TWiV 165: The email zone

T4_tatooHosts: Vincent Racaniello, Dickson DespommierRich Condit, and Alan Dove

Vincent, Dickson, Rich, and Alan answer listener questions about XMRV, cytomegalovirus, latency, shingles vaccine, myxomavirus and rabbits, and more.

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Click the arrow above to play, or right-click to download TWiV 165 (61 MB .mp3, 102 minutes).

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Links for this episode:

Weekly Science Picks

Dickson – Creation
Rich –
America’s Science Decline
AlanOut of context science
Vincent – The Scientist Top 10 Innovations 2011

Listener Pick of the Week

Jim – Christoph Adami: Finding life we can’t imagine (TED)
TimPatient Zero (Radiolab)
Mary – Natural Obsessions by Natalie Angier
Jimmy –
Science Exchange

Send your virology questions and comments (email or mp3 file) to, or call them in to 908-312-0760. You can also post articles that you would like us to discuss at and tag them with twiv.

3 thoughts on “TWiV 165: The email zone”

  1. I had a few comments as I listened to this episode. You discussed Zinc Finger Nuclease (ZFN) technology, and I thought TWIV listeners would love this study:

    Luigi Naldini’s lab used an integrase defective lentiviral vector to express a ZFN and to provide the template DNA used for gene correction. So, they used a virus to provide both the scissors and the patch. This gives highly efficient gene transfer while the integrase deficiency allows transient episomal delivery from a lentivirus, at least in principle. 

    As a stem cell guy, I listened with interest to the portion of the show that discussed pluripotent stem cells. Alan rightfully pointed out that some people dispute whether pluripotent stem cells can make every cell type. For human cells, this is impossible to ethically prove since we cannot make chimeric humans. But for mouse, it has been shown that entire mice can be made from embryonic stem cells (or induced pluripotent stem cells) using a technique called tetraploid complementation. 

    The way this works is that a two-celled embryo is zapped with electricity to fuse both cells together. So your two diploid cells are now one tetraploid cell. This tetraploid cell continues to divide after the fusion and is competent to develop to the blastocyst stage, creating functional extraembryonic tissue. When combined with embryonic stem or induced pluripotent stem cells, the tetraploid cells provide the extraembryonic tissue but will rarely contribute to the embryo itself. Using this assay, it has been shown by many groups that mouse embryonic stem cells and mouse induced pluripotent stem cells can give rise to a mouse that is composed almost entirely from these stem cells. 

    It should be noted that it is almost impossible to prove that 100% of the cells are from the stem cells. And there is data to suggest that not every single cell is derived from the stem cells. But I’d say that, at least where we can do the experiment, there is pretty strong evidence that embryonic stem cells and induced pluripotent stem cells are capable of making nearly every cell in the body.

    Our being able to recreate all of those cell types in a dish is another issue entirely. But this experiment, I believe, demonstrates that the potential exists. Our current challenge is to understand the developmental biology required to get to each cell type. We attempt to translate how different pathways are activated and silenced over the course of time from model organisms to a human developmental timeframe. One such success just happened next door to my lab: Lorenz Studer’s group has recently demonstrated the derivation of transplantable midbrain dopamine neurons from human pluripotent stem cells:

    Mark Tomishima, Ph.D.
    Head, SKI Stem Cell Research Facility

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