Analysis of multiple Invs transcripts in mouse and MDCK cells.

Infantile nephronophthisis is associated with cystic kidneys, situs inversus, and INVS mutations. The function of the INVS product, inversin, is unknown but evidence suggests there are multiple inversin isoforms with differing molecular weights, cellular localization patterns, and binding partners. We used Northern blots, RT-PCR, and sequence analysis to identify alternative INVS transcripts. Northern blots probed with Invs cDNA detected four bands in normal mouse kidney. RT-PCR of mouse kidney RNA revealed Invs transcripts with skipping of exon 5, 11, or 13. We sequenced canine (MDCK-II cells) INVS and determined that the corresponding full-length protein shares identity with mouse (74%) and human (84%) inversin. Canine INVS produces a transcript that skips exon 12. Exon skips cause loss of inversin protein motifs, including ankyrin repeats, IQ domains, destruction boxes, and nuclear localization signals. Identification of INVS splice variants will help us determine which inversin protein motifs contribute to left-right asymmetry and kidney development.