Prothoracicotropic Hormone Acts as a Neuroendocrine Switch between Pupal Diapause and Adult Development

Akira Mizoguchi,Shintaro Ohsumi,Yoshinori Fujimoto,Katuji Kobayashi,Ken Tateishi,Nobuto Yamada,Hiroshi Kataoka,Naoki Okamoto,Guy Smagghe

doi:10.1371/journal.pone.0060824

Abstract

Diapause is a programmed developmental arrest that has evolved in a wide variety of organisms and allows them survive unfavorable seasons. This developmental state is particularly common in insects. Based on circumstantial evidence, pupal diapause has been hypothesized to result from a cessation of prothoracicotropic hormone (PTTH) secretion from the brain. Here, we provide direct evidence for this classical hypothesis by determining both the PTTH titer in the hemolymph and the PTTH content in the brain of diapause pupae in the cabbage army moth Mamestra brassicae. For this purpose, we cloned the PTTH gene, produced PTTH-specific antibodies, and developed a highly sensitive immunoassay for PTTH. While the hemolymph PTTH titer in non-diapause pupae was maintained at high levels after pupation, the titer in diapause pupae dropped to an undetectable level. In contrast, the PTTH content of the post-pupation brain was higher in diapause animals than in non-diapause animals. These results clearly demonstrate that diapause pupae have sufficient PTTH in their brain, but they do not release it into the hemolymph. Injecting PTTH into diapause pupae immediately after pupation induced adult development, showing that a lack of PTTH is a necessary and sufficient condition for inducing pupal diapause. Most interestingly, in diapause-destined larvae, lower hemolymph titers of PTTH and reduced PTTH gene expression were observed for 4 and 2 days, respectively, prior to pupation. This discovery demonstrates that the diapause program is already manifested in the PTTH neurons as early as the mid final instar stage.

Highlights

Diapause is a programmed developmental arrest accompanied by markedly reduced metabolic activity that enables organisms to survive adverse seasons and/or to synchronize their reproductive timing [1,2,3]
The endocrine mechanism of insect diapause bas been most extensively studied for pupal diapause since the mid 20th century, when Carroll Williams proposed that a temporary failure of the secretion of a ‘‘brain hormone’’, which was primarily described by Stefan Kopecin 1922 [4] and is known as the first discovered neurosecretory hormone, and the resulting inactivation of the prothoracic glands (PGs), which secrete the molting hormone needed for pupa-adult development, leads to pupal diapause
Many studies have demonstrated very low ecdysteroid titers in the hemolymph of diapausing pupae [8,9,10] and the induction of adult development by the injection of ecdysteroid into the diapausing pupae [11,12,13]. These experiments establish that the shutdown of ecdysteroid secretion is critical for the initiation and maintenance of pupal diapause. It remains unclear how prothoracicotropic hormone (PTTH) is involved in the regulation of diapause, most researchers believe that the shutdown of PTTH secretion after pupal ecdysis results in PG inactivation

Summary

Introduction

Diapause is a programmed developmental arrest accompanied by markedly reduced metabolic activity that enables organisms to survive adverse seasons and/or to synchronize their reproductive timing [1,2,3]. The endocrine mechanism of insect diapause bas been most extensively studied for pupal diapause since the mid 20th century, when Carroll Williams proposed that a temporary failure of the secretion of a ‘‘brain hormone’’, which was primarily described by Stefan Kopecin 1922 [4] and is known as the first discovered neurosecretory hormone, and the resulting inactivation of the prothoracic glands (PGs), which secrete the molting hormone needed for pupa-adult development, leads to pupal diapause. This hypothesis was based on his elegant tissue ablation/ implantation experiments with diapausing pupae of the giant silk moth Hyalophora cecropia [5,6,7]. It remains unclear how PTTH is involved in the regulation of diapause, most researchers believe that the shutdown of PTTH secretion after pupal ecdysis results in PG inactivation

Methods

Results

Conclusion