Gene expression and specificity in the mature zone of the lobster olfactory organ.

The lobster olfactory organ is an important model for investigating many aspects of the olfactory system. To facilitate study of the molecular basis of olfaction in lobsters, we made a subtracted cDNA library from the mature zone of the olfactory organ of Homarus americanus, the American lobster. Sequencing of the 5'-end of 5,184 cDNA clones produced 2,389 distinct high-quality sequences consisting of 1,944 singlets and 445 contigs. Matches to known sequences corresponded with the types of cells present in the olfactory organ, including specific markers of olfactory sensory neurons, auxiliary cells, secretory cells of the aesthetasc tegumental gland, and epithelial cells. The wealth of neuronal mRNAs represented among the sequences reflected the preponderance of neurons in the tissue. The sequences identified candidate genes responsible for known functions and suggested new functions not previously recognized in the olfactory organ. A cDNA microarray was designed and tested by assessing mRNA abundance differences between two of the lobster's major chemosensory structures: the mature zone of the olfactory organ and the dactyl of the walking legs, a taste organ. The 115 differences detected again emphasized the abundance of neurons in the olfactory organ, especially a cluster of mRNAs encoding cytoskeletal-associated proteins and cell adhesion molecules such as 14-3-3zeta, actins, tubulins, trophinin, Fax, Yel077cp, suppressor of profilin 2, and gelsolin.

Primary culture of lobster (Homarus americanus) olfactory sensory neurons.

Lobster olfactory sensory neurons have contributed to a number of advances in our understanding of olfactory physiology. To facilitate further study of their function, we have developed conditions allowing primary culture of the olfactory sensory neurons in a defined medium. The most common cells in the culture were round cell bodies with diameters of 10-15 micro m that often extended fine processes, features resembling olfactory sensory neurons. We discovered that acetylcholinesterase acted as a growth factor for these cells, improving their survival in culture. We also confirmed previous evidence from spiny lobsters that poly-D-lysine was a superior substrate for olfactory cells of this size and morphology. We then identified olfactory sensory neurons in the culture in two ways. Almost half the cells tested responded to application of a complex odorant with an inward current. An even more rigorous test was made possible by the development of an antiserum to OET-07, an ionotropic glutamate receptor homolog specifically expressed by Homarus americanus olfactory sensory neurons. It labeled a majority of the round cells in the culture, unequivocally identifying them as olfactory sensory neurons.