Lei Bai, Aaron Goldman, John Carlson. MCDB,
Yale University, New Haven, CT.
The selected expression of odor receptor (Or) genes underlies
the odor-specificities of olfactory
receptor neurons. The Or gene family in Drosophila
consists of 60 members, most of which are expressed in either the
larval olfactory organ or one of the adult olfactory organs in a
non-overlapping pattern. Little is known
about how individual neurons select which Or genes to
express. Abnormal chemosensory jump 6, which encodes a POU-domain
transcription factor, has been implicated in this process.
Physiological analysis of individual olfactory neurons shows that in
acj6 mutants, some neurons appear normal, some lose response
to all tested odors, and some acquire a different response profile.
We characterized the expression of a subset of Or genes in
the adult acj6 mutants. Of the Or genes that normally
are expressed in neurons of the maxillary palp or the large
basiconic sensilla of the antenna, a majority are not expressed in
acj6 mutants, resulting in the loss of odor sensitivities of
many neurons. A subset of neurons, however, chooses to express an
odor receptor that normally is expressed in larval, but not adult,
olfactory neurons. The switch in receptor expression accounts for
the change in the odor response profile previously characterized.
Thus Acj6 acts positively on some Or genes, and negatively on
another. Using an in vitro binding selection assay, we characterized
the binding specificities of Acj6 to short oligonucleotides. Based
on the results, we identified predicted Acj6 binding sites in the
promoters of a subset of Or genes. Mutation of some of these
sites greatly reduces reporter gene expression driven by Or
gene promoters, suggesting that Acj6 regulates a subset of Or
genes by directly binding to their promoter sequences.