CRISPR-LRS for mapping transgenes in the mouse genome

Microinjected transgenes, including bacterial artificial chromosomes (BACs), insert randomly in the mouse genome. Traditional methods of mapping a transgene are challenging, thus complicating breeding strategies and the accurate interpretation of phenotypes, particularly when a transgene disrupts critical coding or noncoding sequences. Here, we introduce CRISPR-Cas9 long-read sequencing (CRISPR-LRS) to ascertain transgene integration locus and estimated copy number. This method revealed integration loci for both a BAC and Cre-driver line, and estimated the copy numbers for two other BAC mouse lines. CRISPR-LRS offers an easy approach to establish robust breeding practices and accurate phenotyping of most any transgenic mouse line.

Characterisation of a dual-colour retinoic acid reporter system for analysing cells and embryos

<p>Vitamin A is an important component in the diet as its metabolites, the retinoids, play key roles in a vast range of cellular functions, from production of germ cells, to embryonic development and right through until adulthood. The function of retinoids, in particular retinoic acid (RA), is especially important during early embryonic development, where it is responsible for many different key developmental events. Some of the processes controlled by RA include brain region patterning, Hox gene expression, axis establishment and somite formation. Here, we aimed to characterise the expression pattern of retinoic acid in the early murine embryo and isolate cell populations from a range of RA concentrations to analyse the mRNA expression. To do this, we used a transgenic mouse line which expressed a reporter plasmid that was able to show, through the expression of two fluorescent proteins, areas of high RA concentration and area of low RA concentration. We tested the function of this reporter system in vitro, using cell lines which were transfected with the plasmid and exposed to RA in their growth media. This worked showed a somewhat does-dependent response from the reporter system expressing the fluorescent proteins. We then imaged transgenic embryos at various stages of early development, to ascertain the areas of RA expression and repression. Here, we saw fluorescent protein expression patterns that indicated both high and low concetrations of RA. Using this information, we dissociated transgenic E8.5 embryos and sorted the cells based on their levels of expression of the two fluorescent proteins, as well as by tissue type, which had been marked with antibodies. mRNA was extracted from these populations and PCR was performed to identify the presence of Hox genes and to see any difference in expression patterns across the various cell populations.</p>

Crossed Connections From Insular Cortex to the Contralateral Thalamus

Sensory information in all modalities, except olfaction, is processed at the level of the thalamus before subsequent transmission to the cerebral cortex. This incoming sensory stream is refined and modulated in the thalamus by numerous descending corticothalamic projections originating in layer 6 that ultimately alter the sensitivity and selectivity for sensory features. In general, these sensory thalamo-cortico-thalamic loops are considered strictly unilateral, i.e., no contralateral crosstalk between cortex and thalamus. However, in contrast to this canonical view, we characterize here a prominent contralateral corticothalamic projection originating in the insular cortex, utilizing both retrograde tracing and cre-lox mediated viral anterograde tracing strategies with the Ntsr1-Cre transgenic mouse line. From our studies, we find that the insular contralateral corticothalamic projection originates from a separate population of layer 6 neurons than the ipsilateral corticothalamic projection. Furthermore, the contralateral projection targets a topographically distinct subregion of the thalamus than the ipsilateral projection. These findings suggest a unique bilateral mechanism for the top-down refinement of ascending sensory information.

Characterisation of a dual-colour retinoic acid reporter system for analysing cells and embryos

<p>Vitamin A is an important component in the diet as its metabolites, the retinoids, play key roles in a vast range of cellular functions, from production of germ cells, to embryonic development and right through until adulthood. The function of retinoids, in particular retinoic acid (RA), is especially important during early embryonic development, where it is responsible for many different key developmental events. Some of the processes controlled by RA include brain region patterning, Hox gene expression, axis establishment and somite formation. Here, we aimed to characterise the expression pattern of retinoic acid in the early murine embryo and isolate cell populations from a range of RA concentrations to analyse the mRNA expression. To do this, we used a transgenic mouse line which expressed a reporter plasmid that was able to show, through the expression of two fluorescent proteins, areas of high RA concentration and area of low RA concentration. We tested the function of this reporter system in vitro, using cell lines which were transfected with the plasmid and exposed to RA in their growth media. This worked showed a somewhat does-dependent response from the reporter system expressing the fluorescent proteins. We then imaged transgenic embryos at various stages of early development, to ascertain the areas of RA expression and repression. Here, we saw fluorescent protein expression patterns that indicated both high and low concetrations of RA. Using this information, we dissociated transgenic E8.5 embryos and sorted the cells based on their levels of expression of the two fluorescent proteins, as well as by tissue type, which had been marked with antibodies. mRNA was extracted from these populations and PCR was performed to identify the presence of Hox genes and to see any difference in expression patterns across the various cell populations.</p>

TMOD-09. CREATION OF A P53-INDEPENDENT IN VITRO AND IN VIVO MODEL SYSTEM FOR THE STUDY OF H3.1K27M DIPG

Diffuse Intrinsic Pontine Glioma (DIPG) is a devastating pediatric high-grade glioma that occurs in the brainstem with a median survival of less than 1 year. A greater understanding of the early tumorigenic events is essential for the development of effective therapeutics. DIPG is characterized by founder mutations in histone H3, either H3.1K27M or H3.3K27M. These mutations cause global hypomethylation, resulting in aberrant gene expression. It is unknown how this mechanism contributes to tumorigenesis. Interestingly, H3.1K27M DIPG show an increased incidence in females, whereas H3.3K27M DIPG shows no sex difference. This illustrates that the tumorigenic potential of H3.1K27M may be different between the sexes. Few models of DIPG incorporate the study of H3.1K27M despite the fact that it represents a unique opportunity to obtain valuable information on the tumorigenesis of DIPG through the study of the sex difference. Thus, we have created an in vitro and in vivo model system for H3.1K27M DIPG utilizing the RCAS mouse model system. This system utilizes RCAS vectors and a RCAS-ntva transgenic mouse line to deliver specific mutations to nestin expressing cells in the brainstem, including oligodendrocyte progenitor cells (OPCs), the predicted cell of origin. Delivering H3.1K27M, ACVR1 R206H, and PDGFaa at postnatal day 7 produces DIPG-like tumors in vivo, confirmed by H and E staining, between 60 – 110 days post injection. Additionally, confirmed through immunofluorescence staining, we can isolate a pure population of OPCs via immunopanning and infect them with RCAS vectors in vitro to produce stable expression of H3.1K27M. Introduction of H3.1K27M alone into male and female OPC cultures provides an opportunity to compare the early tumorigenic effects of H3.1K27M between the sexes in vitro. These results demonstrate that we have created an in vitro and in vivo H3.1K27M DIPG model system for the study of sex differences and tumorigenesis in DIPG.

PATH-09. THE SEARCH FOR A NOVEL SUBTYPE OF GLIOBLASTOMA AND ITS CELL-OF-ORIGIN

Glioblastoma (GBM) has been computationally classified into three molecular subtypes (i.e., classical, proneural and mesenchymal). However, these subtypes lack strong biological and clinical implications. Therefore, our group has proposed to classify GBM according to its cell of origins. We have previously shown that different cell of origins give rise to biologically and transcriptionally distinct subtypes of GBM. We termed tumors that derived from subventricular zone (SVZ) neural stem cells as type 1 tumors and that from oligodendrocytic progenitor cells (OPC) as type 2 tumors. Based on murine lineage transcriptional profiles, we have also identified corresponding human GBM (40-50% of the TCGA GBM samples) tumors with conserved lineage properties. However, a majority of the TCGA GBM tumors remains unexplained by the cell-of-origin model. This study aims to search for other distinct GBM subtypes by addressing the tumorigenic potential of a putative stem progenitor population in the murine basilar pons. By using a recently reported Nestin transgenic mouse line (Nestin- C reERT2; e G FP-H2B; h D TR, or CGD in short), we have shown that conditionally deleting the commonly mutated glioma genes, Nf1 f/f ; Tp53 f/f and Pten f/+ (NPP), in pontine GFP+ cells, give rise to tumors that histologically resembles human GBM. Further transcriptomic analysis showed that a subset of these tumors highly express lineage markers of the differentiation-committed oligodendrocytic precursors (COP). We further probed the TCGA GBM database and identified 5% of the tumors to be enriched with our CGD pontine tumor-derived signature. In summary, our results showed that CGD-NPP cells can give rise to a previously uncharacterized tumor subtype with enrichment of COP lineage markers. Therefore, we propose COP as another cell of origin for GBM and that COP-derived tumor may contribute to a novel tumor subtype of the GBM classification.

Transgenic Mice Expressing Human α-Synuclein 1-103 Fragment as a Novel Model of Parkinson’s Disease

Parkinson’s disease (PD) is one of the most common neurodegenerative disorders. However, its cellular and molecular mechanisms still wrap in the mist. This is partially caused by the absence of appropriate animal models mimicking sporadic PD that constitutes the majority of cases. Previously, we reported that a cysteine protease, asparagine endopeptidase (AEP), is activated in an age-dependent manner, and cleaves α-synuclein in the brain of sporadic PD patients. The AEP-derived α-synuclein 1-103 fragment is required for the pathogenesis of PD. Thus, we designed and characterized a novel transgenic mouse line expressing α-synuclein 1-103 (designated N103 mice). This model shows an abundant accumulation of pathological α-synuclein in the central nervous system, loss of dopaminergic neurons in the substantia nigra, and progressive striatal synaptic degeneration. The N103 mice also manifest age-dependent PD-like behavioral impairments. Notably, the mice show weight loss and constipation, which are the common non-motor symptoms in PD. The RNA-sequencing analysis found that the transcriptomics pattern was extensively altered in N103 mice. In conclusion, the N103 mouse line, as a brand-new tool, might provide new insights into PD research.

Dual recombinase action in the normal and neoplastic mammary gland epithelium

We developed a transgenic mouse line that expresses the codon-optimized Flp recombinase under the control of the MMTV promoter in luminal epithelial cells of the mammary gland. In this report, we demonstrate the versatile applicability of the new MMTV-Flp strain to manipulate genes in a temporally and spatially controlled manner in the normal mammary gland, in luminal-type mammary tumors that overexpress ERBB2, and in a new KRAS-associated mammary cancer model. Although the MMTV-Flp is expressed in a mosaic pattern in the luminal epithelium, the Flp-mediated activation of a mutant KrasG12D allele resulted in basal-like mammary tumors that progressively acquired mesenchymal features. Besides its applicability as a tool for gene activation and cell lineage tracing to validate the cellular origin of primary and metastatic tumor cells, we employed the MMTV-Flp transgene together with the tamoxifen-inducible Cre recombinase to demonstrate that the combinatorial action of both recombinases can be used to delete or to activate genes in established tumors. In a proof-of-principle experiment, we conditionally deleted the JAK1 tyrosine kinase in KRAS-transformed mammary cancer cells using the dual recombinase approach and found that lack of JAK1 was sufficient to block the constitutive activation of STAT3. The collective results from the various lines of investigation showed that it is, in principle, feasible to manipulate genes in a ligand-controlled manner in neoplastic mammary epithelial cells, even when cancer cells acquire a state of cellular plasticity that may no longer support the expression of the MMTV-Flp transgene.

A Tendon-Specific Double Reporter Transgenic Mouse Enables Tracking Cell Lineage and Functions Alteration In Vitro and In Vivo

We generated and characterized a transgenic mouse line with the tendon-specific expression of a double fluorescent reporter system, which will fulfill an unmet need for animal models to support real-time monitoring cell behaviors during tendon development, growth, and repair in vitro and in vivo. The mScarlet red fluorescent protein is driven by the Scleraxis (Scx) promoter to report the cell lineage alteration. The blue fluorescent protein reporter is expressed under the control of the 3.6kb Collagen Type I Alpha 1 Chain (Col1a1) proximal promoter. In this promoter, the existence of two promoter regions named tendon-specific cis-acting elements (TSE1, TSE2) ensure the specific expression of blue fluorescent protein (BFP) in tendon tissue. Collagen I is a crucial marker for tendon regeneration that is a major component of healthy tendons. Thus, the alteration of function during tendon repair can be estimated by BFP expression. After mechanical stimulation, the expression of mScarlet and BFP increased in adipose-derived mesenchymal stem cells (ADMSCs) from our transgenic mouse line, and there was a rising trend on tendon key markers. These results suggest that our tendon-specific double reporter system is a novel model used to study cell re-differentiation and extracellular matrix alteration in vitro and in vivo.

Tools for analysis and conditional deletion of subsets of sensory neurons

Background: Somatosensation depends on primary sensory neurons of the trigeminal and dorsal root ganglia (DRG). Transcriptional profiling of mouse DRG sensory neurons has defined at least 18 distinct neuronal cell types. Using an advillin promoter, we have generated a transgenic mouse line that only expresses diphtheria toxin A (DTA) in sensory neurons in the presence of Cre recombinase. This has allowed us to ablate specific neuronal subsets within the DRG using a range of established and novel Cre lines that encompass all sets of sensory neurons. Methods: A floxed-tdTomato-stop-DTA bacterial artificial chromosome (BAC) transgenic reporter line (AdvDTA) under the control of the mouse advillin DRG promoter was generated. The line was first validated using a Nav1.8Cre and then crossed to CGRPCreER (Calca), ThCreERT2, Tmem45bCre, Tmem233Cre, Ntng1Cre and TrkBCreER (Ntrk2) lines. Pain behavioural assays included Hargreaves’, hot plate, Randall-Selitto, cold plantar, partial sciatic nerve ligation and formalin tests. Results: Motor activity, as assessed by the rotarod test, was normal for all lines tested. Noxious mechanosensation was significantly reduced when either Nav1.8 positive neurons or Tmem45b positive neurons were ablated whilst acute heat pain was unaffected. In contrast, noxious mechanosensation was normal following ablation of CGRP-positive neurons but acute heat pain thresholds were significantly elevated and a reduction in nocifensive responses was observed in the second phase of the formalin test. Ablation of TrkB-positive neurons led to significant deficits in mechanical hypersensitivity in the partial sciatic nerve ligation neuropathic pain model. Conclusions: Ablation of specific DRG neuronal subsets using the AdvDTA line will be a useful resource for further functional characterization of somatosensory processing, neuro-immune interactions and chronic pain disorders.