Fig. 1

Alternative splicing of SSPN generates μSPN and nSPN. a A schematic representation of the genomic organization of the SSPN gene on human chromosome 12p11.2. Exons are depicted as solid boxes and are color-coded. Exon 1 (red), exon 2 (yellow), exon 3 (blue), exon 4 (green), and the introns (black lines) are depicted. The approximate size of each intron is indicated (kb). The mRNA splicing patterns generating SSPN, μSPN, and nSPN are also shown. b Predicted membrane topologies for SSPN, μSPN, and nSPN are illustrated in three separate schematic diagrams. Each polypeptide region is color-coded according to its corresponding exon. SSPN possesses four transmembrane domains (TM1 to TM4), a small extracellular loop (SEL), and a large extracellular loop (LEL). μSPN contains two transmembrane domains (TM1 and TM2). N- and C-termini of μSPN are strongly predicted to be intracellular using topology algorithms. nSPN retains the first transmembrane domain of SSPN (TM1) and is predicted to have an extracellular C-terminus. The predicted molecular weight of each SSPN-related protein is indicated. c The primary and deduced amino acid sequence of human nSPN is shown in single-letter code. Each exon and its deduced amino acid sequence are color-coded as follows: exon 1 (red) and exon 4 (green). The open reading frame of nSPN encodes a polypeptide of 99 amino acids. The predicted transmembrane domain (TM1) is underlined. The 12-amino-acid region used as an antigen for polyclonal antibody (Rabbit 20) production is double-underlined. Arrows indicate forward and reverse primers, summarized in Table 1, used in RT-PCR analysis (Additional file 1: Figure S1). The asterisk represents the predicted stop codon