RACE using only a gene-specific primer: application of a template-switching model

MdACO expression during abscission: the use of 33P labeled primers in transcript quantitation

The last step of ethylene biosynthesis in apple is catalyzed by ACO (1-aminocyclopropane 1-carboxylic acid oxidase) encoded by MdACO1 and MdACO2. Both genes were expressed during early fruit development although at different level. Later on, the ACO transcript accumulation in persisting fruitlets decreased whereas in fruitlets undergoing abscission MdACO2 transcripts remained constant and those of MdACO1dramatically increased. The expression of MdACO was assessed by a particular type of semi-quantitative PCR involving 33P labeled primers and the following electrophoresis in polyacrylamide gel. The use of either the reverse primer or the anchored oligo dT13 produced clear and elegant results. Nevertheless, the initial quantity of labeled primer appeared to be a crucial factor for obtaining a wide range titration curve.

Genomic organization of the mouse Msh4 gene producing bicistronic, chimeric and antisense mRNA

By degenerate PCR and screening of mouse testis cDNA library, we have identified seven cDNAs from the meiotic recombination gene Msh4. Variant alpha and probably beta are likely involved in meiotic DNA recombination. Other variants have distinctive structures; variant epsilon, theta; and iota form a bicistronic operon, while variant delta contains antisense RNA for the endoplasmic reticulum (ER) chaperon Hspa5 gene and small open reading frame (ORF) identical to epsilon ORF2. Analysis of the exon-intron structures revealed unusual genomic organizations: the first three exons of delta and the first exon of epsilon are respectively mapped to the Hspa5 locus on chromosome 2 and the Pcbp3 locus on chromosome 10; the remaining exons of both variants are mapped to the Msh4 locus on chromosome 3. The first exon of variant beta is located on chromosome 16, while the others are located on chromosome 3. Synthesis of these mRNAs is assumed to require interchromosomal trans-splicing alone (beta and epsilon) or in combination with converse-splicing (delta). Most Msh4 variant mRNAs are mainly expressed in testis, but a small amount of each variant except for epsilon is also expressed in brain, heart, thymus, ovary and embryonic head. Enhanced green fluorescent protein (EGFP) fusion experiments showed that all the ORFs are translated, and most of those proteins are localized to a particular subcellular compartment. It also appeared that expression of variant delta induces cell death. This study suggests that the dynamic interchromosomal (intergenic) trans-splicing generates functional diversity of the mouse Msh4 gene.