The hormonal pathway controlling cell death during metamorphosis in a hemimetabolous insect

AbstractMetamorphosis in holometabolous insects is mainly based on the destruction of larval tissues. Intensive research in Drosophila melanogaster, a model of holometabolan metamorphosis, has shown that the steroid hormone 20-hydroxyecdysone (20E) signals cell death of larval tissues during metamorphosis. However, D. melanogaster shows a highly derived type of development and the mechanisms regulating apoptosis may not be representative in the insect class context. Unfortunately, no functional studies have been carried out to address whether the mechanisms controlling cell death are present in more basal hemimetabolous species. To address this, we have analyzed the apoptosis of the prothoracic gland of the cockroach Blattella germanica, which undergoes stage-specific degeneration just after the imaginal molt. Here, we first show that B. germanica has two inhibitor of apoptosis (IAP) proteins and that one of them, BgIAP1, is continuously required to ensure tissue viability, including that of the prothoracic gland, during nymphal development. Moreover, we demonstrate that the degeneration of the prothoracic gland is controlled by a complex 20E-triggered hierarchy of nuclear receptors converging in the strong activation of the death-inducer Fushi tarazu-factor 1 (BgFTZ-F1) during the nymphal–adult transition. Finally, we have also shown that prothoracic gland degeneration is effectively prevented by the presence of juvenile hormone (JH). Given the relevance of cell death in the metamorphic process, the characterization of the molecular mechanisms regulating apoptosis in hemimetabolous insects would allow to help elucidate how metamorphosis has evolved from less to more derived insect species

Metamorphosis in hemimetabolous insects. Characterization of the ecdysone regulatory cascade in the cockroach Blattella germanica

Trabajo presentado en el 18th International Ecdysone Workshop, celebrado del 19 al 23 de julio en Ceske Budejovice (República Checa).In hemimetabolan insects, post-embryonic development presents remarkably differences with respect to holometabolan species, in that growth and maturation occur simultaneously throughout successive nymphal stages until the imaginal molt. This type of development, relatively similar to that of vertebrates, contrasts with that presented by holometabolan insects in which an intermediate pupal stage occurs between the larval and adult stages. In holometabolan insects, growth is restricted to larval development whereas maturation occurs during metamorphosis in the pupal stage. A common feature in both types of development, however, is that the ecdysteroid hormone 20-hydroxyecdysone (20E) controls all developmental transitions. Periodic pulses of 20E trigger juvenile molts and, in holometabolan insects, a pulse of 20E at the end of the last larval instar signals the onset of pupariation where it controls the destruction of larval tissues and the formation of the adult structures during metamorphosis. Although there is a detailed understanding of the molecular mechanisms by which 20E regulates the unique metamorphic process in holometabolan insects, little is known about how this hormone operates during the development of hemimetabolan insects. If we aim to understand the molecular basis of the evolution towards complete metamorphosis in insects, then functional characterization of the 20E-induced genetic hierarchy in hemimetabolan species becomes of paramount importance. In this context, we have isolated the majority of the components of this hierarchy in the cockroach Blattella germanica. By using a RNAi in vivo strategy, here we show that a complex cross-regulatory interplay between different 20E-dependent nuclear receptors, namely BgEcR, BgRXR, BgE75, BgHR3, BgHR4 and BgFTZ-F1 tightly controls most of the biological responses to 20E during nymphal and adult development in B. germanica.Peer Reviewe

Nuclear receptor HR4 plays an essential role in the ecdysteroid-triggered gene cascade in the development of the hemimetabolous insect Blattella germanica

Despite the differences in the developmental strategies between hemimetabolous and holometabolous insects, a common feature between both types of development is that periodic pulses of the steroid hormone 20-hydroxyecdysone (20E) dictate each developmental transition. Although the molecular action of 20E has been extensively studied in holometabolous insects, data on hemimetabolous is scarce. To address this, we have used the German cockroach Blattella germanica to show that 20E signals through a transcriptional cascade of the nuclear hormone receptor-encoding genes BgE75, BgHR3 and BgFTZ-F1. Here, we report the isolation and functional characterization of BgHR4, another nuclear receptor involved in this cascade. Expression studies along with tissue incubations and RNAi experiments show that cross-regulation between BgE75 and BgHR3 directs the expression of BgHR4. Finally, we have also shown that BgHR4 is an essential gene required for successfully completing nymphal-nymphal and nymphal-adult transitions, by allowing the appropriate delay in the induction of BgFTZ-F1. © 2011 Elsevier Ireland Ltd.Financial support from the Spanish Ministry of Science and Innovation (Projects BFU2006-13212 and BFU2009-10571 to D.M. and CGL2008-03517/BOS to X.B.) and from the Spanish Council for Scientific Research (Grant 2010TW0019, from the Formosa program, to X.B.) is gratefully acknowledged. D.M.-P. and F.B. are recipients of pre-doctoral research Grants from the Ministry of Science and Innovation.Peer Reviewe

Nuclear receptor BgFTZ-F1 regulates molting and the timing of ecdysteroid production during nymphal development in the hemimetabolous insect Blattella germanica

13 páginas, 10 figuras, 2 tablas.Postembryonic development of holometabolous and hemimetabolous insects occurs through successive molts triggered by 20-hydroxyecdysone (20E). The molecular action of 20E has been extensively studied in holometabolous insects, but data on hemimetabolous are scarce. We have demonstrated that during the nymphal development of the hemimetabolous insect Blattella germanica, 20E binds to the heterodimeric receptor formed by the nuclear receptors BgEcR-A and BgRXR activating a cascade of gene expression, including the nuclear receptors BgE75 and BgHR3. Herein, we report the characterization of BgFTZ-F1, another nuclear hormone receptor involved in 20E action. BgFTZ-F1 is activated at the end of each instar, and RNAi has demonstrated that BgHR3 is needed for BgFTZ-F1 activation, and that BgFTZ-F1 has critical functions of during the last nymphal instar. Nymphs with silenced BgFTZ-F1 cannot ecdyse, arrest development, and show structures of ectodermal origin duplicated. BgFTZ-F1 also controls the timing of the ecdysteroid molting pulse.D.M. and X.B. were funded by the Spanish Ministry of Science and Technology (SMST) and by the Generalitat de Catalunya (GC). J.C. and C.N. are recipients of predoctoral and postdoctoral research grants, respectively, from CSIC, and D.M-P is recipient of a predoctoral research grant from the Spanish Ministry of Education and Science (MEC).Peer reviewe

Dual role of BgFTZ-F1 during nymphal development in the hemimetabolous insect Blattella germanica

Trabajo presentado en el 17th International Ecdysone Workshop, celebrado en Ulm (Alemania) del 20 al 24 de junio de 2008.In insects, the ecdysteroidal hormone 20-hydroxyecdysone (20E) controls key developmental processes during embryogenesis, molting, metamorphosis and reproduction, as it has been extensively studied in holometabolous insects, especially in Drosophila melanogaster. The situation is very different in hemimetabolous insects, which do not develop through complete metamorphosis, their juvenile forms being morphologically similar to the adult. Indeed, in hemimetabolous insects the wealth of information concerning the molecular basis of the 20E-triggered genetic hierarchy is practically non-existent. However, if we aim to understand the molecular basis of the evolution towards complete metamorphosis in insects, then characterization of the 20E-induced genetic hierarchy in primitive species becomes of paramount importance. In the cockroach Blattella germanica, we have previously characterized the two components of the heterodimeric ecdysone receptor, as well as several early and early-late genes. In the present work we extend the knowledge of the 20E genetic hierarchy in B. germanica by identifying a FTZ-F1 homologue in this cockroach, by studying its regulation by ecdysteroids and by determining its functions in nymphal development with RNAi approaches. RNAi experiments reveal that FTZ-F1 is required to molt and to control the timing of ecdysteroid production during the last nymphal stage.Peer Reviewe

Regulatory interplay between JH and 20-hydroxyecdysone in relation with JH production in Blattella germanica

Trabajo presentado en la 9th International Conference on Juvenile Hormones, celebrada en York (UK) del 5 al 10 de agosto de 2007.N

The hormonal pathway controlling cell death during metamorphosis in a hemimetabolous insect

Metamorphosis in holometabolous insects is mainly based on the destruction of larval tissues. Intensive research in Drosophila melanogaster, a model of holometabolan metamorphosis, has shown that the steroid hormone 20-hydroxyecdysone (20E) signals cell death of larval tissues during metamorphosis. However, D. melanogaster shows a highly derived type of development and the mechanisms regulating apoptosis may not be representative in the insect class context. Unfortunately, no functional studies have been carried out to address whether the mechanisms controlling cell death are present in more basal hemimetabolous species. To address this, we have analyzed the apoptosis of the prothoracic gland of the cockroach Blattella germanica, which undergoes stage-specific degeneration just after the imaginal molt. Here, we first show that B. germanica has two inhibitor of apoptosis (IAP) proteins and that one of them, BgIAP1, is continuously required to ensure tissue viability, including that of the prothoracic gland, during nymphal development. Moreover, we demonstrate that the degeneration of the prothoracic gland is controlled by a complex 20E-triggered hierarchy of nuclear receptors converging in the strong activation of the death-inducer Fushi tarazu-factor 1 (BgFTZ-F1) during the nymphal-adult transition. Finally, we have also shown that prothoracic gland degeneration is effectively prevented by the presence of juvenile hormone (JH). Given the relevance of cell death in the metamorphic process, the characterization of the molecular mechanisms regulating apoptosis in hemimetabolous insects would allow to help elucidate how metamorphosis has evolved from less to more derived insect species. © 2010 Elsevier Inc.Financial support from the Spanish Ministry of Science and Innovation (projects BMC2002-03222, BFU2006-13212 and BFU2009-10571 to D.M. and CGL2008-03517/BOS to X.B.) is gratefully acknowledged. D.M-P. and E.U. are recipients of pre-doctoral research grants from the Ministry of Science and Innovation and CSIC, respectively. C.N. is a recipient of a postdoctoral research grant from CSIC.Peer Reviewe

The nuclear receptor BgFTZ-F1 is essential for the onset of the adult developmental program in the hemimetabolous insect Blattella germanica

Trabajo presentado en el 17th International Ecdysone Workshop, celebrado en Ulm (Alemania) del 20 al 24 de julio de 2008.Metamorphosis is one of the most fascinating as well as critical periods of insect development, by which an immature larva transforms into a mature adult insect, concomitant with a cessation of further molting. In holometabolous insects, the changes are so dramatic that an intermediate stage, the pupa, is required to accommodate the replacement of larval structures by adult ones. Conversely, in hemimetabolous insects, the adult body plan is similar to that of the immature nymph, although several stage-specific processes must occur during the nymphal-adult transition, such as the degeneration of the prothoracic gland and a remarkable activation of juvenile hormone production in the corpora allata. All these processes require a coordinated set of changes in different tissues and organs mediated by two main hormones, 20-hydroxyecdysone and juvenile hormone. A great deal of research has been devoted to uncover the molecular mechanisms regulating metamorphosis in holometabolous insects. However, little understanding has been achieved regarding the mechanisms controlling the transition to the adult stage in hemimetabolous species. We are currently using the German cockroach, Blattella germanica, as model to characterize the genetic network controlling the onset of the adult developmental program. The present work describes a detailed analysis of the role of several nuclear hormone receptors, and particularly BgFTZ-F1, on this process, based on systemic RNAi approaches.Peer Reviewe