Expression of SNMP-1 in olfactory neurons and sensilla of male and female antennae of the silkmoth Antheraea polyphemus

SNMP-1 (sensory neuron membrane protein 1) is an olfactory-specific membran e-bound protein which is homologous with the CD36 receptor family. Previous light level immunocytochemical studies suggested that SNMP-1 was localized in the dendrites and distal cell body of sex-pheromone-specific olfactory receptor neurons (ORN); these studies further suggested SNMP-1 was expresse d in only one of two to three neurons in male-specific pheromone-sensitive trichoid sensilla. To better understand the expression and localization of SNMP-1, an immunocytochemical study was performed using electron microscopy to visualize the distribution of SNMP-1 among the neurons of several class es of olfactory sensilla of both male and female antennae of the silkmoth A ntheraea polyphemus. SNMP-1 antigenicity was primarily restricted to the re ceptive dendritic membranes of ORNs of all sensilla types examined and was observed in cytosolic granules, but not plasma membranes, of the cell some. Mean labeling densities ranged from 1 to 16 gold particles per micrometer of dendrite circumference; dendrites of trichoid and intermediate sensilla showed significantly higher labeling densities than those of basiconic sens illa. Larger dendrites of trichoid sensilla showed significantly higher mea n labeling densities (13-16/mum) than smaller diameter dendrites (3-7/mum). Immunofluorescence stud ies using baculovirus expressed SNMP-1 and multiph oton photon laser scanning microscopy (MPLSM) indicated that rSNMP-1, which was post-translationally processed to the in vivo molecular weight, was in serted into the plasma membrane in a topography presenting extracellular ep itopes. These studies suggest SNMP-1 is a common feature of the ORNs, is as ymmetrically expressed among functionally distinct neurons, and possesses a topography which permits interaction with components of the extracellular sensillum lymph.