3-Oxoecdysteroid reductases in Manduca sexta midgut

The 80,000g supernatant o larval midgut homogenates of the tobacco hornworm, Manduca sexta, was fractionated by affinity chromatography on Blue Sepharose CL-6B and by anion exchange chromatography on Q Sepharose. Both methods resolved one major 3-oxoecdysteroid 3α-reductase and three major 3-oxoecdysteroid 3β-reductases. The 3β-reducates reacted only with BADPH as cosubstrate. The 3α-reductase was active with both NADPH and NADH, and the NADPH/NADH activity ratio increased with the NaCl concentration (0–0.5 M) in the incubation mixtures. The 3-α-reductase and one of the 3-β-reductases showed very similar chromatographic properties, and their isoelectric points were 5.2 and 5.8, respectively. © 1992 Wiley-Liss, Inc.     

Ecdysone oxidase and 3-oxoecdysteroid reductases in Manduca sexta midgut: Kinetic parameters

Ecdysone and 20-hydroxyecdysone are converted to their 3-epimers by enzymes in the midgut cytosol of Manduca sexta larvae. A partially purified cytosol preparation has been used to analyze the nature of and the interaction between these enzymes. The cytosol was shown to contain ecdysone oxidase, one or more 3-oxoecdysteroid 3α-reductase(s), and one or more 3-oxoecdysteroid 3β-reductase(s). The reductases reacted at different velocities with NADH and NADPH. With NADH, 3α-reduction was the major reaction; with NADPH, 3β-reduction was the major reaction. The apparent kinetic parameters for the enzymes support the assumed two-step mechanism for the 3-epimerization with a 3-oxoecdysteroid as intermediate.     

Developmental profiles of the mRNAs for Manduca arylphorin and two other storage proteins during the final larval instar of Manduca sexta

When fat body mRNA from the tobacco hornworm larva, Manduca sexta, was translated in a rabbit reticulocyte lysate system, three major polypeptides were found, each having a different developmental profile. One mRNA coded for a 74 kilodalton (K) polypeptide doublet precipitated by an antibody to the arylphorin (manducin). This mRNA was present only during the intermolt feeding phase of the penultimate and the final larval instars. Its appearance 16–24 hr after larval ecdysis was dependent upon the incoming nutrient supply and independent of the juvenile hormone (JH) level. Immunoblots of proteins of the fat body, epidermis, and cuticle revealed the presence of arylphorin in all three tissues. Additionally, several small polypeptides that cross-reacted with the arylphorin antibody were found in the fat body during and up to 24 hr after the last larval molt and in the tanning pupal cuticle. The larval epidermis was also found to contain a small amount of arylphorin mRNA. At the time of the JH decline prior to the onset of metamorphosis, a female-specific mRNA coding for a 79 K translation product appeared. In allatectomized larvae this mRNA was detectable earlier, and its appearance in intact larvae was prevented by application of methoprene, indicating that JH regulates its appearance. At wandering a new mRNA that also codes for a 79 K polypeptide appeared in both sexes and was the major messenger present during the prepupal stage. Neither it nor the female-specific mRNA were translatable after pupal ecdysis.     

Lysozyme in the midgut of Manduca sexta during metamorphosis.

Low levels of lysozyme were found in the midgut epithelium of the tobacco hornworm, Manduca sexta, during the early part of the fifth larval stadium. This was observed in control insects as well as in bacterially challenged insects. No lysozyme was detected in the gut contents of either group of insects which were actively eating or in the early stages of metamorphosis. However, high levels of lysozyme activity were detected in homogenates of midgut tissue collected from insects later in the stadium. Immunocytochemical studies demonstrated that lysozyme accumulates in large apical vacuoles in regenerative cells of the midgut during the larval-pupal molt. These cells, initially scattered basally throughout the larval midgut epithelium, multiply and form a continuous cell layer underneath the larval midgut cells. At the larval/pupal ecdysis the larval midgut epithelium is sloughed off and the regenerative cells, now forming the single cell layer of the midgut, release the contents of their vacuoles into the midgut lumen. This release results in high lysozyme activity in the lumen of the pupal midgut and is thought to confer protection from bacterial infection. This is the first indication that the lysozyme gene may be developmentally regulated in a specific tissue in the absence of a bacterial infection.     

Mechanisms of midgut remodeling: juvenile hormone analog methoprene blocks midgut metamorphosis by modulating ecdysone action

In holometabolous insects such as mosquito, Aedes aegypti, midgut undergoes remodeling during metamorphosis. Insect metamorphosis is regulated by several hormones including juvenile hormone (JH) and 20-hydroxyecdysone (20E). The cellular and molecular events that occur during midgut remodeling were investigated by studying nuclear stained whole mounts and cross-sections of midguts and by monitoring the mRNA levels of genes involved in 20E action in methoprene-treated and untreated Ae. aegypti. We used JH analog, methoprene, to mimic JH action. In Ae. aegypti larvae, the programmed cell death (PCD) of larval midgut cells and the proliferation and differentiation of imaginal cells were initiated at about 36h after ecdysis to the 4th instar larval stage (AEFL) and were completed by 12h after ecdysis to the pupal stage (AEPS). In methoprene-treated larvae, the proliferation and differentiation of imaginal cells was initiated at 36h AEFL, but the PCD was initiated only after ecdysis to the pupal stage. However, the terminal events that occur for completion of PCD during pupal stage were blocked. As a result, the pupae developed from methoprene-treated larvae contained two midgut epithelial layers until they died during the pupal stage. Quantitative PCR analyses showed that methoprene affected midgut remodeling by modulating the expression of ecdysone receptor B, ultraspiracle A, broad complex, E93, ftz-f1, dronc and drice, the genes that are shown to play key roles in 20E action and PCD. Thus, JH analog, methoprene acts on Ae. aegypti by interfering with the expression of genes involved in 20E action resulting in a block in midgut remodeling and death during pupal stage.     

Developmental changes in midgut trehalase activity and its localization in the silkworm, Bombyx mori

The changes in trehalase activity and its localization in the midgut of the silkworm, Bombyx mori, were studied during larval-pupal-adult development. Trehalase activity in larval midgut epithelium increased with the larval growth, reached a maximum level at the middle of the fifth instar, and then decreased gradually. Trehalase activity in larval midgut was found in the epithelial tissue but not in the digestive juice or the midgut contents.The trehalase activity in the whole midgut started to rise at the onset of spinning and increased abruptly at larval-pupal ecdysis to reach an extremely high level 3 days later. This high activity was maintained throughout the subsequent pharate adult development and dropped suddenly at emergence. The midgut trehalase activity during pupal-adult development was mainly found in the midgut contents but scarcely any in the epithelium.Subcellular distribution of midgut trehalase depended upon larval-pupal-adult development. The activity was concentrated in a precipitate fraction of the epithelium until the middle of the fifth instar. During larval-pupal development, however, the activity increased in the soluble fraction with a concomitant decrease in the precipitate fraction. Almost all the trehalase activity in pupal and pharate adult midgut was recovered in the soluble fraction of the midgut contents. The data are discussed from a viewpoint of the histolysis.     

L-Glutamate retrieved with the moulting fluid is processed by a glutamine synthetase in the pupal midgut of Calpodes ethlius

From apolysis until pupal ecdysis, the pharate pupa of the Brazilian Skipper (Calpodes ethlius) lies wrapped in a prepupal shell composed of the larval cuticle and an ecdysial space (ES) filled with enzyme-rich moulting fluid (MF). In the 4h before ecdysis the pharate pupa drinks the moulting fluid through its mouth and anus, and transfers the cuticular degradation products to its midgut (MG). At the same time, extra fluid passes across the body wall of the pharate pupa and flushes out the ES. The MF is recovered at an overall rate of 70μl/h and reabsorbed across the pharate pupal midgut at about 26μl/h. L-Glutamate was found to be the dominant amino acid in the moulting fluid. Total MF glutamate peaked at 850nmol about 8h before pupal ecdysis (P-8), but by ecdysis it had dropped to nearly zero as the MF became diluted with new fluid and was consumed. The drop in glutamate in the ES coincided with a rise in the glutamine content of the fluid in the midgut lumen. The highest rate of glutamine synthesis occurred in midguts isolated from pharate pupae actively drinking MF (P相似文献   

Temporal pattern of changes in mitotic frequency in the epidermis and other larval tissues of Bombyx mori

Temporal changes in mitotic frequency were examined in various tissues through late larval life of Bombyx mori. From the second larval ecdysis to the third and from the third larval ecdysis to the fourth, there was a definite temporal change of mitotic pattern in each tissue. In the epidermis as well as in the tracheal epithelium, mitoses began to appear about 1 day after an ecdysis, and showed a maximum 1 to 2 days after an ecdysis. In the fat body, mitoses were observed continuously through the instars, and the mitotic frequency showed a maximum state just before an ecdysis. In the abdominal muscle the frequency was highest at about the middle of the period between two successive ecdyses. Furthermore, epidermal mitoses coincided with the time when the density of epidermal nuclei per unit area decreased to a half. This suggests that epidermal mitoses may be initiated by some process related to the increase in cell size.     

5α-Réductases: Physiologie et pathologie

In most androgen target tissues, the first step of androgen action is the 5α-reduction of testostérone to DHT which binds to the androgen receptor wih an affinity 3 to 4 fold higher than testostérone. Two genes, encoding two isozymes of 5α-reductase (5α-R) have been cloned. The two isoforms, 5α-R1 and 5α-R2 are located on chromosome 5 and 2 respectively and differ in optimal pH, substrate and inhibitor affinities and tissue expression. 5α-R2 is responsible for sexual différenciation. It is the major form expressed in the prostate where it seems necessary for embryonic growth and development. In this tissue, as in human skin, 5α-R2 is stimulated by androgens thus amplifying androgen action. 5α-reductase deficiency results in androgen insensitivity due to abnormal 5α-R2. Affected patients are XY individuals with a very peculiar form of male pseudohermaphroditism: they have feminine genitalia at birth and masculinize at puberty. Different mutations, spannning the whole coding portion of the gene, have been described; correlation between mutations and enzyme activity have led to the tentative localization of the substrate binding site in exon 1 and the cofactor binding site in exon 4. In contrast to androgen insensitivity due to 5α-reductase deficiency, increased 5α-reductase activity can result in androgen hypersensitivity as described in idiopathic hirsutism or benign prostatic hyperplasia. In these case antiandrogen therapy, using 5α-reductase inhibitors, can be considered.     

Haemolymph ecdysteroid levels and cellular events in the intermoult/moult sequence of Calpodes ethlius

The haemolymph ecdysteroid titre of the last larval and pupal stadia of Calpodes ethlius was determined by radioimmunoassay. During the last larval stadium, four significant ecdysteroid peaks are present, two of which have been reported for other Lepidoptera. The first peak occurs 12 hr after ecdysis and correlates temporally with nucleolar activity, RNA synthesis and organelle formation in the fat body and epidermis. It correlates also with fat body DNA synthesis, polyploidy and the initiation of a low rate of lipid synthesis. Another peak, at 78 hr, starts its increase when the prothoracic glands no longer require the influence of the brain to produce ecdysone for pupation, and marks the first critical period. It correlates with the initiation of epidermal DNA synthesis and mitosis, and with the progressive determination of pupal characteristics (change in commitment, reprogramming). This ecdysteroid peak may also be involved in the massive intermoult syntheses in the epidermis (lamellate cuticle, wax) and the fat body (lipid, protein). The largest ecdysteroid peak is seen at 162 hr, 6 hr after the tissues no longer require the prothoracic glands for pupation (second critical period). It correlates temporally with the cessation of massive synthetic activity in both epidermis and fat body and initiates preparation for pupal synthesis in both tissues. At this time the ratio of ecdysone: 20-hydroxyecdysone is ～ 1 : 6.6.In common with other Lepidoptera, a single large ecdysteroid peak occurs during the first half of the pupal stadium. Comparisons between these events and the ecdysteroid titre are made between Calpodes and other insects.     

Hormonal regulation and patterning of the broad-complex in the epidermis and wing discs of the tobacco hornworm, Manduca sexta

Expression of Manduca Broad-Complex (BR-C) mRNA in the larval epidermis is under the dual control of ecdysone and juvenile hormone (JH). Immunocytochemistry with antibodies that recognize the core, Z2, and Z4 domains of Manduca BR-C proteins showed that BR-C appearance not only temporally correlates with pupal commitment of the epidermis on day 3 of the fifth (final) larval instar, but also occurs in a strict spatial pattern within the abdominal segment similar to that seen for the loss of sensitivity to JH. Levels of Z2 and Z4 BR-C proteins shift with Z2 predominating at pupal commitment and Z4 dominant during early pupal cuticle synthesis. Both induction of BR-C mRNA in the epidermis by 20-hydroxyecdysone (20E) and its suppression by JH were shown to be independent of new protein synthesis. For suppression JH must be present during the initial exposure to 20E. When JH was given 6 h after 20E, suppression was only seen in those regions that had not yet expressed BR-C. In the wing discs BR-C was first detected earlier 1.5 days after ecdysis, coincident with the pupal commitment of the wing. Our findings suggest that BR-C expression is one of the first molecular events underlying pupal commitment of both epidermis and wing discs.     

Stem cells from midguts of Lepidopteran larvae: clues to the regulation of stem cell fate

Previously, we showed that isolated stem cells from midguts of Heliothis virescens can be induced to multiply in response to a multiplication protein (MP) isolated from pupal fat body, or to differentiate to larval types of mature midgut cells in response to either of 4 differentiation factors (MDFs) isolated from larval midgut cell-conditioned medium or pupal hemolymph. In this work, we show that the responses to MDF-2 and MP in H. virescens stem cells decayed at different time intervals, implying that the receptors or response cascades for stem cell differentiation and multiplication may be different. However, the processes appeared to be linked, since conditioned medium and MDF-2 prevented the action of MP on stem cells; MP by itself appeared to repress stem cell differentiation. Epidermal growth factor, retinoic acid, and platelet-derived growth factor induced isolated midgut stem cells of H. virescens and Lymantria dispar to multiply and to differentiate to mature midgut cells characteristic of prepupal, pupal, and adult lepidopteran midgut epithelium, and to squamous-like cells and scales not characteristic of midgut tissue instead of the larval types of mature midgut epithelium induced by the MDFs. Midgut stem cells appear to be multipotent and their various differentiated fates can be influenced by several growth factors.     

Function of the nuclear receptor FTZ‐F1 during the pupal stage in Drosophila melanogaster

The nuclear receptor βFTZ‐F1 is expressed in most cells in a temporally specific manner, and its expression is induced immediately after decline in ecdysteroid levels. This factor plays important roles during embryogenesis, larval ecdysis, and early metamorphic stages. However, little is known about the expression pattern, regulation and function of this receptor during the pupal stage. We analyzed the expression pattern and regulation of ftz‐f1 during the pupal period, as well as the phenotypes of RNAi knockdown or mutant animals, to elucidate its function during this stage. Western blotting revealed that βFTZ‐F1 is expressed at a high level during the late pupal stage, and this expression is dependent on decreasing ecdysteroid levels. By immunohistological analysis of the late pupal stage, FTZ‐F1 was detected in the nuclei of most cells, but cytoplasmic localization was observed only in the oogonia and follicle cells of the ovary. Both the ftz‐f1 genetic mutant and temporally specific ftz‐f1 knockdown using RNAi during the pupal stage showed defects in eclosion and in the eye, the antennal segment, the wing and the leg, including bristle color and sclerosis. These results suggest that βFTZ‐F1 is expressed in most cells at the late pupal stage, under the control of ecdysteroids and plays important roles during pupal development.     

Developmental and hormonal regulation of midgut remodeling in a lepidopteran insect, Heliothis virescens

Midgut tissue undergoes remodeling during metamorphosis in insects belonging to orders Lepidoptera and Diptera. We investigated the developmental and hormonal regulation of these remodeling events in lepidopteran insect, Heliothis virescens. In H. virescens, programmed cell death (PCD) of larval midgut cells as well as proliferation and differentiation of imaginal cells began at 108 h after ecdysis to the final larval instar (AEFL) and proceeded through the pupal stages. Expression patterns of pro- cell death factors (caspase-1 and ICE) and anti-cell death factor, Inhibitor of Apoptosis (IAP) were studied in midguts during last larval and pupal stages. IAP, Caspase-1 and ICE mRNAs showed peaks at 48 h AEFL, 96 h AEFL and in newly formed pupae, respectively. Immunohistochemical analysis substantiated high caspase-3 activity in midgut at 108 h AEFL. Application of methoprene, a juvenile hormone analog (JHA) blocked PCD by maintaining high levels of IAP, downregulating the expression of caspase-1, ICE and inhibiting an increase in caspase-3 protein levels in midgut tissue. Also, the differentiation of imaginal cells was impaired by methoprene treatment. These studies demonstrate that presence of JHA during final instar larvae affects both midgut remodeling and larval-pupal metamorphosis leading to larval/pupal deformities in lepidopteran insects, a mechanism that is different from that in mosquito, Ae. aegypti where JHA uncouples midgut remodeling from metamorphosis.     

Developmental expression of Ultraspiracle proteins in the epidermis of the tobacco hornworm, Manduca sexta, during larval life and the onset of metamorphosis

 During the final two larval instars, a changing pattern of three Ultraspiracle (Usp) proteins (50.5, 52.5, and 57 kDa) was detected in immunoblots of the dorsal abdominal epidermis of the tobacco hornworm, Manduca sexta, by a monoclonal antibody against Drosophila Usp that was shown to detect MsUsp. The 57- and 52.5-kDa bands were present during the intermolt periods and the 50.5- and 52.5-kDa bands during the molting phases. The antibody detected a nuclear antigen present in epidermis, muscle, fat body, and the central nervous system from the time of hatching. In the epidermis Usp was present in all cell nuclei but was especially prominent in the tormogen and trichogen cells immediately after ecdysis in both the penultimate and final instars. This latter immunoreactivity disappeared within 12 h whereas the remainder of the epidermis retained high levels throughout the feeding period. During the molt immunostaining reappeared in the hair cell nuclei. During the wandering stage at the onset of metamorphosis and just before pupal ecdysis, immunoblots showed high levels of Usp, but nuclei showed little or no staining. This discrepancy is likely due to the loss of one Usp isoform from the nucleus and its dispersal in the cytoplasm in preparation for the appearance of the second isoform. Received: 10 June 1997 / Accepted: 22 August 1997     

Isolation and developmental expression of two nuclear receptors, MHR4 and betaFTZ-F1, in the tobacco hornworm, Manduca sexta

The cDNAs for two members of the nuclear receptor superfamily were isolated from the tobacco hornworm, Manduca sexta. The deduced amino acid sequence of MHR4 shows 93-95% identity in the DNA-binding domain and the first portion of the hinge (D) region with the germ cell nuclear factor (GCNF)-related factors (GRFs) of the silkworm, Bombyx mori, and the mealworm, Tenebrio molitor, and with a genomic sequence from the fruit fly, Drosophila melanogaster. Northern blot hybridization showed that a 7.5 kb MHR4 mRNA appeared in Manduca abdominal epidermis just as the ecdysteroid titer began to decline during the larval molt, disappeared about 12 h later, then transiently reappeared shortly before larval ecdysis. During the pupal and adult molts, a similar pattern of expression was seen (the very end of the adult molt was not studied). At peak times of expression in the epidermis, MHR4 mRNA was also present in fat body and the central nervous system (CNS). The deduced amino acid sequence of Manduca FTZ-F1 is 100% and 96% identical to that of B. mori and Drosophila betaFTZ-F1, respectively, in the DNA-binding domain and the adjacent hinge region including the FTZ-F1 box. Northern blot analysis showed that the >9.5 kb betaFTZ-F1 mRNA appeared in Manduca epidermis during the decline of the ecdysteroid titer in the larval, pupal and adult molts as the first peak of MHR4 mRNA declined, then it disappeared in the larval and pupal molts before the second peak of MHR4 appeared. betaFTZ-F1 mRNA was also found in fat body and the CNS at the time of peak expression in the epidermis during the larval and pupal molts. Both MHR4 and betaFTZ-F1 mRNAs were found in the testis during the onset of spermatogenesis in the prepupal period.     

A novel tissue in an established model system: the <Emphasis Type="Italic">Drosophila</Emphasis> pupal midgut

The Drosophila larval and adult midguts are derived from two populations of endodermal progenitors that separate from each other in the early embryo. As larval midgut cells differentiate into an epithelial layer, adult midgut progenitors (AMPs) remain as small clusters of proliferating, undifferentiated cells attached to the basal surface of the larval gut epithelium. During the first few hours of metamorphosis, AMPs merge into a continuous epithelial tube that overgrows the larval layer and differentiates into the adult midgut; at the same time, the larval midgut degenerates. As shown in this paper, there is a second, transient pupal midgut that develops from the AMPs at the beginning of metamorphosis and that intercalates between the adult and larval midgut epithelia. Cells of the transient pupal midgut form a multilayered tube that exhibits signs of differentiation, in the form of septate junctions and rudimentary apical microvilli. Some cells of the pupal midgut develop as endocrine cells. The pupal midgut remains closely attached to the degenerating larval midgut cells. Along with these cells, pupal midgut cells are sequestered into the lumen where they form the compact “yellow body.” The formation of a pupal midgut has been reported from several other species and may represent a general feature of intestinal metamorphosis in insects.