Rodent models of tumours of the central nervous system.

Modelling of human diseases is an essential component of biomedical research, to understand their pathogenesis and ultimately, develop therapeutic approaches. Here, we will describe models of tumours of the central nervous system, with focus on intrinsic CNS tumours. Model systems for brain tumours were established as early as the 1920s, using chemical carcinogenesis, and a systematic analysis of different carcinogens, with a more refined histological analysis followed in the 1950s and 1960s. Alternative approaches at the time used retroviral carcinogenesis, allowing a more topical, organ-centred delivery. Most of the neoplasms arising from this approach were high-grade gliomas. Whilst these experimental approaches did not directly demonstrate a cell of origin, the localisation and growth pattern of the tumours already pointed to an origin in the neurogenic zones of the brain. In the 1980s, expression of oncogenes in transgenic models allowed a more targeted approach by expressing the transgene under tissue-specific promoters, whilst the constitutive inactivation of tumour suppressor genes ('knock out')-often resulted in embryonic lethality. This limitation was elegantly solved by engineering the Cre-lox system, allowing for a promoter-specific, and often also time-controlled gene inactivation. More recently, the use of the CRISPR Cas9 technology has significantly increased experimental flexibility of gene expression or gene inactivation and thus added increased value of rodent models for the study of pathogenesis and establishing preclinical models.

Development of a thermostable Cre/lox-based gene disruption system and in vivo manipulations of the megaplasmid pTT27 in Thermus thermophilus HB27.

We previously reported the development of a Cre/lox-based gene disruption system for multiple markerless gene disruption in Thermus thermophilus; however, it was a time-consuming method because it functioned at 50 °C, the minimum growth temperature of T. thermophilus HB27. In the present study, we improved this system by introducing random mutations into the cre-expressing plasmid, pSH-Cre. One of the resulting mutant plasmids, pSH-CreFM allowed us to remove selection marker genes by Cre-mediated recombination at temperatures up to 70 °C. By using the thermostable Cre/lox system with pSH-CreFM, we successfully constructed two valuable pTT27 megaplasmid mutant strains, a plasmid-free strain and ß-galactosidase gene deletion strain, which were produced by different methods. The thermostable Cre/lox system improved the time-consuming nature of the original Cre/lox system, but it was not suitable for multiple markerless gene disruption in T. thermophilus because of its highly efficient induction of Cre-mediated recombination even at 70 °C. However, in vivo megaplasmid manipulations performed at 65 °C were faster and easier than with the original Cre/lox system. Collectively, these results indicate that this system is a powerful tool for engineering T. thermophilus megaplasmids.

Cardiomyocyte crosstalk with endothelium modulates cardiac structure, function, and ischemia-reperfusion injury susceptibility through erythropoietin.

Erythropoietin (EPO) exerts non-canonical roles beyond erythropoiesis that are developmentally, structurally, and physiologically relevant for the heart as a paracrine factor. The role for paracrine EPO signalling and cellular crosstalk in the adult is uncertain. Here, we provided novel evidence showing cardiomyocyte restricted loss of function in Epo in adult mice induced hyper-compensatory increases in Epo expression by adjacent cardiac endothelial cells via HIF-2α independent mechanisms. These hearts showed concentric cellular hypertrophy, elevated contractility and relaxation, and greater resistance to ischemia-reperfusion injury. Voluntary exercise capacity compared to control hearts was improved independent of any changes to whole-body metabolism or blood O2 content or delivery (i.e., hematocrit). Our findings suggest cardiac EPO had a localized effect within the normoxic heart, which was regulated by cell-specific EPO-reciprocity between cardiomyocytes and endothelium. Within the heart, hyper-compensated endothelial Epo expression was accompanied by elevated Vegfr1 and Vegfb RNA, that upon pharmacological pan-inhibition of VEGF-VEGFR signaling, resulted in a paradoxical upregulation in whole-heart Epo. Thus, we provide the first evidence that a novel EPO-EPOR/VEGF-VEGFR axis exists to carefully mediate cardiac homeostasis via cardiomyocyte-endothelial EPO crosstalk.

Zona Glomerulosa-Derived Klotho Modulates Aldosterone Synthase Expression in Young Female Mice.

Klotho plays a critical role in the regulation of ion and fluid homeostasis. A previous study reported that haplo-insufficiency of Klotho in mice results in increased aldosterone synthase (CYP11B2) expression, elevated plasma aldosterone, and high blood pressure. This phenotype was presumed to be the result of diminished Klotho expression in zona glomerulosa (zG) cells of the adrenal cortex; however, systemic effects on adrenal aldosterone production could not be ruled out. To examine whether Klotho expressed in the zG is indeed a critical regulator of aldosterone synthesis, we generated a tamoxifen-inducible, zG-specific mouse model of Klotho deficiency by crossing Klotho-flox mice with Cyp11b2-CreERT mice (zG-Kl-KO). Tamoxifen-treated Cyp11b2-CreERT animals (zG-Cre) served as controls. Rosa26-mTmG reporter mice were used for Cre-dependent lineage-marking. Two weeks after tamoxifen induction, the specificity of the zG-Cre line was verified using immunofluorescence analysis to show that GFP expression was restricted to the zG. RNA in situ hybridization revealed a 65% downregulation of Klotho messenger RNA expression in the zG of zG-Kl-KO female mice at age 12 weeks compared to control mice. Despite this significant decrease, zG-Kl-KO mice exhibited no difference in plasma aldosterone levels. However, adrenal CYP11B2 expression and the CYP11B2 promotor regulatory transcription factors, NGFIB and Nurr1, were enhanced. Together with in vitro experiments, these results suggest that zG-derived Klotho modulates Cyp11b2 but does not evoke a systemic phenotype in young adult mice on a normal diet. Further studies are required to investigate the role of adrenal Klotho on aldosterone synthesis in aged animals.

Harnessing the power of new genetic tools to illuminate Giardia biology and pathogenesis.

Giardia is a prevalent single-celled microaerophilic intestinal parasite causing diarrheal disease and significantly impacting global health. Double diploid (essentially tetraploid) Giardia trophozoites have presented a formidable challenge to the development of molecular genetic tools to interrogate gene function. High sequence divergence and the high percentage of hypothetical proteins lacking homology to proteins in other eukaryotes have limited our understanding of Giardia protein function, slowing drug target validation and development. For more than 25 years, Giardia A and B assemblages have been readily amenable to transfection with plasmids or linear DNA templates. Here, we highlight the utility and power of genetic approaches developed to assess protein function in Giardia, with particular emphasis on the more recent clustered regularly interspaced palindromic repeats/Cas9-based methods for knockdowns and knockouts. Robust and reliable molecular genetic approaches are fundamental toward the interrogation of Giardia protein function and evaluation of druggable targets. New genetic approaches tailored for the double diploid Giardia are imperative for understanding Giardia's unique biology and pathogenesis.

Glycosylation as a tracer of off-target Cre-lox activation in development.

The Cre-lox system is one of the most widely used methods for lineage-specific and inducible genome editing in vivo. However, incomplete penetrance and off-target effects due to transient promoter expression in a stem or pluripotent precursor cell can be problematic and difficult to detect, especially if the target gene is not normally present in the fully differentiated but off-target cells. Yet, the loss of the target gene through the transient expression of Cre may impact the differentiation of those cells by virtue of transient expression in a precursor population. In these situations, off-target effects in an unknown precursor cell can, at best, complicate conclusions drawn from the model, and at worst, invalidate all data generated from that knockout strain. Thus, identifying Cre-driver promoter expression along entire cell lineages is crucial to improve rigor and reproducibility. As an example, transient expression in an early precursor cell has been documented in a variety of Cre strains such as the Tie2-based Cre-driver system that is used as an "endothelial cell-specific" model 1. Yet, Tie2 is now known to be transiently expressed in a stem cell upstream of both hematopoietic and endothelial cell lineages. Here, we use the Tie2 Cre-driver strain to demonstrate that due to its ubiquitous nature, plasma membrane glycans are a useful marker of both penetrance and specificity of a Cre-based knockout.

Established and emerging techniques for the study of microglia: visualization, depletion, and fate mapping.

The central nervous system (CNS) is an essential hub for neuronal communication. As a major component of the CNS, glial cells are vital in the maintenance and regulation of neuronal network dynamics. Research on microglia, the resident innate immune cells of the CNS, has advanced considerably in recent years, and our understanding of their diverse functions continues to grow. Microglia play critical roles in the formation and regulation of neuronal synapses, myelination, responses to injury, neurogenesis, inflammation, and many other physiological processes. In parallel with advances in microglial biology, cutting-edge techniques for the characterization of microglial properties have emerged with increasing depth and precision. Labeling tools and reporter models are important for the study of microglial morphology, ultrastructure, and dynamics, but also for microglial isolation, which is required to glean key phenotypic information through single-cell transcriptomics and other emerging approaches. Strategies for selective microglial depletion and modulation can provide novel insights into microglia-targeted treatment strategies in models of neuropsychiatric and neurodegenerative conditions, cancer, and autoimmunity. Finally, fate mapping has emerged as an important tool to answer fundamental questions about microglial biology, including their origin, migration, and proliferation throughout the lifetime of an organism. This review aims to provide a comprehensive discussion of these established and emerging techniques, with applications to the study of microglia in development, homeostasis, and CNS pathologies.

Novel roles of cardiac-derived erythropoietin in cardiac development and function.

The role of erythropoietin (EPO) has extended beyond hematopoiesis to include cytoprotection, inotropy, and neurogenesis. Extra-renal EPO has been reported for multiple tissue/cell types, but the physiological relevance remains unknown. Although the EPO receptor is expressed by multiple cardiac cell types and human recombinant EPO increases contractility and confers cytoprotection against injury, whether the heart produces physiologically meaningful amounts of EPO in vivo is unclear. We show a distinct circadian rhythm of cardiac EPO mRNA expression in adult mice and increased mRNA expression during embryogenesis, suggesting physiological relevance to cardiac EPO production throughout life. We then generated constitutive, cardiomyocyte-specific EPO knockout mice driven by the Mlc2v promoter (EPOfl/fl:Mlc2v-cre+/-; EPOΔ/Δ-CM). During cardiogenesis, cardiac EPO mRNA expression and cellular proliferation were reduced in EPOΔ/Δ-CM hearts. However, in adult EPOΔ/Δ- CM mice, total heart weight was preserved through increased cardiomyocyte cross-sectional area, indicating the reduced cellular proliferation was compensated for by cellular hypertrophy. Echocardiography revealed no changes in cardiac dimensions, with modest reductions in ejection fraction, stroke volume, and tachycardia, whereas invasive hemodynamics showed increased cardiac contractility and lusitropy. Paradoxically, EPO mRNA expression in the heart was elevated in adult EPOΔ/Δ-CM, along with increased serum EPO protein content and hematocrit. Using RNA fluorescent in situ hybridization, we found that Epo RNA colocalized with endothelial cells in the hearts of adult EPOΔ/Δ-CM mice, identifying the endothelial cells as a cell responsible for the EPO hyper-expression. Collectively, these data identify the first physiological roles for cardiomyocyte-derived EPO. We have established cardiac EPO mRNA expression is a complex interplay of multiple cell types, where loss of embryonic cardiomyocyte EPO production results in hyper-expression from other cells within the adult heart.

Neuropilin-1 regulates renin synthesis in juxtaglomerular cells.

Renin is the key enzyme of the systemic renin-angiotensin-aldosterone system, which plays an essential role in regulating blood pressure and maintaining electrolyte and extracellular volume homeostasis. Renin is mainly produced and secreted by specialized juxtaglomerular (JG) cells in the kidney. In the present study, we report for the first time that the conserved transmembrane receptor neuropilin-1 (NRP1) participates in the development of JG cells and plays a key role in renin production. We used the myelin protein zero-Cre (P0-Cre) to abrogate Nrp1 constitutively in P0-Cre lineage-labelled cells of the kidney. We found that the P0-Cre precursor cells differentiate into renin-producing JG cells. We employed a lineage-tracing strategy combined with RNAscope quantification and metabolic studies to reveal a cell-autonomous role for NRP1 in JG cell function. Nrp1-deficient animals displayed abnormal levels of tissue renin expression and failed to adapt properly to a homeostatic challenge to sodium balance. These findings provide new insights into cell fate decisions and cellular plasticity operating in P0-Cre-expressing precursors and identify NRP1 as a novel key regulator of JG cell maturation. KEY POINTS: Renin is a centrepiece of the renin-angiotensin-aldosterone system and is produced by specialized juxtaglomerular cells (JG) of the kidney. Neuropilin-1 (NRP1) is a conserved membrane-bound receptor that regulates vascular and neuronal development, cancer aggressiveness and fibrosis progression. We used conditional mutagenesis and lineage tracing to show that NRP1 is expressed in JG cells where it regulates their function. Cell-specific Nrp1 knockout mice present with renin paucity in JG cells and struggle to adapt to a homeostatic challenge to sodium balance. The results support the versatility of renin-producing cells in the kidney and may open new avenues for therapeutic approaches.

Development of genetic markers in Yarrowia lipolytica.

The oleaginous yeast Yarrowia lipolytica represents a potential microbial cell factory for the recombinant production of various valuable products. Currently, the commonly used selection markers for transformation in Y. lipolytica are limited, and successive genetic manipulations are often restricted by the number of available selection markers. In our study, we developed a dominant marker, dsdA, which encodes a D-serine deaminase for genetic manipulation in Y. lipolytica. In Y. lipolytica, this marker confers the ability to use D-serine as a nitrogen source. In addition, the selection conditions of several infrequently used dominant markers including bleoR (zeocin resistance), kanMX (G418 resistance), and guaB (mycophenolic acid resistance) were also analyzed. Our results demonstrated that these selection markers can be used for the genetic manipulation of Y. lipolytica and their selection conditions were different for various strains. Ultimately, the selection markers tested here will be useful to expand the genetic toolbox of Y. lipolytica. KEY POINTS: • The dsdA from Escherichia coli was developed as a dominant marker. • The applicability of several resistance markers in Y. lipolytica was determined. • We introduced the Cre/mutant lox system for marker recycling.

A toolbox for manipulating the genome of the major goat pathogen, Mycoplasma capricolum subsp. capripneumoniae.

Mycoplasma capricolum subspecies capripneumoniae (Mccp) is the causative agent of contagious caprine pleuropneumonia (CCPP), a devastating disease listed by the World Organisation for Animal Health (WOAH) as a notifiable disease and threatening goat production in Africa and Asia. Although a few commercial inactivated vaccines are available, they do not comply with WOAH standards and there are serious doubts regarding their efficacy. One of the limiting factors to comprehend the molecular pathogenesis of CCPP and develop improved vaccines has been the lack of tools for Mccp genome engineering. In this work, key synthetic biology techniques recently developed for closely related mycoplasmas were adapted to Mccp. CReasPy-Cloning was used to simultaneously clone and engineer the Mccp genome in yeast, prior to whole-genome transplantation into M. capricolum subsp. capricolum recipient cells. This approach was used to knock out an S41 serine protease gene recently identified as a potential virulence factor, leading to the generation of the first site-specific Mccp mutants. The Cre-lox recombination system was then applied to remove all DNA sequences added during genome engineering. Finally, the resulting unmarked S41 serine protease mutants were validated by whole-genome sequencing and their non-caseinolytic phenotype was confirmed by casein digestion assay on milk agar. The synthetic biology tools that have been successfully implemented in Mccp allow the addition and removal of genes and other genetic features for the construction of seamless targeted mutants at ease, which will pave the way for both the identification of key pathogenicity determinants of Mccp and the rational design of novel, improved vaccines for the control of CCPP.

Control of cardiac contractions using Cre-lox and degron strategies in zebrafish.

Cardiac contractions and hemodynamic forces are essential for organ development and homeostasis. Control over cardiac contractions can be achieved pharmacologically or optogenetically. However, these approaches lack specificity or require direct access to the heart. Here, we compare two genetic approaches to control cardiac contractions by modulating the levels of the essential sarcomeric protein Tnnt2a in zebrafish. We first recombine a newly generated tnnt2a floxed allele using multiple lines expressing Cre under the control of cardiomyocyte-specific promoters, and show that it does not recapitulate the tnnt2a/silent heart mutant phenotype in embryos. We show that this lack of early cardiac contraction defects is due, at least in part, to the long half-life of tnnt2a mRNA, which masks the gene deletion effects until the early larval stages. We then generate an endogenous Tnnt2a-eGFP fusion line that we use together with the zGRAD system to efficiently degrade Tnnt2a in all cardiomyocytes. Using single-cell transcriptomics, we find that Tnnt2a depletion leads to cardiac phenotypes similar to those observed in tnnt2a mutants, with a loss of blood and pericardial flow-dependent cell types. Furthermore, we achieve conditional degradation of Tnnt2a-eGFP by splitting the zGRAD protein into two fragments that, when combined with the cpFRB2-FKBP system, can be reassembled upon rapamycin treatment. Thus, this Tnnt2a degradation line enables non-invasive control of cardiac contractions with high spatial and temporal specificity and will help further understand how they shape organ development and homeostasis.

Prolonged tamoxifen-enriched diet is associated with cardiomyopathy and nutritional frailty in mice.

Tamoxifen (TAM) is required for gene recombination in the inducible Cre/lox system. The TAM-enriched diet is considered safe, with negligible impact on animal wellbeing. However, studies reporting the long-term effects of the TAM diet and its potential impact on experimental outcomes are scarce. We conducted a longitudinal study on mice exposed to a 4-week dietary TAM citrate supplementation. Several parameters were recorded, such as body weight, body composition, mortality, and cardiac function. The collagen1a2 (Col1a2) transgenic mouse was used to assess TAM-induced recombination in vivo in cardiac fibroblasts followed by myocardial infarction (MI). The impact of TAM on the MI outcome was also evaluated. The recombination efficiency and cytotoxic effect of the TAM active metabolite, 4-hydroxy-tamoxifen (4-OHT), were assessed in vitro. Mice exposed to a TAM diet showed body weight loss and a 10% increase in mortality (P = 0.045). The TAM diet decreased cardiac function and induced cardiac remodeling, indicated by decreased fractional shortening from 32.23% to 19.23% (P = 0.001) and left ventricular (LV) wall thinning. All measured parameters were reversed to normal when mice were returned to a normal diet. Infarcted Col1a2-CreER mice on the TAM regimen showed gene recombination in fibroblasts, but it was associated with a substantial increase in mortality post-surgery (2.5-fold) compared to the controls. In vitro, 4-OHT induced gene editing in fibroblasts; however, cell growth arrest and cytotoxicity were observed at high concentrations. In conclusion, prolonged exposure to the TAM diet can be detrimental and necessitates careful model selection and interpretation of the results.

Towards a Light-mediated Gene Therapy for the Eye using Caged Ethinylestradiol and the Inducible Cre/lox System.

Increasingly, retinal pathologies are being treated with virus-mediated gene therapies. To be able to target viral transgene expression specifically to the pathological regions of the retina with light, we established an in vivo photoactivated gene expression paradigm for retinal tissue. Based on the inducible Cre/lox system, we discovered that ethinylestradiol is a suitable alternative to Tamoxifen as ethinylestradiol is more amenable to modification with photosensitive protecting compounds, i.e., "caging." Identification of ethinylestradiol as a ligand for the mutated human estradiol receptor was supported by in silico binding studies showing the reduced binding of caged ethinylestradiol. Caged ethinylestradiol was injected into the eyes of double transgenic GFAP-CreERT2 mice with a Cre-dependent tdTomato reporter transgene followed by irradiation with light of 450 nm. Photoactivation significantly increased retinal tdTomato expression compared to controls. We thus demonstrated a first step towards the development of a targeted, light-mediated gene therapy for the eyes.

In Vivo Optical Interrogation of Neuronal Responses to Genetic, Cell Type-Specific Silencing.

We established a low background, Cre-dependent version of the inducible Tet-On system for fast, cell type-specific transgene expression in vivo Coexpression of a constitutive, Cre-dependent fluorescent marker selectively allowed single-cell analyses before and after inducible, Tet-dependent transgene expression. Here, we used this method for precise, acute manipulation of neuronal activity in the living brain. The goal was to study neuronal network homeostasis at cellular resolution. Single induction of the potassium channel Kir2.1 produced cell type-specific silencing within hours that lasted for at least 3 d. Longitudinal in vivo imaging of spontaneous calcium transients and neuronal morphology demonstrated that prolonged silencing did not alter spine densities or synaptic input strength. Furthermore, selective induction of Kir2.1 in parvalbumin interneurons increased the activity of surrounding neurons in a distance-dependent manner. This high-resolution, inducible interference and interval imaging of individual cells (high I5, HighFive) method thus allows visualizing temporally precise, genetic perturbations of defined cells.SIGNIFICANCE STATEMENT Gene function is studied by KO or overexpression of a specific gene followed by analyses of phenotypic changes. However, being able to predict and analyze exactly those cells in which genetic manipulation will occur is not possible. We combined two prominent transgene overexpression methods to fluorescently highlight the targeted cells appropriately before cell type-specific transgene induction. By inducing a potassium channel that decreases neuronal firing, we investigated how neuronal networks in the living mouse brain possibly compensate swift changes in cellular activities. Unlike in vitro, known compensatory homeostatic mechanisms, such as changes in synapses, were not observed in vivo Overall, we demonstrated with our method rapid genetic manipulation and analysis of neuronal activities as well as precision transgene expression.

Pax7 haploinsufficiency impairs muscle stem cell function in Cre-recombinase mice and underscores the importance of appropriate controls.

Ever since its introduction as a genetic tool, the Cre-lox system has been widely used for molecular genetic studies in vivo in the context of health and disease, as it allows time- and cell-specific gene modifications. However, insertion of the Cre-recombinase cassette in the gene of interest can alter transcription, protein expression, or function, either directly, by modifying the landscape of the locus, or indirectly, due to the lack of genetic compensation or by indirect impairment of the non-targeted allele. This is sometimes the case when Cre-lox is used for muscle stem cell studies. Muscle stem cells are required for skeletal muscle growth, regeneration and to delay muscle disease progression, hence providing an attractive model for stem cell research. Since the transcription factor Pax7 is specifically expressed in all muscle stem cells, tamoxifen-inducible Cre cassettes (CreERT2) have been inserted into this locus by different groups to allow targeted gene recombination. Here we compare the two Pax7-CreERT2 mouse lines that are mainly used to evaluate muscle regeneration and development of pathological features upon deletion of specific factors or pathways. We applied diverse commonly used tamoxifen schemes of CreERT2 activation, and we analyzed muscle repair after cardiotoxin-induced injury. We show that consistently the Pax7-CreERT2 allele targeted into the Pax7 coding sequence (knock-in/knock-out allele) produces an inherent defect in regeneration, manifested as delayed post-injury repair and reduction in muscle stem cell numbers. In genetic ablation studies lacking proper controls, this inherent defect could be misinterpreted as being provoked by the deletion of the factor of interest. Instead, using an alternative Pax7-CreERT2 allele that maintains bi-allelic Pax7 expression or including appropriate controls can prevent misinterpretation of experimental data. The findings presented here can guide researchers establish appropriate experimental design for muscle stem cell genetic studies.

A simple, rapid fluorescent reporter-based method for detection of ectopic cre recombinase expression in presumed retinal cell type-targeted mouse lines.

Although cell type-specific Cre recombinase-expressing mouse lines are commonly used to generate conditional knockout of genes of interest, germline recombination and ectopic "leakiness" in Cre recombinase expression in non-specific cell types has been observed in several neuronal and glial-specific Cre lines. This often leads to inadvertent loss of conditional mouse lines, requiring rederivation. It is therefore imperative to be able to monitor and validate cell type-specific Cre recombinase-mediated gene editing. Herein, we describe a simple, inexpensive, rapid ZsGreen fluor-reporter-based strategy for genotype-free identification of ectopic leakiness using a custom-designed, 3-D blue LED light box. We assessed cell type-specific expression in several allegedly specific Cre recombinase mouse lines commonly used in vision research: retinal pigment epithelium (RPE)-specific (VMD2 (Best1) Cre, RPE65 Cre); astrocyte-specific (GFAP Cre); as well as photoreceptor-bipolar progenitor cell-specific (CRX Cre). Our standardized workflow allows facile, rapid identification of ectopic and non-specific Cre recombinase expression in any presume specific Cre mouse line, without the need for genotyping and without causing animal distress.

Growth hormone receptor gene disruption.

Much of our understanding of growth hormone's (GH)'s numerous activities stems from studies utilizing GH receptor (GHR) knockout mice. More recently, the role of GH action has been examined by creating mice with tissue-specific or temporal GHR disruption. To date, 37 distinct GHR knockout mouse lines have been created. Targeted tissues include fat, liver, muscle, heart, bone, brain, macrophage, intestine, hematopoietic stem cells, pancreatic ß cells, and inducible multi-tissue "global" disruption at various ages. In this chapter, a summary of each mouse line is provided with background information on the generation of the mouse line as well as important physiological outcomes resulting from GHR gene disruption. Collectively, these mouse lines provide unique insights into GH action and have resulted in the development of new hypotheses about the functions ascribed to GH action in particular tissues.

Efficiency of NHEJ-CRISPR/Cas9 and Cre-LoxP Engineered Recombinant Turkey Herpesvirus Expressing Pasteurella multocida OmpH Protein for Fowl Cholera Prevention in Ducks.

Fowl cholera is caused by the bacterium Pasteurella multocida, a highly transmissible avian ailment with significant global implications, leading to substantial economic repercussions. The control of fowl cholera outbreaks primarily relies on vaccination using traditional vaccines that are still in use today despite their many limitations. In this research, we describe the development of a genetically engineered herpesvirus of turkeys (HVT) that carries the OmpH gene from P. multocida integrated into UL 45/46 intergenic region using CRISPR/Cas9-NHEJ and Cre-Lox system editing. The integration and expression of the foreign cassettes were confirmed using polymerase chain reaction (PCR), indirect immunofluorescence assays, and Western blot assays. The novel recombinant virus (rHVT-OmpH) demonstrated stable integration of the OmpH gene even after 15 consecutive in vitro passages, along with similar in vitro growth kinetics as the parent HVT virus. The protective efficacy of the rHVT-OmpH vaccine was evaluated in vaccinated ducks by examining the levels of P. multocida OmpH-specific antibodies in serum samples using ELISA. Groups of ducks that received the rHVT-OmpH vaccine or the rOmpH protein with Montanide™ (SEPPIC, Paris, France) adjuvant exhibited high levels of antibodies, in contrast to the negative control groups that received the parental HVT or PBS. The recombinant rHVT-OmpH vaccine also provided complete protection against exposure to virulent P. multocida X-73 seven days post-vaccination. This outcome not only demonstrates that the HVT vector possesses many characteristics of an ideal recombinant viral vaccine vector for protecting non-chicken hosts, such as ducks, but also represents significant research progress in identifying a modern, effective vaccine candidate for combatting ancient infectious diseases.