PubMed Health⌕ Search

Biomedical subjects

C S Thummel

Publications and source records attributed to C S Thummel.

At least 19 recordsLinked to original sources
PubMed2002

Ecdysone-regulated puff genes 2000.

The Ashburner model for the hormonal control of polytene chromosome puffing has provided a strong foundation for understanding the basic mechanisms of steroid-regulated gene expression (Cold Spring Harbor Symp. Quant. Biol. 38 (1974) 655). According to this model, the steroid hormone 20-hydroxyecdysone (referred here as ecdysone) directly induces the expression of a small set of early regulatory genes. These genes, in turn, induce a much larger set of late target genes that play a more direct role in controlling the biological responses to the hormone. The recent characterization of two early puff genes, E63-1 and E23, and three late puff genes, D-spinophilin, L63, and L82, provide further confirmation of the Ashburner model. In addition, these studies provide exciting new directions for our understanding of ecdysone signaling. Overexpression studies of E63-1 implicate this gene in directing calcium-dependent salivary gland glue secretion. In contrast, overexpression of E23 indicates that this ABC transporter family member may negatively regulate ecdysone signaling by actively transporting the hormone out of target cells. Finally, genetic studies of the L63 and L82 late genes reveal unexpected possible functions for ecdysone in controlling developmental timing and growth. This review surveys the recent characterization of these ecdysone-inducible genes and provides an overview of how they expand our understanding of ecdysone functions during development.

ATP-Binding Cassette Transporters↗
PubMed2002

AP-1, but not NF-kappa B, is required for efficient steroid-triggered cell death in Drosophila.

Extensive studies in vertebrate cells have assigned a central role to Rel/NF-kappa B and AP-1 family members in the control of apoptosis. We ask here whether parallel pathways might function in Drosophila by determining if Rel/NF-kappa B or AP-1 family members contribute to the steroid-triggered death of larval salivary glands during Drosophila metamorphosis. We show that two of the three Drosophila Rel/NF-kappa B genes are expressed in doomed salivary glands and that one family member, Dif, is induced in a stage-specific manner immediately before the onset of programmed cell death. Similarly, Djun is expressed for many hours before salivary gland cell death while Dfos is induced in a stage-specific manner, immediately before this tissue is destroyed. We show that null mutations in the three Drosophila Rel/NF-kappa B family members, either alone or in combination, have no apparent effect on this death response. In contrast, Dfos is required for the proper timing of larval salivary gland cell death as well as the proper induction of key death genes. This study demonstrates a role for AP-1 in the stage-specific steroid-triggered programmed cell death of larval tissues during Drosophila metamorphosis.

Animals↗
PubMed2001

Steroid-triggered death by autophagy.

Programmed cell death is a critical part of normal development, removing obsolete tissues or cells and sculpting body parts to assume their appropriate form and function. Most programmed cell death occurs by apoptosis of individual cells or autophagy of groups of cells. Although these pathways have distinct morphological characteristics, they also have a number of features in common, suggesting some overlap in their regulation. A recent paper by Lee and Baehrecke provides further support for this proposal.(1) These authors present, for the first time, a genetic analysis of autophagy, using the steroid-triggered metamorphosis of Drosophila as a model system. They demonstrate a remarkable degree of overlap between the control of apoptosis and autophagy as well as a key role for the steroid-inducible gene E93 in directing the autophagic death response. This paper also shows that E93 can direct cell death independently from the known death-inducer genes, defining a novel death pathway in Drosophila.

Animals↗
PubMed2001

Molecular mechanisms of developmental timing in C. elegans and Drosophila.

Characterization of the heterochronic genes has provided a strong foundation for understanding the molecular mechanisms of developmental timing in C. elegans. In apparent contrast, studies of developmental timing in Drosophila have demonstrated a central role for gene cascades triggered by the steroid hormone ecdysone. In this review, I survey the molecular mechanisms of developmental timing in C. elegans and Drosophila and outline how common regulatory pathways are beginning to emerge.

Animals↗
PubMed2000

Inducible expression of double-stranded RNA directs specific genetic interference in Drosophila.

BACKGROUND: The introduction of double-stranded RNA (dsRNA) can selectively interfere with gene expression in a wide variety of organisms, providing an ideal approach for functional genomics. Although this method has been used in Drosophila, it has been limited to studies of embryonic gene function. Only inefficient effects have been seen at later stages of development. RESULTS: When expressed under the control of a heat-inducible promoter, dsRNA interfered efficiently and specifically with gene expression during larval and prepupal development in Drosophila. Expression of dsRNA corresponding to the EcR ecdysone receptor gene generated defects in larval molting and metamorphosis, resulting in animals that failed to pupariate or prepupae that died with defects in larval tissue cell death and adult leg formation. In contrast, expression of dsRNA corresponding to the coding region of the betaFTZ-F1 orphan nuclear receptor had no effect on puparium formation, but led to an arrest of prepupal development, generating more severe lethal phenotypes than those seen with a weak betaFTZ-F1 loss-of-function allele. Animals that expressed either EcR or betaFTZ-F1 dsRNA showed defects in the expression of corresponding target genes, indicating that the observed developmental defects are caused by disruption of the genetic cascades that control the onset of metamorphosis. CONCLUSIONS: These results confirm and extend our understanding of EcR and betaFTZ-F1 function. They also demonstrate that dsRNA expression can inactivate Drosophila gene function at later stages of development, providing a new tool for functional genomic studies in Drosophila.

Animals↗
PubMed2000

The ecdysone regulatory pathway controls wing morphogenesis and integrin expression during Drosophila metamorphosis.

Drosophila imaginal discs are specified and patterned during embryonic and larval development, resulting in each cell acquiring a specific fate in the adult fly. Morphogenesis and differentiation of imaginal tissues, however, does not occur until metamorphosis, when pulses of the steroid hormone ecdysone direct these complex morphogenetic responses. In this paper, we focus on the role of ecdysone in regulating adult wing development during metamorphosis. We show that mutations in the EcR ecdysone receptor gene and crooked legs (crol), an ecdysone-inducible gene that encodes a family of zinc finger proteins, cause similar defects in wing morphogenesis and cell adhesion, indicating a role for ecdysone in these morphogenetic responses. We also show that crol and EcR mutations interact with mutations in genes encoding integrin subunits-a family of alphabeta heterodimeric cell surface receptors that mediate cell adhesion in many organisms. alpha-Integrin transcription is regulated by ecdysone in cultured larval organs and some changes in the temporal patterns of integrin expression correlate with the ecdysone titer profile during metamorphosis. Transcription of alpha- and beta-integrin subunits is also altered in crol and EcR mutants, indicating that integrin expression is dependent upon crol and EcR function. Finally, we describe a new hypomorphic mutation in EcR which indicates that different EcR isoforms can direct the development of adult appendages. This study provides evidence that ecdysone controls wing morphogenesis and cell adhesion by regulating integrin expression during metamorphosis. We also propose that ecdysone modulation of integrin expression might be widely used to control multiple aspects of adult development.

Alleles↗
PubMed2000

Transcriptional activation of the Drosophila ecdysone receptor by insect and plant ecdysteroids.

A number of insect ecdysteroids, plant ecdysteroids and juvenoids were assayed for their ability to activate Drosophila nuclear receptors in transfected tissue culture cells. Discrete modifications to 20-hydroxyecdysone, the apparent natural ligand for the ecdysone receptor (EcR), conferred dramatic changes on the transcriptional activity of this receptor, suggesting that other biologically relevant EcR ligands may exist. Conversely, none of the compounds tested had a significant effect on the activity of three Drosophila orphan nuclear receptors: DHR38, DHR78 or DHR96. Taken together, these results demonstrate the selectivity of EcR for a series of natural and synthetic ecdysone agonists and suggest that as yet untested compounds may be responsible for activating DHR38, DHR78 and DHR96.

Animals↗
PubMed2000

Steroid regulation of postembryonic development and reproduction in Drosophila.

Ecdysteroids trigger major developmental transitions in Drosophila, including larval molts and metamorphosis. Recent genetic studies strongly support a role for the Ecdysteroid receptor (EcR)/Ultraspiracle (USP) heterodimer as an ecdysteroid receptor at the onset of metamorphosis, functioning as both a transcriptional activator and repressor in vivo. Genetic analysis also indicates that USP, like its vertebrate homolog retinoid X receptor (RXR), might be involved in regulatory pathways independently of EcR. The ecdysteroid hierarchy was also shown recently to regulate Drosophila oogenesis and reproduction.

Animals↗
PubMed2000

E93 directs steroid-triggered programmed cell death in Drosophila.

Steroid hormones coordinate multiple cellular changes, yet the mechanisms by which these systemic signals are refined into stage- and tissue-specific responses remain poorly understood. Here we show that the Drosophila E93 gene determines the nature of a steroid-induced biological response. E93 mutants possess larval salivary glands that fail to undergo steroid-triggered programmed cell death, and E93 is expressed in cells immediately before the onset of death. E93 protein is bound to the sites of steroid-regulated and cell death genes on polytene chromosomes, and the expression of these genes is defective in E93 mutants. Furthermore, expression of E93 is sufficient to induce programmed cell death. We propose that the steroid induction of E93 determines a programmed cell death response during development.

Animals↗
PubMed2000

A steroid-triggered transcriptional hierarchy controls salivary gland cell death during Drosophila metamorphosis.

The steroid hormone ecdysone signals the stage-specific programmed cell death of the larval salivary glands during Drosophila metamorphosis. This response is preceded by an ecdysone-triggered switch in gene expression in which the diap2 death inhibitor is repressed and the reaper (rpr) and head involution defective (hid) death activators are induced. Here we show that rpr is induced directly by the ecdysone-receptor complex through an essential response element in the rpr promoter. The Broad-Complex (BR-C) is required for both rpr and hid transcription, while E74A is required for maximal levels of hid induction. diap2 induction is dependent on betaFTZ-F1, while E75A and E75B are each sufficient to repress diap2. This study identifies transcriptional regulators of programmed cell death in Drosophila and provides a direct link between a steroid signal and a programmed cell death response.

Animals↗
PubMed2000

Genetic analysis of the Drosophila 63F early puff. Characterization of mutations in E63-1 and maggie, a putative Tom22.

The 63F early puff in the larval salivary gland polytene chromosomes contains the divergently transcribed E63-1 and E63-2 ecdysone-inducible genes. E63-1 encodes a member of the EF-hand family of Ca(2+)-binding proteins, while E63-2 has no apparent open reading frame. To understand the functions of the E63 genes, we have determined the temporal and spatial patterns of E63-1 protein expression, as well as undertaken a genetic analysis of the 63F puff. We show that E63-1 is expressed in many embryonic and larval tissues, but the third-instar larval salivary gland is the only tissue where increases in protein levels correlate with increases in ecdysone titer. Furthermore, the subcellular distribution of E63-1 protein changes dynamically in the salivary glands at the onset of metamorphosis. E63-1 and E63-2 null mutations, however, have no effect on development or fertility. We have characterized 40 kb of the 63F region, defined as the interval between Ubi-p and E63-2, and have identified three lethal complementation groups that correspond to the dSc-2, ida, and mge genes. We show that mge mutations lead to first-instar larval lethality and that Mge protein is similar to the Tom22 mitochondrial import proteins of fungi, suggesting that it has a role in mitochondrial function.

Amino Acid Sequence↗
PubMed2000

An enhancer trap screen for ecdysone-inducible genes required for Drosophila adult leg morphogenesis.

Although extensive studies of Drosophila imaginal disc development have focused on proliferation and patterning, relatively little is known about how the patterned imaginal discs are transformed into adult structures during metamorphosis. Studies focused primarily on leg development have shown that this remarkable transformation is coordinated by pulses of the steroid hormone ecdysone and requires the function of ecdysone-inducible transcription factors as well as proteases and components of the contractile cytoskeleton and adherens junctions. Here, we describe a genetic screen aimed at expanding our understanding of the hormonal regulation of Drosophila adult leg morphogenesis. We screened 1300 lethal P-element enhancer trap insertions on the second chromosome for a series of sequential parameters including pupal lethality, defects in leg morphogenesis, and ecdysone-induced lacZ reporter gene expression. From this screen we identified four mutations, one of which corresponds to bancal, which encodes the Drosophila homolog of hnRNP K. We also identified vulcan, which encodes a protein that shares sequence similarity with a family of rat SAPAP proteins. Both bancal and vulcan are inducible by ecdysone, thus linking the hormone signal with leg morphogenesis. This screen provides new directions for understanding the hormonal regulation of leg development during Drosophila metamorphosis.

Amino Acid Sequence↗
PubMed1999

DHR3 is required for the prepupal-pupal transition and differentiation of adult structures during Drosophila metamorphosis.

Pulses of the steroid hormone ecdysone activate genetic regulatory hierarchies that coordinate the developmental changes associated with Drosophila metamorphosis. A high-titer ecdysone pulse at the end of larval development triggers puparium formation and induces expression of the DHR3 orphan nuclear receptor. Here we use both a heat-inducible DHR3 rescue construct and clonal analysis to define DHR3 functions during metamorphosis. Clonal analysis reveals requirements for DHR3 in the development of adult bristles, wings, and cuticle, and no apparent function in eye or leg development. DHR3 mutants rescued to the third larval instar also reveal essential functions during the onset of metamorphosis, leading to lethality during prepupal and early pupal stages. The phenotypes associated with these lethal phases are consistent with the effects of DHR3 mutations on ecdysone-regulated gene expression. Although DHR3 has been shown to be sufficient for early gene repression at puparium formation, it is not necessary for this response, indicating that other negative regulators may contribute to this pathway. In contrast, DHR3 is required for maximal expression of the midprepupal regulatory genes, EcR, E74B, and betaFTZ-1. Reductions in EcR and betaFTZ-F1 expression, in turn, lead to submaximal early gene induction in response to the prepupal ecdysone pulse and corresponding defects in adult head eversion and salivary gland cell death. These studies demonstrate that DHR3 is an essential regulator of the betaFTZ-F1 midprepupal competence factor, providing a functional link between the late larval and prepupal responses to ecdysone. Induction of DHR3 in early prepupae ensures that responses to the prepupal ecdysone pulse will be distinct from responses to the late larval pulse and thus that the animal progresses in an appropriate manner through the early stages of metamorphosis.

Animals↗
PubMed1999

The Drosophila beta FTZ-F1 orphan nuclear receptor provides competence for stage-specific responses to the steroid hormone ecdysone.

The acquisition of competence is a key mechanism for refining global signals to distinct spatial and temporal responses. The molecular basis of competence, however, remains poorly understood. Here, we show that the beta FTZ-F1 orphan nuclear receptor functions as a competence factor for stage-specific responses to the steroid hormone ecdysone during Drosophila metamorphosis. beta FTZ-F1 mutants pupariate normally in response to the late larval pulse of ecdysone but display defects in stage-specific responses to the subsequent ecdysone pulse in prepupae. The ecdysone-triggered genetic hierarchy that directs these developmental responses is severely attenuated in beta FTZ-F1 mutants, although ecdysone receptor expression is unaffected. This study define beta FTZ-F1 as an essential competence factor for stage-specific responses to a steroid signal and implicates interplay among nuclear receptors as a mechanism for achieving hormonal competence.

Alleles↗
PubMed1998

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.

Animals↗
PubMed1998

The RXR homolog ultraspiracle is an essential component of the Drosophila ecdysone receptor.

Pulses of the steroid hormone ecdysone function as key temporal signals during insect development, coordinating the major postembryonic developmental transitions, including molting and metamorphosis. In vitro studies have demonstrated that the EcR ecdysone receptor requires an RXR heterodimer partner for its activity, encoded by the ultraspiracle (usp) locus. We show here that usp exerts no apparent function in mid-third instar larvae, when a regulatory hierarchy prepares the animal for the onset of metamorphosis. Rather, usp is required in late third instar larvae for appropriate developmental and transcriptional responses to the ecdysone pulse that triggers puparium formation. The imaginal discs in usp mutants begin to evert but do not elongate or differentiate, the larval midgut and salivary glands fail to undergo programmed cell death and the adult midgut fails to form. Consistent with these developmental phenotypes, usp mutants show pleiotropic defects in ecdysone-regulated gene expression at the larval-prepupal transition. usp mutants also recapitulate aspects of a larval molt at puparium formation, forming a supernumerary cuticle. These observations indicate that usp is required for ecdysone receptor activity in vivo, demonstrate that the EcR/USP heterodimer functions in a stage-specific manner during the onset of metamorphosis and implicate a role for usp in the decision to molt or pupariate in response to ecdysone pulses during larval development.

Animals↗
PubMed1998

crooked legs encodes a family of zinc finger proteins required for leg morphogenesis and ecdysone-regulated gene expression during Drosophila metamorphosis.

Drosophila imaginal discs undergo extensive pattern formation during larval development, resulting in each cell acquiring a specific adult fate. The final manifestation of this pattern into adult structures is dependent on pulses of the steroid hormone ecdysone during metamorphosis, which trigger disc eversion, elongation and differentiation. We have defined genetic criteria that allow us to screen for ecdysone-inducible regulatory genes that are required for this transformation from patterned disc to adult structure. We describe here the first genetic locus isolated using these criteria: crooked legs (crol). crol mutants die during pupal development with defects in adult head eversion and leg morphogenesis. The crol gene is induced by ecdysone during the onset of metamorphosis and encodes at least three protein isoforms that contain 12-18 C2H2 zinc fingers. Consistent with this sequence motif, crol mutations have stage-specific effects on ecdysone-regulated gene expression. The EcR ecdysone receptor, and the BR-C, E74 and E75 early regulatory genes, are submaximally induced in crol mutants in response to the prepupal ecdysone pulse. These changes in gene activity are consistent with the crol lethal phenotypes and provide a basis for understanding the molecular mechanisms of crol action. The genetic criteria described here provide a new direction for identifying regulators of adult tissue development during insect metamorphosis.

Amino Acid Sequence↗