olfactory system of Drosophila and has a known physiological role. Obp76a, better known as LUSH, is located trichoid sensilla and is necessary for normal response of the odor receptor Or67d to its pheromone ligand cis-vaccenyl acetate (cVA), although responses of Or67d to cVA have been detected in the absence of Obp76a LUSH has also been found to bind cVA in vitro and is known to bind other insect pheromones, short-chain alcohols, and phthalates. In 2016, Larter et al. found that the deletion of the sole abundant OBP, Obp28a, in ab8 sensilla of Drosophila does not reduce the magnitude of their olfactory responses, suggesting that Obp28a is not required for odorant transport and that ab8 sensilla do not require an abundant OBP. Their results further suggest Obp28a may be buffering changes in the odor environment, possibly as molecular gain control, which has not been previously reported for OBPs. OBPs are thought to have multiple roles besides olfaction, including reproduction, egg laying and antiinflammatory responses. Expression OBPs are numerous and diverse. In Drosophila, they are encoded by 52 genes of the same family yet only share 20% amino acid similarity between themselves. Some are encoded by the most abundant mRNAs of the antennae. Within and between species, OBPs are expressed in several different tissues, including the antennal sensilla, the taste system, and chemosensory organs. They are also known to be ectopically expressed in tissues such as the gut. Genomic analysis of Drosophila and other insect species (Anopheles gambiae, Apis mellifera, Bombyx mori, and Triboliumcastaneum) has revealed that the OBP genes significantly differ between species. The OBP family contains 21 (in A. mellifera) to 66 genes (in A. gambiae), whereas it ranges from 52 members in Drosophila to 20 in T. castaneum. Generally these genes are irregularly scattered across the genome. Most (69% of the OBP genes in Drosophila) are arranged in small clusters from 2 to 6 OBP genes. The Drosophila OBP gene family has been classified into several subfamilies based on structural features, functional information, and phylogenetic relationships: the Classic, Minus-C, Plus-C, Dimer, PBP/GOBP, ABPI and ABPII, CRLBP, and D7 subfamilies. These subfamilies are unequally distributed across arthropods, even among the dipterans and are totally absent in some species. See also Insect pheromone-binding protein Odorant Olfactory receptor Olfactory receptor neuron References Olfactory system Lipocalins