sorting dim cells

Flow Sorters

There is an investigator who has a mouse model with the animals 
expressing a DsRed-tagged protein in a subset of bone marrow cells 
(probably less than 0.01%).

When we look for the DsRed signal, we do not see a difference in the 
frequency of DsRed positive events when comparing these DsRed mice to 
the wild type mice - we don't see anything above background.

The investigator says she expected not to be able to actually see the 
fluorescent signal because the amount of DsRed in the cells is very 
low.

Therefore, when looking at a dot plot of DsRed (x-axis) versus SSC 
(y-axis), she wants to place a sort region on the right-hand edge of 
this dot plot encompassing 1% or 3% or 5% of the cells and sort them. 
She says this will be a DsRed-enriched population because the DsRed 
expressing cells are detected in the channels above the mean of the 
total population.

It will then become a post-doc's project to characterize these 'cells 
on the edge.'

My interpretation of events whose fluorescent signal falls 'below the 
threshold of detection' means 'undetectable.'

I would appreciate any advice and comments

Thanks

Barbara J Taylor
Facility Manager, FACS Core Lab
Bldg 37 Room 6008
37 Convent Drive
CCR, NCI, NIH
Bethesda, MD 20892-4255
phone 301.594.6892
fax   301.496.8709
taylorba@pop.nci.nih.gov