Serotonin receptor B may lock the gate of PTTH release/synthesis in the Chinese silk moth, Antheraea pernyi; a diapause initiation/maintenance mechanism?

Qiushi Wang,Ahmed A M Mohamed,Makio Takeda

doi:10.1371/journal.pone.0079381

Abstract

The release of prothoracicotropic hormone, PTTH, or its blockade is the major endocrine switch regulating the developmental channel either to metamorphosis or to pupal diapause in the Chinese silk moth, Antheraea pernyi. We have cloned cDNAs encoding two types of serotonin receptors (5HTRA and B). 5HTRA-, and 5HTRB-like immunohistochemical reactivities (-ir) were colocalized with PTTH-ir in two pairs of neurosecretory cells at the dorsolateral region of the protocerebrum (DL). Therefore, the causal involvement of these receptors was suspected in PTTH release/synthesis. The level of mRNA5HTRB responded to 10 cycles of long-day activation, falling to 40% of the original level before activation, while that of 5HTRA was not affected by long-day activation. Under LD 16:8 and 12:12, the injection of dsRNA5HTRB resulted in early diapause termination, whereas that of dsRNA5HTRA did not affect the rate of diapause termination. The injection of dsRNA5HTRB induced PTTH accumulation, indicating that 5HTRB binding suppresses PTTH synthesis also. This conclusion was supported pharmacologically; the injection of luzindole, a melatonin receptor antagonist, plus 5th inhibited photoperiodic activation under LD 16:8, while that of 5,7-DHT, induced emergence in a dose dependent fashion under LD 12:12. The results suggest that 5HTRB may lock the PTTH release/synthesis, maintaining diapause. This could also work as diapause induction mechanism.

Highlights

Many living organisms can monitor day or night length to adjust their behavior, metabolism, physiology and developmental course to maximally adapt for an adverse or favorable season
The results suggest that the indolamine metabolic pathway may mediate circadian output pathway to prothoracicotropic hormone (PTTH) release
This study focused on the roles of 5HTRs in photoperiodism that regulates pupal diapause in A. pernyi. 5HTRs have been investigated in many insects, including Drosophila melanogaster [28], Apis mellifera [29], two crickets (Dianemobius. nigrofasciatus and Allonemobius. allardi) [25] and M. sexta [8]

Summary

Introduction

Many living organisms can monitor day or night length to adjust their behavior, metabolism, physiology and developmental course to maximally adapt for an adverse or favorable season. This is called photoperiodism, which remains as a biological mystery, at least at the molecular level. This system is complex, consisting of several functional subunits; a photoreceptor, a clock/timer, a summation mechanism counting effective photoperiodic cycles and an endocrine switch. It is important to understand the photoperiodic mechanism and its effects on the seasonal demography of pest insects from the pest management point of view, as well as scientific curiosity. The molecular mechanism still remains obscure and dispute over the mode of photoperiodic time measurement continues; hourglass timer vs. circadian clock [3,4]

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Discussion

Conclusion