Before revision: Each mammalian olfactory sensory neuron stochastically expresses only one out of  thousands of olfactory receptor alleles and the molecular mechanism for this selection remains as one of the biggest puzzles in neurobiology. Through constructing and analyzing a mathematical model based on extensive experimental observations , we identified an evolutionarily optimized three-layer regulation mechanism that robustly generates single-allele expression.
After revision: Each mammalian olfactory sensory neuron stochastically expresses only one out of thousands of olfactory receptor (OR) gene alleles; URLanism level the types of expressed ORs need to be maximized. Existing models focus only on monoallele activation, and cannot explain recent observations in mutants, especially the reduced global diversity of expressed ORs in G9a/GLP knockouts. In this work we integrated existing information on OR expression, and proposed an evolutionarily optimized three-layer regulation mechanism that robustly generates single-allele expression.