RESUMEN
Holometaboly is a key evolutionary innovation that has facilitated the spectacular radiation of insects. Despite the undeniable advantage of complete metamorphosis, the female of some holometabolous species have lost the typical holometabolous development through neoteny. In Xenos vesparum Rossi (Strepsiptera: Stylopidae), a derived species of the holometabolous endoparasitic order Strepsiptera, neotenic females reach sexual maturity without the pupal and the imaginal stages, thus retaining their larval morphology (with the exception of the anterior part of the body or cephalothorax), while males undergo normal pupal-based metamorphosis. Expression of the "adult-specifier" E93 factor has been shown to be required for proper metamorphosis in holometabolous insects. Here, we investigated the involvement of E93 in female neoteny by cloning XvE93. Interestingly, while we detected a clear up-regulation of XvE93 expression in pupal and adult stages of males, persistent low levels of XvE93 were detected in X. vesparum females. However, a specific up-regulation of XvE93 was observed in the cephalothorax of late 4th female instar larva, which correlates with the occurrence of neotenic-specific features in the anterior part of the female body. Moreover, the same expression dynamic in the cephalothorax and abdomen was also observed for other two critical metamorphic regulators, the anti-metamorphic XvKr-h1 and the pupal specifier XvBr-C. The specific up-regulation of XvE93 and XvBr-C in the female cephalothorax seems to be the result of an increase in 20-hydroxyecdysone (20E) signaling in this region for we detected higher expression levels of the 20E-dependent nuclear receptors XvHR3 and XvE75 in the cephalothorax. Overall, our results detect a sex-specific expression pattern of critical metamorphic genes in X. vesparum, suggesting that neoteny in Strepsiptera results from the modification of the normal expression of E93, Br-C and Kr-h1 genes.
Asunto(s)
Proteínas de Insectos/metabolismo , Insectos/metabolismo , Animales , Ecdisterona/metabolismo , Femenino , Regulación del Desarrollo de la Expresión Génica/fisiología , Larva/metabolismo , Masculino , Metamorfosis Biológica/fisiología , Pupa/metabolismo , Transducción de Señal/fisiología , Factores de Transcripción/metabolismo , Regulación hacia Arriba/fisiologíaRESUMEN
Hormones play essential roles during development and maintaining homeostasis in adult organisms, regulating a plethora of biological processes. Generally, hormones are secreted by glands and perform a systemic action. Here we show that Juvenile Hormones (JHs), insect sesquiterpenoids synthesized by the corpora allata, are also synthesized by the adult Drosophila gut. This local, gut specific JH activity, is synthesized by and acts on the intestinal stem cell and enteroblast populations, regulating their survival and cellular growth through the JH receptors Gce/Met and the coactivator Tai. Furthermore, we show that this local JH activity is important for damage response and is necessary for intestinal tumor growth driven by activating mutations in Wnt and EGFR/Ras pathways. Together, our results identify JHs as key hormonal regulators of gut homeostasis and open the possibility that analogous hormones may play a similar role in maintaining vertebrate adult intestinal stem cell population and sustaining tumor growth.
Asunto(s)
Proliferación Celular/efectos de los fármacos , Drosophila/fisiología , Tracto Gastrointestinal/fisiología , Homeostasis , Neoplasias Intestinales/patología , Hormonas Juveniles/metabolismo , Células Madre/efectos de los fármacos , AnimalesRESUMEN
The Drosophila tracheal system is a model for the study of the mechanisms that guide cell migration. The general conclusion from many studies is that migration of tracheal cells relies on directional cues provided by nearby cells. However, very little is known about which paths are followed by the migrating tracheal cells and what kind of interactions they establish to move in the appropriate direction. Here we analyze how tracheal cells migrate relative to their surroundings and which tissues participate in tracheal cell migration. We find that cells in different branches exploit different strategies for their migration; while some migrate through preexisting grooves, others make their way through homogeneous cell populations. We also find that alternative migratory pathways of tracheal cells are associated with distinct subsets of mesodermal cells and propose a model for the allocation of groups of tracheal cells to different branches. These results show how adjacent tissues influence morphogenesis of the tracheal system and offer a model for understanding how organ formation is determined by its genetic program and by the surrounding topological constraints.