. Local gene knockdown in the brain using viral-mediated RNA interference. Nat Med. 2003 Dec;9(12):1539-44. PubMed.

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  1. Tools to selectively knock down specific mRNA species in cells and tissues have developed at a spectacular pace over the past few years (reviewed by Scherer and Rossi, 2003). A major advance was the development of short interfering RNA technology (siRNA), where short stretches of antisense or hairpins, generally less than 20 nucleotides, have been used in invertebrate and mammalian systems to remarkable specificity. This report raises the bar a little further by grafting a hairpin antisense RNA into a viral vector, adeno-associated virus, which can be used in the brain of rodents in vivo. As the authors rightly state, this may be a way to generate disease models in species where knockouts are technically difficult, such as non-human primates, or to test regional specificity in gene function.

    As an example of the latter application, Hommel et al. show that knockdown of tyrosine hydroxylase (TH) in the substantia nigra is sufficient to induce motor deficits, which they suggest might be useful for modeling Parkinson’s disease. In contrast, knockdown in another midbrain dopaminergic region, the ventral tegmental area (VTA), decreases amphetamine-induced hyperactivity. What are not shown, probably for reasons of space in the journal, are the important reciprocal experiments; does VTA knockdown cause any rotorod deficits, or does SN knockdown induce hyperactivity after amphetamine challenge? It’s not quite clear that this is a substantially better PD model than current strategies, as the dopaminergic neurons are still alive, which is not the case in the human disease. Such discussion aside, the experiment described in this paper would have been extremely difficult to achieve using current knockout technology; homozygous TH knockout is lethal and promoters that drive expression in the VTA or SN selectively are poorly characterized, so selective knockout would be difficult. One can now imagine any number of ways to use these approaches; finding genes that normally maintain dopaminergic cell survival, modeling recessive genetic lesions in different species, and refining our understanding of the different properties of neurons that express similar transmitter phenotypes, to name a few.

    View all comments by Mark Cookson

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