Ooceraea biroi ants can read a single odour receptor gene by silencing the surrounding genes. PHOTO: DANIEL KRONAUER
By blocking transcription elsewhere, ants are able to link odour receptors to specific neurons.
Ooceraea biroi ants possess a refined sense of smell thanks to a remarkable gene-regulation mechanism. American researchers unravel that mechanism in Current Biology of 19 September.
To distinguish between different odours, it is essential that a single olfactory neuron corresponds to just one odour receptor. O. biroi ants have 503 odour receptors, and the genes encoding them are often clustered together. That the ants nonetheless manage to read only a single odour receptor gene at a time is because they silence the surrounding genes.
Roadblock
The RNA polymerase that reads the correct receptor gene turns out not to stop there. It continues transcribing, in the process generating products with a particular tag that prevents them from leaving the cell nucleus. In this way, the polymerase effectively ‘occupies’ the neighbouring genes, preventing them from being read normally. Moreover, the promoter of the correct gene not only serves as the starting point for normal transcription, but also drives an RNA polymerase in the opposite direction. This too prevents normal transcripts from being produced from the genes on that side. The polymerase thus acts as a kind of roadblock.
Duplication
From RNA sequencing data published elsewhere, the American researchers conclude that honeybees (Apis mellifera) and Harpegnathos saltator ants also use this gene-regulation mechanism; other (social) insects presumably do so as well. This mechanism may also explain how odour receptor genes were able to duplicate without difficulty during evolution, giving rise to new receptors. In this way, the olfactory repertoire of ants could expand rapidly.