ALBERT

Description: Nucleotide insertions/deletions are ubiquitous in eukaryotic genomes, and the resulting hemizygous (unpaired) DNA has significant, heritable effects on adjacent DNA. However, little is known about the genetic behavior of insertion DNA. Here, we describe a binary transgenic system to study the behavior of insertion DNA during meiosis. Transgenic Arabidopsis lines were generated to carry two different defective reporter genes on nonhomologous chromosomes, designated as "recipient" and "donor" lines. Double hemizygous plants (harboring unpaired DNA) were produced by crossing between the recipient and the donor, and double homozygous lines (harboring paired DNA) via self-pollination. The transfer of the donor’s unmutated sequence to the recipient generated a functional β-glucuronidase gene, which could be visualized by histochemical staining and corroborated by polymerase chain reaction amplification and sequencing. More than 673 million seedlings were screened, and the results showed that meiotic ectopic recombination in the hemizygous lines occurred at a frequency 〉6.49-fold higher than that in the homozygous lines. Gene conversion might have been exclusively or predominantly responsible for the gene correction events. The direct measurement of ectopic recombination events provided evidence that an insertion, in the absence of an allelic counterpart, could scan the entire genome for homologous counterparts with which to pair. Furthermore, the unpaired (hemizygous) architectures could accelerate ectopic recombination between itself and interchromosomal counterparts. We suggest that the ectopic recombination accelerated by hemizygous architectures may be a general mechanism for interchromosomal recombination through ubiquitously dispersed repeat sequences in plants, ultimately contributing to genetic renovation and eukaryotic evolution.

Description: Neurons in the brain produce lamin C but almost no lamin A, a consequence of the removal of prelamin A transcripts by miR-9, a brain-specific microRNA. We have proposed that miR-9-mediated regulation of prelamin A in the brain could explain the absence of primary neurological disease in Hutchinson-Gilford progeria syndrome, a genetic disease caused by the synthesis of an internally truncated form of farnesyl–prelamin A (progerin). This explanation makes sense, but it is not entirely satisfying because it is unclear whether progerin—even if were expressed in neurons—would be capable of eliciting neuropathology. To address that issue, we created a new Lmna knock-in allele, Lmna HG-C , which produces progerin transcripts lacking an miR-9 binding site. Mice harboring the Lmna HG-C allele produced progerin in neurons, but they had no pathology in the central nervous system. However, these mice invariably developed esophageal achalasia, and the enteric neurons and nerve fibers in gastrointestinal tract were markedly abnormal. The same disorder, achalasia, was observed in genetically modified mice that express full-length farnesyl–prelamin A in neurons ( Zmpste24- deficient mice carrying two copies of a Lmna knock-in allele yielding full-length prelamin A transcripts lacking a miR-9 binding site). Our findings indicate that progerin and full-length farnesyl–prelamin A are toxic to neurons of the enteric nervous system.

Description: CRISPR/Cas9 has been used to genetically modify genomes in a variety of species, including non-human primates. Unfortunately, this new technology does cause mosaic mutations, and we do not yet know whether such mutations can functionally disrupt the targeted gene or cause the pathology seen in human disease. Addressing these issues is necessary if we are to generate large animal models of human diseases using CRISPR/Cas9. Here we used CRISPR/Cas9 to target the monkey dystrophin gene to create mutations that lead to Duchenne muscular dystrophy (DMD), a recessive X-linked form of muscular dystrophy. Examination of the relative targeting rate revealed that Crispr/Cas9 targeting could lead to mosaic mutations in up to 87% of the dystrophin alleles in monkey muscle. Moreover, CRISPR/Cas9 induced mutations in both male and female monkeys, with the markedly depleted dystrophin and muscle degeneration seen in early DMD. Our findings indicate that CRISPR/Cas9 can efficiently generate monkey models of human diseases, regardless of inheritance patterns. The presence of degenerated muscle cells in newborn Cas9-targeted monkeys suggests that therapeutic interventions at the early disease stage may be effective at alleviating the myopathy.

Description: Parkinson's disease (PD) is an age-dependent neurodegenerative disease that can be caused by genetic mutations in α-synuclein (α-syn) or duplication of wild-type α-syn; PD is characterized by the deposition of α-syn aggregates, indicating a gain of toxicity from accumulation of α-syn. Although the major neuropathologic feature of PD is the degeneration of dopaminergic (DA) neurons in the substantia nigra, non-motor symptoms including anxiety, cognitive defect and sleep disorder precede the onset of motor impairment, and many clinical symptoms of PD are not caused by degeneration of DA neurons. Non-human primate models of PD are important for revealing the early pathology in PD and identifying effective treatments. We established transgenic PD rhesus monkeys that express mutant α-syn (A53T). Six transgenic A53T monkeys were produced via lentiviral vector expressing A53T in fertilized monkey eggs and subsequent embryo transfer to surrogates. Transgenic A53T is expressed in the monkey brain and causes age-dependent non-motor symptoms, including cognitive defects and anxiety phenotype, without detectable sleeping disorders. The transgenic α-syn monkeys demonstrate the specific early symptoms caused by mutant α-syn and provide insight into treatment of early PD.

Description: The Monts de Cristal Complex of Gabon consists of several igneous bodies interpreted to be remnants of a tectonically dismembered, 〉100 km long and 1–3 km wide, ultramafic–mafic intrusion emplaced at 2765–2775 Ma. It is the most significant mafic–ultramafic layered complex yet identified on the Congo Craton. The complex consists largely of orthopyroxenite cumulates, with less abundant olivine-orthopyroxenite and norite, and rare harzburgite and dunite. Mineral compositions (Fo ol 84, Mg# Opx 85, An plag 60–68, Cr/Fe chromite 1–1·45) and whole-rock data suggest that the parent magma was a low-Ti basalt containing approximately 10% MgO and 0·5% TiO 2 . Trace element and Rb–Sr and Sm–Nd isotope data indicate the presence of an enriched component, possibly derived from crustal contamination of a magma generated in the sub-lithospheric mantle. Most rocks show a highly unusual pattern of strong Pt enrichment (10–150 ppb) at low concentrations of Pd (1–15 ppb), Au (1–2 ppb), Cu (1–20 ppm), and S (〈500 ppm), suggesting that unlike in most other PGE-rich intrusions globally, platinum in the Monts de Cristal Complex is not hosted in magmatic sulfides. Synchrotron X-ray fluorescence mapping has revealed the location of buried small Pt particles, most of which are associated with As. We propose that this constitutes some of the strongest evidence yet in support of magmatic crystallization of a Pt–As phase from S-undersaturated magma.