HSP90 regulates larval settlement of the bryozoan Bugula neritina through NO pathway

Abstract

The larvae of many sessile marine invertebrates go through a settlement process, during which the planktonic larvae attach to a substrate and metamorphose into sessile juveniles. Larval attachment and metamorphosis (herein defined as “settlement”) are complex processes mediated by many signaling pathways. Nitric oxide (NO) signaling is one of the pathways that inhibits larval settlement in marine invertebrates across different phyla. NO is synthesized by NO synthase (NOS), which is a client of molecular chaperon heat shock protein 90 (HSP90). In the present study, we provide evidence that NO, a gaseous messenger, regulates larval settlement of B. neritina. By using pharmacological bioassays and western blotting, we demonstrated that NO inhibits larval settlement of B. neritina and that NO signals occur mainly in the sensory organ of swimming larvae. The settlement rate of B. neritina larvae decreased after heat shock treatment. Inhibition of HSP90 induced larval settlement, and attenuated the inhibition of NO donors during larval settlement. In addition, the expression level of both HSP90 and NOS declined upon settlement. These results demonstrate that HSP90 regulates the larval settlement of B. neritina by interacting with the NO pathway.