Genomic organization of zebrafish grn1, grn2 and their complementary antisense gene. Zebrafish grn1 and grn2 genes are found in tandem in a head-to-tail orientation and share an identical exonic organization (exons 1–5, orange and blue boxes, respectively), but differ in their respective intron lengths (A, C, D). The spliced and polyadenylated non-protein coding ASgrn1-2 is encoded on four exons (pink boxes) and shares exon/intron complementarity to both grn1 and grn2 (see text for details). Shown on top is a schematic representation of the chimeric progranulin transcript, suggesting trans-splicing as a mechanism for its generation. Bars (-) above or below exons indicate the relative position of primer pairs (grn1+2 forward and reverse; ASgrn1-2 forward and reverse) used for discriminating between ASgrn1-2 and combined grn1/grn2 expression using RT-PCR.