Tag Archives: neuroscience

Awakening dormant genes with cancer drugs

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From Figure 1 of Huang et al.

Here’s one that first appeared online at the end of last year by Benjamin Philpot, Bryan Roth and Mark Zylka about a finding that could lead to a therapy for Angelman Syndrome. Angelman syndrome is a rare neurodevelopmental disorder affecting 1 in 15,000 live births and is characterized by developmental delay, lack of speech, seizures, and motor difficulties. There are no therapies available for core symptoms and individuals generally require care throughout life. Autism is often diagnosed in Angelman Syndrome individuals, and the same genomic region has been fingered as a culprit in both disorders. Angelman Syndrome is most commonly caused by deletion of a region on the maternal copy of chromosome 15 containing the gene UBE3A, conversely, some forms of autism may also be caused by duplication of this region.

Although we all possess two copies of UBE3A, only the one inherited from the mother is active. Normally, the paternal copy is epigenetically silenced. This means that in Angelman Syndrome there is no functioning copy at all, which has consequences for multiple signaling pathways and brain circuits. The authors of this paper set out to find a workaround: something that could activate the intact, but dormant, paternal copy of UBE3A.  They made a reporter assay from neurons of mice expressing fluorescent paternal UBE3A protein, and performed a large-scale drug screen, testing over 2000 compounds for ones that would activate paternal Ube3A. None of the most likely suspects worked, but an unlikely class of drugs, topoisomerase inhibitors, did so reliably. Even better,  one of the best (topotecan) is already an FDA-approved cancer drug.

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Patients help bring the study of Alzheimer’s to the dish

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Israel et al. Supp Fig1: Experimental design.

Alzheimer’s disease (AD) is a devastating neurodegenerative disease that could become an even more massive public health problem than it already is, if current projections hold. Some predict that by 2050, 1 in 85 individuals will be affected by the disease. Currently, there is no cure, but there are neurotransmitter-enhancement-based strategies to slow down the cognitive deficits [the loss of cholinergic neurons is implicated in some of the memory problems associated with AD so therefore, pharmacological enhancement of brain acetylcholine concentration can partially alleviate some memory-based symptoms.] However, as with many neurodegenerative diseases, these stop-gap treatments only work for so long, until the cells responding to neurotransmitter supplementation treatments die off completely. Therefore, diverse strategies designed to cure or at least slow down AD are imperative.

While a number of AD transgenic mouse models have been created, based on the various mutations identified in patients, the trouble is that these models still utilize the cross-species approach of studying “diseased” mouse neurons expressing mutated human genes. And perhaps an even bigger problem with many mouse models, genetically-inherited forms of AD represent only ~0.1% of cases, with the remainder being “sporadic” (although there are genetic risk factors influencing the emergence of sporadic AD.)

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Timely inhibition

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Image: Tamily Weissman

This week’s paper is by Abigail Person and Indira Raman and is about information transmission between two cell populations in the cerebellum – purkinje cells in the cortex and their targets in the deep nuclei. Purkinje cells are justifiably famous for their spectacular anatomy  which enables integration of thousands of inputs. This paper, however, is about their output and how these exclusively GABAergic cells control the activity of downstream neurons. Conventional wisdom holds that there should be a straightforward inverse relationship between the firing rate of the two populations, but this has not always been observed. Person and Raman present a new solution based on spike timing – when purkinje cells spike asynchronously, their targets are inhibited (as expected), but when they spike synchronously, nuclear neurons can spike during the gaps in inhibition and end up time locking their activity to their inputs.

This is an intriguing proposal for how information is transmitted in the cerebellum that could have implications for how this brain structure controls movement, but it’s just the first step. The proposal is built from in vitro experiments, deduction, and some supporting in vivo data, but several crucial unknowns have to be resolved before we’ll know whether it’s relevant to actual behavior. There was plenty of spirited discussion during the review process about the strength of some of the authors’ assumptions. There were deeply divided views on whether the authors had made sufficiently strong a case for how the cerebellum IS operating, as opposed to just proposing how it COULD be. We had to decide whether to publish a paper that everyone agreed was interesting, but one that contained some pieces of indirect evidence and some good (but by no means universally agreed-upon) assumptions.

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Pulling back the editorial curtain on Nature’s papers

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After a brief resurrection during the 2012  Society for Neuroscience meeting, the time has come to get a more regular series going on the old Action Potential blog! There are a lot of great (neuro)science writers out there (just to name a few,) so here at Nature, we wanted to be able to offer something different, something unique to supplement your weekly intake of neuroscience knowledge. Therefore, my editorial colleague I-han Chou and I will regularly blog about the latest neuro papers we publish in the journal, with particular attention to the back stories and our reasoning for offering publication.

Every paper has a story and this will be your opportunity to hear them. We’ll be discussing why we believe a particular paper is a potential game-changer, why we highlighted a technical advance with no biological insight, how two papers with similar findings were co-published and when possible, we will also be inviting commentary from the authors themselves or critical experts in the field to provide balance on the issue of novelty and the future importance of a finding.

We hope you’ll enjoy this series and we’ll try to post something 1-2 times a week, depending on the scheduling of neuroscience publications. On slower weeks, we may re-visit past papers that have a particularly interesting story or lesson. You are free to also make suggestions on coverage (new and old papers.) You can always comment below or use the contact information in the “About this Blog” section.

Finally, for additional coverage, please make sure to bookmark the RSS feed (if you still use that,) circle the Action Potential Google+ Page, circle I-han or myself on G+ and follow I-han or myself on Twitter and let this experimental journey begin…