CXCL12 promotes the crossing of retinal ganglion cell axons at the optic chiasm.

Binocular vision requires the segregation of retinal ganglion cell (RGC) axons extending from the retina into the ipsilateral and contralateral optic tracts. RGC axon segregation occurs at the optic chiasm, which forms at the ventral diencephalon midline. Using expression analyses, retinal explants and genetically modified mice, we demonstrate that CXCL12 (SDF1) is required for axon segregation at the optic chiasm. CXCL12 is expressed by the meninges bordering the optic pathway, and CXCR4 by both ipsilaterally and contralaterally projecting RGCs. CXCL12 or ventral diencephalon meninges potently promoted axon outgrowth from both ipsilaterally and contralaterally projecting RGCs. Further, a higher proportion of axons projected ipsilaterally in mice lacking CXCL12 or its receptor CXCR4 compared with wild-type mice as a result of misrouting of presumptive contralaterally specified RGC axons. Although RGCs also expressed the alternative CXCL12 receptor ACKR3, the optic chiasm developed normally in mice lacking ACKR3. Our data support a model whereby meningeal-derived CXCL12 helps drive axon growth from CXCR4-expressing RGCs towards the diencephalon midline, enabling contralateral axon growth. These findings further our understanding of the molecular and cellular mechanisms controlling optic pathway development.

Donor template delivery by recombinant adeno-associated virus for the production of knock-in mice.

BACKGROUND: The ability of recombinant adeno-associated virus to transduce preimplantation mouse embryos has led to the use of this delivery method for the production of genetically altered knock-in mice via CRISPR-Cas9. The potential exists for this method to simplify the production and extend the types of alleles that can be generated directly in the zygote, obviating the need for manipulations of the mouse genome via the embryonic stem cell route. RESULTS: We present the production data from a total of 13 genetically altered knock-in mouse models generated using CRISPR-Cas9 electroporation of zygotes and delivery of donor repair templates via transduction with recombinant adeno-associated virus. We explore the efficiency of gene targeting at a total of 12 independent genetic loci and explore the effects of allele complexity and introduce strategies for efficient identification of founder animals. In addition, we investigate the reliability of germline transmission of the engineered allele from founder mice generated using this methodology. By comparing our production data against genetically altered knock-in mice generated via gene targeting in embryonic stem cells and their microinjection into blastocysts, we assess the animal cost of the two methods. CONCLUSIONS: Our results confirm that recombinant adeno-associated virus transduction of zygotes provides a robust and effective delivery route for donor templates for the production of knock-in mice, across a range of insertion sizes (0.9-4.7 kb). We find that the animal cost of this method is considerably less than generating knock-in models via embryonic stem cells and thus constitutes a considerable 3Rs reduction.

Erythro-myeloid progenitors contribute endothelial cells to blood vessels.

The earliest blood vessels in mammalian embryos are formed when endothelial cells differentiate from angioblasts and coalesce into tubular networks. Thereafter, the endothelium is thought to expand solely by proliferation of pre-existing endothelial cells. Here we show that a complementary source of endothelial cells is recruited into pre-existing vasculature after differentiation from the earliest precursors of erythrocytes, megakaryocytes and macrophages, the erythro-myeloid progenitors (EMPs) that are born in the yolk sac. A first wave of EMPs contributes endothelial cells to the yolk sac endothelium, and a second wave of EMPs colonizes the embryo and contributes endothelial cells to intraembryonic endothelium in multiple organs, where they persist into adulthood. By demonstrating that EMPs constitute a hitherto unrecognized source of endothelial cells, we reveal that embryonic blood vascular endothelium expands in a dual mechanism that involves both the proliferation of pre-existing endothelial cells and the incorporation of endothelial cells derived from haematopoietic precursors.

KIT is dispensable for physiological organ vascularisation in the embryo.

Blood vessels form vast networks in all vertebrate organs to sustain tissue growth, repair and homeostatic metabolism, but they also contribute to a range of diseases with neovascularisation. It is, therefore, important to define the molecular mechanisms that underpin blood vessel growth. The receptor tyrosine kinase KIT is required for the normal expansion of hematopoietic progenitors that arise during embryogenesis from hemogenic endothelium in the yolk sac and dorsal aorta. Additionally, KIT has been reported to be expressed in endothelial cells during embryonic brain vascularisation and has been implicated in pathological angiogenesis. However, it is neither known whether KIT expression is widespread in normal organ endothelium nor whether it promotes blood vessel growth in developing organs. Here, we have used single-cell analyses to show that KIT is expressed in endothelial cell subsets of several organs, both in the adult and in the developing embryo. Knockout mouse analyses revealed that KIT is dispensable for vascularisation of growing organs in the midgestation embryo, including the lung, liver and brain. By contrast, vascular changes emerged during late-stage embryogenesis in these organs from KIT-deficient embryos, concurrent with severe erythrocyte deficiency and growth retardation. These findings suggest that KIT is not required for developmental tissue vascularisation in physiological conditions, but that KIT deficiency causes foetal anaemia at late gestation and thereby pathological vascular remodelling.

VEGF-A and neuropilin 1 (NRP1) shape axon projections in the developing CNS via dual roles in neurons and blood vessels.

Visual information is relayed from the eye to the brain via retinal ganglion cell (RGC) axons. Mice lacking NRP1 or NRP1-binding VEGF-A isoforms have defective RGC axon organisation alongside brain vascular defects. It is not known whether axonal defects are caused exclusively by defective VEGF-A signalling in RGCs or are exacerbated by abnormal vascular morphology. Targeted NRP1 ablation in RGCs with a Brn3bCre knock-in allele reduced axonal midline crossing at the optic chiasm and optic tract fasciculation. In contrast, Tie2-Cre-mediated endothelial NRP1 ablation induced axon exclusion zones in the optic tracts without impairing axon crossing. Similar defects were observed in Vegfa120/120 and Vegfa188/188 mice, which have vascular defects as a result of their expression of single VEGF-A isoforms. Ectopic midline vascularisation in endothelial Nrp1 and Vegfa188/188 mutants caused additional axonal exclusion zones within the chiasm. As in vitro and in vivo assays demonstrated that vessels do not repel axons, abnormally large or ectopically positioned vessels are likely to present physical obstacles to axon growth. We conclude that proper axonal wiring during brain development depends on the precise molecular control of neurovascular co-patterning.

Colour Doppler ultrasound imaging of blood flows variations in neoplastic and non-neoplastic testicular lesions in dogs.

Testicular tumours are the most common neoplasms in male dogs accounting for approximately 90% of all tumours affecting the genitourinary tract. Gray-scale ultrasonography in combination with colour and power Doppler imaging has been well accepted as an accurate technique for assessing scrotal lesions and vascularization of the testis. Colour Doppler sensitivity for low blood flows appears promising in the study of testicular disorders. The aim of this study was to assess if colour and power Doppler ultrasound is a good tool for the investigation of testicular lesions in dogs, to report the sonographic features of lesions and to measure colour and power Doppler parameters such as resistive index (RI), pulsatility index (PI), hypovascularization and hypervascularization (VI) determining if they can be used to distinguish testicular neoplasms from the wide spectrum of non-neoplastic pathological findings. In this study, 50 male dogs of various breeds, aged between 7 and 14 years, presented with testicular disorders were selected. RI and PI were calculated. Mean RI values for neoplastic, inflammatory and degenerative lesions were 0.54, 0.45 and 0.58, respectively. Mean PI values were 0.62, 0.55 and 0.63, respectively. Hypovascularization and hypervascularization of the lesion were evaluated throughout the vascularity index (VI). Vascular signals in neoplasms were significantly intensified around and inside the mass if compared with those measured during inflammatory and degenerative lesions. VI markedly increased in solid tumours. Pathological testes were removed; macroscopical, histological and immunoistochemical evaluations were carried out. Colour Doppler showed increased intralesional and peripheral flows in all neoplastic lesions analysed. No flows were detected around cysts.

VEGF189 binds NRP1 and is sufficient for VEGF/NRP1-dependent neuronal patterning in the developing brain.

The vascular endothelial growth factor (VEGFA, VEGF) regulates neurovascular patterning. Alternative splicing of the Vegfa gene gives rise to three major isoforms termed VEGF121, VEGF165 and VEGF189. VEGF165 binds the transmembrane protein neuropilin 1 (NRP1) and promotes the migration, survival and axon guidance of subsets of neurons, whereas VEGF121 cannot activate NRP1-dependent neuronal responses. By contrast, the role of VEGF189 in NRP1-mediated signalling pathways has not yet been examined. Here, we have combined expression studies and in situ ligand-binding assays with the analysis of genetically altered mice and in vitro models to demonstrate that VEGF189 can bind NRP1 and promote NRP1-dependent neuronal responses.

Neuropilin 1 (NRP1) hypomorphism combined with defective VEGF-A binding reveals novel roles for NRP1 in developmental and pathological angiogenesis.

Neuropilin 1 (NRP1) is a receptor for class 3 semaphorins and vascular endothelial growth factor (VEGF) A and is essential for cardiovascular development. Biochemical evidence supports a model for NRP1 function in which VEGF binding induces complex formation between NRP1 and VEGFR2 to enhance endothelial VEGF signalling. However, the relevance of VEGF binding to NRP1 for angiogenesis in vivo has not yet been examined. We therefore generated knock-in mice expressing Nrp1 with a mutation of tyrosine (Y) 297 in the VEGF binding pocket of the NRP1 b1 domain, as this residue was previously shown to be important for high affinity VEGF binding and NRP1-VEGFR2 complex formation. Unexpectedly, this targeting strategy also severely reduced NRP1 expression and therefore generated a NRP1 hypomorph. Despite the loss of VEGF binding and attenuated NRP1 expression, homozygous Nrp1(Y297A/Y297A) mice were born at normal Mendelian ratios, arguing against NRP1 functioning exclusively as a VEGF164 receptor in embryonic angiogenesis. By overcoming the mid-gestation lethality of full Nrp1-null mice, homozygous Nrp1(Y297A/Y297A) mice revealed essential roles for NRP1 in postnatal angiogenesis and arteriogenesis in the heart and retina, pathological neovascularisation of the retina and angiogenesis-dependent tumour growth.

Myeloid-Derived Vascular Endothelial Growth Factor and Hypoxia-Inducible Factor Are Dispensable for Ocular Neovascularization--Brief Report.

OBJECTIVE: Ocular neovascularization (ONV) is a pathological feature of sight-threatening human diseases, such as diabetic retinopathy and age-related macular degeneration. Macrophage depletion in mouse models of ONV reduces the formation of pathological blood vessels, and myeloid cells are widely considered an important source of the vascular endothelial growth factor A (VEGF). However, the importance of VEGF or its upstream regulators hypoxia-inducible factor-1α (HIF1α) and hypoxia-inducible factor-2α (HIF2α) as myeloid-derived regulators of ONV remains to be determined. APPROACH AND RESULTS: We used 2 mouse models of ONV, choroidal neovascularization and oxygen-induced retinopathy, to show that Vegfa is highly expressed by several cell types, but not myeloid cells during ONV. Moreover, myeloid-specific VEGF ablation did not reduce total ocular VEGF during choroidal neovascularization or oxygen-induced retinopathy. In agreement, the conditional inactivation of Vegfa, Hif1a, or Epas1 in recruited and resident myeloid cells that accumulated at sites of neovascularization did not significantly reduce choroidal neovascularization or oxygen-induced retinopathy. CONCLUSIONS: The finding that myeloid cells are not a significant local source of VEGF in these rodent models of ONV suggests that myeloid function in neovascular eye disease differs from skin wound healing and other neovascular pathologies.

NRP1 acts cell autonomously in endothelium to promote tip cell function during sprouting angiogenesis.

Neuropilin (NRP) 1 is a receptor for the vascular endothelial growth factor (VEGF)-A and is essential for normal angiogenesis. Previous in vitro experiments identified NRP1 interactions with VEGF-A's main signaling receptor VEGFR2 within endothelial cells, but also between nonendothelial NRP1 and endothelial VEGFR2. Consistent with an endothelial role for NRP1 in angiogenesis, we found that VEGFR2 and NRP1 were coexpressed in endothelial tip and stalk cells in the developing brain. In addition, NRP1 was expressed on two cell types that interact with growing brain vessels-the neural progenitors that secrete VEGF-A to stimulate tip cell activity and the pro-angiogenic macrophages that promote tip cell anastomosis. Selective targeting of Nrp1 in each of these cell types demonstrated that neural progenitor- and macrophage-derived NRP1 were dispensable, whereas endothelial NRP1 was essential for normal brain vessel growth. NRP1 therefore promotes brain angiogenesis cell autonomously in endothelium, independently of heterotypic interactions with nonendothelial cells. Genetic mosaic analyses demonstrated a key role for NRP1 in endothelial tip rather than stalk cells during vessel sprouting. Thus, NRP1-expressing endothelial cells attained the tip cell position when competing with NRP1-negative endothelial cells in chimeric vessel sprouts. Taken together, these findings demonstrate that NRP1 promotes endothelial tip cell function during angiogenesis.

The cytoplasmic domain of neuropilin 1 is dispensable for angiogenesis, but promotes the spatial separation of retinal arteries and veins.

Neuropilin 1 (NRP1) is a transmembrane glycoprotein that is essential for blood vessel development in vertebrates. Best known for its ability to bind members of the vascular endothelial growth factor (VEGF) and class 3 semaphorin families through its extracellular domain, it also has a highly conserved cytoplasmic domain, which terminates in a SEA motif that binds the PDZ protein synectin/GIPC1/NIP. Previous studies in zebrafish embryos and tissue culture models raised the possibility that the SEA motif of NRP1 is essential for angiogenesis. Here, we describe the generation of mice that express a form of NRP1 that lacks the cytoplasmic domain and, therefore, the SEA motif (Nrp1(cyto)(Δ)(/)(Δ) mice). Our analysis of pre- and perinatal vascular development revealed that vasculogenesis and angiogenesis proceed normally in these mutants, demonstrating that the membrane-anchored extracellular domain is sufficient for vessel growth. By contrast, the NRP1 cytoplasmic domain is required for normal arteriovenous patterning, because arteries and veins crossed each other at an abnormally high frequency in the Nrp1(cyto)(Δ)(/)(Δ) retina, as previously reported for mice with haploinsufficient expression of VEGF in neural progenitors. At crossing sites, the artery was positioned anteriorly to the vein, and both vessels were embedded in a shared collagen sleeve. In human eyes, similar arteriovenous crossings are risk factors for branch retinal vein occlusion (BRVO), an eye disease in which compression of the vein by the artery disrupts retinal blood flow, causing local tissue hypoxia and impairing vision. Nrp1(cyto)(Δ)(/)(Δ) mice may therefore provide a suitable genetic model to study the aetiology of BRVO.

Tamoxifen exacerbates morbidity and mortality in male mice receiving medetomidine anaesthesia.

Tamoxifen-induced CreER-LoxP recombination is often used to induce spatiotemporally controlled gene deletion in genetically modified mice. Prior work has shown that tamoxifen and tamoxifen-induced CreER activation can have off-target effects that should be controlled. However, it has not yet been reported whether tamoxifen administration, independently of CreER expression, interacts adversely with commonly used anaesthetic drugs such as medetomidine or its enantiomer dexmedetomidine in laboratory mice (Mus musculus). Here, we report a high incidence of urinary plug formation and morbidity in male mice on a mixed C57Bl6/J6 and 129/SvEv background when tamoxifen treatment was followed by ketamine-medetomidine anaesthesia. Medetomidine is therefore contra-indicated for male mice after tamoxifen treatment. As dexmedetomidine causes morbidity and mortality in male mice at higher rates than medetomidine even without tamoxifen treatment, our findings suggest that dexmedetomidine is not a suitable alternative for anaesthesia of male mice after tamoxifen treatment. We conclude that the choice of anaesthetic drug needs to be carefully evaluated in studies using male mice that have undergone tamoxifen treatment for inducing CreER-LoxP recombination.

Tissue macrophages act as cellular chaperones for vascular anastomosis downstream of VEGF-mediated endothelial tip cell induction.

Blood vessel networks expand in a 2-step process that begins with vessel sprouting and is followed by vessel anastomosis. Vessel sprouting is induced by chemotactic gradients of the vascular endothelial growth factor (VEGF), which stimulates tip cell protrusion. Yet it is not known which factors promote the fusion of neighboring tip cells to add new circuits to the existing vessel network. By combining the analysis of mouse mutants defective in macrophage development or VEGF signaling with live imaging in zebrafish, we now show that macrophages promote tip cell fusion downstream of VEGF-mediated tip cell induction. Macrophages therefore play a hitherto unidentified and unexpected role as vascular fusion cells. Moreover, we show that there are striking molecular similarities between the pro-angiogenic tissue macrophages essential for vascular development and those that promote the angiogenic switch in cancer, including the expression of the cell-surface proteins TIE2 and NRP1. Our findings suggest that tissue macrophages are a target for antiangiogenic therapies, but that they could equally well be exploited to stimulate tissue vascularization in ischemic disease.

Evaluation of Biochemical Composition of Amniotic and Allantoic Fluids at Different Stages of Pregnancy in Queens.

Fetal fluid contents have functions in protecting fetuses and are essential for fetal development and maturation. However, little is known about the exact physiological functions of fetal fluids in fetal development, as well as the changing composition throughout the gestational period in cats. In this study, the biochemical composition of amniotic (AMN) and allantoic (ALL) fluids was investigated, as well as in the maternal serum of pregnant queens. Eighteen queens were included in this study and assigned to six different groups, D20, D25, D30, D40, D45 and D60, according to the gestational stage of fetal development. A total of 44 amniotic and 37 allantoic samples were collected. Fetal fluids contained lesser concentrations of alanine aminotransferase, albumin, cholesterol, triglycerides, creatine kinase, amylase, total protein and globulin than maternal serum. Other variables, such as aspartate aminotransferase, gamma-glutamyl transferase, bilirubin and alkaline phosphatase, were in different concentrations at specific stages of gestation when compared to maternal serum. There were no differences between fetal fluids and maternal serum for lactate dehydrogenase, urea, lipase or glucose concentrations. There were greater concentrations of creatinine in amniotic fluid than in allantoic fluid or maternal serum. Based on the results of this study, fetal fluids do not accumulate as a result of the simple filtration of maternal blood, but rather, the fetus produces many of these components as a consequence of organ development and maturation.

Metaplastic Ossification of a Giant Paraprostatic Cyst in a Dog: A Case Report.

A 7-year-old male Caucasian shepherd presented with a 3 month history of intermittent hematuria, penile discharge, and abdominal pain and distension. The dog had a history of prostatic hyperplasia with multiple cysts, diagnosed by the referring clinician two years prior to the case presentation. Two oral courses of antibiotics and antiandrogens were administered by the treating veterinarian without resolution. At the case presentation visit, massive swelling was present in the mid- and caudal parts of the abdomen. Abdominal ultrasound and exploratory laparotomy revealed a paraprostatic cyst (size: 25 × 20 × 18 cm) in the caudal part of the abdomen. The cyst had a bony ridge along the wall with multiple cauliflower-like lesions extending inside. Histopathologic examination revealed an intermittently epithelial-lined inner wall of the cyst, which was partially degenerated and flattened due to the pressure of the intraluminal fluid. The luminal surface of the cyst appeared markedly irregular with multiple structures made of dense, fibrous connective tissue protruding inside with metaplastic ossification foci, consistent with severe osseous metaplasia. The epithelium showed focal secretory activity. Numerous subepithelial multifocal neutrophil and mononuclear cellular infiltrates were found. The lumen of the cyst contained a reddish-brown (blood and protein-rich) fluid. Complete surgical excision of the cyst and omentalization of the capsular remnant resulted in successful resolution of the clinical signs.

KIT Is Required for Fetal Liver Hematopoiesis.

In the mouse embryo, endothelial cell (EC) progenitors almost concomitantly give rise to the first blood vessels in the yolk sac and the large vessels of the embryo proper. Although the first blood cells form in the yolk sac before blood vessels have assembled, consecutive waves of hematopoietic progenitors subsequently bud from hemogenic endothelium located within the wall of yolk sac and large intraembryonic vessels in a process termed endothelial-to-hematopoietic transition (endoHT). The receptor tyrosine kinase KIT is required for late embryonic erythropoiesis, but KIT is also expressed in hematopoietic progenitors that arise via endoHT from yolk sac hemogenic endothelium to generate early, transient hematopoietic waves. However, it remains unclear whether KIT has essential roles in early hematopoiesis. Here, we have combined single-cell expression studies with the analysis of knockout mice to show that KIT is dispensable for yolk sac endoHT but required for transient definitive hematopoiesis in the fetal liver.

Antimicrobial activity of a standardized medical honey on bacterial isolates from infected skin lesions of non-traditional companion animals.

In recent years, due to the growing phenomenon of antimicrobial resistance, the search for alternative strategies to antibiotic treatments is increasing and a considerable interest for the use of medical honey in clinical practice has emerged. Honey has been used for the treatment of skin lesions, in both humans and animals. However, knowledge concerning the use of medical honey in non­traditional companion animals is scarce. The aim of this study was to assess the antibacterial activity of a standardized medical honey (Revamil, BFactory) against bacterial strains isolated from skin lesions of non­traditional companion animals. The minimum bactericidal concentration (MBC) of Revamil honey against seventeen clinical isolates and three reference strains was established.The medical honey showed antimicrobial activity against both Gram­positive and Gram­negative bacteria. Growth was inhibited for all the strains at concentrations of medical honey ranging from 10 to 40%. Pseudomonas oryzihabitans and Alcaligenes faecalis showed the lowest MBC (10%). The reference strain Staphylococcus aureus ATCC25923 showed a higher sensitivity to 20% honey compare to the corresponding clinical isolate (P = 0.001). The observed results suggest that Revamil could represent an effective therapeutic aid, useful for the reduction of antibiotic use, in case of pathological skin infections in non­traditional companion animals.

Cytobrushing of the oral mucosa as a possible tool for early detection of testudinid herpesvirus in Horsfield's tortoises with nonspecific clinical signs.

Forty-five Horsfield's tortoises (Testudo horsfieldii; syn. Agrionemys horfieldii, Russian tortoise) belonging to different owners had decreased appetite and respiratory issues. Twenty-nine tortoises had epiphora, dyspnea, and white necrotic diphtheroid oral plaques (group G1). Ten of the remaining 16 tortoises had serious dehydration, appetite disorder, and depression (G2). The last 6 tortoises had only decreased appetite and moderate conjunctival discharge (G3). During the physical examination of all 45 tortoises, a cytologic sample and an oral swab for herpesvirus and Mycoplasma agassizii PCR testing were taken. In 20 of 29 specimens from G1, in 8 of 16 from G2, and 0 of 6 from G3, the cytologic exam revealed intranuclear acidophilic inclusion bodies, multinucleate cellular syncytia, and further abnormalities caused by herpesviral infection. Moreover, all 45 tested subjects were found to be positive for testudinid herpesvirus 1; 2 were positive for M. agassizii. This prospective study suggests that Horsfield's tortoises with such signs would benefit from this screening procedure, given that it was effective in a significant proportion of infected and symptomatic animals, and no negative effects were seen.

VEGF188 promotes corneal reinnervation after injury.

Vascular endothelial growth factor A (VEGF) induces angiogenesis and vascular hyperpermeability in ocular tissues and is therefore a key therapeutic target for eye conditions in which these processes are dysregulated. In contrast, the therapeutic potential of VEGF's neurotrophic roles in the eye has remained unexploited. In particular, it is not known whether modulating levels of any of the 3 major alternatively spliced VEGF isoforms might provide a therapeutic approach to promote neural health in the eye without inducing vascular pathology. Here, we have used a variety of mouse models to demonstrate differences in overall VEGF levels and VEGF isoform ratios across tissues in the healthy eye. We further show that VEGF isoform expression was differentially regulated in retinal versus corneal disease models. Among the 3 major isoforms - termed VEGF120, VEGF164, and VEGF188 - VEGF188 was upregulated to the greatest extent in injured cornea, where it was both necessary and sufficient for corneal nerve regeneration. Moreover, topical VEGF188 application further promoted corneal nerve regeneration without inducing pathological neovascularization. VEGF isoform modulation should therefore be explored further for its potential in promoting neural health in the eye.