Characterisation and quantification of earthworm cyclophilins: identification of invariant and heavy metal responsive isoforms.

We report the identification of two earthworm cyclophilin genes, which resemble the cytosolic cyclophilin-A and the signal sequence containing cyclophilin-B. Using fully quantitative PCR we were able to assess the transcript regulation of both cyclophilin isoforms, as well as a further independent control gene (actin), during exposure to heavy metals. Whilst the expression of cyclophilin-B and actin remained exceptionally constant, cyclophilin-A was up-regulated 38-fold. This intriguing observation has profound implications regarding cyclophilin's use as an invariant control and highlights the fact that it is essential to treat cyclophilin isoforms as separate entities, rather than one functional unit.