Probes for rare mRNAs reveal distributed cell subsets in canary brain.

cDNA clones of 7 low-abundance canary brain RNAs hybridize in situ to different subsets of brain cells. Although these cell sets are distinct, they are dispersed in a variety of brain regions with overlapping anatomical distributions. These cDNA clones were initially selected by their relative hybridization to forebrain and rest-of-brain RNAs and represent a sampling of a much larger population of differentially expressed RNAs present at individual concentrations of 10(-7) to 10(-4) as a fraction of polyadenylated RNA mass. Our results suggest the existence of several thousand low-abundance brain mRNAs likely to be distributed in diverse and overlapping brain cell subsets. Furthermore, our experiments define a simple and general strategy for producing and analyzing molecular probes for subsets of brain cells and provide an initial set of useful reagents for further study of brain organization and development.