A murine model for the del(GJB6-D13S1830) deletion recapitulating the phenotype of human DFNB1 hearing impairment: generation and functional and histopathological study.

Inherited hearing impairment is a remarkably heterogeneous monogenic condition, involving hundreds of genes, most of them with very small (< 1%) epidemiological contributions. The exception is GJB2, the gene encoding connexin-26 and underlying DFNB1, which is the most frequent type of autosomal recessive non-syndromic hearing impairment (ARNSHI) in most populations (up to 40% of ARNSHI cases). DFNB1 is caused by different types of pathogenic variants in GJB2, but also by large deletions that keep the gene intact but remove an upstream regulatory element that is essential for its expression. Such large deletions, found in most populations, behave as complete loss-of-function variants, usually associated with a profound hearing impairment. By using CRISPR-Cas9 genetic edition, we have generated a murine model (Dfnb1em274) that reproduces the most frequent of those deletions, del(GJB6-D13S1830). Dfnb1em274 homozygous mice are viable, bypassing the embryonic lethality of the Gjb2 knockout, and present a phenotype of profound hearing loss (> 90 dB SPL) that correlates with specific structural abnormalities in the cochlea. We show that Gjb2 expression is nearly abolished and its protein product, Cx26, is nearly absent all throughout the cochlea, unlike previous conditional knockouts in which Gjb2 ablation was not obtained in all cell types. The Dfnb1em274 model recapitulates the clinical presentation of patients harbouring the del(GJB6-D13S1830) variant and thus it is a valuable tool to study the pathological mechanisms of DFNB1 and to assay therapies for this most frequent type of human ARNSHI.

Safe Procedure for Efficient Hydrodynamic Gene Transfer to Isolated Porcine Liver in Transplantation.

Although calcineurin inhibitors are very effective as immunosuppressants in organ transplantation, complete graft acceptance remains as a challenge. Transfer of genes with immunosuppressant functions could contribute to improving the clinical evolution of transplantation. In this sense, hydrodynamic injection has proven very efficacious for liver gene transfer. In the present work, the hIL-10 gene was hydrofected 'ex vivo' to pig livers during the bench surgery stage, to circumvent the cardiovascular limitations of the procedure, in a model of porcine orthotopic transplantation with a 10-day follow-up. We used IL-10 because human and porcine proteins can be differentially quantified and for its immunomodulatory pleiotropic functions. Safety (biochemical parameters and histology), expression efficacy (RNA transcription and blood protein expression), and acute inflammatory response (cytokines panel) of the procedure were evaluated. The procedure proved safe as no change in biochemical parameters was observed in treated animals, and human IL-10 was efficaciously expressed, with stationary plasma protein levels over 20 pg/mL during the follow-up. Most studied cytokines showed increments (interferon-α, IFN-α; interleukin-1ß, IL-1ß; tumor necrosis factor α, TNFα; interleukin-6, IL-6; interleukin-8, IL-8; interleukin-4, IL-4; and transforming growth factor-ß, TGF-ß) in treated animals, without deleterious effects on tissue. Collectively, the results support the potential clinical interest in this gene therapy model that would require further longer-term dose-response studies to be confirmed.

A Slc38a8 Mouse Model of FHONDA Syndrome Faithfully Recapitulates the Visual Deficits of Albinism Without Pigmentation Defects.

Purpose: We aimed to generate and phenotype a mouse model of foveal hypoplasia, optic nerve decussation defects, and anterior segment dysgenesis (FHONDA), a rare disease associated with mutations in Slc38a8 that causes severe visual alterations similar to albinism without affecting pigmentation. Methods: The FHONDA mouse model was generated with clustered regularly interspaced short palindromic repeats (CRISPR)/Cas9 technology using an RNA guide targeting the Scl38a8 murine locus. The resulting mice were backcrossed to C57BL/6J. Melanin content was measured using spectrophotometry. Retinal cell architecture was analyzed through light and electron microscopy. Retinal projections to the brain were evaluated with anterograde labelling in embryos and adults. Visual function was assessed by electroretinography (ERG) and the optomotor test (OT). Results: From numerous Slc38a8 mouse mutant alleles generated, we selected one that encodes a truncated protein (p.196Pro*, equivalent to p.199Pro* in the human protein) closely resembling a mutant allele described in patients (p.200Gln*). Slc38a8 mutant mice exhibit wild-type eye and coat pigmentation with comparable melanin content. Subcellular abnormalities were observed in retinal pigment epithelium cells of Slc38a8 mutant mice. Anterograde labeling experiments of retinal projections in embryos and adults showed a reduction of ipsilateral fibers. Functional visual analyses revealed a decreased ERG response in scotopic conditions and a reduction of visual acuity in mutant mice measured by OT. Conclusions: Slc38a8 mutant mice recapitulate the phenotype of patients with FHONDA concerning their normal pigmentation and their abnormal visual system, in the latter being a hallmark of all types of albinism. These mice will be helpful in better understanding the pathophysiology of this genetic condition.

Naked (N) mutant mice carry a nonsense mutation in the homeobox of Hoxc13.

Loss of function mutations in HOXC13 have been associated with Ectodermal Dysplasia-9, Hair/Nail Type (ECTD9) in consanguineous families, characterized by sparse to complete absence of hair and nail dystrophy. Here we characterize the spontaneous mouse mutation Naked (N) as a terminal truncation in the Hoxc13 (homeobox C13) gene. Similar to previous reports for homozygous Hoxc13 knock-out (KO) mice, homozygous N/N mice exhibit generalized alopecia with abnormal nails and a short lifespan. However, in contrast to Hoxc13 heterozygous KO mice, N/+ mice show generalized or partial alopecia, associated with loss of hair fibres, along with normal lifespan and fertility. Our data point to a lack of nonsense-mediated Hoxc13 transcript decay and the presence of the truncated mutant protein in N/N and N/+ hair follicles, thus suggesting a dominant-negative mutation. To our knowledge, this is the first report of a semi-dominant and potentially dominant-negative mutation affecting Hoxc13/HOXC13. Furthermore, recreating the N mutant allele in mice using CRISPR/Cas9-mediated genome editing resulted in the same spectrum of deficiencies as those associated with the spontaneous Naked mutation, thus confirming that N is indeed a Hoxc13 mutant allele. Considering the low viability of the Hoxc13 KO mice, the Naked mutation provides an attractive new model for studying ECTD9 disease mechanisms.

Boundary sequences flanking the mouse tyrosinase locus ensure faithful pattern of gene expression.

Control of gene expression is dictated by cell-type specific regulatory sequences that physically organize the structure of chromatin, including promoters, enhancers and insulators. While promoters and enhancers convey cell-type specific activating signals, insulators prevent the cross-talk of regulatory elements within adjacent loci and safeguard the specificity of action of promoters and enhancers towards their targets in a tissue specific manner. Using the mouse tyrosinase (Tyr) locus as an experimental model, a gene whose mutations are associated with albinism, we described the chromatin structure in cells at two distinct transcriptional states. Guided by chromatin structure, through the use of Chromosome Conformation Capture (3C), we identified sequences at the 5' and 3' boundaries of this mammalian gene that function as enhancers and insulators. By CRISPR/Cas9-mediated chromosomal deletion, we dissected the functions of these two regulatory elements in vivo in the mouse, at the endogenous chromosomal context, and proved their mechanistic role as genomic insulators, shielding the Tyr locus from the expression patterns of adjacent genes.

Rab27a co-ordinates actin-dependent transport by controlling organelle-associated motors and track assembly proteins.

Cell biologists generally consider that microtubules and actin play complementary roles in long- and short-distance transport in animal cells. On the contrary, using melanosomes of melanocytes as a model, we recently discovered that the motor protein myosin-Va works with dynamic actin tracks to drive long-range organelle dispersion in opposition to microtubules. This suggests that in animals, as in yeast and plants, myosin/actin can drive long-range transport. Here, we show that the SPIRE-type actin nucleators (predominantly SPIRE1) are Rab27a effectors that co-operate with formin-1 to generate actin tracks required for myosin-Va-dependent transport in melanocytes. Thus, in addition to melanophilin/myosin-Va, Rab27a can recruit SPIREs to melanosomes, thereby integrating motor and track assembly activity at the organelle membrane. Based on this, we suggest a model in which organelles and force generators (motors and track assemblers) are linked, forming an organelle-based, cell-wide network that allows their collective activity to rapidly disperse the population of organelles long-distance throughout the cytoplasm.

Simple Protocol for Generating and Genotyping Genome-Edited Mice With CRISPR-Cas9 Reagents.

The simple protocol described in this article aims to provide all required information, as a comprehensive, easy-to-follow step-by-step method, to ensure the generation of the expected genome-edited mice. Here, we provide protocols for the preparation of CRISPR-Cas9 reagents for microinjection and electroporation into one-cell mouse embryos to create knockout or knock-in mouse models, and for genotyping the resulting offspring with the latest innovative next-generation sequencing methods. © 2020 by John Wiley & Sons, Inc. Basic Protocol 1: Designing the best RNA guide for your gene disruption/editing strategy Basic Protocol 2: Preparing and validating CRISPR-Cas9 reagents Basic Protocol 3: Preparing and injecting CRISPR-Cas9 compounds into fertilized mouse oocytes Basic Protocol 4: Genotyping genome-edited mice Support Protocol: Genotyping for CRISPR-generated "indel" mutations.

Nucleotide exchange factor Rab3GEP requires DENN and non-DENN elements for activation and targeting of Rab27a.

Rab GTPases are compartment-specific molecular switches that regulate intracellular vesicular transport in eukaryotes. GDP/GTP exchange factors (GEFs) control Rab activation, and current models propose that localised and regulated GEF activity is important in targeting Rabs to specific membranes. Here, we investigated the mechanism of GEF function using the Rab27a GEF, Rab3GEP (also known as MADD), in melanocytes as a model. We show that Rab3GEP-deficient melanocytes (melan-R3GKO) manifest partial disruption of melanosome dispersion, a read-out of Rab27a activation and targeting. Using rescue of melanosome dispersion in melan-R3GKO cells and effector pull-down approaches we show that the DENN domain of Rab3GEP (conserved among RabGEFs) is necessary, but insufficient, for its cellular function and GEF activity. Finally, using a mitochondrial re-targeting strategy, we show that Rab3GEP can target Rab27a to specific membranes in a GEF-dependent manner. We conclude that Rab3GEP facilitates the activation and targeting of Rab27a to specific membranes, but that it differs from other DENN-containing RabGEFs in requiring DENN and non-DENN elements for both of these activities and by lacking compartment-specific localisation.

Efficient up-conversion in Yb:Er:NaT(XO4)2 thermal nanoprobes. Imaging of their distribution in a perfused mouse.

Yb and Er codoped NaT(XO4)2 (T = Y, La, Gd, Lu and X = Mo, W) disordered oxides show a green (Er3+ related) up-conversion (UC) efficiency comparable to that of Yb:Er:ß-NaYF4 compound and unless 3 times larger UC ratiometric thermal sensitivity. The similar UC efficiency of Yb:Er doped NaT(XO4)2 and ß-NaYF4 compounds allowed testing equal subcutaneous depths of ex-vivo chicken tissue in both cases. This extraordinary behavior for NaT(XO4)2 oxides with large cutoff phonon energy (hω≈ 920 cm-1) is ascribed to 4F9/2 electron population recycling to higher energy 4G11/2 level by a phonon assisted transition. Crystalline nanoparticles of Yb:Er:NaLu(MoO4)2 have been synthesized by sol-gel with sizes most commonly in the 50-80 nm range, showing a relatively small reduction of the UC efficiency with regards to bulk materials. Fluorescence lifetime and multiphoton imaging microscopies show that these nanoparticles can be efficiently distributed to all body organs of a perfused mouse.

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.

Myosin-Va and dynamic actin oppose microtubules to drive long-range organelle transport.

In animal cells, microtubule and actin tracks and their associated motors (dynein, kinesin, and myosin) are thought to regulate long- and short-range transport, respectively. Consistent with this, microtubules extend from the perinuclear centrosome to the plasma membrane and allow bidirectional cargo transport over long distances (>1 µm). In contrast, actin often comprises a complex network of short randomly oriented filaments, suggesting that myosin motors move cargo short distances. These observations underpin the "highways and local roads" model for transport along microtubule and actin tracks. The "cooperative capture" model exemplifies this view and suggests that melanosome distribution in melanocyte dendrites is maintained by long-range transport on microtubules followed by actin/myosin-Va-dependent tethering. In this study, we used cell normalization technology to quantitatively examine the contribution of microtubules and actin/myosin-Va to organelle distribution in melanocytes. Surprisingly, our results indicate that microtubules are essential for centripetal, but not centrifugal, transport. Instead, we find that microtubules retard a centrifugal transport process that is dependent on myosin-Va and a population of dynamic F-actin. Functional analysis of mutant proteins indicates that myosin-Va works as a transporter dispersing melanosomes along actin tracks whose +/barbed ends are oriented toward the plasma membrane. Overall, our data highlight the role of myosin-Va and actin in transport, and not tethering, and suggest a new model in which organelle distribution is determined by the balance between microtubule-dependent centripetal and myosin-Va/actin-dependent centrifugal transport. These observations appear to be consistent with evidence coming from other systems showing that actin/myosin networks can drive long-distance organelle transport and positioning.

An insulator embedded in the chicken α-globin locus regulates chromatin domain configuration and differential gene expression.

Genome organization into transcriptionally active domains denotes one of the first levels of gene expression regulation. Although the chromatin domain concept is generally accepted, only little is known on how domain organization impacts the regulation of differential gene expression. Insulators might hold answers to address this issue as they delimit and organize chromatin domains. We have previously identified a CTCF-dependent insulator with enhancer-blocking activity embedded in the 5' non-coding region of the chicken α-globin domain. Here, we demonstrate that this element, called the αEHS-1.4 insulator, protects a transgene against chromosomal position effects in stably transfected cell lines and transgenic mice. We found that this insulator can create a regulated chromatin environment that coincides with the onset of adult α-globin gene expression. Furthermore, such activity is in part dependent on the in vivo regulated occupancy of CTCF at the αEHS-1.4 element. Insulator function is also regulated by CTCF poly(ADP-ribosyl)ation. Our results suggest that the αEHS-1.4 insulator contributes in organizing the chromatin structure of the α-globin gene domain and prevents activation of adult α-globin gene expression at the erythroblast stage via CTCF.

Genetic polymorphisms among C57BL/6 mouse inbred strains.

Mice from the inbred C57BL/6 strain have been commonly used for the generation and analysis of transgenic and knockout animal models. However, several C57BL/6 substrains exist, and these are genetically and phenotypically different. In addition, each of these substrains can be purchased from different animal providers and, in some cases, they have maintained their breeding stocks separated for a long time, allowing genetic differences to accumulate due to individual variability and genetic drift. With the aim of describing the differences in the genotype of several C57BL/6 substrains, we applied the Illumina(®) Mouse Medium Density Linkage Mapping panel, with 1,449 single nucleotide polymorphisms (SNPs), to individuals from ten C57BL/6-related strains: C57BL/6JArc, C57BL/6J from The Jackson Lab, C57BL/6J from Crl, C57BL6/JRccHsd, C57BL/6JOlaHsd, C57BL/6JBomTac, B6(Cg)-Tyr ( c-2j )/J, C57BL/6NCrl, C57BL/6NHsd and C57BL/6NTac. Twelve SNPs were found informative to discriminate among the mouse strains considered. Mice derived from the original C57BL/6J: C57BL/6JArc, C57BL/6J from The Jackson Lab and C57BL/6J from Crl, were indistinguishable. Similarly, all C57BL/6N substrains displayed the same genotype, whereas the additional substrains showed intermediate cases with substrain-specific polymorphisms. These results will be instrumental for the correct genetic monitoring and appropriate mouse colony handling of different transgenic and knockout mice produced in distinct C57BL/6 inbred substrains.

Melanin precursors prevent premature age-related and noise-induced hearing loss in albino mice.

Strial melanocytes are required for normal development and correct functioning of the cochlea. Hearing deficits have been reported in albino individuals from different species, although melanin appears to be not essential for normal auditory function. We have analyzed the auditory brainstem responses (ABR) of two transgenic mice: YRT2, carrying the entire mouse tyrosinase (Tyr) gene expression-domain and undistinguishable from wild-type pigmented animals; and TyrTH, non-pigmented but ectopically expressing tyrosine hydroxylase (Th) in melanocytes, which generate the precursor metabolite, L-DOPA, but not melanin. We show that young albino mice present a higher prevalence of profound sensorineural deafness and a poorer recovery of auditory thresholds after noise-exposure than transgenic mice. Hearing loss was associated with absence of cochlear melanin or its precursor metabolites and latencies of the central auditory pathway were unaltered. In summary, albino mice show impaired hearing responses during ageing and after noise damage when compared to YRT2 and TyrTH transgenic mice, which do not show the albino-associated ABR alterations. These results demonstrate that melanin precursors, such as L-DOPA, have a protective role in the mammalian cochlea in age-related and noise-induced hearing loss.

Generation and phenotypic analysis of sigma receptor type I (sigma 1) knockout mice.

Sigma (sigma) sites are a type of nonopiate receptor whose role has been associated with several behaviours, including anxiety, depression, analgesia, learning processes and psychosis. Although there are several known sigma receptor types, only the type I receptor (sigma 1) has been cloned. To uncover the in vivo relevance of sigma-receptors, we have generated knockout mice for sigma 1. Despite the broad expression pattern found for the sigma 1-gene, homozygous mutant mice are viable, fertile and do not display any overt phenotype, compared with their wild-type litter-mates, in mixed genetic backgrounds. However, a significant decrease in the hypermotility response has been measured in knockout mice upon challenge with (+)SKF-10 047, in agreement with the involvement of sigma 1-receptors in the induction of psychostimulant actions. The activity of sigma 2-receptors seems to be unaffected in sigma 1-mutant mice. These knockout mice could contribute to better understand the in vivo role of sigma-receptors.