Differentiation in an Olfactory Cell Line: Analysis via Differential Display

Abstract

The olfactory epithelium is a unique system, in which new neurons are continually generated throughout adult life. Olfactory neurons are derived from stem cells that lie adjacent to the basal lamina of the olfactory epithelium; these stem cells divide several times and their progeny differentiate into mature sensory neurons. In our laboratory immortalized cell lines have been derived from these dividing cells. The morphology of these cell lines and their expression of neuronal markers varies with culture conditions. When grown in low serum medium one of these cells lines, OLF 442, differentiates by extending long neurites and increasing its expression of neurofilament and B50/GAP43 proteins at the same time reducing expression of glial fibrillary acidic protein (GFAP). Identification of differentially expressed mRNA in cell lines has previously relied on both screening for known markers, and the use of subtractive techniques for identification of unique mRNA species. The differential display technique allows simultaneous detection of differentially expressed mRNA at different time periods and growth conditions. A modified Liang and Pardee differential display technique was used to screen OLF 442 over a number of time intervals in serum-depleted media, and compared with OLF 442 grown in complete media. The differentially displayed fragments were cloned and sequenced, leading to the identification of a number of sequences, both known and unknown. The known sequences include SPARC (encoding a Ca2+ binding secreted Protein which is Acidic and Rich in Cysteine), which is reported to function as a modulator of the cell matrix, and RHAMM, the receptor for hyaluronan-mediated motility. Both the known and the unknown sequences are being studied further to provide insight into the differentiation of olfactory neurons.