Chemosensory proteins (CSPs) are ubiquitous soluble small proteins isolated from sensory organs thought to be involved in chemical communication. Here we report the first cDNA of CSPs, called Ac-ASP3, cloned and characterized from antennas of adult worker bees in Chinese honeybee, Apis cerana cerana. The Ac-ASP3 cDNA comprises 2 exons, with an ORF of 393-bp encoding 130 aa. Protein signature analyses show that the protein consists of four conserved cysteines and a signal peptide with 19 aa in the N-terminal sequence. The deduced protein sequence shares high homology with Am-ASP3 of Apis mellifera and low similarity with other species of insects. Immunocytochemical localization shows that Ac-ASP3 is only specifically expressed on the antenna contact chemosensilla such as sensilla trichodea B and sensilla basiconica, whereas Ac-ASP3 is scarcely expressed on olfactory chemosensilla such as sensilla placodea. Real-time PCR of Ac-ASP3 transcripts shows that Ac-ASP3 is highly expressed on wings and legs, but expression is lower on antenna. Temporal expression patterns suggest that Ac-ASP3 is expressed during the period of pupa and adults from 1-d to 6-d stages when bees act as house bees, cleaning the comb and taking care of the queen and larvae in comb. The above evidence suggests that Ac-ASP3 is unique in species and is generally not involved in olfaction during searching for honey and pollen. Rather, the protein seems to function in recognition of chemosensory substances on bees' cuticle and mechanical movement of antenna.
