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

Steroid hormone-induced wingless ligands tune female intestinal size in Drosophila

Female reproduction comes at great expense to energy metabolism compensated by extensive organ adaptations including intestinal size. Upon mating, endocrine signals orchestrate a 30% net increase of absorptive epithelium. Mating increases production of the steroid hormone Ecdysone released by the Drosophila ovaries that stimulates intestinal stem cell (ISC) divisions. Here, we uncover the transcription factor crooked legs (crol) as an intraepithelial coordinator of Ecdysone-induced ISC mitosis. For the precise investigation of non-autonomous factors on ISC behaviour, we establish Rapport, a spatiotemporally-controlled dual expression and tracing system for the analysis of paracrine genetic manipulation while tracing ISC behaviour. Rapport tracing reveals that Ecdysone-induced Crol controls mitogenic Wnt/Wg-ligand expression from epithelial enterocytes activating ISC mitosis. Paracrine Wg stimulation is counterbalanced by Crol-repression of string/CDC25 and CyclinB autonomously in ISC. Rapport-based ISC tumours confirm paracrine stimulation through the Ecdysone-Crol-Wg axis on mitotic behaviour, whereas the autonomous anti-proliferative role of Crol in ISC is conserved in models of colorectal cancer. Finally, mathematical modelling corroborates increasing enterocyte numbers and Wnt/Wg-degradation to set a stable post-mating intestinal size. Together, our findings provide insights into the complex endocrine growth control mechanisms during mating-induced adaptations and might help untangling pleiotropic hormonal effects observed in gastrointestinal tumorigenesis.

Integrative genomic analyses reveal putative cell type-specific targets of the Drosophila ets transcription factor Pointed

The Ets domain transcription factors direct diverse biological processes throughout all metazoans and are implicated in development as well as in tumor initiation, progression and metastasis. The Drosophila Ets transcription factor Pointed (Pnt) is the downstream effector of the Epidermal growth factor receptor (Egfr) pathway and is required for cell cycle progression, specification, and differentiation of most cell types in the larval eye disc. Despite its critical role in development, very few targets of Pnt have been reported previously. Here, we employed an integrated approach by combining genome-wide single cell and bulk data to identify putative cell type-specific Pnt targets. First, we used chromatin immunoprecipitation with high-throughput sequencing (ChIP-seq) to determine the genome-wide occupancy of Pnt in late larval eye discs. We identified enriched regions that mapped to an average of 6,941 genes, the vast majority of which are novel putative Pnt targets. Next, we integrated ChIP-seq data with two other larval eye single cell genomics datasets (scRNA-seq and snATAC-seq) to reveal 157 putative cell type-specific Pnt targets that may help mediate unique cell type responses upon Egfr-induced differentiation. Finally, our integrated data also predicts cell type-specific functional enhancers that were not reported previously. Together, our study provides a greatly expanded list of putative cell type-specific Pnt targets in the eye and is a resource for future studies that will allow mechanistic insights into complex developmental processes regulated by Egfr signaling.

Opposing effects of ecdysone signaling regulate neuroblast proliferation to ensure coordination of brain and organism development

Growth regulation must be robust to ensure correct final size, but also adaptative to adjust to less favorable environmental conditions. Developmental coordination between whole-organism and the brain is particularly important, as the brain is a critical organ with little adaptability. Brain growth mainly depends on neural stem cell (NSC) proliferation to generate differentiated neural cells, it is however unclear how organism developmental progression is coordinated with NSCs. Here we demonstrate that the steroid hormone ecdysone plays a multi-step, stage specific role in regulating Drosophila NSCs, the neuroblasts. We used animals that are unable to synthesize ecdysone, to show that the developmental milestone called "critical weight peak", the peak that informs the body has reached minimum viable weight to survive metamorphosis, acts a checkpoint necessary to set neuroblast cell cycle pace during larval neurogenesis. The peaks of ecdysone that occur post-critical weight are no longer required to maintain neuroblast division rate. We additionally show that in a second stage, at the onset of pupariation, ecdysone is instead required to trigger neuroblast's proliferation exit and consequently the end of neurogenesis. We demonstrate that, without this signal from ecdysone, neuroblasts lose their ability to exit proliferation. Interestingly, although these neuroblasts proliferate for a longer period, the number of differentiated neurons is smaller compared to wild-type brains, suggesting a role for ecdysone in neuron maintenance. Our study provides insights into how neural stem cells coordinate their division rate with the pace of body growth, identifying a novel coordination mechanism between animal development and NSC proliferation.

Crol contributes to PRE-mediated repression and Polycomb group proteins recruitment in Drosophila

The Polycomb group (PcG) proteins are fundamental epigenetic regulators that control the repressive state of target genes in multicellular organisms. One of the open questions is defining the mechanisms of PcG recruitment to chromatin. In Drosophila, the crucial role in PcG recruitment is thought to belong to DNA-binding proteins associated with Polycomb response elements (PREs). However, current data suggests that not all PRE-binding factors have been identified. Here, we report the identification of the transcription factor Crooked legs (Crol) as a novel PcG recruiter. Crol is a C2H2-type Zinc Finger protein that directly binds to poly(G)-rich DNA sequences. Mutation of Crol binding sites as well as crol CRISPR/Cas9 knockout diminish the repressive activity of PREs in transgenes. Like other PRE-DNA binding proteins, Crol co-localizes with PcG proteins inside and outside of H3K27me3 domains. Crol knockout impairs the recruitment of the PRC1 subunit Polyhomeotic and the PRE-binding protein Combgap at a subset of sites. The decreased binding of PcG proteins is accompanied by dysregulated transcription of target genes. Overall, our study identified Crol as a new important player in PcG recruitment and epigenetic regulation.

Rethinking the ecdysteroid source during Drosophila pupal-adult development

Ecdysteroids, typified by 20-hydroxyecdysone (20E), are essential hormones for the development, reproduction and physiology of insects and other arthropods. For over half a century, the vinegar fly Drosophila melanogaster (Ephydroidea: Diptera) has been used as a model of ecdysteroid biology. Many aspects of the biosynthesis and regulation of ecdysteroids in this species are understood at the molecular level, particularly with respect to their secretion from the prothoracic gland (PG) cells of the ring gland, widely considered the dominant biosynthetic tissue during development. Discrete pulses of 20E orchestrate transitions during the D. melanogaster life cycle, the sources of which are generally well understood, apart from the large 20E pulse at the onset of pharate adult development, which has received little recent attention. As the source of this pharate adult pulse (PAP) is a curious blind spot in Drosophila endocrinology, we evaluate published biochemical and genetic data as they pertain to three hypotheses for the source of PAP 20E: the PG; an alternative biosynthetic tissue; or the recycling of stored 20E. Based on multiple lines of evidence, we contend the PAP cannot be derived from biosynthesis, with other data consistent with D. melanogaster able to recycle ecdysteroids before and during metamorphosis. Published data also suggest the PAP is conserved across Diptera, with evidence for pupal-adult ecdysteroid recycling occurring in other cyclorrhaphan flies. Further experimental work is required to test the ecdysteroid recycling hypothesis, which would establish fundamental knowledge of the function, regulation, and evolution of metamorphic hormones in dipterans and other insects.

Transient leg deformations during eclosion out of a tight confinement: A comparative study on seven species of flies, moths, ants and bees

Legs in dipteran pupae are tightly packed in a zigzag configuration. Changes in the shape or configuration of long podomeres during eclosion have been overlooked because they occur rapidly (in a few minutes) and the legs are hidden inside a tight opaque confinement: the puparium in the Cyclorrhapha, the obtect pupa in mosquitoes. We fixed insects at different times during eclosion and obtained a temporal description of changes in leg shape. At the start of eclosion in Calliphora vicina and Drosophila melanogaster, femora are buckled in between the joints. Later, the chain of podomeres straightened, pointing posterad. Initial deformation and further stretching were passive, exerted by forces external to the legs. The prerequisites for this are pliability of the tubular podomeres and anchoring of the tarsi to the confinement. Each femur was strongly crooked instead of buckled in the mosquito Aedes cantans. The site of bending shifted distad in the course of eclosion: a sort of peeling. In contrast, other insects (the moth Bombyx mori, the ants Formica polyctena and Formica rufa, the honey bee Apis mellifera) left their tight confinements without any change in the initial zigzag leg configuration and without transient deformations of initially straight femora and tibiae.

A Genetic Mosaic Screen Reveals Ecdysone-Responsive Genes Regulating Drosophila Oogenesis

Multiple aspects of Drosophila oogenesis, including germline stem cell activity, germ cell differentiation, and follicle survival, are regulated by the steroid hormone ecdysone. While the transcriptional targets of ecdysone signaling during development have been studied extensively, targets in the ovary remain largely unknown. Early studies of salivary gland polytene chromosomes led to a model in which ecdysone stimulates a hierarchical transcriptional cascade, wherein a core group of ecdysone-sensitive transcription factors induce tissue-specific responses by activating secondary branches of transcriptional targets. More recently, genome-wide approaches have identified hundreds of putative ecdysone-responsive targets. Determining whether these putative targets represent bona fide targets in vivo, however, requires that they be tested via traditional mutant analysis in a cell-type specific fashion. To investigate the molecular mechanisms whereby ecdysone signaling regulates oogenesis, we used genetic mosaic analysis to screen putative ecdysone-responsive genes for novel roles in the control of the earliest steps of oogenesis. We identified a cohort of genes required for stem cell maintenance, stem and progenitor cell proliferation, and follicle encapsulation, growth, and survival. These genes encode transcription factors, chromatin modulators, and factors required for RNA transport, stability, and ribosome biogenesis, suggesting that ecdysone might control a wide range of molecular processes during oogenesis. Our results suggest that, although ecdysone target genes are known to have cell type-specific roles, many ecdysone response genes that control larval or pupal cell types at developmental transitions are used reiteratively in the adult ovary. These results provide novel insights into the molecular mechanisms by which ecdysone signaling controls oogenesis, laying new ground for future studies.

Ecdysteroid promotes cell cycle progression in the Bombyx wing disc through activation of c-Myc

Developmental switching from growth to metamorphosis in imaginal primordia is an essential process of adult body planning in holometabolous insects. Although it is disciplined by a sequential action of the ecdysteroid, molecular mechanisms linking to cell proliferation are poorly understood. In the present study, we investigated the expression control of cell cycle-related genes by the ecdysteroid using the wing disc of the final-instar larvae of the silkworm, Bombyx mori. We found that the expression level of c-myc was remarkably elevated in the post-feeding cell proliferation phase, which coincided with a small increase in ecdysteroid titer. An in vitro wing disc culture showed that supplementation of the moderate level of the ecdysteroid upregulated c-myc expression within an hour and subsequently increased the expression of cell cycle core regulators, including A-, B-, D-, and E-type cyclin genes, Cdc25 and E2F1. We demonstrated that c-myc upregulation by the ecdysteroid was not inhibited in the presence of a protein synthesis inhibitor, suggesting a possibility that the ecdysteroid directly stimulates c-myc expression. Finally, results from the administration of a c-Myc inhibitor demonstrated that c-Myc plays an essential role in 20E-inducible cell proliferation. These findings suggested a novel pathway for ecdysteroid-inducible cell proliferation in insects, and it is likely to be conserved between insects and mammals in terms of steroid hormone regulation.

Genetic control of specificity to steroid-triggered responses in Drosophila

Steroid hormones trigger a wide variety of biological responses through stage- and tissue-specific activation of target gene expression. The mechanisms that provide specificity to systemically released pulses of steroids, however, remain poorly understood. We previously completed a forward genetic screen for mutations that disrupt the destruction of larval salivary glands during metamorphosis in Drosophila melanogaster, a process triggered by the steroid hormone 20-hydroxyecdysone (ecdysone). Here, we characterize 10 complementation groups mapped to genes from this screen. Most of these mutations disrupt the ecdysone-induced expression of death activators, thereby failing to initiate tissue destruction. However, other responses to ecdysone, even within salivary glands, occur normally in mutant animals. Many of these newly identified regulators of ecdysone signaling, including brwd3, med12, med24, pak, and psg2, represent novel components of the ecdysone-triggered transcriptional hierarchy. These genes function combinatorially to provide specificity to ecdysone pulses, amplifying the hormonal cue in a stage-, tissue-, and target gene-specific manner. Most of the ecdysone response genes identified in this screen encode homologs of mammalian nuclear receptor coregulators, demonstrating an unexpected degree of functional conservation in the mechanisms that regulate steroid signaling between insects and mammals.

The BTB-zinc finger transcription factor abrupt acts as an epithelial oncogene in Drosophila melanogaster through maintaining a progenitor-like cell state

The capacity of tumour cells to maintain continual overgrowth potential has been linked to the commandeering of normal self-renewal pathways. Using an epithelial cancer model in Drosophila melanogaster, we carried out an overexpression screen for oncogenes capable of cooperating with the loss of the epithelial apico-basal cell polarity regulator, scribbled (scrib), and identified the cell fate regulator, Abrupt, a BTB-zinc finger protein. Abrupt overexpression alone is insufficient to transform cells, but in cooperation with scrib loss of function, Abrupt promotes the formation of massive tumours in the eye/antennal disc. The steroid hormone receptor coactivator, Taiman (a homologue of SRC3/AIB1), is known to associate with Abrupt, and Taiman overexpression also drives tumour formation in cooperation with the loss of Scrib. Expression arrays and ChIP-Seq indicates that Abrupt overexpression represses a large number of genes, including steroid hormone-response genes and multiple cell fate regulators, thereby maintaining cells within an epithelial progenitor-like state. The progenitor-like state is characterised by the failure to express the conserved Eyes absent/Dachshund regulatory complex in the eye disc, and in the antennal disc by the failure to express cell fate regulators that define the temporal elaboration of the appendage along the proximo-distal axis downstream of Distalless. Loss of scrib promotes cooperation with Abrupt through impaired Hippo signalling, which is required and sufficient for cooperative overgrowth with Abrupt, and JNK (Jun kinase) signalling, which is required for tumour cell migration/invasion but not overgrowth. These results thus identify a novel cooperating oncogene, identify mammalian family members of which are also known oncogenes, and demonstrate that epithelial tumours in Drosophila can be characterised by the maintenance of a progenitor-like state.

Cancer is a multigenic process, involving cooperative interactions between oncogenes or tumour suppressors. In this study, in a genetic screen in the vinegar fly, Drosophila melanogaster, for genes that cooperate with a mutation in the cell polarity (shape) regulator, scribbled (scrib), we identify a novel cooperative oncogene, abrupt. Expression of abrupt in scrib mutant tissue in the developing eye/antennal epithelium results in overgrown invasive tumours. abrupt encodes a BTB-zinc finger transcription factor, which has homology to several cancer-causing proteins in humans, such as BCL6. Analysis of the Abrupt targets and misexpressed genes in abrupt expressing-tissue and abrupt-expressing scrib mutant tumours, revealed cell fate regulators as a major class of targets. Thus, our results reveal that deregulation of multiple cell fate factors by Abrupt expression in the context of polarity disruption is associated with a progenitor-like cell state and the formation of overgrown invasive tumours. Our findings suggest that defective polarity may also be a critical factor in BTB-zinc finger-driven human cancers, and warrants further investigation into this issue.

The Ecdysone receptor constrains wingless expression to pattern cell cycle across the Drosophila wing margin in a Cyclin B-dependent manner

Background

Ecdysone triggers transcriptional changes via the ecdysone receptor (EcR) to coordinate developmental programs of apoptosis, cell cycle and differentiation. Data suggests EcR affects cell cycle gene expression indirectly and here we identify Wingless as an intermediary factor linking EcR to cell cycle.

Results

We demonstrate EcR patterns cell cycle across the presumptive Drosophila wing margin by constraining wg transcription to modulate CycB expression, but not the previously identified Wg-targets dMyc or Stg. Furthermore co-knockdown of Wg restores CycB patterning in EcR knockdown clones. Wg is not a direct target of EcR, rather we demonstrate that repression of Wg by EcR is likely mediated by direct interaction between the EcR-responsive zinc finger transcription factor Crol and the wg promoter.

Conclusions

Thus we elucidate a critical mechanism potentially connecting ecdysone with patterning signals to ensure correct timing of cell cycle exit and differentiation during margin wing development.

Ecdysone control of developmental transitions: lessons from Drosophila research

The steroid hormone ecdysone is the central regulator of insect developmental transitions. Recent new advances in our understanding of ecdysone action have relied heavily on the application of Drosophila melanogaster molecular genetic tools to study insect metamorphosis. In this review, we focus on three major aspects of Drosophila ecdysone biology: (a) factors that regulate the timing of ecdysone release, (b) molecular basis of stage- and tissue-specific responses to ecdysone, and (c) feedback regulation and coordination of ecdysone signaling.

Transcriptome analysis of the planarian eye identifies ovo as a specific regulator of eye regeneration

Among the millions of invertebrate species with visual systems, the genetic basis of eye development and function is well understood only in Drosophila melanogaster. We describe an eye transcriptome for the planarian Schmidtea mediterranea. Planarian photoreceptors expressed orthologs of genes required for phototransduction and microvillus structure in Drosophila and vertebrates, and optic pigment cells expressed solute transporters and melanin synthesis enzymes similar to those active in the vertebrate retinal pigment epithelium. Orthologs of several planarian eye genes, such as bestrophin-1 and Usher syndrome genes, cause eye defects in mammals when perturbed and were not previously described to have roles in invertebrate eyes. Five previously undescribed planarian eye transcription factors were required for normal eye formation during head regeneration. In particular, a conserved, transcription-factor-encoding ovo gene was expressed from the earliest stages of eye regeneration and was required for regeneration of all cell types of the eye.

Why cyclin Y? A highly conserved cyclin with essential functions

Cyclin Y is one of the most highly conserved members of the cyclin superfamily of proteins, which are famous for their crucial roles in regulating the cell cycle and transcription. Despite this high degree of conservation, very little was known about Cyclin Y function prior to a handful of studies published in this past year. Cyclins typically function by activating cyclin-dependent kinases (Cdks) and one insight has come from the identification of a Cdk that is activated by Cyclin Y. Yeast two-hybrid data first linked Cyclin Y with Cdk14, known as Eip63E in Drosophila or PFTAIRE1 in vertebrates. In Drosophila, both Cyclin Y and Eip63E are essential at many stages of development, from embryogenesis to metamorphosis and null mutants show a similar spectrum of developmental defects. In cultured cells, Cyclin Y and Eip63E were shown to phosphorylate the Wg/Wnt co-receptor Arrow/LRP6 in a ligand-independent manner. Eip63E is recruited to LRP6 at the plasma membrane by interacting with Cyclin Y, which is tethered to the membrane through an N-terminal myristoylation. Cyclin Y-dependent LRP6 phosphorylation appears to prime the receptor for subsequent ligand-dependent phosphorylation and activation of the canonical Wnt signaling pathway. Interestingly, Wnt receptor phosphorylation and signaling is maximal in G₂/M when Cyclin Y is at its highest levels, suggesting that Cyclin Y may serve to entrain Wnt signaling to the cell cycle. Given the wide range of roles for Wnt signaling during development, these studies may help explain why Cyclin Y is required at several developmental stages and in turn why these proteins are so well conserved in metazoans.

Modifiers of notch transcriptional activity identified by genome-wide RNAi

Background

The Notch signaling pathway regulates a diverse array of developmental processes, and aberrant Notch signaling can lead to diseases, including cancer. To obtain a more comprehensive understanding of the genetic network that integrates into Notch signaling, we performed a genome-wide RNAi screen in Drosophila cell culture to identify genes that modify Notch-dependent transcription.

Results

Employing complementary data analyses, we found 399 putative modifiers: 189 promoting and 210 antagonizing Notch activated transcription. These modifiers included several known Notch interactors, validating the robustness of the assay. Many novel modifiers were also identified, covering a range of cellular localizations from the extracellular matrix to the nucleus, as well as a large number of proteins with unknown function. Chromatin-modifying proteins represent a major class of genes identified, including histone deacetylase and demethylase complex components and other chromatin modifying, remodeling and replacement factors. A protein-protein interaction map of the Notch-dependent transcription modifiers revealed that a large number of the identified proteins interact physically with these core chromatin components.

Conclusions

The genome-wide RNAi screen identified many genes that can modulate Notch transcriptional output. A protein interaction map of the identified genes highlighted a network of chromatin-modifying enzymes and remodelers that regulate Notch transcription. Our results open new avenues to explore the mechanisms of Notch signal regulation and the integration of this pathway into diverse cellular processes.

Cyclin Y is a novel conserved cyclin essential for development in Drosophila

The Drosophila gene CG14939 encodes a member of a highly conserved family of cyclins, the Y-type cyclins, which have not been functionally characterized in any organism. Here we report the generation and phenotypic characterization of a null mutant of CG14939, which we rename Cyclin Y (CycY). We show that the null mutant, CycY(E8), is homozygous lethal with most mutant animals arresting during pupal development. The mutant exhibits delayed larval growth and major developmental defects during metamorphosis, including impaired gas bubble translocation, head eversion, leg elongation, and adult tissue growth. Heat-shock-induced expression of CycY at different times during development resulted in variable levels of rescue, the timing of which suggests a key function for zygotic CycY during the transition from third instar larvae to prepupae. CycY also plays an essential role during embryogenesis since zygotic null embryos from null mothers fail to hatch into first instar larvae. We provide evidence that the CycY protein (CycY) interacts with Eip63E, a cyclin-dependent kinase (Cdk) for which no cyclin partner had previously been identified. Like CycY, the Eip63E gene has essential functions during embryogenesis, larval development, and metamorphosis. Our data suggest that CycY/Eip63E form a cyclin/Cdk complex that is essential for several developmental processes.

Nuclear receptors homo sapiens Rev-erbbeta and Drosophila melanogaster E75 are thiolate-ligated heme proteins which undergo redox-mediated ligand switching and bind CO and NO

Nuclear receptors E75, which regulates development in Drosophila melanogaster, and Rev-erbbeta, which regulates circadian rhythm in humans, bind heme within their ligand binding domains (LBD). The heme-bound ligand binding domains of E75 and Rev-erbbeta were studied using electronic absorption, MCD, resonance Raman, and EPR spectroscopies. Both proteins undergo redox-dependent ligand switching and CO- and NO-induced ligand displacement. In the Fe(III) oxidation state, the nuclear receptor hemes are low spin and 6-coordinate with cysteine(thiolate) as one of the two axial heme ligands. The sixth ligand is a neutral donor, presumably histidine. When the heme is reduced to the Fe(II) oxidation state, the cysteine(thiolate) is replaced by a different neutral donor ligand, whose identity is not known. CO binds to the Fe(II) heme in both E75(LBD) and Rev-erbbeta(LBD) opposite a sixth neutral ligand, plausibly the same histidine that served as the sixth ligand in the Fe(III) state. NO binds to the heme of both proteins; however, the NO-heme is 5-coordinate in E75 and 6-coordinate in Rev-erbbeta. These nuclear receptors exhibit coordination characteristics that are similar to other known redox and gas sensors, suggesting that E75 and Rev-erbbeta may function in heme-, redox-, or gas-regulated control of cellular function.

A genetic screen identifies new regulators of steroid-triggered programmed cell death in Drosophila

The steroid hormone ecdysone triggers the rapid and massive destruction of larval tissues through transcriptional cascades that culminate in rpr and hid expression and caspase activation. Here we describe the use of genetic screens to further our understanding of this steroid-triggered programmed cell death response. Pupal lethal mutants were screened for specific defects in larval salivary gland destruction. A pilot screen using existing P-element collections resulted in the identification of mutations in known cell death regulators, E74 and hid, as well as multiple alleles in CBP (nejire) and dTrf2. A large-scale EMS mutagenesis screen on the third chromosome resulted in the recovery of 48 mutants. These include seven multiallelic complementation groups, at least five of which do not map to regions or genes previously associated with cell death. Five mutants display defects in the transcriptional induction of rpr and hid, and all display a penetrant block in caspase activation. Three were mapped to specific genes: CG5146, which encodes a protein of unknown function, Med24, which encodes a component of the RNA polymerase II mediator complex, and CG7998, which encodes a putative mitochondrial malate dehydrogenase. These genetic screens provide new directions for understanding the regulation of programmed cell death during development.

The Drosophila jumonji gene encodes a JmjC-containing nuclear protein that is required for metamorphosis

Jumonji (Jmj) is a transcriptional repressor that plays important roles in the suppression of cell proliferation and development of various tissues in the mouse. To further clarify the roles of Jmj during development and gain insight into mechanisms of Jmj-mediated transcriptional regulation, we have taken advantage of Drosophila as a model organism. Drosophila Jmj (dJmj) shares high homology with mammalian Jmj in the JmjN, JmjC and AT-rich interaction domains, as well as in the N-terminal repression domain. dJmj localizes to hundreds of euchromatic sites but not to chromocenter heterochromatin on salivary gland polytene chromosomes. In addition, dJmj is excluded from regions stained with an antibody against Ser5-phosphorylated RNA polymerase II, suggesting a function of dJmj in transcriptionally inactive chromatin. Loss of djmj results in larval and pupal lethality with phenotypes similar to those observed in mutants of ecdysone-regulated genes, implying the involvement of dJmj in the repression of gene expression in the ecdysone pathway. Transgenic mouse Jmj mostly colocalizes with dJmj and partially rescues the phenotypes of djmj mutants, indicating that dJmj is a functional homolog of mammalian Jmj. Furthermore, mutation in djmj suppresses position effect variegation of the T(2;3)Sb(V) rearrangement. These findings suggest that dJmj controls expression of developmentally important genes through modification of chromatin into a transcriptionally silenced state.

Quantitative trait loci for locomotor behavior in Drosophila melanogaster

Locomotion is an integral component of most animal behaviors and many human diseases and disorders are associated with locomotor deficits, but little is known about the genetic basis of natural variation in locomotor behavior. Locomotion is a complex trait, with variation attributable to the joint segregation of multiple interacting quantitative trait loci (QTL), with effects that are sensitive to the environment. We assessed variation in a component of locomotor behavior (locomotor reactivity) in a population of 98 recombinant inbred lines of Drosophila melanogaster and mapped four QTL affecting locomotor reactivity by linkage to polymorphic roo transposable element insertion sites. We used complementation tests of deficiencies to fine map these QTL to 12 chromosomal regions and complementation tests of mutations to identify 13 positional candidate genes affecting locomotor reactivity, including Dopa decarboxylase (Ddc), which catalyzes the final step in the synthesis of serotonin and dopamine. Linkage disequilibrium mapping in a population of 164 second chromosome substitution lines derived from a single natural population showed that polymorphisms at Ddc were associated with naturally occurring genetic variation in locomotor behavior. These data implicate variation in the synthesis of bioamines as a factor contributing to natural variation in locomotor reactivity.

Identification and characterization of a novel zinc finger protein (HZF1) gene and its function in erythroid and megakaryocytic differentiation of K562 cells

A novel zinc finger protein (HZF1) gene was identified and characterized by screening a human bone marrow cDNA library, using a new expression sequence tag probe that contains sequences encoding zinc finger motifs. There are at least three transcripts that may result from different splicing of the pre-mRNA, but the differences among them are only involved in 5' non-translation region of HZF1 mRNA. HZF1 gene contains four exons and three introns. The putative protein consists of 670 amino-acid residues including 15 typical C2H2 and 2 C2RH zinc finger motifs. This structure characterization of HZF1 and the nuclear location of the protein suggest that HZF1 may function as a transcription factor. HZF1 mRNA expression was detected in ubiquitous tissues and various hematopoietic cell lines. Increased HZF1 mRNA expression was observed following erythroid differentiation of K562 cells induced by hemin or megakaryocytic differentiation of K562 cells induced by phorbol myristate acetate (PMA). Both of the antisense method and RNA interference assay revealed that repression of the intrinsic expression of HZF1 blocked the hemin-induced erythroid differentiation and reduced the PMA-induced megakaryocytic differentiation of K562 cells, which suggested that HZF1 play important roles in erythroid and megakaryocytic differentiation.

how functions in leg development duringDrosophila metamorphosis

The Drosophila how gene encodes a KH RNA binding protein with strong similarity to GLD-1 from nematodes and QK1 from mice. Here, we investigate the function of how during metamorphosis. We show that how RNA and protein are present in a variety of tissues, and phenotypic analyses of how mutants reveal multiple lethal phases and defects during metamorphosis. In addition to previously reported abnormalities in muscle and wing development, how mutants exhibit defects in leg development. how mutant leg imaginal discs undergo cell shape changes associated with elongation, but are oriented improperly, do not evert normally, and often remain incased in peripodial epithelium longer than normal. Consequently, how mutants exhibit short, crooked legs. Our findings suggest that how functions in interactions between imaginal epithelium, peripodial epithelium, and larval epidermal cells during imaginal disc eversion.

The zinc finger-only protein Zfp260 is a novel cardiac regulator and a nuclear effector of alpha1-adrenergic signaling

alpha1-Adrenergic receptors mediate several biological effects of catecholamines, including the regulation of myocyte growth and contractility and transcriptional regulation of the atrial natriuretic factor (ANF) gene whose promoter contains an alpha1-adrenergic response element. The nuclear pathways and effectors that link receptor activation to genetic changes remain poorly understood. Here, we describe the isolation by the yeast one-hybrid system of a cardiac cDNA encoding a novel nuclear zinc finger protein, Zfp260, belonging to the Krüppel family of transcriptional regulators. Zfp260 is highly expressed in the embryonic heart but is downregulated during postnatal development. Functional studies indicate that Zfp260 is a transcriptional activator of ANF and a cofactor for GATA-4, a key cardiac regulator. Knockdown of Zfp260 in cardiac cells decreases endogenous ANF gene expression and abrogates its response to alpha1-adrenergic stimulation. Interestingly, Zfp260 transcripts are induced by alpha1-adrenergic agonists and are elevated in genetic models of hypertension and cardiac hypertrophy. The data identify Zfp260 as a novel transcriptional regulator in normal and pathological heart development and a nuclear effector of alpha1-adrenergic signaling.

The purine synthesis gene Prat2 is required for Drosophila metamorphosis, as revealed by inverted-repeat-mediated RNA interference

PRAT (phosphoribosylamidotransferase; E.C. 2.4.2.14) catalyzes the first reaction in de novo purine nucleotide biosynthesis. In Drosophila melanogaster, the Prat and Prat2 genes are both highly conserved with PRAT sequences from prokaryotes and eukaryotes. However, Prat2 organization and expression during development is different from Prat. We used RNA interference (RNAi) to knock down expression of both Prat and Prat2 to investigate their functions. Using the GAL4-UAS system, Prat RNAi driven by Act5c-GAL4 or tubP-GAL4 causes variable pupal lethality (48-100%) and approximately 50% female sterility, depending on the transgenic strains and drivers used. This observation agrees with the phenotype previously observed for Prat EMS-induced mutations. Prat2 RNAi driven by Act5C-GAL4 or tubP-GAL4 also results in variable pupal lethality (61-93%) with the different transgenic strains, showing that Prat2 is essential for fly development. However, Prat2 RNAi-induced arrested pupae have a head eversion defect reminiscent of the "cryptocephal" phenotype, whereas Prat RNAi-induced arrested pupae die later as pharate adults. We conclude that Prat2 is required during the prepupal stage while Prat is more important for the pupal stage. In addition, Prat and Prat2 double RNAi results in more severe pupal lethal phenotypes, suggesting that Prat and Prat2 have partially additive functions during Drosophila metamorphosis.

The histone H3 acetylase dGcn5 is a key player in Drosophila melanogaster metamorphosis

Although it has been well established that histone acetyltransferases (HATs) are involved in the modulation of chromatin structure and gene transcription, there is only little information on their developmental role in higher organisms. Gcn5 was the first transcription factor with HAT activity identified in eukaryotes. Here we report the isolation and characterization of Drosophila melanogaster dGcn5 mutants. Null dGcn5 alleles block the onset of both oogenesis and metamorphosis, while hypomorphic dGcn5 alleles impair the formation of adult appendages and cuticle. Strikingly, the dramatic loss of acetylation of the K9 and K14 lysine residues of histone H3 in dGcn5 mutants has no noticeable effect on larval tissues. In contrast, strong cell proliferation defects in imaginal tissues are observed. In vivo complementation experiments revealed that dGcn5 integrates specific functions in addition to chromosome binding and acetylation. Surprisingly, a dGcn5 variant protein with a deletion of the bromodomain, which has been shown to recognize acetylated histones, appears to be fully functional. Our results establish dGcn5 as a major histone H3 acetylase in Drosophila which plays a key role in the control of specific morphogenetic cascades during developmental transitions.

A major bristle QTL from a selected population of Drosophila uncovers the zinc-finger transcription factor poils-au-dos, a repressor of achaete-scute

Traditional screens aiming at identifying genes regulating development have relied on mutagenesis. Here, we describe a new gene involved in bristle development, identified through the use of natural variation and selection. Drosophila melanogaster bears a pattern of 11 macrochaetes per heminotum. From a population initially sampled in Marrakech, a strain was selected for an increased number of thoracic macrochaetes. Using recombination and single nucleotide polymorphisms, the factor responsible was mapped to a single locus on the third chromosome, poils au dos, that encodes a zinc-finger-ZAD protein. The original, as well as new, presumed null, alleles of poils au dos, is associated with ectopic achaete-scute expression that results in the additional bristles. This suggests a possible role for Poils au dos as a repressor of achaete and scute. Ectopic expression appears to be independent of the activity of known cis-regulatory enhancer sequences at the achaete-scute complex that mediate activation at specific sites on the notum. The target sequences for Poils au dos activity were mapped to a 14 kb region around scute. In addition, we show that pad interacts synergistically with the repressor hairy and with Dpp signaling in posterior and anterior regions of the notum, respectively.

The Drosophila nuclear receptor e75 contains heme and is gas responsive

Nuclear receptors are a family of transcription factors with structurally conserved ligand binding domains that regulate their activity. Despite intensive efforts to identify ligands, most nuclear receptors are still "orphans." Here, we demonstrate that the ligand binding pocket of the Drosophila nuclear receptor E75 contains a heme prosthetic group. E75 absorption spectra, resistance to denaturants, and effects of site-directed mutagenesis indicate a single, coordinately bound heme molecule. A correlation between the levels of E75 expression and the levels of available heme suggest a possible role as a heme sensor. The oxidation state of the heme iron also determines whether E75 can interact with its heterodimer partner DHR3, suggesting an additional role as a redox sensor. Further, the E75-DHR3 interaction is also regulated by the binding of NO or CO to the heme center, suggesting that E75 may also function as a diatomic gas sensor. Possible mechanisms and roles for these interactions are discussed.

Developmental roles of the Mi-2/NURD-associated protein p66 in Drosophila

The NURD and Sin3 histone deacetylase complexes are involved in transcriptional repression through global deacetylation of chromatin. Both complexes contain many different components that may control how histone deacetylase complexes are regulated and interact with other transcription factors. In a genetic screen for modifiers of wingless signaling in the Drosophila eye, we isolated mutations in the Drosophila homolog of p66, a protein previously purified as part of the Xenopus NURD/Mi-2 complex. p66 encodes a highly conserved nuclear zinc-finger protein that is required for development and we propose that the p66 protein acts as a regulatory component of the NURD complex. Animals homozygous mutant for p66 display defects during metamorphosis possibly caused by misregulation of ecdysone-regulated expression. Although heterozygosity for p66 enhances a wingless phenotype in the eye, loss-of-function clones in the wing and the eye discs do not have any detectable phenotype, possibly due to redundancy with the Sin3 complex. Overexpression of p66, on the other hand, can repress wingless-dependent phenotypes. Furthermore, p66 expression can repress multiple reporters in a cell culture assay, including a Wnt-responsive TCF reporter construct, implicating the NURD complex in repression of Wnt target genes. By co-immunoprecipitation, p66 associates with dMi-2, a known NURD complex member.

Ecdysteroid control of metamorphosis in the differentiating adult leg structures of Drosophila melanogaster

During insect metamorphosis, the steroid hormone 20-hydroxyecdysone (20E) is responsible for coordinating the differentiation of adult structures. Several structures of the Drosophila melanogaster adult leg, the six distalmost joints, the bristles, and the pretarsal claws, were examined to investigate how 20E controls their development in vitro. Joints, bristles, and claws were dependent on 20E for differentiation between 20-22 and 24-26 h after puparium formation (APF). After 26-28 h APF, differentiation became hormone independent. Tissue-specific markers in 20E-free cultures showed that the bristle and joint cells had not undergone any further morphogenetic progression. In contrast, the pretarsi underwent partial differentiation. The concentration of 20E required for differentiation was structure specific; tarsal joints required higher concentrations of 20E (greater than 400 ng 20 E/ml) than pretarsal claws, bristles, and other joints (greater than 40 ng 20E/ml). The 20E precursor ecdysone (E) was also able to induce differentiation at concentrations over 700 ng E/ml, but did not show any synergistic interactions with 20E. Lastly, leg structures had a finite ability to respond to 20E; tarsal joints lost competence to respond after 32-34 h APF, while the remaining structures became incompetent after 44-46 h APF.

Identification of cDNAs associated with late dedifferentiation in adult newt forelimb regeneration

Epimorphic limb regeneration in the adult newt involves the dedifferentiation of differentiated cells to yield a pluripotent blastemal cell. These mesenchymal-like cells proliferate and subsequently respond to patterning and differentiation cues to form a new limb. Understanding the dedifferentiation process requires the selective identification of dedifferentiating cells within the heterogeneous population of cells in the regenerate. In this study, representational differences analysis was used to produce an enriched population of dedifferentiation-associated cDNA fragments. Fifty-nine unique cDNA fragments were identified, sequenced, and analyzed using bioinformatics tools and databases. Some of these clones demonstrate significant similarity to known genes in other species. Other clones can be linked by homology to pathways previously implicated in the dedifferentiation process. These data will form the basis for further analyses to elucidate the role of candidate genes in the dedifferentiation process during newt forelimb regeneration.

Mutations in sticky lead to defective organization of the contractile ring during cytokinesis and are enhanced by Rho and suppressed by Rac

The contractile ring is a highly dynamic structure, but how this dynamism is accomplished remains unclear. Here, we report the identification and analysis of a novel Drosophila gene, sticky (sti), essential for cytokinesis in all fly proliferating tissues. sti encodes the Drosophila orthologue of the mammalian Citron kinase. RNA interference–mediated silencing of sti in cultured cells causes them to become multinucleate. Components of the contractile ring and central spindle are recruited normally in such STICKY-depleted cells that nevertheless display asymmetric furrowing and aberrant blebbing. Together with an unusual distribution of F-actin and Anillin, these phenotypes are consistent with defective organization of the contractile ring. sti shows opposite genetic interactions with Rho and Rac genes suggesting that these GTPases antagonistically regulate STICKY functions. Similar genetic evidence indicates that RacGAP50C inhibits Rac during cytokinesis. We discuss that antagonism between Rho and Rac pathways may control contractile ring dynamics during cytokinesis.

Rho-LIM kinase signaling regulates ecdysone-induced gene expression and morphogenesis during Drosophila metamorphosis

The steroid hormone 20-hydroxyecdysone (ecdysone) is the key regulator of postembryonic developmental transitions in insects and controls metamorphosis by triggering the morphogenesis of adult tissues from larvae. The Rho GTPase, which mediates cell shape change and migration, is also an essential regulator of tissue morphogenesis during development. Rho activity can modulate gene expression, in part, by activating LIM kinase (LIMK) and consequently affecting actin-induced SRF transcriptional activity. We have established a link between Rho-LIMK-SRF signaling and the ecdysone-induced transcriptional response during Drosophila development. Specifically, we determined that the Rho GTPase, via LIMK, regulates the expression of several ecdysone-responsive genes, including those encoding the ecdysone receptor itself, a downstream transcription factor (Br-C), and Stubble, a transmembrane protease required for proper leg formation. Stubble and Br-C mutants exhibit strong genetic interactions with several Rho pathway components in the formation of adult structures, but not with Rac or Cdc42. In cultured SL2 cells, inhibition of Rho, F-actin assembly, or SRF blocks the transcriptional response to ecdysone. Together, these findings indicate a link between Rho-LIMK signaling and steroid hormone-induced gene expression in the context of metamorphosis and thereby establish a novel role for the Rho GTPase in development.

Quantitative Trait Loci Affecting Starvation Resistance in Drosophila melanogaster

The ability to withstand periods of scarce food resources is an important fitness trait. Starvation resistance is a quantitative trait controlled by multiple interacting genes and exhibits considerable genetic variation in natural populations. This genetic variation could be maintained in the face of strong selection due to a trade-off in resource allocation between reproductive activity and individual survival. Knowledge of the genes affecting starvation tolerance and the subset of genes that affect variation in starvation resistance in natural populations would enable us to evaluate this hypothesis from a quantitative genetic perspective. We screened 933 co-isogenic P-element insertion lines to identify candidate genes affecting starvation tolerance. A total of 383 P-element insertions induced highly significant and often sex-specific mutational variance in starvation resistance. We also used deficiency complementation mapping followed by complementation to mutations to identify 12 genes contributing to variation in starvation resistance between two wild-type strains. The genes we identified are involved in oogenesis, metabolism, and feeding behaviors, indicating a possible link to reproduction and survival. However, we also found genes with cell fate specification and cell proliferation phenotypes, which implies that resource allocation during development and at the cellular level may also influence the phenotypic response to starvation.

Characterization of a putative extracellular matrix protein from the beetle Tenebrio molitor: hormonal regulation during metamorphosis

We used differential display to isolate epidermis cDNAs corresponding to juvenile-hormone analog-regulated mRNA from the beetle Tenebrio molitor. One of them encodes a putative extracellular matrix (ECM) protein, named Tenebrin. Indeed, the deduced protein sequence contains ECM typical features like the presence of a signal peptide, internal repeats, a RGD tripeptide sequence motif known to bind integrins and von Willebrand factor type c domains involved in protein-protein interactions. Northern blot analysis reveals a single transcript of about 11 kb with an expression pattern correlated to 20-hydroxyecdysone fluctuations during metamorphosis. In vivo injections of exogenous 20-hydroxyecdysone alone or combined with cycloheximide show that Tenebrin expression is directly induced by this hormone. Methoprene (a juvenile hormone analog) application experiments show that Tenebrin expression is rapidly induced by this analog. This gene is still up-regulated in the presence of protein synthesis inhibitor but, in these conditions, the mRNA induction level is not maximal.

Insect basic leucine zipper proteins and their role in cyclic AMP-dependent regulation of gene expression

The cAMP-protein kinase A (PKA) pathway is an important intracellular signal transduction cascade that can be activated by a large variety of stimuli. Activation or inhibition of this pathway will ultimately affect the transcriptional regulation of various genes through distinct responsive sites. In vertebrates, the best- characterized nuclear targets of PKA are the cyclic AMP response element-binding (CREB) proteins. It is now well established that CREB is not only regulated by PKA, but many other kinases can exert an effect as well. Since CREB-like proteins were also discovered in invertebrates, several studies unraveling their physiological functions in this category of metazoans have been performed. This review will mainly focus on the presence and regulation of CREB proteins in insects. Differences in transcriptional responses to the PKA pathway and other CREB-regulating stimuli between cells, tissues, and even organisms can be partially attributed to the presence of different CREB isoforms. In addition, the regulation of CREB appears to show some important differences between insects and vertebrates. Since CREB is a basic leucine zipper (bZip) protein, other insect members of this important family of transcriptional regulators will be briefly discussed as well.

Genetic Modifier Screens in Drosophila Demonstrate a Role for Rho1 Signaling in Ecdysone-Triggered Imaginal Disc Morphogenesis

Drosophila adult leg development provides an ideal model system for characterizing the molecular mechanisms of hormone-triggered morphogenesis. A pulse of the steroid hormone ecdysone at the onset of metamorphosis triggers the rapid transformation of a flat leg imaginal disc into an immature adult leg, largely through coordinated changes in cell shape. In an effort to identify links between the ecdysone signal and the cytoskeletal changes required for leg morphogenesis, we performed two large-scale genetic screens for dominant enhancers of the malformed leg phenotype associated with a mutation in the ecdysoneinducible broad early gene (br1). From a screen of >750 independent deficiency and candidate mutation stocks, we identified 17 loci on the autosomes that interact strongly with br1. In a complementary screen of ∼112,000 F1 progeny of EMS-treated br1 animals, we recovered 26 mutations that enhance the br1 leg phenotype [E(br) mutations]. Rho1, stubbloid, blistered (DSRF), and cytoplasmic Tropomyosin were identified from these screens as br1-interacting genes. Our findings suggest that ecdysone exerts its effects on leg morphogenesis through a Rho1 signaling cascade, a proposal that is supported by genetic interaction studies between the E(br) mutations and mutations in the Rho1 signaling pathway. In addition, several E(br) mutations produce unexpected defects in midembryonic morphogenetic movements. Coupled with recent evidence implicating ecdysone signaling in these embryonic morphogenetic events, our results suggest that a common ecdysone-dependent, Rho1-mediated regulatory pathway controls morphogenesis during the two major transitions in the life cycle, embryogenesis and metamorphosis.

Genetic Interactions Between the RhoA and Stubble-stubbloid Loci Suggest a Role for a Type II Transmembrane Serine Protease in Intracellular Signaling During Drosophila Imaginal Disc Morphogenesis

The Drosophila RhoA (Rho1) GTPase is essential for postembryonic morphogenesis of leg and wing imaginal discs. Mutations in RhoA enhance leg and wing defects associated with mutations in zipper, the gene encoding the heavy chain of nonmuscle myosin II. We demonstrate here that mutations affecting the RhoA signaling pathway also interact genetically with mutations in the Stubble-stubbloid (Sb-sbd) locus that encodes an unusual type II transmembrane serine protease required for normal leg and wing morphogenesis. In addition, a leg malformation phenotype associated with overexpression of Sb-sbd in prepupal leg discs is suppressed when RhoA gene dose is reduced, suggesting that RhoA and Sb-sbd act in a common pathway during leg morphogenesis. We also characterized six mutations identified as enhancers of zipper mutant leg defects. Three of these genes encode known members of the RhoA signaling pathway (RhoA, DRhoGEF2, and zipper). The remaining three enhancer of zipper mutations interact genetically with both RhoA and Sb-sbd mutations, suggesting that they encode additional components of the RhoA signaling pathway in imaginal discs. Our results provide evidence that the type II transmembrane serine proteases, a class of proteins linked to human developmental abnormalities and pathology, may be associated with intracellular signaling required for normal development.

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.

Ecdysone triggers the expression of Golgi genes in Drosophila imaginal discs via broad-complex

One of the most significant morphogenic events in the development of Drosophila melanogaster is the elongation of imaginal discs during puparium formation. We have shown that this macroscopic event is accompanied by the formation of Golgi stacks from small Golgi larval clusters of vesicles and tubules that are present prior to the onset of disc elongation. We have shown that the fly steroid hormone 20-hydroxyecdysone triggers both the elongation itself and the formation of Golgi stacks (V. Kondylis, S. E. Goulding, J. C. Dunne, and C. Rabouille, 2001, Mol. Biol. Cell, 12, 2308). Using mRNA in situ hybridisation, we show here that ecdysone triggers the upregulation of a subset of genes encoding Golgi-related proteins (such as dnsf1, dsec23, dsed5, and drab1) and downregulates the expression of others (such as dergic53, dbeta'COP, and drab6). We show that the transcription factor Broad-complex, itself an "early" ecdysone target, mediates this regulation. And we show that the ecdysone-independent upregulation of dnsf1 and dsnap prior to the ecdysone peak leads to a precocious formation of large Golgi stacks. The ecdysone-triggered biogenesis of Golgi stacks at the onset of imaginal disc elongation offers the exciting possibility of advancing our understanding of the relationship between gene expression and organelle biogenesis.

Molecular genetic dissection of the sex-specific and vital functions of the Drosophila melanogaster sex determination gene fruitless

A multibranched hierarchy of regulatory genes controls all aspects of somatic sexual development in Drosophila melanogaster. One branch of this hierarchy is headed by the fruitless (fru) gene and functions in the central nervous system, where it is necessary for male courtship behavior as well as the differentiation of a male-specific abdominal structure, the muscle of Lawrence (MOL). A preliminary investigation of several of the mutations described here showed that the fru gene also has a sex-nonspecific vital function. The fru gene produces a complex set of transcripts through the use of four promoters and alternative splicing. Only the primary transcripts produced from the most distal (P1) promoter are sex-specifically spliced under direction of the sex-determination hierarchy. We have analyzed eight new fru mutations, created by X-ray mutagenesis and P-element excision, to try to gain insight into the relationship of specific transcript classes to specific fru functions. Males that lack the P1-derived fru transcripts show a complete absence of sexual behavior, but no other defects besides the loss of the MOL. Both males and females that have reduced levels of transcripts from the P3 promoter develop into adults but frequently die after failing to eclose. Analysis of the morphology and behavior of adult escapers showed that P3-encoded functions are required for the proper differentiation and eversion of imaginal discs. Furthermore, the reduction in the size of the neuromuscular junctions on abdominal muscles in these animals suggests that one of fru's sex-nonspecific functions involves general aspects of neuronal differentiation. In mutants that lack all fru transcripts as well as a small number of adjacent genes, animals die at an early pupal stage, indicating that fru's function is required only during late development. Thus, fru functions both in the sex-determination regulatory hierarchy to control male sexual behavior through sex-specific transcripts and sex-nonspecifically to control the development of imaginal discs and motorneuronal synapses during adult development through sex-nonspecific transcript classes.

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.

The midline glia of Drosophila: a molecular genetic model for the developmental functions of glia

The Midline Glia of Drosophila are required for nervous system morphogenesis and midline axon guidance during embryogenesis. In origin, gene expression and function, this lineage is analogous to the floorplate of the vertebrate neural tube. The expression or function of over 50 genes, summarised here, has been linked to the Midline Glia. Like the floorplate, the cells which generate the Midline Glia lineage, the mesectoderm, are determined by the interaction of ectoderm and mesoderm during gastrulation. Determination and differentiation of the Midline Glia involves the Drosophila EGF, Notch and segment polarity signaling pathways, as well as twelve identified transcription factors. The Midline Glia lineage has two phases of cell proliferation and of programmed cell death. During embryogenesis, the EGF receptor pathway signaling and Wrapper protein both function to suppress apoptosis only in those MG which are appropriately positioned to separate and ensheath midline axonal commissures. Apoptosis during metamorphosis is regulated by the insect steroid, Ecdysone. The Midline Glia participate in both the attraction of axonal growth cones towards the midline, as well as repulsion of growth cones from the midline. Midline axon guidance requires the Drosophila orthologs of vertebrate genes expressed in the floorplate, which perform the same function. Genetic and molecular evidence of the interaction of attractive (Netrin) and repellent (Slit) signaling is reviewed and summarised in a model. The Midline Glia participate also in the generation of extracellular matrix and in trophic interactions with axons. Genetic evidence for these functions is reviewed.

PHM is required for normal developmental transitions and for biosynthesis of secretory peptides in Drosophila

To understand the roles of secretory peptides in developmental signaling, we have studied Drosophila mutant for the gene peptidylglycine alpha-hydroxylating monooxygenase (PHM). PHM is the rate-limiting enzyme for C-terminal alpha-amidation, a specific and necessary modification of secretory peptides. In insects, more than 90% of known or predicted neuropeptides are amidated. PHM mutants lack PHM protein and enzyme activity; most null animals die as late embryos with few morphological defects. Natural and synthetic PHM hypomorphs revealed phenotypes that resembled those of animals with mutations in genes of the ecdysone-inducible regulatory circuit. Animals bearing a strong hypomorphic allele contain no detectable PHM enzymatic activity or protein; approximately 50% hatch and initially display normal behavior, then die as young larvae, often while attempting to molt. PHM mutants were rescued with daily induction of a PHM transgene and complete rescue was seen with induction limited to the first 4 days after egg-laying. The rescued mutant adults produced progeny which survived to various stages up through metamorphosis (synthetic hypomorphs) and displayed prepupal and pupal phenotypes resembling those of ecdysone-response gene mutations. Examination of neuropeptide biosynthesis in PHM mutants revealed specific disruptions: Amidated peptides were largely absent in strong hypomorphs, but peptide precursors, a nonamidated neuropeptide, nonpeptide transmitters, and other peptide biosynthetic enzymes were readily detected. Mutant adults that were produced by a minimal rescue schedule had lowered PHM enzyme levels and reproducibly altered patterns of amidated neuropeptides in the CNS. These deficits were partially reversed within 24 h by a single PHM induction in the adult stage. These genetic results support the hypothesis that secretory peptide signaling is critical for transitions between developmental stages, without strongly affecting morphogenetic events within a stage. Further, they show that PHM is required for peptide alpha-amidating activity throughout the life of Drosophila. Finally, they define novel methods to study neural and endocrine peptide biosynthesis and functions in vivo.

The cryptocephal gene (ATF4) encodes multiple basic-leucine zipper proteins controlling molting and metamorphosis in Drosophila

The cryptocephal (crc) mutation causes pleiotropic defects in ecdysone-regulated events during Drosophila molting and metamorphosis. Here we report that crc encodes a Drosophila homolog of vertebrate ATF4, a member of the CREB/ATF family of basic-leucine zipper (bZIP) transcription factors. We identified three putative protein isoforms. CRC-A and CRC-B contain the bZIP domain, and CRC-D is a C-terminally truncated form. We have generated seven new crc alleles. Consistent with the molecular diversity of crc, these alleles show that crc is a complex genetic locus with two overlapping lethal complementation groups. Alleles representing both groups were rescued by a cDNA encoding CRC-B. One lethal group (crc(1), crc(R6), and crc(Rev8)) consists of strong hypomorphic or null alleles that are associated with mutations of both CRC-A and CRC-B. These mutants display defects associated with larval molting and pupariation. In addition, they fail to evert the head and fail to elongate the imaginal discs during pupation, and they display variable defects in the subsequent differentiation of the adult abdomen. The other group (crc(R1), crc(R2), crc(E85), crc(E98), and crc(929)) is associated with disruptions of CRC-A and CRC-D; except for a failure to properly elongate the leg discs, these mutants initiate metamorphosis normally. Subsequently, they display a novel metamorphic phenotype, involving collapse of the head and abdomen toward the thorax. The crc gene is expressed throughout development and in many tissues. In third instar larvae, crc expression is high in targets of ecdysone signaling, such as the leg and wing imaginal discs, and in the ring gland, the source of ecdysone. Together, these findings implicate CREB/ATF proteins in essential functions during molting and metamorphosis. In addition, the similarities between the mutant phenotypes of crc and the ecdysone-responsive genes indicate that these genes are likely to be involved in common signaling pathways.

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.

The Berkeley Drosophila Genome Project gene disruption project: Single P-element insertions mutating 25% of vital Drosophila genes

A fundamental goal of genetics and functional genomics is to identify and mutate every gene in model organisms such as Drosophila melanogaster. The Berkeley Drosophila Genome Project (BDGP) gene disruption project generates single P-element insertion strains that each mutate unique genomic open reading frames. Such strains strongly facilitate further genetic and molecular studies of the disrupted loci, but it has remained unclear if P elements can be used to mutate all Drosophila genes. We now report that the primary collection has grown to contain 1045 strains that disrupt more than 25% of the estimated 3600 Drosophila genes that are essential for adult viability. Of these P insertions, 67% have been verified by genetic tests to cause the associated recessive mutant phenotypes, and the validity of most of the remaining lines is predicted on statistical grounds. Sequences flanking >920 insertions have been determined to exactly position them in the genome and to identify 376 potentially affected transcripts from collections of EST sequences. Strains in the BDGP collection are available from the Bloomington Stock Center and have already assisted the research community in characterizing >250 Drosophila genes. The likely identity of 131 additional genes in the collection is reported here. Our results show that Drosophila genes have a wide range of sensitivity to inactivation by P elements, and provide a rationale for greatly expanding the BDGP primary collection based entirely on insertion site sequencing. We predict that this approach can bring >85% of all Drosophila open reading frames under experimental control.