Saturday, June 30, 2007

And now for something completely different: MMTV

Mouse Mammary Tumor Virus is a cool little retrovirus, and Ill probably be talking about it a lot more in the future.

MMTV still comes in two forms-- exogenous, and endogenous, which is neat in and of itself. The endogenous guys get passed along as proviruses in germ-line cells, and exogenous versions get passed from a lactating mother to the guts of her feeding pups.

Another reason I think MMTV is neat is that unlike HIV, which has a protein to carry the HIV genome to our cell nucleus (which means HIV can infect terminally differentiated cells), exogenous MMTV doesnt have a nifty nuclear tug-boat. It has to infect diving cells. MMTV waits until the nucleus dissolves during cell division to sneak into the infected cells genome. Berry berry sneaky.

The endogenous guys are also berry sneaky. While they are no longer completely functional they still can transcribe-->translate a superantigen. Its a viral protein, but because it is expressed before the immune system matures, the immune system recognizes the viral protein as 'self.' That means that all the T-cells that would kill an MMTV infected cell are killed, like all T-cells that recognize 'self' proteins. Mice basically lose an arm of their immune system.

Remember the classes of T-Cell Receptors I was talking about with the possums? Endogenous MMTVs (and the infection of pups before their immune system matures) can cause the loss of all T-cells that have certain Variable Beta chains. This deletion increase the mouses susceptibility to new MMTV infections, and also increases susceptibility to other pathogens, like cholera. Yup-- A virus screwing around with how well you can fight off bacteria.

But dont forget, folks, every little ERV is special!

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