  In vertebrates, olfactory sensory neurons choose only one olfactory receptor
to produce out of ~2000 possibilities. The mechanism for how this singular
receptor expression occurs is unknown. Here we propose a mechanism that can
stochastically select a single gene out of a large number of possibilities. In
this model, receptor genes compete for a limited pool of transcription factors
(TFs). The gene that recruits a target number of TFs is selected for
expression. To support this mechanism, we have attempted to detect repeated
motifs within known sequences of mouse olfactory receptor promoters. We find
motifs that are significantly overrepresented in olfactory versus other gene
promoters. We identify possible TFs that can target these motifs. Our model
suggests that a small number of TFs can control the selection of a single gene
out of ~2000 possibilities.
