Rhombex-29, a novel gene of the PLP/DM20-M6 family cloned from rat medullaoblongata by differential display

The ventral medullary surface (VMS) is known as the site of the central che mosensitive neurons. These neurons sense excess CO2/H+ dissolved in the cer ebrospinal fluid that superfuses the VMS and induce hyperventilation. We hy pothesized that genes specific for hyperventilation are expressed much more highly in VMS neurons than in extra-VMS neurons in other parts of the cent ral nervous system (CNS). Applying the differential display technique to th e brain of adult rats, we differentiated the mRNAs of the VMS neurons from those of cerebral cortex neurons. Seventeen candidate clones were selected, and their sequences were analyzed. Among these 17 clones, one encodes a no vel four-transmembrane protein, which we named rat Rhombex-29. Structural a nalysis and the phylogenic tree showed that rat Rhombex-29 is homologous to the major CNS myelin protein PLP/DM20-M6 family and belongs to the interme diate type between mouse M6b and shark DM gamma. As the embryos grew into a dult rats, constant expression of rat Rhombex-29 mRNA was found in the brai n. Hypercapnic stimulation increased expression of rat Rhombex-29 mRNA in t he VMS neurons but not in the cerebral cortex neurons. These results indica te that the VMS neurons are endowed with a novel gene, rat Rhombex-29, that is sensitive to H+. (C) 2000 Wiley-Liss, Inc.