Molecular cloning, characterization, cellular localization, and possible function of a novel CUB-serine protease in the olfactory organ of the spiny lobster Panulirus argus

A novel gene encoding a protein product with high homology to trypsin-like serine protease and CUB was identified from a spiny lobster Panulirus argus olfactory cDNA library. 5′ and 3 ′ RACE showed that its full-length transcript is 1801 bp, encoding a 50.251 kD protein with three domains: a signal peptide, a CUB domain (named after C&barbelow;omplement subcomponents Clr/Cls, U&barbelow;egf, B&barbelow;one morphogenic protein (1), and a trypsin-like serine protease domain. RT-PCR, Northern blots and Western blot showed that this gene is predominantly expressed in antennular lateral flagella and eyes, but not in other organs (brain, antennular medial flagella, abdominal muscle, hepatopancreas, intestine, and legs); there may be trace amount of the expression in second antennae and dactyl tips. Immunocytochemistry showed that in the lateral flagellum, CSP is present in and around the auxiliary (glial) cells that envelope the inner dendritic segments of mature aesthetasc olfactory receptor neurons (ORNs) and around the entire length of the outer dendritic segments. This suggests that CSP is expressed by aesthetasc auxiliary cells and secreted into the lumen of the aesthetascs. CSP is expressed in all molt stages and in auxiliary cells associated with ORNs at all developmental ages; however, the precise pattern of expression appears to differ somewhat with molt stage. In the eye, CSP also appears to be expressed in glial cells, but mostly in glia surrounding axonal tracts that connect neuropils in the eye. I propose that in P. argus, the CSP gene encodes a protein that is expressed in and secreted by glial cells in peripheral sensory organs, associates with cell membranes or extracellular matrix via the CUB domain, and has trypsin-like activity that may function in (i) perireception (activation or inactivation of odorant stimuli); (ii) maintenance and regulation of the dendritic growth and functions of mature ORNs; (iii) molting of the olfactory system of the spiny lobster. It may also function in the maintenance of the function of mature sensory neurons in the eye. To our knowledge, this is the first report of a gene encoding a protein with serine protease and CUB domains in any olfactory system.