EXPRESSION OF A NOVEL MURINE PHOSPHOLIPASE-D HOMOLOG COINCIDES WITH LATE NEURONAL DEVELOPMENT IN THE FOREBRAIN

Members of the phospholipase D (PLD) superfamily are defined by the co nserved HXKXXXXD motif, which is essential for the catalytic function of mammalian-PLD. PLD enzymes are thought to play roles in signal tran sduction and membrane vesicular trafficking in mammalian cells. Here w e describe a 54-kDa novel murine polypeptide (designated SAM-9) that i s predicted to be a membrane-associated member of the PLD superfamily. SAM-9 shares 40, 30, and 29% amino acid identity with potential ortho logs, in vaccinia virus, Caenorhabditis elegans, and Dictyostelium dis coideum, respectively, and belongs to a subclass of PLD homologs in wh ich the second HXKXXXXD motif is imperfect and harbors a conserved Asp to Glu substitution. The san-g gene has more than eight exons, and th e two HXhXXXXD motifs are encoded by two highly conserved exons. The e xpression of the sam-g gene is greater in the brain than in non-nervou s tissue and appears to be predominantly of neuronal origin. sam-g exp ression is pronounced in mature neurons of the forebrain and appears t o be turned on at late stages of neurogenesis as revealed by in situ h ybridization analysis of sam-9 expression during postnatal development of the hippocampal formation and the primary somatosensory cortex.