Alex Palazzo is an Assistant Professor in the Department of Biochemistry at The University of Toronto.
If you have the time, pick up a copy of the latest Nature. There is a paper that describes how a lab, based here at Harvard Medical School, used a random gene splicing strategy to express various fluorescent proteins in each neuron inside of the brain of a transgenic mouse. As a result of the random splicing event (using a cre/lox recombination system), each neuron expressed a different subset of the fluorescent proteins. Here is an example of the brainbow mouse's mosaic brain:
So, how many distinguishable colors did the different cells express?
To determine [the number of distinguishable colors], we analysed the distribution of colour profiles in the reconstructed volume from line H above (eight transgene copies). The population of axons exhibited many different colour profiles (Fig. 5c); the mean colour values calculated for the different axons varied greatly in hue and saturation and filled a large portion of colour space (Supplementary Fig. 5c). Using a visual colour discrimination test, we found that 98.9% of randomly selected rosette pairs expressed colours distinct enough to discriminate (see Methods). This degree of colour variation is equivalent to having approximately 89 distinct colours (that is, if 98.9% of axon pairs appear different, then the remaining 1.1% or 1 out of 88.7 pairs are too similar to discriminate). An alternative computer-based colour analysis of hippocampal neuron cell bodies from Brainbow-1.0 line L (see Fig. 4c) gave an estimated 166 colours. This large number of colours should be useful in resolving individual components of many neural circuits.
Wow.
Again from the article:
Given the colour constancy within a cell, colour differences provide a way to distinguish between neurons and thus could be useful for detailed circuit analysis, such as to count the number of neurons that innervate a postsynaptic cell.
Yes, we may now have a tool to map the wiring of the brain. This is a huge advance for neuroscience.
For more read Dan's entry at his new home at bitesize bio.
[Update]
Mo posted an entry on this work last week and Sparc has three different posts (see comments).
Brain & Behavior
Life Science
Comments
For those who are interested: I've prepared two figures outlining the underlying inversions and deletions confered by Cre recombinase and on the necessity of the presence of several concatenated constructs to produce so many colors.
I wonder how many different colors remained if they would have used a constitutively active Cre transgene.
Posted by: sparc | November 7, 2007 11:02 AM
That is so beautiful! Both aesthetically and scientifically.
Posted by: Joolya | November 7, 2007 3:48 PM
Tell that to the editors of the Scienceblogs Main Page who chose
as the quote of the day.Posted by: apalazzo | November 7, 2007 5:32 PM
Hey, a good anaphase is miles more entertaining than "The Biggest Bachelor" or "Dancing With A Millionaire" or "America's Next Crime Scene Investigation" or whatever other tripe is on!
Posted by: joolya | November 8, 2007 1:35 PM