THE MOUSE FORMIN (FMN) GENE - ABUNDANT CIRCULAR RNA TRANSCRIPTS AND GENE-TARGETED DELETION ANALYSIS

Background: Mutations in the mouse formin (Fmn) gene result in limb de formities and incompletely penetrant renal aplasia. A molecular geneti c approach was taken to characterize novel circular RNAs from the Fmn gene and to understand the developmental effects of gene-targeted muta tions. Materials and Methods: RT-PCR and ribonuclease protection analy ses were done to characterize the circular RNA transcripts arising fro m the Fmn gene. Two lines of mice with gene-targeted deletions of spec ific Ann exons, namely exon 4 or exon 5, were generated and analyzed. Results: In our analysis of formin cDNAs, we discovered a class of tra nscripts in which the exon order is reversed such that downstream exon s are joined to the acceptor end of a specific exon that lies 5' to th em in the genome. RT-PCR and ribonuclease protection analyses indicate that these transcripts are circular and are the major transcripts ari sing from this locus in adult brain and kidney. To gain insight into t he biological function of these transcripts, we have systematically de leted the relevant exons using gene-targeted homologous recombination. The resulting mice fail to produce circular transcripts, but appear t o produce normal amounts of the linear RNA isoforms hom this locus. Wh ile these deficient mice have normal limbs, they display variably pene trant renal aplasia characteristic of other mutant formin alleles. Con clusions: Our results demonstrate novel circular transcripts arising f rom the Fmn gene. Moreover, their high levels oi expression suggest th at they are not products of aberrant splicing events, but instead, map play important biological roles. Mice with gene-targeted deletions of Fmn exons 4 or 5 lack these circular transcripts and have an incomple tely penetrant renal agenesis phenotype. While the biologic function o f circular Fmn RNA transcripts is not entirely known, our work suggest s their possible involvement in kidney development.