We previously reported the nucleotide sequences and diversity of mytimycin (MytM) from the Mediterranean
mussel, Mytilus galloprovincialis. Using real-time PCR (q-PCR), we observed that the MytM gene
was mainly expressed in circulating hemocytes and to a less extent in the mantle. In vivo challenge with
bacteria or with the yeast, Candida albicans, did not increase the expression as measured by q-PCR in
hemocytes. By contrast, injection of the filamentous fungus, Fusarium oxysporum, induced a sudden and
strong increase of expression at 9h p.i. (stimulation index of 25.7 +- 2.1). Optimum stimulating dose was
104 spores of F. oxysporum per mussel. In the same samples, AMP mytilin and myticin showed no
stimulation. Consequently, we hypothesized the existence of 2 different signal transduction pathways,
one activated by bacteria and yeast, the other triggered by filamentous fungi. A second challenge performed
with F. oxysporum 24 h after the first challenge induced an increase of MytM gene expression
(stimulation index of 3.5 +- 1.7). However, this second increase was significantly lower than the first,
suggesting less efficient response rather than significant protection
