SciCombinator

Discover the most talked about and latest scientific content & concepts.

Journal: Nature biotechnology

42

Efforts to develop gene therapies for hearing loss have been hampered by the lack of safe, efficient, and clinically relevant delivery modalities. Here we demonstrate the safety and efficiency of Anc80L65, a rationally designed synthetic vector, for transgene delivery to the mouse cochlea. Ex vivo transduction of mouse organotypic explants identified Anc80L65 from a set of other adeno-associated virus (AAV) vectors as a potent vector for the cochlear cell targets. Round window membrane injection resulted in highly efficient transduction of inner and outer hair cells in mice, a substantial improvement over conventional AAV vectors. Anc80L65 round window injection was well tolerated, as indicated by sensory cell function, hearing and vestibular function, and immunologic parameters. The ability of Anc80L65 to target outer hair cells at high rates, a requirement for restoration of complex auditory function, may enable future gene therapies for hearing and balance disorders.

Concepts: Bacteria, Organ of Corti, Mouse, Genetics, Inner ear, Gene, Cochlea, Auditory system

41

A lack of techniques to image multiple genomic loci in living cells has limited our ability to investigate chromosome dynamics. Here we describe CRISPRainbow, a system for labeling DNA in living cells based on nuclease-dead (d) Cas9 combined with engineered single guide RNA (sgRNA) scaffolds that bind sets of fluorescent proteins. We demonstrate simultaneous imaging of up to six chromosomal loci in individual live cells and document large differences in the dynamic properties of different chromosomal loci.

Concepts: Protein, RNA, Bacteria, Cell, Chromosome, Cell nucleus, DNA, Gene

39

The heartbeat originates within the sinoatrial node (SAN), a small structure containing <10,000 genuine pacemaker cells. If the SAN fails, the ∼5 billion working cardiomyocytes downstream of it become quiescent, leading to circulatory collapse in the absence of electronic pacemaker therapy. Here we demonstrate conversion of rodent cardiomyocytes to SAN cells in vitro and in vivo by expression of Tbx18, a gene critical for early SAN specification. Within days of in vivo Tbx18 transduction, 9.2% of transduced, ventricular cardiomyocytes develop spontaneous electrical firing physiologically indistinguishable from that of SAN cells, along with morphological and epigenetic features characteristic of SAN cells. In vivo, focal Tbx18 gene transfer in the guinea-pig ventricle yields ectopic pacemaker activity, correcting a bradycardic disease phenotype. Myocytes transduced in vivo acquire the cardinal tapering morphology and physiological automaticity of native SAN pacemaker cells. The creation of induced SAN pacemaker (iSAN) cells opens new prospects for bioengineered pacemakers.

Concepts: Cardiac anatomy, Cardiac electrophysiology, Cardiology, Artificial pacemaker, Gene, Sinoatrial node, Heart, Cardiac pacemaker

38

Differentiation of human pluripotent stem cells to small brain-like structures known as brain organoids offers an unprecedented opportunity to model human brain development and disease. To provide a vascularized and functional in vivo model of brain organoids, we established a method for transplanting human brain organoids into the adult mouse brain. Organoid grafts showed progressive neuronal differentiation and maturation, gliogenesis, integration of microglia, and growth of axons to multiple regions of the host brain. In vivo two-photon imaging demonstrated functional neuronal networks and blood vessels in the grafts. Finally, in vivo extracellular recording combined with optogenetics revealed intragraft neuronal activity and suggested graft-to-host functional synaptic connectivity. This combination of human neural organoids and an in vivo physiological environment in the animal brain may facilitate disease modeling under physiological conditions.

Concepts: Pluripotency, Synapse, Human brain, Brain, Stem cell, Neuron, Developmental biology, Nervous system

38

Manufacturing processes for biological molecules in the research laboratory have failed to keep pace with the rapid advances in automization and parellelization. We report the development of a digital-to-biological converter for fully automated, versatile and demand-based production of functional biologics starting from DNA sequence information. Specifically, DNA templates, RNA molecules, proteins and viral particles were produced in an automated fashion from digitally transmitted DNA sequences without human intervention.

Concepts: Genetics, DNA sequencing, Manufacturing, DNA sequence, RNA, Molecular biology, Gene, DNA

38

Because there are currently no biological treatments for hearing loss, we sought to advance gene therapy approaches to treat genetic deafness. We focused on Usher syndrome, a devastating genetic disorder that causes blindness, balance disorders and profound deafness, and studied a knock-in mouse model, Ush1c c.216G>A, for Usher syndrome type IC (USH1C). As restoration of complex auditory and balance function is likely to require gene delivery systems that target auditory and vestibular sensory cells with high efficiency, we delivered wild-type Ush1c into the inner ear of Ush1c c.216G>A mice using a synthetic adeno-associated viral vector, Anc80L65, shown to transduce 80-90% of sensory hair cells. We demonstrate recovery of gene and protein expression, restoration of sensory cell function, rescue of complex auditory function and recovery of hearing and balance behavior to near wild-type levels. The data represent unprecedented recovery of inner ear function and suggest that biological therapies to treat deafness may be suitable for translation to humans with genetic inner ear disorders.

Concepts: Biology, Cochlea, Vestibular system, Genetics, Auditory system, Inner ear, DNA, Gene

36

Gene drive systems that enable super-Mendelian inheritance of a transgene have the potential to modify insect populations over a timeframe of a few years. We describe CRISPR-Cas9 endonuclease constructs that function as gene drive systems in Anopheles gambiae, the main vector for malaria. We identified three genes (AGAP005958, AGAP011377 and AGAP007280) that confer a recessive female-sterility phenotype upon disruption, and inserted into each locus CRISPR-Cas9 gene drive constructs designed to target and edit each gene. For each targeted locus we observed a strong gene drive at the molecular level, with transmission rates to progeny of 91.4 to 99.6%. Population modeling and cage experiments indicate that a CRISPR-Cas9 construct targeting one of these loci, AGAP007280, meets the minimum requirement for a gene drive targeting female reproduction in an insect population. These findings could expedite the development of gene drives to suppress mosquito populations to levels that do not support malaria transmission.

Concepts: Allele, Biology, Genetics, Gene, Anopheles gambiae, Mosquito, Malaria, Anopheles

35

Specifically targeting genomic rearrangements and mutations in tumor cells remains an elusive goal in cancer therapy. Here, we used Cas9-based genome editing to introduce the gene encoding the prodrug-converting enzyme herpes simplex virus type 1 thymidine kinase (HSV1-tk) into the genomes of cancer cells carrying unique sequences resulting from genome rearrangements. Specifically, we targeted the breakpoints of TMEM135-CCDC67 and MAN2A1-FER fusions in human prostate cancer or hepatocellular carcinoma cells in vitro and in mouse xenografts. We designed one adenovirus to deliver the nickase Cas9(D10A) and guide RNAs targeting the breakpoint sequences, and another to deliver an EGFP-HSV1-tk construct flanked by sequences homologous to those surrounding the breakpoint. Infection with both viruses resulted in breakpoint-dependent expression of EGFP-tk and ganciclovir-mediated apoptosis. When mouse xenografts were treated with adenoviruses and ganciclovir, all animals showed decreased tumor burden and no mortality during the study. Thus, Cas9-mediated suicide-gene insertion may be a viable genotype-specific cancer therapy.

Concepts: Herpes simplex, Bacteria, Genome, DNA, Gene, Genetics, Cancer, Virus

33

Cell replacement therapies for neurodegenerative disease have focused on transplantation of the cell types affected by the pathological process. Here we describe an alternative strategy for Parkinson’s disease in which dopamine neurons are generated by direct conversion of astrocytes. Using three transcription factors, NEUROD1, ASCL1 and LMX1A, and the microRNA miR218, collectively designated NeAL218, we reprogram human astrocytes in vitro, and mouse astrocytes in vivo, into induced dopamine neurons (iDANs). Reprogramming efficiency in vitro is improved by small molecules that promote chromatin remodeling and activate the TGFβ, Shh and Wnt signaling pathways. The reprogramming efficiency of human astrocytes reaches up to 16%, resulting in iDANs with appropriate midbrain markers and excitability. In a mouse model of Parkinson’s disease, NeAL218 alone reprograms adult striatal astrocytes into iDANs that are excitable and correct some aspects of motor behavior in vivo, including gait impairments. With further optimization, this approach may enable clinical therapies for Parkinson’s disease by delivery of genes rather than cells.

Concepts: Neurotransmitter, Chromosome, Gene expression, Substantia nigra, Cell nucleus, Gene, Dopamine, DNA

33

Cultivated citrus are selections from, or hybrids of, wild progenitor species whose identities and contributions to citrus domestication remain controversial. Here we sequence and compare citrus genomes-a high-quality reference haploid clementine genome and mandarin, pummelo, sweet-orange and sour-orange genomes-and show that cultivated types derive from two progenitor species. Although cultivated pummelos represent selections from one progenitor species, Citrus maxima, cultivated mandarins are introgressions of C. maxima into the ancestral mandarin species Citrus reticulata. The most widely cultivated citrus, sweet orange, is the offspring of previously admixed individuals, but sour orange is an F1 hybrid of pure C. maxima and C. reticulata parents, thus implying that wild mandarins were part of the early breeding germplasm. A Chinese wild ‘mandarin’ diverges substantially from C. reticulata, thus suggesting the possibility of other unrecognized wild citrus species. Understanding citrus phylogeny through genome analysis clarifies taxonomic relationships and facilitates sequence-directed genetic improvement.

Concepts: Clementine, Grapefruit, Rutaceae, Pomelo, Tangerine, Mandarin orange, Orange, Citrus