Protein kinase C is involved with upstream signaling of methyl farnesoate for photoperiod-dependent sex determination in the water flea Daphnia pulex

Abstract

Sex determination of Daphnia pulex is decided by environmental conditions. We established a suitable experimental system for this study using D. pulex WTN6 strain, in which the sex of the offspring can be controlled by photoperiod. Long-day conditions induced females and short-day conditions induced males. Using this system, we previously found that methy farnesoate (MF), which is a putative innate juvenile hormone molecule in daphnids, is necessary for male sex determination and that protein kinase C (PKC) is a candidate factor of male sex determiner. In this study, we demonstrated that a PKC inhibitor (bisindolylmaleimide IV: BIM) strongly suppressed male offspring induction in the short-day condition. Moreover, co-treatment of BIM with MF revealed that PKC signalling acts up-stream of the MF signalling for male sex determination. This is the first experimental evidence that PKC is involved in the male sex determination process.