RESUMEN
In starved larvae of the tobacco hornworm moth Manduca sexta, larval and imaginal tissues stop growing, the former because they lack nutrient-dependent signals but the latter because of suppression by juvenile hormone. Without juvenile hormone, imaginal discs form and grow despite severe starvation. This hormone inhibits the intrinsic signaling needed for disc morphogenesis and does so independently of ecdysteroid action. Starvation and juvenile hormone treatments allowed the separation of intrinsic and nutrient-dependent aspects of disc growth and showed that both aspects must occur during the early phases of disc morphogenesis to ensure normal growth leading to typical-sized adults.
Asunto(s)
Fenómenos Fisiológicos Nutricionales de los Animales , Hormonas Juveniles/fisiología , Manduca/fisiología , Animales , Ecdisteroides/fisiología , Larva , Manduca/embriología , Manduca/crecimiento & desarrollo , Morfogénesis/efectos de los fármacos , Morfogénesis/fisiología , Piridinas/farmacologíaRESUMEN
Proliferation of neural precursors in the optic lobe of Manduca sexta is controlled by circulating steroids and by local production of nitric oxide (NO). Diaphorase staining, anti-NO synthase (NOS) immunocytochemistry and the NO-indicator, DAF-2, show that cells throughout the optic anlage contain NOS and produce NO. Signaling via NO inhibits proliferation in the anlage. When exposed to low levels of ecdysteroid, NO production is stimulated and proliferation ceases. When steroid levels are increased, NO production begins to decrease within 15 minutes independent of RNA or protein synthesis and cells rapidly resume proliferation. Resumption of proliferation is not due simply to the removal of NO repression though, but also requires an ecdysteroid stimulatory pathway. The consequence of these opposing pathways is a sharpening of the responsiveness to the steroid, thereby facilitating a tight coordination between development of the different elements of the adult visual system.
Asunto(s)
Ecdisterona/metabolismo , Neuronas/fisiología , Óxido Nítrico/metabolismo , Transducción de Señal , Células Madre/fisiología , Animales , División Celular , Ecdisterona/farmacología , Inhibidores Enzimáticos/farmacología , Manduca , NG-Nitroarginina Metil Éster/farmacología , Óxido Nítrico/biosíntesis , Óxido Nítrico Sintasa/antagonistas & inhibidores , Óxido Nítrico Sintasa de Tipo I , Lóbulo Óptico de Animales no Mamíferos/citología , Lóbulo Óptico de Animales no Mamíferos/metabolismoRESUMEN
Both the proliferation and differentiation of ventral diaphragm myoblasts are controlled by ecdysteroid during metamorphosis of the moth, Manduca sexta, but the responses have different hormonal requirements. Tonic exposure to moderate levels of ecdysteroid are required to stimulate myoblast proliferation. This is due to the presence of an ecdysteroid-dependent control point in the G(2) phase of the cell cycle. As a result, proliferation can be repeatedly turned on or off simply by adjusting the concentration of ecdysteroid to be above or below a critical threshold concentration. In contrast, high levels of ecdysteroid trigger irreversible proliferative arrest and differentiation of myofibers. Myoblast proliferation and differentiation also differ in their response to the juvenile hormone mimic, methoprene. Ecdysteroid-dependent proliferative arrest and differentiation are blocked by coculture with methoprene but methoprene has no effect on ecdysteroid-dependent proliferation. In the animal, premature exposure to high levels of ecdysteroid in the absence of juvenile hormone triggers precocious differentiation of the myoblasts, resulting in the formation of several thin bands of muscle rather than a complete diaphragm. Thus, ecdysteroid and juvenile hormone collaborate to determine the size and shape of the adult musculature.
Asunto(s)
Diafragma/crecimiento & desarrollo , Manduca/crecimiento & desarrollo , Metamorfosis Biológica/fisiología , Desarrollo de Músculos , Esteroides/fisiología , Animales , Bromodesoxiuridina/metabolismo , Ciclo Celular , División Celular/fisiología , Diafragma/citología , Diafragma/metabolismo , Ecdisteroides , InmunohistoquímicaRESUMEN
The eye primordium of the moth, Manduca sexta, shows two different developmental responses to ecdysteroids depending on the concentration to which it is exposed. Tonic exposure to moderate levels of 20-hydroxyecdysone (20E) or its precursor, ecdysone, are required for progression of the morphogenetic furrow across the primordium. Proliferation, cell-type specification and organization of immature ommatidial clusters occur in conjunction with furrow progression. These events can be reversibly started or stopped in cultured primordia simply by adjusting levels of ecdysteroid to be above or below a critical threshold concentration. In contrast, high levels of 20E cause maturation of the photoreceptors and the support cells that comprise the ommatidia. Ommatidial maturation normally occurs after the furrow has crossed the primordium, but premature exposure to high levels of 20E at any time causes precocious maturation. In such cases, the furrow arrests irreversibly and cells behind the furrow produce a well-formed, but miniature, eye. Precocious and catastrophic metamorphosis occurs throughout such animals, suggesting that ecdysteroids control development of other tissues in a manner similar to the eye. The threshold concentrations of 20E required for furrow progression versus ommatidial maturation differ by about 17-fold. This capacity to regulate distinct phases of development by different concentrations of a single hormone is probably achieved by differential sensitivity of target gene promoters to induction by the hormone-bound receptor(s).
Asunto(s)
Ecdisona/metabolismo , Ecdisterona/metabolismo , Ojo/crecimiento & desarrollo , Manduca/crecimiento & desarrollo , Metamorfosis Biológica/fisiología , Células Fotorreceptoras de Invertebrados/crecimiento & desarrollo , Anfibios/crecimiento & desarrollo , Animales , Ecdisteroides , Regulación de la Expresión Génica , Genes de Insecto , Larva , Manduca/genética , Pupa , Especificidad de la Especie , Esteroides/metabolismo , Factores de TiempoRESUMEN
Cell proliferation within the optic lobe anlagen is dependent on ecdysteroids during metamorphosis of the moth Manduca sexta. We use cultured tissues to show that ecdysteroids must be maintained above a sharp threshold concentration to sustain proliferation. Proliferation can be turned on and off repeatedly simply by shifting the ecdysteroid concentration to above or below this threshold. In subthreshold hormone, cells arrest in the G2 phase of the cell cycle. Ecdysteroid control of proliferation is distinguished from differentiative and maturational responses to ecdysteroids by requiring tonic exposure to the hormone and lower levels of 20-hydroxyecdysone, and by being sensitive to either 20-hydroxyecdysone or its precursor, ecdysone. These characteristics allow optic lobe development to be divided into two ecdysteroid-dependent phases. Initially, moderate levels of ecdysteroid stimulate proliferation. Later, high levels of 20-hydroxyecdysone trigger a wave of apoptosis within the anlage that marks completion of its proliferative phase.
Asunto(s)
Ecdisona/farmacología , Ecdisterona/farmacología , Manduca/crecimiento & desarrollo , Animales , Apoptosis/efectos de los fármacos , División Celular/efectos de los fármacos , Técnicas de Cultivo , ADN/biosíntesis , Demecolcina/farmacología , Ecdisterona/sangre , Larva , Manduca/citología , Metamorfosis Biológica , Mitosis , Lóbulo Óptico de Animales no Mamíferos/citología , Lóbulo Óptico de Animales no Mamíferos/crecimiento & desarrollo , Lóbulo Óptico de Animales no Mamíferos/metabolismoRESUMEN
Drosophila B52 protein is a homologue of human ASF/SF2 that functions in vitro as an essential pre-mRNA splicing factor. Immunofluorescence analysis of polytene chromosomes has shown that B52 generally colocalizes with RNA polymerase II; however, in contrast to other splicing factors, B52 brackets RNA polymerase II at highly active heat-shock puffs. Also, UV cross-linking in nonpolytene cells has shown that B52 cross-links in vivo to DNA flanking the highly active transcription units. Here, we find that the distribution of cross-linked B52 at heat-shock loci depends on transcription levels. Heat shocks at low and moderate temperatures, which induce corresponding levels of transcription, recruit B52 both to transcribed DNA and to flanking DNA, whereas a full heat-shock induction concentrates B52 on the DNA that brackets the entire activated region. We have also identified a 46-kDa protein from Chironomus tentans that binds Drosophila B52 antibodies and has a distribution on chromosomes analogous to B52. This protein is found throughout the moderately transcribed Balbiani rings. However, when transcription at these rings is hyperinduced to levels comparable to fully induced Drosophila heat-shock genes, the protein is restricted to the boundaries of highly decondensed chromatin. We suggest that B52 tracks to chromatin fibers that are folding or unfolding, and we discuss this in light of B52's proposed roles in pre-mRNA splicing and control.
Asunto(s)
Cromosomas/metabolismo , Proteínas de Drosophila , Drosophila melanogaster/metabolismo , Proteínas de Choque Térmico/biosíntesis , Hormonas de Insectos/análisis , Fosfoproteínas , Empalme del ARN , Transcripción Genética , Animales , Anticuerpos Monoclonales/inmunología , Chironomidae/inmunología , Chironomidae/metabolismo , Cromatina/metabolismo , Cromatina/ultraestructura , Reacciones Cruzadas , Drosophila melanogaster/genética , Proteínas de Choque Térmico/genética , Hormonas de Insectos/inmunología , Proteínas Nucleares/química , Pilocarpina/farmacología , ARN Polimerasa II/metabolismo , Precursores del ARN/metabolismo , Factores de Empalme de ARN , Proteínas de Unión al ARN , Homología de Secuencia de Ácido Nucleico , Factores de Empalme Serina-Arginina , Transcripción Genética/efectos de los fármacosRESUMEN
We have used indirect immunofluorescence of polytene chromosomes to examine the chromatin distribution of a 52-kD Drosophila protein designated B52. B52 is localized to transcriptionally active loci and, at the highly decondensed heat shock loci, can be seen to bracket the RNA polymerase II fluorescence signals symmetrically. We have also examined the distribution of B52 on nonpolytene chromosomes in Drosophila cell cultures with an in vivo UV cross-linking method and find that, here too, B52 is associated with boundaries of transcriptionally active chromatin. The predicted primary amino acid sequence of B52 reveals two regions with similarities to a number of other proteins known to interact with nucleic acids.