces quiescence in naive human ESCs. Our study suggests a general function of the MOF/FAO/OXPHOS axis in regulating cell fate determination in stem cells.

Principles of Genetic Engineering

Genetic engineering is the use of molecular biology technology to modify DNA sequence(s) in genomes, using a variety of approaches. For example, homologous recombination can be used to target specific sequences in mouse embryonic stem (ES) cell genomes or other cultured cells, but it is cumbersome, poorly efficient, and relies on drug positive/negative selection in cell culture for success. Other routinely applied methods include random integration of DNA after direct transfection (microinjection), transposon-mediated DNA insertion, or DNA insertion mediated by viral vectors for the production of transgenic mice and rats. Random integration of DNA occurs more frequently than homologous recombination, but has numerous drawbacks, despite its efficiency. The most elegant and effective method is technology based on guided endonucleases, because these can target specific DNA sequences. Since the advent of clustered regularly interspaced short palindromic repeats or CRISPR/Cas9 technology, endonuclease-mediated gene targeting has become the most widely applied method to engineer genomes, supplanting the use of zinc finger nucleases, transcription activator-like effector nucleases, and meganucleases. Future improvements in CRISPR/Cas9 gene editing may be achieved by increasing the efficiency of homology-directed repair. Here, we describe principles of genetic engineering and detail: (1) how common elements of current technologies include the need for a chromosome break to occur, (2) the use of specific and sensitive genotyping assays to detect altered genomes, and (3) delivery modalities that impact characterization of gene modifications. In summary, while some principles of genetic engineering remain steadfast, others change as technologies are ever-evolving and continue to revolutionize research in many fields.

A Simple Guide for Generating BAC Transgenic Animals for Retinal Research

Bacterial artificial chromosomes (BACs) are genomic tools that can carry several hundred kilobases of exogenous genomic material. This allows to incorporate sufficiently large DNA stretches to include most if not all upstream and downstream cis-regulatory elements of a gene in order to mimic and analyze its endogenous regulation of expression using a reporter protein in vivo. Here, we illustrate the generation of a BAC:LIF-EGFP transgenic mouse line to describe a simplified version of BAC transgenesis using galK-based recombineering.

Functional evaluation of a monotreme-specific antimicrobial protein, EchAMP, against experimentally induced mastitis in transgenic mice

EchAMP, the tenth most abundant transcript expressed in the mammary gland of echidna, has in vitro broad-spectrum antibacterial effects. However, the effects of EchAMP on mastitis, a condition where inflammation is triggered following mammary gland infection, has not been investigated. To investigate the impact of EchAMP against mastitis, EchAMP transgenic mice were generated. In antibacterial assays, the whey fractions of milk from transgenic mice significantly reduced growth of Staphylococcus aureus, Bacillus subtilis, Escherichia coli and Pseudomonas aeruginosa compared with whey fractions from wildtype mice. Furthermore, a mastitis model created by infecting mammary gland with these four bacterial strains displayed a significant reduction in bacterial load in transgenic mice injected with S. aureus and B. subtilis. On further confirmation, histomorphologic analysis showed absence of necrosis and cell infiltration in the mammary glands of transgenic mice. To understand the role of EchAMP against inflammation, we employed an LPS-injected mastitis mouse model. LPS is known to induce phopshorylation of NF-κB and MAPK pathways, which in turn activate downstream proinflammatory signaling mediators, to promote inflammation. In LPS-treated EchAMP transgenic mice, phosphorylation levels of NF-κB, p38 and ERK1/2 were significantly downregulated. Furthermore, in mammary gland of transgenic mice, there was a significant downregulation of mRNA levels of proinflammatory cytokines, namely TNF-α, IL-6 and IL-1β. Taken together, these data suggest that EchAMP has an antiinflammatory response and is effective against S. aureus and B. subtilis. We suggest that EchAMP may be a potential prophylactic protein against mastitis in dairy animals by expressing this gene in their mammary gland.

Testis-specific Arf promoter expression in a transposase-aided BAC transgenic mouse model

CDKN2A is an evolutionarily conserved gene encoding proteins implicated in tumor suppression, ocular development, aging, and metabolic diseases. Like the human form, mouse Cdkn2a encodes two distinct proteins-p16^Ink4a, which blocks cyclin-dependent kinase activity, and p19^Arf, which is best known as a positive regulator of the p53 tumor suppressor-and their functions have been well-studied in genetically engineered mouse models. Relatively little is known about how expression of the two transcripts is controlled in normal development and in certain disease states. To better understand their coordinate and transcript-specific expression in situ, we used a transposase-aided approach to generate a new BAC transgenic mouse model in which the first exons encoding Arf and Ink4a are replaced by fluorescent reporters. We show that mouse embryo fibroblasts generated from the transgenic lines faithfully display induction of each transgenic reporter in cell culture models, and we demonstrate the expected expression of the Arf reporter in the normal testis, one of the few places where that promoter is normally expressed. Interestingly, the TGFβ-2-dependent induction of the Arf reporter in the eye-a process essential for normal eye development-does not occur. Our findings illustrate the value of BAC transgenesis in mapping key regulatory elements in the mouse by revealing the genomic DNA required for Cdkn2a induction in cultured cells and the developing testis, and the apparent lack of elements driving expression in the developing eye.

Siglec-8 antibody reduces eosinophils and mast cells in a transgenic mouse model of eosinophilic gastroenteritis

Aberrant accumulation and activation of eosinophils and potentially mast cells (MCs) contribute to the pathogenesis of eosinophilic gastrointestinal diseases (EGIDs), including eosinophilic esophagitis (EoE), gastritis (EG), and gastroenteritis (EGE). Current treatment options, such as diet restriction and corticosteroids, have limited efficacy and are often inappropriate for chronic use. One promising new approach is to deplete eosinophils and inhibit MCs with a monoclonal antibody (mAb) against sialic acid-binding immunoglobulin-like lectin 8 (Siglec-8), an inhibitory receptor selectively expressed on MCs and eosinophils. Here, we characterize MCs and eosinophils from human EG and EoE biopsies using flow cytometry and evaluate the effects of an anti-Siglec-8 mAb using a potentially novel Siglec-8-transgenic mouse model in which EG/EGE was induced by ovalbumin sensitization and intragastric challenge. MCs and eosinophils were significantly increased and activated in human EG and EoE biopsies compared with healthy controls. Similar observations were made in EG/EGE mice. In Siglec-8-transgenic mice, anti-Siglec-8 mAb administration significantly reduced eosinophils and MCs in the stomach, small intestine, and mesenteric lymph nodes and decreased levels of inflammatory mediators. In summary, these findings suggest a role for both MCs and eosinophils in EGID pathogenesis and support the evaluation of anti-Siglec-8 as a therapeutic approach that targets both eosinophils and MCs.

Generation of Amelx-iCre Mice Supports Ameloblast-Specific Role for Stim1

The identification and targeting of the molecular pathways regulating amelogenesis is an ongoing challenge in dental research, and progress has been restricted by the limited number of genetic tools available to study gene function in ameloblasts. Here, we generated 4 transgenic Cre-driver mouse lines that express improved Cre (iCre)-recombinase from the locus of the mouse ameloblast-specific gene amelogenin X (Amelx-iCre) with a large (250-kb) bacterial artificial chromosome DNA vector. All 4 Amelx-iCre transgenic lines were bred with ROSA26 reporter mice to characterize the iCre developmental pattern with the LacZ gene encoding β-galactosidase enzyme activity assay and Cre protein immunohistochemistry. From the 4 generated transgenic lines, 2 were selected for further analysis because they expressed a high amount of Cre recombinase exclusively in ameloblasts and showed developmental stage- and cell-specific β-galactosidase activity mimicking the endogenous amelogenin expression. To test the functionality of the selected transgenic models, we bred the 2 Amelx-iCre mice lines with stromal interaction molecule 1 (Stim1) floxed mice to generate ameloblast-specific Stim1 conditional knockout mice (Stim1 cKO). STIM1 protein serves as one of the main calcium sensors in ameloblasts and plays a major role in enamel mineralization and ameloblast differentiation. Amelx-iCre mice displayed exclusive CRE-mediated recombination in incisor and molar ameloblasts. Stim1 cKO mice showed a severely defected enamel phenotype, including reduced structural integrity concomitant with increased attrition and smaller teeth. The phenotype and genotype of the Amelx-iCre/Stim1 cKO showed significant differences with the previously reported Ker14-Cre/Stim1 cKO, highlighting the need for cell- and stage-specific Cre lines for an accurate phenotype-genotype comparison. Furthermore, our model has the advantage of carrying the entire Amelx gene locus rather than being limited to an Amelx partial promoter construct, which greatly enhances the stability and the specificity of our Cre expression. As such, the Amelx-iCre transgenic lines that we developed may serve as a powerful tool for targeting ameloblast-specific gene expression in future investigations.

Exome Sequencing Reveals the POLR3H Gene as a Novel Cause of Primary Ovarian Insufficiency

CONTEXT

Primary ovarian insufficiency (POI) is a cause of female infertility. However, the genetic etiology of this disorder remains unknown in most patients with POI.

OBJECTIVE

To investigate the genetic etiology of idiopathic POI.

PATIENTS AND METHODS

We performed whole-exome sequencing of 11 families with idiopathic POI. To gain insights into the potential mechanisms associated with this mutation, we generated two mouse lines via clustered regularly interspaced short palindromic repeats/Cas9 technology.

RESULTS

A pathogenic homozygous missense mutation (c.149A>G; p.Asp50Gly) in the POLR3H gene in two unrelated families was identified. Pathogenic mutations in this subunit have not been associated with human disorders. Loss-of-function Polr3h mutation in mice caused early embryonic lethality. Mice with homozygous point mutation (Polr3hD50G) were viable but showed delayed pubertal development, characterized by late first estrus or preputial separation. The Polr3hD50G female and male mice showed decreased fertility later in life, associated with small litter size and increased time to pregnancy or to impregnate a female. Polr3hD50G mice displayed decreased expression of ovarian Foxo3a and lower numbers of primary follicles.

CONCLUSION

Our manuscript provides a case of POI caused by missense mutation in POLR3H, expanding the knowledge of molecular pathways of the ovarian function and human infertility. Screening of the POLR3H gene may elucidate POI cases without previously identified genetic causes, supporting approaches of genetic counseling.

Production of Transgenic Mice by Pronuclear Microinjection

Pronuclear microinjection remains the most widely used method for the germline modification of mice and other species. The method is conceptually quite simple and at least in rodents can produce transgenic offspring with relatively high efficiency. Here, we describe the various components of the production of transgenic mice including a detailed list of materials and equipment. We outline in detail the preparation of animals, the retrieval, culture and transfer of embryos, the preparation of DNA, and the microinjection process. We have added a substantial collection of notes with helpful suggestions that reflect the many years of experience we have using this technology and our continuing efforts to improve animal welfare and the efficiency of producing transgenics.

Next Generation Transgenic Rat Model Production

The next generation of new genetically engineered rat models by microinjection is described. Genome editors such as CRISPR/Cas9 have greatly increased the efficiency with which the rat genome can be modified to generate research models for biomedical research. Pronuclear microinjection of transgene DNA into rat zygotes results in random multicopy transgene integration events that use exogenous promoters to drive expression. Best practices in transgenic animal design indicate the use of precise single copy transgene integration in the genome. This ideal can be achieved by repair of CRISPR/Cas9 chromosome breaks by homology directed repair. The most effective way to achieve this type of transgenic rat model is to deliver genome modification reagents to rat zygotes by pronuclear microinjection. The keys to success in this process are to obtain fertilized eggs (zygotes) from the rat strain of choice, to purify the microinjection reagents, to deliver the reagents to the eggs by pronuclear microinjection, to use the surgical transfer of microinjected eggs to pseudopregnant rats to obtain G0 founder animals that carry the novel genetic modification. Ultimately the success of new rat models is measured by changes in gene expression as in the expression of a new reporter protein such as eGFP, Cre recombinase, or other protein of interest.

Transgene Recombineering in Bacterial Artificial Chromosomes

Bacterial Artificial Chromosome (BAC) libraries are a valuable research resource. Any one of the clones in these libraries can carry hundreds of thousands of base pairs of genetic information. Often the entire coding sequence and significant upstream and downstream regions, including regulatory elements, can be found in a single BAC clone. BACs can be put to many uses, such as to study the function of human genes in knockout mice, to drive reporter gene expression in transgenic animals, and for gene discovery. In order to use BACs for experimental purposes it is often desirable to genetically modify them by introducing reporter elements or heterologous cDNA sequences. It is not feasible to use conventional DNA cloning approaches to modify BACs due to their size and complexity, thus a specialized field "recombineering" has developed to modify BAC clones through the use of homologous recombination in bacteria with short homology regions. Genetically engineered BACs can then be used in cell culture, mouse, or rat models to study cancer, neurology, and genetics.

Characterisation and use of a functional Gadd45g bacterial artificial chromosome

Bacterial artificial chromosomes (BACs) offer a means of manipulating gene expression and tagging gene products in the mammalian genome without the need to alter endogenous gene structure and risk deleterious phenotypic consequences. However, for a BAC clone to be useful for such purposes it must be shown to contain all the regulatory elements required for normal gene expression and allow phenotypic rescue in the absence of an endogenous gene. Here, we report identification of a functional BAC containing Gadd45g, a gene implicated in DNA repair, DNA demethylation and testis determination in mice and exhibiting a broad pattern of embryonic expression. Mouse fetuses lacking the endogenous Gadd45g gene undergo normal testis development in the presence of the Gadd45g BAC transgene. Moreover, a survey of embryonic Gadd45g expression from the BAC reveals that all reported sites of expression are maintained. This functional BAC can now be used for subsequent manipulation of the Gadd45g gene with the confidence that regulatory elements required for embryonic expression, including testis determination, are present. We describe the generation and characterisation of a Gadd45g-mCherry fluorescent reporter exhibiting strong expression in developing gonads and neural tissue, recapitulating endogenous gene expression, as evidence of this.

Long intergenic noncoding RNAs in cardiovascular diseases: Challenges and strategies for physiological studies and translation

Long intergenic noncoding RNAs (lincRNAs) are increasingly recognized as important mediators of many biological processes relevant to human pathophysiologies, including cardiovascular diseases. In vitro studies have provided important knowledge of cellular functions and mechanisms for an increasing number of lincRNAs. Dysregulated lncRNAs have been associated with cell fate programming and development, vascular diseases, atherosclerosis, dyslipidemia and metabolic syndrome, and cardiac pathological hypertrophy. However, functional interrogation of individual lincRNAs in physiological and disease states is largely limited. The complex nature of lincRNA actions and poor species conservation of human lincRNAs pose substantial challenges to physiological studies in animal model systems and in clinical translation. This review summarizes recent findings of specific lincRNA physiological studies, including MALAT1, MeXis, Lnc-DC and others, in the context of cardiovascular diseases, examines complex mechanisms of lincRNA actions, reviews in vivo research strategies to delineate lincRNA functions and highlights challenges and approaches for physiological studies of primate-specific lincRNAs.

A robust Pax7EGFP mouse that enables the visualization of dynamic behaviors of muscle stem cells

Background

Pax7 is a transcription factor involved in the specification and maintenance of muscle stem cells (MuSCs). Upon injury, MuSCs leave their quiescent state, downregulate Pax7 and differentiate, contributing to skeletal muscle regeneration. In the majority of regeneration studies, MuSCs are isolated by fluorescence-activated sorting (FACS), based on cell surface markers. It is known that MuSCs are a heterogeneous population and only a small percentage of isolated cells are true stem cells that are able to self-renew. A strong Pax7 reporter line would be valuable to study the in vivo behavior of Pax7-expressing stem cells.

Methods

We generated and characterized the muscle properties of a new transgenic Pax7EGFP mouse. Utilizing traditional immunofluorescence assays, we analyzed whole embryos and muscle sections by fluorescence microscopy, in addition to whole skeletal muscles by 2-photon microscopy, to detect the specificity of EGFP expression. Skeletal muscles from Pax7EGFP mice were also evaluated in steady state and under injury conditions. Finally, MuSCs-derived from Pax7EGFP and control mice were sorted and analyzed by FACS and their myogenic activity was comparatively examined.

Results

Our studies provide a new Pax7 reporter line with robust EGFP expression, detectable by both flow cytometry and fluorescence microscopy. Pax7EGFP-derived MuSCs have identical properties to that of wild-type MuSCs, both in vitro and in vivo, excluding any positional effect due to the transgene insertion. Furthermore, we demonstrated high specificity of EGFP to label MuSCs in a temporal manner that recapitulates the reported Pax7 expression pattern. Interestingly, immunofluorescence analysis showed that the robust expression of EGFP marks cells in the satellite cell position of adult muscles in fixed and live tissues.

Conclusions

This mouse could be an invaluable tool for the study of a variety of questions related to MuSC biology, including but not limited to population heterogeneity, polarity, aging, regeneration, and motility, either by itself or in combination with mice harboring additional genetic alterations.

Electronic supplementary material

The online version of this article (10.1186/s13395-018-0169-7) contains supplementary material, which is available to authorized users.

Characterization of Tissue Plasminogen Activator Expression and Trafficking in the Adult Murine Brain

Tissue plasminogen activator (tPA) is an immediate-early gene important for regulating physiological processes like synaptic plasticity and neurovascular coupling. It has also been implicated in several pathological processes including blood-brain barrier (BBB) permeability, seizure progression, and stroke. These varied reports suggest that tPA is a pleiotropic mediator whose actions are highly compartmentalized in space and time. The specific localization of tPA, therefore, can provide useful information about its function. Accordingly, the goal of this study was to provide a detailed characterization of tPA's regional, cellular, and subcellular localization in the brain. To achieve this, two new transgenic mouse lines were utilized: (1) a PlatβGAL reporter mouse, which houses the β-galactosidase gene in the tPA locus and (2) a tPABAC-Cerulean mouse, which has a cerulean-fluorescent protein fused in-frame to the tPA C-terminus. Using these two transgenic reporters, we show that while tPA is expressed throughout most regions of the adult murine brain, it appears to be preferentially targeted to fiber tracts in the limbic system. In the hippocampus, confocal microscopy revealed tPA-Cerulean (tPA-Cer) puncta localized to giant mossy fiber boutons (MFBs) and astrocytes in stratum lucidum. With amplification of the tPA-Cer signal, somatically localized tPA was also observed in the stratum oriens (SO)/alveus layer of both CA1 and CA3 subfields. Coimmunostaining of tPA-Cer and interneuronal markers indicates that these tPA-positive cell bodies belong to a subclass of somatostatin (SST)/oriens-lacunosum moleculare (O-LM) interneurons. Together, these data imply that tPA's localization is differentially regulated, suggesting that its neuromodulatory effects may be compartmentalized and specialized to cell type.

New genetic tools for the in vivo study of hematopoietic stem cell function

The production of blood cells is dependent on the activity of a rare stem cell population that normally resides in the bone marrow (BM) of the organism. These hematopoietic stem cells (HSCs) have the ability to both self-renew and differentiate, ensuring this lifelong hematopoiesis. Determining the regulation of HSC functions should thus provide critical insight to advancing regenerative medicine. Until quite recently, HSCs were primarily studied using in vitro studies and transplantations into immunodeficient hosts. Indeed, the definition of a bona fide HSC is its ability to reconstitute lymphopenic hosts. In this review, we discuss the development of novel, HSC-specific genetic reporter systems that enable the prospective identification of HSCs and the study of their functions in the absence of transplantation. Coupled with additional technological advances, these studies are now defining the fundamental properties of HSCs in vivo. Furthermore, complex cellular and molecular mechanisms that regulate HSC dormancy, self-renewal, and differentiation are being identified and further dissected. These novel reporter systems represent a major technological advance for the stem cell field and allow new questions to be addressed.

Insertional Mutagenesis Confounds the Mechanism of the Morbid Phenotype of a PLNR9C Transgenic Mouse Line

BACKGROUND

A mouse line with heterozygous transgenic expression of phospholamban carrying a substitution of cysteine for arginine 9 (TgPLN^R9C) under the control of α-myosin heavy chain (αMHC) promoter features dilated cardiomyopathy, heart failure, and premature death.

METHODS AND RESULTS

Determination of transgene chromosomal localization by conventional methods shows that in this line the transgenic array of 13 PLN^R9C expression cassettes, arranged in a head-to-tail tandem orientation, have integrated into the bidirectional promoter of the αMHC (Myh6) gene and the gene for the regulatory noncoding RNA Myheart (Mhrt), both of which are known to be involved in cardiac development and pathology. Expression of the noncoding RNA Mhrt in TgPLN^R9C mice exhibits profound deregulation, despite the presence of the second, intact allele.

CONCLUSIONS

The TgPLN^R9C mouse strain is, in the best case, a functionally ambiguous phenocopy of the human PLN^R9C heterozygote, because a similar constellation of genetically programmed events can not occur in a patient. Publications featuring "cardiac-specific overexpression" are focused on the phenotype and typically forgo the definition of the transgene integration site or transgene temporal expression profile, so caution should be exercised in attributing clinical relevance to pathologic phenomena observed in αMHC-driven transgenes.

Sexually dimorphic distribution of Prokr2 neurons revealed by the Prokr2-Cre mouse model

Prokineticin receptor 2 (PROKR2) is predominantly expressed in the mammalian central nervous system. Loss-of-function mutations of PROKR2 in humans are associated with Kallmann syndrome due to the disruption of gonadotropin releasing hormone neuronal migration and deficient olfactory bulb morphogenesis. PROKR2 has been also implicated in the neuroendocrine control of GnRH neurons post-migration and other physiological systems. However, the brain circuitry and mechanisms associated with these actions have been difficult to investigate mainly due to the widespread distribution of Prokr2-expressing cells, and the lack of animal models and molecular tools. Here, we describe the generation, validation and characterization of a new mouse model that expresses Cre recombinase driven by the Prokr2 promoter, using CRISPR-Cas9 technology. Cre expression was visualized using reporter genes, tdTomato and GFP, in males and females. Expression of Cre-induced reporter genes was found in brain sites previously described to express Prokr2, e.g., the paraventricular and the suprachiasmatic nuclei, and the area postrema. The Prokr2-Cre mouse model was further validated by colocalization of Cre-induced GFP and Prokr2 mRNA. No disruption of Prokr2 expression, GnRH neuronal migration or fertility was observed. Comparative analysis of Prokr2-Cre expression in male and female brains revealed a sexually dimorphic distribution confirmed by in situ hybridization. In females, higher Cre activity was found in the medial preoptic area, ventromedial nucleus of the hypothalamus, arcuate nucleus, medial amygdala and lateral parabrachial nucleus. In males, Cre was higher in the amygdalo-hippocampal area. The sexually dimorphic pattern of Prokr2 expression indicates differential roles in reproductive function and, potentially, in other physiological systems.

Motor Dysfunctions and Neuropathology in Mouse Models of Spinocerebellar Ataxia Type 2: A Comprehensive Review

Spinocerebellar ataxia type 2 (SCA2) is an autosomal dominant ataxia caused by an expansion of CAG repeats in the exon 1 of the gene ATXN2, conferring a gain of toxic function that triggers the appearance of the disease phenotype. SCA2 is characterized by several symptoms including progressive gait ataxia and dysarthria, slow saccadic eye movements, sleep disturbances, cognitive impairments, and psychological dysfunctions such as insomnia and depression, among others. The available treatments rely on palliative care, which mitigate some of the major symptoms but ultimately fail to block the disease progression. This persistent lack of effective therapies led to the development of several models in yeast, C. elegans, D. melanogaster, and mice to serve as platforms for testing new therapeutic strategies and to accelerate the research on the complex disease mechanisms. In this work, we review 4 transgenic and 1 knock-in mouse that exhibit a SCA2-related phenotype and discuss their usefulness in addressing different scientific problems. The knock-in mice are extremely faithful to the human disease, with late onset of symptoms and physiological levels of mutant ataxin-2, while the other transgenic possess robust and well-characterized motor impairments and neuropathological features. Furthermore, a new BAC model of SCA2 shows promise to study the recently explored role of non-coding RNAs as a major pathogenic mechanism in this devastating disorder. Focusing on specific aspects of the behavior and neuropathology, as well as technical aspects, we provide a highly practical description and comparison of all the models with the purpose of creating a useful resource for SCA2 researchers worldwide.

Direct introduction of gene constructs into the pronucleus-like structure of cloned embryos: a new strategy for the generation of genetically modified pigs

Due to a rising demand of porcine models with complex genetic modifications for biomedical research, the approaches for their generation need to be adapted. In this study we describe the direct introduction of a gene construct into the pronucleus (PN)-like structure of cloned embryos as a novel strategy for the generation of genetically modified pigs, termed "nuclear injection". To evaluate the reliability of this new strategy, the developmental ability of embryos in vitro and in vivo as well as the integration and expression efficiency of a transgene carrying green fluorescence protein (GFP) were examined. Eighty percent of the cloned pig embryos (633/787) exhibited a PN-like structure, which met the prerequisite to technically perform the new method. GFP fluorescence was observed in about half of the total blastocysts (21/40, 52.5%), which was comparable to classical zygote PN injection (28/41, 68.3%). In total, 478 cloned embryos injected with the GFP construct were transferred into 4 recipients and from one recipient 4 fetuses (day 68) were collected. In one of the fetuses which showed normal development, the integration of the transgene was confirmed by PCR in different tissues and organs from all three primary germ layers and placenta. The integration pattern of the transgene was mosaic (48 out of 84 single-cell colonies established from a kidney were positive for GFP DNA by PCR). Direct GFP fluorescence was observed macro- and microscopically in the fetus. Our novel strategy could be useful particularly for the generation of pigs with complex genetic modifications.

All Hormone-Producing Cell Types of the Pituitary Intermediate and Anterior Lobes Derive From Prop1-Expressing Progenitors

Mutations in PROP1, the most common known cause of combined pituitary hormone deficiency in humans, can result in the progressive loss of all hormones of the pituitary anterior lobe. In mice, Prop1 mutations result in the failure to initiate transcription of Pou1f1 (also known as Pit1) and lack somatotropins, lactotropins, and thyrotropins. The basis for this species difference is unknown. We hypothesized that Prop1 is expressed in a progenitor cell that can develop into all anterior lobe cell types, and not just the somatotropes, thyrotropes, and lactotropes, which are collectively known as the PIT1 lineage. To test this idea, we produced a transgenic Prop1-cre mouse line and conducted lineage-tracing experiments of Prop1-expressing cells. The results reveal that all hormone-secreting cell types of both the anterior and intermediate lobes are descended from Prop1-expressing progenitors. The Prop1-cre mice also provide a valuable genetic reagent with a unique spatial and temporal expression for generating tissue-specific gene rearrangements early in pituitary gland development. We also determined that the minimal essential sequences for reliable Prop1 expression lie within 10 kilobases of the mouse gene and demonstrated that human PROP1 can substitute functionally for mouse Prop1. These studies enhance our understanding of the pathophysiology of disease in patients with PROP1 mutations.

LINE-1 Mediated Insertion into Poc1a (Protein of Centriole 1 A) Causes Growth Insufficiency and Male Infertility in Mice

Skeletal dysplasias are a common, genetically heterogeneous cause of short stature that can result from disruptions in many cellular processes. We report the identification of the lesion responsible for skeletal dysplasia and male infertility in the spontaneous, recessive mouse mutant chagun. We determined that Poc1a, encoding protein of the centriole 1a, is disrupted by the insertion of a processed Cenpw cDNA, which is flanked by target site duplications, suggestive of a LINE-1 retrotransposon-mediated event. Mutant fibroblasts have impaired cilia formation and multipolar spindles. Male infertility is caused by defective spermatogenesis early in meiosis and progressive germ cell loss. Spermatogonial stem cell transplantation studies revealed that Poc1a is essential for normal function of both Sertoli cells and germ cells. The proliferative zone of the growth plate is small and disorganized because chondrocytes fail to re-align after cell division and undergo increased apoptosis. Poc1a and several other genes associated with centrosome function can affect the skeleton and lead to skeletal dysplasias and primordial dwarfisms. This mouse mutant reveals how centrosome dysfunction contributes to defects in skeletal growth and male infertility.

Heterologous protein production using euchromatin-containing expression vectors in mammalian cells

Upon stable cell line generation, chromosomal integration site of the vector DNA has a major impact on transgene expression. Here we apply an active gene environment, rather than specified genetic elements, in expression vectors used for random integration. We generated a set of Bacterial Artificial Chromosome (BAC) vectors with different open chromatin regions, promoters and gene regulatory elements and tested their impact on recombinant protein expression in CHO cells. We identified the Rosa26 BAC as the most efficient vector backbone showing a nine-fold increase in both polyclonal and clonal production of the human IgG-Fc. Clonal protein production was directly proportional to integrated vector copy numbers and remained stable during 10 weeks without selection pressure. Finally, we demonstrated the advantages of BAC-based vectors by producing two additional proteins, HIV-1 glycoprotein CN54gp140 and HIV-1 neutralizing PG9 antibody, in bioreactors and shake flasks reaching a production yield of 1 g/l.

Functional validation of mouse tyrosinase non-coding regulatory DNA elements by CRISPR-Cas9-mediated mutagenesis

Newly developed genome-editing tools, such as the clustered regularly interspaced short palindromic repeat (CRISPR)-Cas9 system, allow simple and rapid genetic modification in most model organisms and human cell lines. Here, we report the production and analysis of mice carrying the inactivation via deletion of a genomic insulator, a key non-coding regulatory DNA element found 5' upstream of the mouse tyrosinase (Tyr) gene. Targeting sequences flanking this boundary in mouse fertilized eggs resulted in the efficient deletion or inversion of large intervening DNA fragments delineated by the RNA guides. The resulting genome-edited mice showed a dramatic decrease in Tyr gene expression as inferred from the evident decrease of coat pigmentation, thus supporting the functionality of this boundary sequence in vivo, at the endogenous locus. Several potential off-targets bearing sequence similarity with each of the two RNA guides used were analyzed and found to be largely intact. This study reports how non-coding DNA elements, even if located in repeat-rich genomic sequences, can be efficiently and functionally evaluated in vivo and, furthermore, it illustrates how the regulatory elements described by the ENCODE and EPIGENOME projects, in the mouse and human genomes, can be systematically validated.