Bispecific IgG neutralizes SARS-CoV-2 variants and prevents escape in mice.

Neutralizing antibodies that target the receptor-binding domain (RBD) of the SARS-CoV-2 spike protein are among the most promising approaches against COVID-191,2. A bispecific IgG1-like molecule (CoV-X2) has been developed on the basis of C121 and C135, two antibodies derived from donors who had recovered from COVID-193. Here we show that CoV-X2 simultaneously binds two independent sites on the RBD and, unlike its parental antibodies, prevents detectable spike binding to the cellular receptor of the virus, angiotensin-converting enzyme 2 (ACE2). Furthermore, CoV-X2 neutralizes wild-type SARS-CoV-2 and its variants of concern, as well as escape mutants generated by the parental monoclonal antibodies. We also found that in a mouse model of SARS-CoV-2 infection with lung inflammation, CoV-X2 protects mice from disease and suppresses viral escape. Thus, the simultaneous targeting of non-overlapping RBD epitopes by IgG-like bispecific antibodies is feasible and effective, and combines the advantages of antibody cocktails with those of single-molecule approaches.

Transcription factor Meis1b regulates craniofacial morphogenesis in zebrafish.

BACKGROUND: Meis family of transcription factors operates in Pbx-Meis-Hox regulatory network controlling development of various tissues including eye, limbs, heart, hindbrain or craniofacial skeletal elements originating from the neural crest. Although studies in mouse provide abundant information about Meis factors function in embryogenesis, little is known about their role in zebrafish. RESULTS: We generated zebrafish lines carrying null mutations in meis1a, meis1b, meis2a, and meis2b genes. Only meis1b mutants are lethal at larval stage around 13 dpf whereas the other mutant lines are viable and fertile. We focused on development of neural crest-derived craniofacial structures such as tendons, cranial nerves, cartilage and accompanying muscles. Meis1b mutants displayed morphogenetic abnormalities in the cartilage originating from the first and second pharyngeal arches. Meckel's cartilage was shorter and wider with fused anterior symphysis and abnormal chondrocyte organization. This resulted in impaired tendons and muscle fiber connections while tenocyte development was not largely affected. CONCLUSIONS: Loss-of-function mutation in meis1b affects cartilage morphology in the lower jaw that leads to disrupted organization of muscles and tendons.

Multistep allelic conversion in mouse pre-implantation embryos by AAV vectors.

Site-specific recombinases (SSRs) are critical for achieving precise spatiotemporal control of engineered alleles. These enzymes play a key role in facilitating the deletion or inversion of loci flanked by recombination sites, resulting in the activation or repression of endogenous genes, selection markers or reporter elements. However, multiple recombination in complex alleles can be laborious. To address this, a new and efficient method using AAV vectors has been developed to simplify the conversion of systems based on Cre, FLP, Dre and Vika recombinases. In this study, we present an effective method for ex vivo allele conversion using Cre, FLP (flippase), Dre, and Vika recombinases, employing adeno-associated viruses (AAV) as delivery vectors. AAVs enable efficient allele conversion with minimal toxicity in a reporter mouse line. Moreover, AAVs facilitate sequential allele conversion, essential for fully converting alleles with multiple recombination sites, typically found in conditional knockout mouse models. While simple allele conversions show a 100% efficiency rate, complex multiple conversions consistently achieve an 80% conversion rate. Overall, this strategy markedly reduces the need for animals and significantly speeds up the process of allele conversion, representing a significant improvement in genome engineering techniques.

Skeletal dysmorphology and mineralization defects in Fgf20 KO mice.

Introduction: Fibroblast growth factor 20 (Fgf20), a member of the Fgf9 subfamily, was identified as an important regulator of bone differentiation and homeostasis processes. However, the role of Fgf20 in bone physiology has not been approached yet. Here we present a comprehensive bone phenotype analysis of mice with functional ablation of Fgf20. Methods: The study conducts an extensive analysis of Fgf20 knockout mice compared to controls, incorporating microCT scanning, volumetric analysis, Fgf9 subfamily expression and stimulation experiment and histological evaluation. Results: The bone phenotype could be detected especially in the area of​ the lumbar and caudal part of the spine and in fingers. Regarding the spine, Fgf20-/- mice exhibited adhesions of the transverse process of the sixth lumbar vertebra to the pelvis as well as malformations in the distal part of their tails. Preaxial polydactyly and polysyndactyly in varying degrees of severity were also detected. High resolution microCT analysis of distal femurs and the fourth lumbar vertebra showed significant differences in structure and mineralization in both cortical and trabecular bone. These findings were histologically validated and may be associated with the expression of Fgf20 in chondrocytes and their progenitors. Moreover, histological sections demonstrated increased bone tissue formation, disruption of Fgf20-/- femur cartilage, and cellular-level alterations, particularly in osteoclasts. We also observed molar dysmorphology, including root taurodontism, and described variations in mineralization and dentin thickness. Discussion: Our analysis provides evidence that Fgf20, together with other members of the Fgf9 subfamily, plays a crucial regulatory role in skeletal development and bone homeostasis.

Ablation of Gabra5 Influences Corticosterone Levels and Anxiety-like Behavior in Mice.

Stress responses are activated by the hypothalamic-pituitary-adrenal axis (HPA axis), culminating in the release of glucocorticoids. During prolonged periods of secretion of glucocorticoids or inappropriate behavioral responses to a stressor, pathologic conditions may occur. Increased glucocorticoid concentration is linked to generalized anxiety, and there are knowledge gaps regarding its regulation. It is known that the HPA axis is under GABAergic control, but the contribution of the individual subunits of the GABA receptor is largely unknown. In this study, we investigated the relationship between the α5 subunit and corticosterone levels in a new mouse model deficient for Gabra5, which is known to be linked to anxiety disorders in humans and phenologs observed in mice. We observed decreased rearing behavior, suggesting lower anxiety in the Gabra5-/- animals; however, such a phenotype was absent in the open field and elevated plus maze tests. In addition to decreased rearing behavior, we also found decreased levels of fecal corticosterone metabolites in Gabra5-/- mice indicating a lowered stress response. Moreover, based on the electrophysiological recordings where we observed a hyperpolarized state of hippocampal neurons, we hypothesize that the constitutive ablation of the Gabra5 gene leads to functional compensation with other channels or GABA receptor subunits in this model.

Generation and Characterization of a Novel Angelman Syndrome Mouse Model with a Full Deletion of the Ube3a Gene.

Angelman syndrome (AS) is a neurodevelopmental disorder caused by deficits in maternally inherited UBE3A. The disease is characterized by intellectual disability, impaired motor skills, and behavioral deficits, including increased anxiety and autism spectrum disorder features. The mouse models used so far in AS research recapitulate most of the cardinal AS characteristics. However, they do not mimic the situation found in the majority of AS patients who have a large deletion spanning 4-6 Mb. There is also a large variability in phenotypes reported in the available models, which altogether limits development of therapeutics. Therefore, we have generated a mouse model in which the Ube3a gene is deleted entirely from the 5' UTR to the 3' UTR of mouse Ube3a isoform 2, resulting in a deletion of 76 kb. To investigate its phenotypic suitability as a model for AS, we employed a battery of behavioral tests directed to reveal AS pathology and to find out whether this model better mirrors AS development compared to other available models. We found that the maternally inherited Ube3a-deficient line exhibits robust motor dysfunction, as seen in the rotarod and DigiGait tests, and displays abnormalities in additional behavioral paradigms, including reduced nest building and hypoactivity, although no apparent cognitive phenotype was observed in the Barnes maze and novel object recognition tests. The AS mice did, however, underperform in more complex cognition tasks, such as place reversal in the IntelliCage system, and exhibited a different circadian rhythm activity pattern. We show that the novel UBE3A-deficient model, based on a whole-gene deletion, is suitable for AS research, as it recapitulates important phenotypes characteristic of AS. This new mouse model provides complementary possibilities to study the Ube3a gene and its function in health and disease as well as possible therapeutic interventions to restore function.

Bispecific antibody neutralizes circulating SARS-CoV-2 variants, prevents escape and protects mice from disease.

Neutralizing antibodies targeting the receptor binding domain (RBD) of the SARS-CoV-2 Spike (S) are among the most promising approaches against coronavirus disease 2019 (COVID-19) 1,2 . We developed a bispecific, IgG1-like molecule (CoV-X2) based on two antibodies derived from COVID-19 convalescent donors, C121 and C135 3 . CoV-X2 simultaneously binds two independent sites on the RBD and, unlike its parental antibodies, prevents detectable S binding to Angiotensin-Converting Enzyme 2 (ACE2), the virus cellular receptor. Furthermore, CoV-X2 neutralizes SARS-CoV-2 and its variants of concern, as well as the escape mutants generated by the parental monoclonals. In a novel animal model of SARS-CoV-2 infection with lung inflammation, CoV-X2 protects mice from disease and suppresses viral escape. Thus, simultaneous targeting of non-overlapping RBD epitopes by IgG-like bispecific antibodies is feasible and effective, combining into a single molecule the advantages of antibody cocktails.

CRISPR/Cas9 Epigenome Editing Potential for Rare Imprinting Diseases: A Review.

Imprinting diseases (IDs) are rare congenital disorders caused by aberrant dosages of imprinted genes. Rare IDs are comprised by a group of several distinct disorders that share a great deal of homology in terms of genetic etiologies and symptoms. Disruption of genetic or epigenetic mechanisms can cause issues with regulating the expression of imprinted genes, thus leading to disease. Genetic mutations affect the imprinted genes, duplications, deletions, and uniparental disomy (UPD) are reoccurring phenomena causing imprinting diseases. Epigenetic alterations on methylation marks in imprinting control centers (ICRs) also alters the expression patterns and the majority of patients with rare IDs carries intact but either silenced or overexpressed imprinted genes. Canonical CRISPR/Cas9 editing relying on double-stranded DNA break repair has little to offer in terms of therapeutics for rare IDs. Instead CRISPR/Cas9 can be used in a more sophisticated way by targeting the epigenome. Catalytically dead Cas9 (dCas9) tethered with effector enzymes such as DNA de- and methyltransferases and histone code editors in addition to systems such as CRISPRa and CRISPRi have been shown to have high epigenome editing efficiency in eukaryotic cells. This new era of CRISPR epigenome editors could arguably be a game-changer for curing and treating rare IDs by refined activation and silencing of disturbed imprinted gene expression. This review describes major CRISPR-based epigenome editors and points out their potential use in research and therapy of rare imprinting diseases.