Control of the ecdysteroid level plays a crucial role in density-dependent metamorphosis in the giant mealworm beetle Zophobas atratus.

Metamorphic transition in some tenebrionid beetles is dependent on population density. This phenomenon is useful for pupae that are vulnerable to cannibalism. The physiological mechanism of this adaptive developmental phenomenon remains unclear. In Zophobas atratus, which show density-dependent metamorphosis, larval isolation can induce metamorphosis. We herein demonstrated that the return of isolated larvae to a crowded condition (re-crowding) inhibited their metamorphosis. The timing of metamorphic initiation was slightly extended according to the duration of re-crowding experienced by the isolated larvae. Therefore, the re-crowding induced physiological changes needed for metamorphic inhibition. We investigated whether hormone-related genes involved in signaling of metamorphic inhibitor (juvenile hormone, JH) and molting hormone (ecdysteroid) responded to the re-crowding. An expression analysis showed that gene expression of ecdysteroid signaling was maintained at low levels under the re-crowded condition. Actually, ecdysteroid levels decreased responding to re-crowding. Ecdysteroid injections induced metamorphosis in re-crowded larvae. In contrast, the JH signaling gene showed little fluctuation in both isolated and re-crowded conditions, and knockdown of JH signaling factors did not affect inhibition of metamorphosis under the re-crowded condition. The present study suggests that regulation of ecdysteroid level rather than JH is more crucial in the density dependent metamorphosis in Z. atratus.

The Mitochondrial Phosphatase PTPMT1 is Required for the Proper Growth Rate in the Red Flour Beetle, Tribolium castaneum.

Protein tyrosine phosphatase, mitochondrial 1 (PTPMT1) is a mitochondrial phosphatase that is highly conserved in animals. Functional analyses using knockout animals have revealed a variety of physiological roles of PTPMT1 in vertebrates and insects. However, because of the high lethality of knockout in these animals, the roles of PTPMT1 in the later postembryonic development remain relatively obscure. In the present study, using the RNA interference technique, we analyzed PTPMT1 functions in later larval stages of the red flour beetle, Tribolium castaneum. PTPMT1 was expressed in both anterior and posterior parts of the body constitutively without obvious fluctuations from the middle larval instar through pupation. The PTPMT1-knockdown larvae injected with PTPMT1 double-stranded RNA at the middle instar showed a prolonged larval period, which was mainly caused by an extra larval molt. On the other hand, the increase in adult body length was subtle in the PTPMT1-knockdown T. castaneum, and the head capsule width was smaller than that of the control animals at the same larval instar. The expression levels of genes encoded by the mitochondrial genome were reduced in PTPMT1-knockdown larvae, indicating that PTPMT1 plays an important role in mitochondrial function in T. castaneum, like in other species. By contrast, the expression levels of a juvenile hormone (JH)-biosynthetic gene and a JH-signaling gene were rather increased in the PTPMT1-knockdown larvae, which may have been caused indirectly by the reduction of larval growth rate. Altogether, these findings indicate that PTPMT1 is required for the proper growth rate via some mitochondrial physiological role in T. castaneum larvae.

A mitochondrial phosphatase PTPMT1 is essential for the early development of silkworm, Bombyx mori.

Juvenile hormone (JH) plays important roles in the control of many biological processes in insects, such as development, reproduction, and polyphenism. JH is primarily produced in the corpora allata (CA) by specific JH biosynthetic enzymes under strict temporal regulation. In a previous study, we identified a novel putative JH biosynthetic gene, protein tyrosine phosphatase, mitochondrial 1 (PTPMT1), from silkworm, Bombyx mori, whose expression is nearly exclusive in the CA and is correlated with JH synthetic activities during late larval development. In this study, to reveal the function of PTPMT1 in vivo, we generated PTPMT1 knockout silkworms using TALEN. In the knockout mutants, no signs indicating defects in JH activity were observed. Instead, PTPMT1 knockout silkworms showed embryonic lethality, developmental arrest, and 3rd-instar lethality not only in mutants lacking total enzymatic activity but also in mutants lacking mitochondrial translocation signals. Moreover, in PTPMT1 knockout embryos, the expression of two genes encoded by the mitochondrial genome, CYTB and ND3, was decreased, indicating a mitochondrial disorder. These results suggested that PTPMT1 plays conserved vital role(s) reported in vertebrates in insect mitochondria.