Cloning and characterization of a novel variant (mM-rdgBβ1) of mouse M-rdgBs, mammalian homologs of Drosophila retinal degeneration B gene proteins, and its mRNA localization in mouse brain in comparison with other M-rdgBs

We report the cloning, characterization and localization in the brain of a novel isoform termed mM-rdgBβ1 (mouse type of mammalian retinal degeneration Bβ1 protein) in comparison with the localization of three known mammalian homologs (M-rdgBβ, M-rdgB1, M-rdgB2). mM-rdgBβ1 cDNA contains a sequence of 119 bp as a form of insertion in the open reading frame of the known mM-rdgBβ, and encodes a protein of 269 amino acids with a calculated molecular mass of 31.7 kDa, different from the molecular mass of 38.3 kDa of mM-rdgBβ. It also contains a phosphatidylinositol transfer protein (PITP)-like domain similar to the known three homologs, as well as D-rdgB. The recombinant mM-rdgBβ1 protein shows the specific binding activity to phosphatidylinositol but not to other phospholipids. This novel molecule is localized not only in the cytoplasm but also in the nucleus, different from the cytoplasmic localization of mM-rdgBβ. In in situ hybridization analysis, the gene expression for mM-rdgBβ1 in the brain, though weak, is rather confined to the embryonic stage, different from wider expression of mM-rdgBβ in the gray matters of pre- and post-natal brains. Taken together, mM-rdgBβ1 is suggested to play a role in the phosphoinositide-mediated signaling in the neural development.