INSECT HORMONES IN DEVELOPMENT

RNA sequencing reveals distinct gene expression patterns during the development of parasitic larval stages of the salmon louse (Lepeophtheirus salmonis)

The salmon louse (Lepeophtheirus salmonis), an ectoparasitic copepod on salmonids, has become a major threat for the aquaculture industry. In search for new drugs and vaccines, transcriptome analysis is increasingly used to find differently regulated genes and pathways in response to treatment. However, the underlying gene expression changes going along with developmental processes could confound such analyses. The life cycle of L. salmonis consists of eight stages divided by moults. The developmental rate of salmon lice on the host is not uniform. Individual- and sex-related differences are found leading to individuals of unlike developmental status at same sampling time point after infection. In this study, we analyse L. salmonis from a time series by RNA sequencing applying a method of separating individuals of different instar age independent of sampling time point. Lice of four stages divided into up to four age groups within the stage were analysed in triplicate (total of 66 samples). Gene expression analysis shows that the method for sorting individuals was successful. Many genes show cyclic expression patterns over the moulting cycles. Overall gene expression differs more between lice of different age within the same stage than between lice of different stage but same instar age.

Adaptive developmental plasticity: compartmentalized responses to environmental cues and to corresponding internal signals provide phenotypic flexibility

BACKGROUND

The environmental regulation of development can result in the production of distinct phenotypes from the same genotype and provide the means for organisms to cope with environmental heterogeneity. The effect of the environment on developmental outcomes is typically mediated by hormonal signals which convey information about external cues to the developing tissues. While such plasticity is a wide-spread property of development, not all developing tissues are equally plastic. To understand how organisms integrate environmental input into coherent adult phenotypes, we must know how different body parts respond, independently or in concert, to external cues and to the corresponding internal signals.

RESULTS

We quantified the effect of temperature and ecdysone hormone manipulations on post-growth tissue patterning in an experimental model of adaptive developmental plasticity, the butterfly Bicyclus anynana. Following a suite of traits evolving by natural or sexual selection, we found that different groups of cells within the same tissue have sensitivities and patterns of response that are surprisingly distinct for the external environmental cue and for the internal hormonal signal. All but those wing traits presumably involved in mate choice responded to developmental temperature and, of those, all but the wing traits not exposed to predators responded to hormone manipulations. On the other hand, while patterns of significant response to temperature contrasted traits on autonomously-developing wings, significant response to hormone manipulations contrasted neighboring groups of cells with distinct color fates. We also showed that the spatial compartmentalization of these responses cannot be explained by the spatial or temporal compartmentalization of the hormone receptor protein.

CONCLUSIONS

Our results unravel the integration of different aspects of the adult phenotype into developmental and functional units which both reflect and impact evolutionary change. Importantly, our findings underscore the complexity of the interactions between environment and physiology in shaping the development of different body parts.

Ligand binding pocket function of Drosophila USP is necessary for metamorphosis

The widely accepted paradigm that epoxidized methyl farnesoates ("juvenile hormones," JHs) are the principal sesquiterpenoid hormones regulating insect metamorphosis was assessed in Drosophila melanogaster. GC-MS analysis of circulating methyl farnesoids during the mid to late 3rd instar showed that methyl farnesoate is predominant over methyl epoxyfarnesoate (=JH III). The circulating concentration of methyl farnesoate (reaching nearly 500 nM), was easily high enough on a kinetic basis to load the Drosophila ortholog of the nuclear hormone receptor RXR (also known as "ultraspiracle," USP), whereas the circulating concentrations of JH III and methyl bisepoxyfarnesoate (bisepoxyJH III) were not. The hypothesis that the ligand pocket of USP necessarily binds an endogenous ligand for differentiation of the immature to the adult was tested with USP mutated at residue that normally extends a side chain into the ligand binding pocket. An equilibrium binding assay confirmed that the mutation (Q288A) strongly altered methyl farnesoate interaction with USP, while a heterologous cell-line transfection assay confirmed that the mutation did not allosterically alter the transcriptional response of the ultraspiracle/ecdysone receptor heterodimer to ecdysteroid signaling. Transgenic wildtype USP driven by the cognate natural promoter rescued null animals to develop to the adult inside a normally formed puparium, while in contrast animals transgenically expressing instead the ligand pocket mutant exhibited developmental derangement at the larval to pupal transition, including failure to form a properly shaped or sclerotized puparium. Other point mutations to the pocket strongly reducing affinity for methyl farnesoate similarly disrupted the larval to pupal metamorphosis. These results suggest that normal larval to pupal maturation in this mecopteran model insect requires the involvement of a distinct endocrine axis of USP binding to its own endogenous terpenoid ligand.

The coordination of growth among Drosophila organs in response to localized growth-perturbation

The developmental mechanisms by which growth is coordinated among developing organs are largely unknown and yet are essential to generate a correctly proportioned adult. In particular, such coordinating mechanisms must be able to accommodate perturbations in the growth of individual organs caused by environmental or developmental stress. By autonomously slowing the growth of the developing wing discs within Drosophila larvae, we show that growing organs are able to signal localized growth perturbation to the other organs in the body and slow their growth also. Growth rate is so tightly coordinated among organs that they all show approximately the same reduction in growth rate as the developing wings, thereby maintaining their correct size relationship relative to one another throughout development. Further, we show that the systemic growth effects of localized growth-perturbation are mediated by ecdysone. Application of ecdysone to larvae with growth-perturbed wing discs rescues the growth rate of other organs in the body, indicating that ecdysone is limiting for their growth, and disrupts the coordination of their growth with growth of the wing discs. Collectively our data demonstrate the existence of a novel growth-coordinating mechanism in Drosophila that synchronizes growth among organs in response to localized growth perturbation.

Temporal regulation of microRNA expression in Drosophila melanogaster mediated by hormonal signals and broad-Complex gene activity

lin-4 and let-7 are founding members of an extensive family of genes that produce small transcripts, termed microRNAs (miRNAs). In Caenorhabditis elegans, lin-4 and let-7 control the timing of postembryonic events by translational repression of target genes, permitting progression from early to late developmental programs. To identify Drosophila melanogaster miRNAs that could play similar roles in the control of developmental timing, we characterized the developmental expression profile of 24 miRNAs in Drosophila, and found 7 miRNAs that are either upregulated or downregulated in conjunction with metamorphosis. The upregulation of three of these miRNAs (mir-100, mir-125, and let-7), and the downregulation of a fourth (mir-34) requires the hormone ecdysone (Ecd) and the activity of the Ecd-inducible gene Broad-Complex. Interestingly, mir-125 is a putative homologue of lin-4. mir-100, -125, and let-7 are clustered within an 800-bp region on chromosome 2L, suggesting that these three miRNAs may be coordinately regulated via common cis-acting elements during metamorphosis. In S2 cells, Ecd and the juvenile hormone analog methoprene exert opposite effects on the expression of these four miRNAs, indicating the participation of both these hormones in the temporal regulation of mir-34, -100, -125, and let-7 expression in vivo.

GFP in living animals reveals dynamic developmental responses to ecdysone during Drosophila metamorphosis

Studies of Drosophila metamorphosis have been hampered by our inability to visualize many of the remarkable changes that occur within the puparium. To circumvent this problem, we have expressed GFP in specific tissues of living prepupae and pupae and compiled images of these animals into time-lapse movies. These studies reveal, for the first time, the dynamics and coordination of morphogenetic movements that could only be inferred from earlier studies of dissected staged animals. We also identify responses that have not been described previously. These include an unexpected variation in some wild-type animals, where one of the first pairs of legs elongates in the wrong position relative to the second pair of legs and then relocates to its appropriate location. At later stages, the antennal imaginal discs migrate from a lateral position in the head to their final location at the anterior end, as leg and mouth structures are refined and the wings begin to fold. The larval salivary glands translocate toward the dorsal aspect of the animal and undergo massive cell death following head eversion, in synchrony with death of the abdominal muscles. These death responses fail to occur in rbp(5) mutants of the Broad-Complex (BR-C), and imaginal disc elongation and eversion is abolished in br(5) mutants of the BR-C. Leg malformations associated with the crol(3) mutation can be seen to arise from defects in imaginal disc morphogenesis during prepupal stages. This approach provides a new tool for characterizing the dynamic morphological changes that occur during metamorphosis in both wild-type and mutant animals.

Cellular basis of the dynamic behavior of the imaginal thoracic discs during Drosophila metamorphosis

The eversion, migration, spreading, and fusion of the thoracic imaginal discs during metamorphosis of Drosophila are described using timed whole-mount preparations and several molecular markers. The leading edge of the migrating disc epithelia consists of two groups of cells, stalk cells (S cells) and specialized imaginal cells (I cells), that both express the gene puckered. With this and other markers, opening of the stalk, eversion of the discs, migration of the leading edges, and fusion of the imaginal epithelia can be visualized in detail. Fusion is initiated by S cells that migrate over the larval epithelium and constitute a bridge between two imaginal epithelia. S cells are subsequently lost and imaginal fusion is mediated by the I cells that remain at the site of fusion. The possible cellular basis of this process is discussed. Fusion along the dorsal midline of the notum from the mesothoracic wing discs occurs earlier than that of the prothoracic and metathoracic discs, which remain in a lateral position. For a relatively long period (30 h) the mesothoracic epithelium becomes attached to the head and abdomen, causing a temporary local discontinuity of the order of segments. Later the pro- and metathoracic discs intercalate between head and mesothorax and between abdomen and mesothorax, respectively, to reestablish the normal order.

The E23 early gene of Drosophila encodes an ecdysone-inducible ATP-binding cassette transporter capable of repressing ecdysone-mediated gene activation

At the onset of Drosophila metamorphosis, the steroid hormone 20-OH ecdysone directly induces a small number of early puffs in the polytene chromosomes of the larval salivary gland. Proteins encoded by the early genes corresponding to these transcriptional puffs then regulate the activity of both the early puffs themselves and a much larger set of late puffs. Three of these early genes encode transcription factors that play critical regulatory roles during metamorphosis. Here we report the cloning, DNA sequence, genomic structure, ecdysone inducibility, and temporal expression of an early gene residing in the 23E early puff and denoted E23 (Early gene at 23). In contrast to other early genes, E23 encodes a protein with similarity to ATP-binding cassette transporters. Using heat shock-inducible transgenes, we found that E23 overexpression not only produces phenotypic abnormalities and lethality, but also interferes with ecdysone-mediated gene activation, demonstrating that E23 is capable of modulating the ecdysone response. Our results suggest the existence of a previously unrecognized regulatory mechanism for modulating steroid hormone signaling in Drosophila.

A dual role of 20-hydroxyecdysone in the control of protein synthesis related to DNA puff activity in the anterior region of Bradysia hygida (Diptera, Sciaridae) salivary gland

During the last 30 h of the larval stage, the salivary glands of Bradysia hygida show the amplification of some genes, resulting in the formation of two successive groups of DNA puffs, which direct the synthesis of two different sets of polypeptides. Incubation of anterior (S1) salivary gland regions, at age E7, beginning of first group of DNA puffs activity, in culture medium for 2 to 10 h results in a decrease in the synthesis of the polypeptides characteristic of this period. However, during subsequent incubation (from E7 to E7+12 h-24 h), when the second group of DNA puffs is active, S1 regions were able to synthesize some polypeptides characteristic of this period. The role of 20-OH ecdysone was studied, in vitro and in vivo, during these two periods of protein synthesis in S1 regions. The presence of the hormone was shown to be necessary to maintain, in vitro, the synthesis of the first set of polypeptides and was strongly inhibitory, in vitro and in vivo, to the synthesis of the second set of polypeptides. Thus, it is likely that the activity of the two distinct groups of DNA puffs is under opposite 20-OH-ecdysone control mechanisms.

The DHR78 nuclear receptor is required for ecdysteroid signaling during the onset of Drosophila metamorphosis

Pulses of ecdysteroids direct Drosophila through its life cycle by activating stage- and tissue-specific genetic regulatory hierarchies. Here we show that an orphan nuclear receptor, DHR78, functions at the top of the ecdysteroid regulatory hierarchies. Null mutations in DHR78 lead to lethality during the third larval instar with defects in ecdysteroid-triggered developmental responses. Consistent with these phenotypes, DHR78 mutants fail to activate the mid-third instar regulatory hierarchy that prepares the animal for metamorphosis. DHR78 protein is bound to many ecdysteroid-regulated puff loci, suggesting that DHR78 directly regulates puff gene expression. In addition, ectopic expression of DHR78 has no effects on development, indicating that its activity is regulated post-translationally. We propose that DHR78 is a ligand-activated receptor that plays a central role in directing the onset of Drosophila metamorphosis.

Drosophila ecdysone receptor functions as a constitutive activator in yeast

Transcriptional activation of the Drosophila ecdysone receptor (EcR) was studied in yeast cells, which carry a reporter plasmid containing the ecdysone response element in the absence or presence of its heterodimeric partners, ultraspiracle protein (USP) or human retinoid X receptor (RXRalpha). High constitutive transcriptional activation was detected in the yeast strain expressing EcR, but not USP or RXRalpha in the absence of ponasterone or muristerone A. Incubation of these ligands with yeast cells coexpressing EcR and USP or RXRalpha did not enhance the constitutive transcriptional activity. However, specific ligand binding using [3H]ponasterone A as a radioactive ligand was detected only in yeast extracts prepared from the yeast strain coexpressing EcR and USP, but not from yeast strains expressing only EcR or USP. The ligand binding characteristics of the EcR/USP complexes were similar to those reported in an insect cell line with a Kd value of 1.8 nM for [3H]ponasterone A. These data are in contrast to mammalian cell transfection studies, and indicate that the EcR is the only member of the nuclear receptor superfamily of ligand-activated transcription factors which functions as a constitutive transcriptional activator in yeast, although the EcR/USP complexes exhibit normal ligand binding properties.

The Drosophila 63F early puff contains E63-1, an ecdysone-inducible gene that encodes a novel Ca(2+)-binding protein

Pulses of ecdysone at the end of Drosophila larval development dramatically reprogram gene expression as they signal the onset of metamorphosis. Ecdysone directly induces several early puffs in the salivary gland polytene chromosomes that, in turn, activate many late puffs. Three early puffs, at 2B5, 74EF, and 75B, have been studied at the molecular level. Each contains a single ecdysone primary-response gene that encodes a family of widely expressed transcription factors. We report here a molecular characterization of the 63F early puff. Unexpectedly, we have found this locus to be significantly different from the previously characterized early puff loci. First, the 63F puff contains a pair of ecdysone-inducible genes that are transcribed in the larval salivary glands: E63-1 and E63-2. Second, E63-1 induction in late third instar larvae appears to be highly tissue-specific, restricted to the salivary gland. Third, E63-1 encodes a novel Ca(2+)-binding protein related to calmodulin. The discovery of an ecdysone-inducible Ca(2+)-binding protein provides a foundation for integrating steroid hormone and calcium second messenger signaling pathways and generates an additional level for potential regulation of the ecdysone response.

The Drosophila E74 gene is required for metamorphosis and plays a role in the polytene chromosome puffing response to ecdysone

The steroid hormone ecdysone initiates Drosophila metamorphosis by reprogramming gene expression during late larval and prepupal development. The ecdysone-inducible gene E74, a member of the ets proto-oncogene family, has been proposed to play a key role in this process. E74 is encoded within the 74EF early puff and consists of two overlapping transcription units, E74A and E74B. To assess the function(s) of E74 during metamorphosis, we have isolated and characterized recessive loss-of-function mutations specific to each transcription unit. We find that mutations in E74A and E74B are predominantly lethal during prepupal and pupal development, consistent with a critical role for their gene products in metamorphosis. Phenotypic analysis reveals that E74 function is required for both pupariation and pupation, and for the metamorphosis of both larval and imaginal tissues. E74B mutants are defective in puparium formation and head eversion and die as prepupae or cryptocephalic pupae, while E74A mutants pupariate normally and die either as prepupae or pharate adults. We have also investigated the effects of the E74 mutations on gene expression by examining the puffing pattern of the salivary gland polytene chromosomes in newly formed mutant prepupae. Most puffs are only modestly affected by the E74B mutation, whereas a subset of late puffs are sub-maximally induced in E74A mutant prepupae. These observations are consistent with Ashburner's proposal that early puff proteins induce the formation of late puffs, and define E74A as a regulator of late puff activity. They also demonstrate that E74 plays a wide role in reshaping the insect during metamorphosis, affecting tissues other than the salivary gland in which it was originally identified.

The Drosophila E74 gene is required for the proper stage- and tissue-specific transcription of ecdysone-regulated genes at the onset of metamorphosis

The steroid hormone ecdysone directly induces a small set of early genes, visible as puffs in the larval salivary gland polytene chromosomes, as it signals the onset of Drosophila metamorphorsis. The products of these genes appear to function as regulators that both repress their own expression and induce a large set of secondary-response late genes. We have identified recessive loss-of-function mutations in the early gene E74, a member of the ets protooncogene family that encodes two related DNA-binding proteins, E74A and E74B. These mutations cause defects in pupariation and pupation, and result in lethality during metamorphosis. Here we extend our phenotypic characterization of the E74A and E74B mutant alleles to the molecular level by examining their effects on the transcription of over 30 ecdysone-regulated genes. We show that the transcription of most ecdysone primary-response genes during late larval and prepupal development is unaffected by the E74 mutations. Rather, we find that E74 is necessary for the appropriate regulation of many ecdysone secondary-response genes. E74B is required for the maximal induction of glue genes in mid third instar larval salivary glands, while E74A is required in early prepupae for the proper timing and maximal induction of a subset of late genes. E74 activity is also necessary for the correct regulation of genes expressed predominantly in the fat body, epidermis or imaginal discs. These observations confirm that E74 plays a critical role in regulating transcription during the early stages of Drosophila metamorphosis. In addition, the widespread effects of the E74 mutations on transcription indicate that E74 functions in regulatory hierarchies not only in the larval salivary gland, but throughout the entire organism.

Cloning and developmental expression of the ecdysone receptor gene from the spruce budworm, Choristoneura fumiferana

Degenerate oligonucleotides were designed on the basis of conserved amino acid sequences in the DNA and ligand-binding regions of the members of the steroid hormone receptor superfamily. Using these oligonucleotides in RNA-PCR, a cDNA fragment was isolated from the spruce budworm, Choristoneura fumiferana. Comparison of the deduced amino acid sequence of this cDNA fragment with the members of the steroid hormone receptor superfamily suggested that this PCR fragment is a region of the ecdysone receptor from C. fumiferana. Using this cDNA fragment as a probe, 10 clones were isolated from a cDNA library that was constructed using the RNA from 4- and 5-day old embryos of C. fumiferana. Two cDNA clones (1.3 and 3 kb) that overlap and show amino acid identity with Drosophila melanogaster ecdysone receptor B-1 isoform (DmEcR) were characterized and sequenced. The longest open reading frame had 539 codons and covered the complete EcR coding region. The deduced amino acid sequence of this open reading frame had all five of the regions typical for a steroid hormone nuclear receptor. The C domain or DNA binding region showed the highest identity wit EcR proteins from D. melanogaster, Chironomus tendons, Aedes aegypti, Manduca sexta, and Bombyx mori. The A/B region, D domain or hinge region, E domain, or ligand binding region also showed significant amino acid similarity with the EcR proteins from the five insects mentioned above. The C. fumiferana ecdysteroid receptor (CfEcR) cDNA probe detected a 6.0-kb mRNA that was present throughout the development of C. fumiferana. The CfEcR mRNA increases in abundance at the time of the ecdysteroid peak during the molting phase in the embryonic, larval and pupal stages but remains low during the intermolt period. In the 6th instar larvae, the 6-kb CfEcR mRNA was detected in the epidermis, fat body, and midgut and maximum expression was observed during the prepupal peak of ecdysteroids in the hemolymph. CfEcR mRNA was induced in ecdysone treated CF-203 cells as well in the epidermis and midgut of larvae that were fed the nonsteroidal ecdysteroid agonist, RH-5992. The induction occurred within an hour and reached maximum levels around 3 hr, after which it decreased to the basal level by 6 hr. In vitro transcription and translation of the CfEcR cDNA yielded a 67-Kda protein that bound to the ecdysone response element (EcRE) as a heterodimer, along with the ultraspiracle protein.

A molecular mechanism for the stage specificity of the Drosophila prepupal genetic response to ecdysone

Two successive pulses of ecdysone signal the ends of larval and prepupal development in Drosophila, inducing early and late puffs in the salivary gland polytene chromosomes. Early puff induction in prepupae is dependent on a preceding period of protein synthesis and low ecdysone concentration. We demonstrate here that the competence acquired during this interval can be provided by beta FTZ-F1, a nuclear hormone receptor superfamily member derived from the 75CD mid-prepupal puff. We show that beta FTZ-F1 represses its own transcription and is repressed by ecdysone, explaining its brief expression in mid-prepupae. We further show that ectopic beta FTZ-F1 expression leads to enhanced levels of ecdysone-induced BR-C, E74, and E75 early gene transcription and premature induction of the stage-specific 93F early puff and E93 transcription. These findings indicate that beta FTZ-F1 plays a central role in the prepupal genetic response to ecdysone and provide a molecular mechanism for stage-specific responses to steroid hormones.

The Drosophila 78C early late puff contains E78, an ecdysone-inducible gene that encodes a novel member of the nuclear hormone receptor superfamily

We report the molecular definition of an early late puff locus, at position 78C, that is inducible by ecdysone at the onset of Drosophila metamorphosis. This puff contains a single ecdysone-inducible gene consisting of two nested transcription units, E78A and E78B. E78A mRNA is expressed during a brief interval in mid-pupal development and encodes a novel member of the nuclear hormone receptor superfamily. E78B encodes a truncated receptor isoform that lacks the DNA-binding domain and is predominantly expressed at puparium formation and immediately following E78A in pupae. E78B is directly inducible by ecdysone in late third instar larvae and depends on ecdysone-induced protein synthesis for its maximal level of expression. These observations indicate that E78 represents a distinct subset of early ecdysone-inducible regulatory genes.

The Drosophila Broad-Complex plays a key role in controlling ecdysone-regulated gene expression at the onset of metamorphosis

During Drosophila third instar larval development, one or more pulses of the steroid hormone ecdysone activate three temporally distinct sets of genes in the salivary glands, represented by puffs in the polytene chromosomes. The intermolt genes are induced first, in mid-third instar larvae; these genes encode a protein glue used by the animal to adhere itself to a solid substrate for metamorphosis. The intermolt genes are repressed at puparium formation as a high titer ecdysone pulse directly induces a small set of early regulatory genes. The early genes both repress their own expression and activate more than 100 late secondary-response genes. The Broad-Complex (BR-C) is an early ecdysone-inducible gene that encodes a family of DNA binding proteins defined by at least three lethal complementation groups: br, rbp, and l(1)2Bc. We have found that the BR-C is critical for the appropriate regulation of all three classes of ecdysone-inducible genes. Both rbp and l(1)2Bc are required for glue gene induction in mid-third instar larvae. In addition, the l(1)2Bc function is required for glue gene repression in prepupae; in l(1)2Bc mutants the glue genes are re-induced by the late prepupal ecdysone pulse, recapitulating a mid-third instar regulatory response at an inappropriate stage in development. The l(1)2Bc function is also required for the complete ecdysone induction of some early mRNAs (E74A, E75A, and BR-C) and efficient repression of most early mRNAs in prepupae. Like the intermolt secondary-response genes, the late secondary-response genes are absolutely dependent on rbp for their induction. An effect of l(1)2Bc mutations on late gene activity can also be detected, but is most likely a secondary consequence of the submaximal ecdysone-induction of a subset of early regulatory products. Our results indicate that the BR-C plays a key role in dictating the stage-specificity of the ecdysone response. In addition, the ecdysone-receptor protein complex alone is not sufficient for appropriate induction of the early primary-response genes, but requires the prior expression of BR-C proteins. These studies define the BR-C as a key regulator of gene activity at the onset of metamorphosis in Drosophila.

Developmental changes in the presence of ecdysteroid receptors in the central nervous system of third instar larvae of Sarcophaga bullata

Radiolabeled ponasterone A, a high affinity ligand for ecdysteroid receptors which agonises the effects of 20-hydroxyecdysone, was used in combination with thaw-mount autoradiography to study the stage-specific presence of ecdysteroid receptors in the central nervous system of Sarcophaga bullata. In third instar larvae, nuclear high affinity binding of tritiated or iodinated ponasterone A occurs in the same target cells and both radioligands were displaced by an 100-fold excess of unlabeled ponasterone A or an 500-fold excess of 20-hydroxyecdysone. Target neurons for ponasterone A appear first in the third instar larvae on day 4.0 (early wandering stage) where many cells of the perineurium, ring gland, lateral neurosecretory cells in the brain and certain neurons in abdominal ganglia exhibit nuclear high-affinity binding for ponasterone A. At day 5.5 after larviposition, less binding is present in the perineurium but many neurons, including certain neurosecretory cells in the pars intercerebralis, pars lateralis, tritocerebrum, and neurosecretory cell groups 7, 8, 9, and 10 of the dipteran suboesophageal and abdominal ganglia show increased nuclear ecdysteroid binding. At this stage nuclear binding also occurs in the ring gland except in the central corpus allatum and for the first time in the neurons of the inner optic lobes. The results show that ecdysteroid receptors are present in distinct cerebral neurons and that their expression or ecdysteroid-binding capability is under developmental control.

The Drosophila EcR gene encodes an ecdysone receptor, a new member of the steroid receptor superfamily

The steroid hormone ecdysone triggers coordinate changes in Drosophila tissue development that result in metamorphosis. To advance our understanding of the genetic regulatory hierarchies controlling this tissue response, we have isolated and characterized a gene, EcR, for a new steroid receptor homolog and have shown that it encodes an ecdysone receptor. First, EcR protein binds active ecdysteroids and is antigenically indistinguishable from the ecdysone-binding protein previously observed in extracts of Drosophila cell lines and tissues. Second, EcR protein binds DNA with high specificity at ecdysone response elements. Third, ecdysone-responsive cultured cells express EcR, whereas ecdysone-resistant cells derived from them are deficient in EcR. Expression of EcR in such resistant cells by transfection restores their ability to respond to the hormone. As expected, EcR is nuclear and found in all ecdysone target tissues examined. Furthermore, the EcR gene is expressed at each developmental stage marked by a pulse of ecdysone.

Developmental changes in fat body and midgut chromosomes of Drosophila auraria

Changes in puffing activity of fat body (FB) and midgut (MG) chromosomes of Drosophila auraria during late larval and white prepupal development as well as after in vitro culture with or without ecdysterone were studied and compared with those of the salivary gland (SG). The Balbiani Rings characteristic of the SG chromosomes of D. auraria, are not formed in FB and MG. Most of the inverted tandem chromosomal duplications that have been found to be common to all three tissues showed differentiation of puffing activity of the bands considered to be homologous. The major early ecdysone puffs 73A and 73B (considered to be homologues of D. melanogaster puffs 74EF and 75B, respectively), together with other early ecdysone puffs were present in all three tissues. Clear intermoult and postintermoult puffs were not evident in FB and MG chromosomes. However, a small set of late ecdysone puffs could be scored in FB, while no late ecdysone puffs were abserved in MG. Other tissue-specific puffs were identified, but a very small number of them were limited to MG.

Ecdysone coordinates the timing and amounts of E74A and E74B transcription in Drosophila

Pulses of the steroid hormone ecdysone function as temporal signals to coordinate the development of both larval and adult tissues in Drosophila. Ecdysone acts by triggering a genetic regulatory hierarchy that can be visualized as puffs in the larval polytene chromosomes. In an effort to understand how the ecdysone signal is transduced to result in sequential gene activation, we are studying the transcriptional control of E74, an early gene that appears to play a regulatory role in the hierarchy. Northern blot analysis of RNA isolated from staged animals or cultured organs was used to characterize the effects of ecdysone on E74 transcription. Ecdysone directly activates both E74A and E74B promoters. E74B mRNA precedes that of E74A, each mRNA appearing with delay times that agree with their primary transcript lengths and our previous transcription elongation rate measurement of approximately 1.1 kb/min. The earlier appearance of E74B transcripts is enhanced by its activation at an approximately 25-fold lower ecdysone concentration than E74A. E74B is further distinguished from E74A by its repression at a significantly higher ecdysone concentration than that required for its induction, close to the concentration required for E74A activation. These regulatory properties lead to an ecdysone-induced switch in E74 expression, with an initial burst of E74B transcription followed by a burst of E74A transcription. We also show that the patterns of ecdysone-induced E74A and E74B transcription vary in four ecdysone target tissues. These studies provide a means to translate the profile of a hormone pulse into different amounts and times of regulatory gene expression that, in turn, could direct different developmental responses in a temporally and spatially regulated manner.

Puffs and gene regulation--molecular insights into the Drosophila ecdysone regulatory hierarchy

Sixteen years ago, Michael Ashburner and his colleagues proposed a hierarchical model for the genetic control of polytene chromosome puffing by the steroid hormone ecdysone. The recent molecular isolation and characterization of three early ecdysone-inducible genes has confirmed many aspects of this model--these genes are directly induced by ecdysone, repressed by ecdysone-induced proteins, and appear to encode DNA binding regulatory proteins. The three early genes are also remarkably similar in structure. They are all unusually long and complex, with multiple transcripts that direct the synthesis of several related proteins from each locus. Proteins encoded by two of the early genes bind to both early and late ecdysone-induced puffs, implying that they are key regulators in the hierarchy.

Spatial and temporal patterns of E74 transcription during Drosophila development

The E74 gene occupies one of the early puff loci (74EF) central to the Ashburner model for the ecdysone-induced puffing pattern in Drosophila. In support of this model, we show that the E74A promoter is directly activated by ecdysone and is subsequently repressed by ecdysone-induced proteins. Further support derives from the correspondence observed between 74EF puff size and the accumulation of nascent transcripts on the E74A unit. These transcripts elongate at 1.1 kb/min so that this 60 kb unit acts as a timer, delaying the appearance of its mRNA by 1 hr. E74A transcription is induced in a variety of ecdysone target tissues in late third instar larvae and during each of the ecdysone pulses that mark the six stages of Drosophila development. These results support an extension of the Ashburner model in which ecdysone pulses coordinate tissue development. The temporal pattern of E74B transcription overlaps but is distinct from that of E74A.

Effects of juvenile hormone on the ecdysone response of Drosophila Kc cells

Drosophila Kc cells are ecdysone-responsive: hormone treatment leads rapidly to increased synthesis of several ecdysone-inducible polypeptides (EIPs) and to commitment to eventual proliferative arrest. Later, the treated cells undergo morphological transformation, cease to proliferate, and develop new enzymatic activities, notably, acetylcholinesterase (AChE) activity. These responses have proven useful as models for studying ecdysone action. Here we report the sensitivity of Kc cells to another important insect developmental regulator--juvenile hormone (JH). We find that JH inhibits some, but not all, aspects of the ecdysone response. When Kc cells are treated with ecdysone in the presence of either natural JHs or synthetic analogues, the morphological and proliferative responses are inhibited and AChE induction is blocked. Most striking is that JHs protect the cells from the rapid proliferative commitment induced by ecdysone alone. The JH effects exhibit reasonable dose-response curves with half-maximal responses occurring at very low JH concentrations. Nonetheless, even at high JH concentrations the inhibitory effects are incomplete. It is interesting that EIP induction appears to be refractory to JH. It seems clear that JH is not simply a generalized inhibitor of ecdysone-induced responses.

Hormonal control of behavior: amines and the biasing of behavioral output in lobsters

Hormones and neurohormones act on the nervous system to produce important changes in behavior. Amine actions in the lobster nervous system and their possible relations to aggressive behavior in lobsters were studied in order to explore how such changes might come about.

Genetics of esterases in Drosophila. IX. Characterization of the JH-esterase in D. virilis

The kinetic characteristics of the main isozymes of Drosophila virilis esterase were studied and Km values of esterase-2, -4, and -6 and p-esterase for alpha- and beta-naphthyl acetate were obtained. Juvenile hormone (JH) was shown to inhibit the p-esterase activity when in competition with beta-naphthyl acetate and the general esterase inhibitor, diisopropylphosphofluoridate (DFP), was shown to inhibit all the components of the D. virilis esterase patterns except p-esterase. While studying the changes of p-esterase activity in D. virilis ontogenesis, the increase in p-esterase activity in the wandering larvae, prepupae, and early pupae was found to correlate with a decrease in JH titer at these stages. The decrease in JH level in a temperature-sensitive lethal mutant larvae of D. virilis at high temperatures was shown to correlate with increased p-esterase activity. These results confirm that p-esterase of D. virilis is JH-esterase.

20 (OH) ecdysone-induced transition from intermolt to premolt protein biosynthesis patterns in the hypodermis of the crayfish, Astacus leptodactylus, in vitro

20 (OH) Ecdysone-induced alteration of protein biosynthesis and secretion by the hypodermis of the crayfish Astacus leptodactylus was studied using isolated tissues in vitro. Characteristic quantitative and qualitative changes of late intermolt tissues are governed by the hormone in a dose- and time-dependent manner. The greatest response to the hormone was observed in tissues which were exposed for 48 hr to 10(-8) M 20 (OH) ecdysone, followed by 1 day of hormone withdrawal. The observed differences correspond to the reprogramming in protein biosynthesis after transition from intermolt to the premolt stage.

Ecdysteroids during the third larval instar in 1(3)ecd-1ts, a temperature-sensitive mutant of Drosophila melanogaster

The temperature-sensitive 1(3)ecd-1ts mutation (A. Garen, L. Kauvar, and J.A. Lepesant (1977). Proc. Natl. Acad. Sci USA 74, 5099-5103.) has been used in several laboratories to obtain Drosophila larvae deprived of moulting hormone. The development of mutants and controls during the third larval instar at permissive (20 degrees C) and restrictive temperatures (29 degrees C) was compared. Pupariation was inhibited when larvae were shifted to the restrictive temperature immediately at the second moult. The permanent larvae obtained remained active, did not leave the food, and reached a maximum weight superior to the weight of controls. Ecdysteroids were studied during the third larval instar by HPLC analysis and radioimmunoassays. A careful synchronization of the larvae at the second moult enabled the confirmation that at least one ecdysteroid peak occurs during the third larval instar, prior to the wandering stage in controls (20 or 29 degrees C). Ecdysone was then the predominant moulting hormone, whereas 20-hydroxyecdysone was the main ecdysteroid at the time of pupariation. Low levels of ecdysteroid were measured in mutant larvae shifted to 29 degrees C immediately at the second moult but larvae completely deprived of immunoreactive material were never observed. Nearly normal levels of ecdysteroids appeared at 27.5 degrees C. Feeding ecd-1 larvae maintained at restrictive temperature on 20-hydroxyecdysone-yeast mixture for 16 hr triggered abortive pupariation. Ecdysteroid levels were measured after the return of the larvae to the standard medium; normal levels were restored 24 hr later. The mutant ecd-1 appears to present interesting opportunities for the detailed study of the hormonal induction of a developmental process during the third larval instar.(ABSTRACT TRUNCATED AT 250 WORDS)

The occurrence of ecdysteroids in the cestode, Moniezia expansa

The occurrence of free ecdysteroids in the sheep cestode, Moniezia expansa, was demonstrated. Significant amounts of conjugated ecdysteroids were not detected. Characterization of the free hormones by high-performance liquid chromatography monitoring fractions by radioimmunoassay, and by gas chromatography/mass spectrometry (selected ion monitoring) indicated the presence of ecdysone, 20-hydroxyecdysone and 20,26-dihydroxyecdysone. Analysis of the ecdysteroids by radioimmunoassay in segments along part of the strobila indicated that the anterior parts contained the greatest amount of hormone. GC/MS (SIM) analysis of the hormones in a strobilar segment containing the most mature proglottids suggested the presence of several ecdysteroid metabolites.

Changes in cell surface proteins of culturedDrosophila cells exposed to 20-hydroxyecdysone

Drosophila cell lines have provided popular material for study of the mechanisms by which steroid hormones regulate cellular events. Previous investigations at the organismic or organ level have suggested that ecdysteroids are bound by a cytoplasmic receptor, and that the resulting complex translocates to the nucleus where it results in active transcription of a few genes. The protein products of these primary responding genes then modulate a larger series of secondary transcriptional changes. In cultured cells, other investigators have detected the hormonally-induced synthesis of only 4-5 new polypeptides through 72 h of treatment. Although these proteins may represent the gene products associated with the primary response, this small number of changes is surprising in view of the rapid morphological alteration of the cells and changes in such surface-mediated behavior as substrate adhesion and agglutinability observed within the same time interval. In this report, we show that lactoperoxidase-catalyzed radioiodination followed by 2-dimensional polyacrylamide gel electrophoresis and autoradiography provide an effective protocol for visualizing cell surface proteins of a Drosophila cell line. Among the more than 175 labeled species detected, comparisons of control cells with those treated by 20-hydroxyecdysone for 72 h shows at least 27 differences. We interpret these differences as the result of the secondary transcriptional response to the hormone.