Non-human primates are valuable for modelling human disorders and for developing therapeutic strategies; however, little work has been reported in establishing transgenic non-human primate models of human diseases. Huntington's disease (HD) is an autosomal dominant neurodegenerative disorder characterized by motor impairment, cognitive deterioration and psychiatric disturbances followed by death within 10-15 years of the onset of the symptoms 1-4 . HD is caused by the expansion of cytosineadenine-guanine (CAG, translated into glutamine) trinucleotide repeats in the first exon of the human huntingtin (HTT) gene 5 . Mutant HTT with expanded polyglutamine (polyQ) is widely expressed in the brain and peripheral tissues 2,6 , but causes selective neurodegeneration that is most prominent in the striatum and cortex of the brain. Although rodent models of HD have been developed, these models do not satisfactorily parallel the brain changes and behavioural features observed in HD patients. Because of the close physiological 7 , neurological and genetic similarities 8,9 between humans and higher primates, monkeys can serve as very useful models for understanding human physiology and diseases 10,11 . Here we report our progress in developing a transgenic model of HD in a rhesus macaque that expresses polyglutamine-expanded HTT. Hallmark features of HD, including nuclear inclusions and neuropil aggregates, were observed in the brains of the HD transgenic monkeys. Additionally, the transgenic monkeys showed important clinical features Correspondence to: Anthony W. S. Chan.Author Information Reprints and permissions information is available at www.nature.com/reprints. Correspondence and requests for materials should be addressed to A.W.S.C. (achan@genetics.emory.edu).. * These authors contributed equally to this work. Author Contributions S.-H.Y. carried out assisted reproductive technique (ART) in monkeys, viral gene transfer, construct design and molecular analysis; P.-H.C., construct design and evaluation; K.P.-N., ART in monkeys; H.B., animal management; behavioural testing and all animal procedures; K.L., animal care and behavioural testing; E.C.H.C., molecular analysis; J.-J.Y., preparation of high titre lentiviruses; B.S., J.L. and Z.H.F., neuropathological analysis; J.O., surgical procedures and animal care; Y.S., neuropathological analysis; J.B., design of behavioural and cognitive testing; S.M.Z., experimental design and manuscript preparation; S.H.L. and X.J.-L., construct design, analysis and manuscript preparation; A.W.S.C., ART in monkey, viral gene transfer, experimental design, construct design, molecular analysis and manuscript preparation. We injected 130 mature rhesus oocytes with high titre lentiviruses expressing exon 1 of the human HTT gene with 84 CAG repeats (HTT-84Q; Fig. 1c) and lentiviruses expressing the green fluorescent protein (GFP) gene (Fig. 1c), under the control of the human polyubiquitin-C promoter, into the perivitelline space. After fertilization by intracytoplasmic sperm injecti...

Magnetic resonance imaging (MRI) is routinely used to obtain anatomical images that have greatly advanced biomedical research and clinical health care today, but the full potential of MRI in providing functional, physiological, and molecular information is only beginning to emerge. In this work, we sought to provide a gene expression marker for MRI based on bacterial magnetosomes, tiny magnets produced by naturally occurring magnetotactic bacteria. Specifically, magA, a gene in magnetotactic bacteria known to be involved with iron transport, is expressed in a commonly used human cell line, 293FT, resulting in the production of magnetic, iron-oxide nanoparticles by these cells and leading to increased transverse relaxivity. MRI shows that these particles can be formed in vivo utilizing endogenous iron and can be used to visualize cells positive for magA. Synthetic superparamagnetic iron-oxide (SPIO) nanoparticles have been widely used for targeted molecular imaging applications (1-5). One major application is in vivo tracking of stem cells (6,7) and tumor progression (5). Labeling nonphagocytic cells in culture using modified particles, followed by transplantation or transfusion into living organisms, has made it possible to monitor cellular distribution in vivo, including cell migration and trafficking.A limitation of using synthetic SPIO is the need to label cells in vitro with presynthesized nanoparticles prior to cell transplant. As a result, particle concentration within cells decreases over time as the cells grow and divide, and particles cannot be readily linked directly to in vivo gene expression. One way to overcome this is to utilize a genetic approach. Green fluorescent protein (GFP) is perhaps the most well-known genetic marker for optical imaging. Magnetic resonance spectroscopy (MRS) has been used to detect creatine kinase (8) and chemical shift imaging (CSI) to observe betagalactosidase (9) activity. MRI gene expression strategies thus far include detection of beta-galactosidase activity (10,11), frequency-selective targeting of amide protons of expressed proteins (12), and expression of natural iron homeostasis proteins such as the transferrin receptor (13) and ferritin (14,15). For the transferrin receptor approach, administration of exogenous transferrin coupled to magnetic particles is required. Thus far, only ferritin exists as a purely in vivo superparamagnetic MRI marker. Although the relaxivity of ferritin is dependent on factors such as iron loading, data obtained on solutions of iron-containing materials suggest iron-oxide particles could provide higher relaxivity (16). In the present work, we report the gene-mediated cellular production of magnetic iron-oxide nanoparticles of the same composition as synthetic SPIO preparations using a gene present in magnetotactic bacteria, making it a possible MRI gene reporter.Magnetotactic bacteria, a diverse set of Gram-negative bacteria that exhibit motility thought to be directed by the earth's magnetic field (17), produce magnetosomes which are na...

A number of mouse models expressing mutant huntingtin (htt) with an expanded polyglutamine (polyQ) domain are useful for studying the pathogenesis of Huntington's disease (HD) and identifying appropriate therapies. However, these models exhibit neurological phenotypes that differ in their severity and nature. Understanding how transgenic htt leads to variable neuropathology in animal models would shed light on the pathogenesis of HD and help us to choose HD models for investigation. By comparing the expression of mutant htt at the transcriptional and protein levels in transgenic mice expressing N-terminal or full-length mutant htt, we found that the accumulation and aggregation of mutant htt in the brain is determined by htt context. HD mouse models demonstrating more severe phenotypes show earlier accumulation of N-terminal mutant htt fragments, which leads to the formation of htt aggregates that are primarily present in neuronal nuclei and processes, as well as glial cells. Similarly, transgenic monkeys expressing exon-1 htt with a 147-glutamine repeat (147Q) died early and showed abundant neuropil aggregates in swelling neuronal processes. Fractionation of HD150Q knock-in mice brains revealed an age-dependent accumulation of N-terminal mutant htt fragments in the nucleus and synaptosomes, and this accumulation was most pronounced in the striatum due to decreased proteasomal activity. Our findings suggest that the neuropathological phenotypes of HD stem largely from the accumulation of N-terminal mutant htt fragments and that this accumulation is determined by htt context and cell-type-dependent clearance of mutant htt.