Vectors for P element-mediated gene transfer in Drosophila

The white gene as a transgenesis marker for the cricket Gryllus bimaculatus

The cricket Gryllus bimaculatus is an emerging model insect of the order Orthoptera that is used in a wide variety of biological research themes. This hemimetabolous species appears highly complementary to Drosophila and other well-established holometabolous models. To improve transgenesis applications in G. bimaculatus, we have designed a transformation marker gene inspired from the widespread Drosophila mini-white+. Using CRISPR/Cas9, we first generated a loss-of-function mutant allele of the Gb-white gene (Gb-w), which exhibits a white eye coloration at all developmental stages. We then demonstrate that transgenic insertions of a piggyBac vector containing a 3xP3-Gb-w+ cassette rescue eye pigmentation. As an application, we used this vector to generate G. bimaculatus lines expressing a centromeric histone H3 variant (CenH3.1) fused to EGFP and validated EGFP-CenH3.1 detection at cricket centromeres. Finally, we demonstrate that Minos-based germline transformation and site-specific plasmid insertion with the ΦC31 integrase system function in G. bimaculatus.

Tolerance thresholds underlie responses to DNA damage during germline development

Selfish DNA modules like transposable elements (TEs) are particularly active in the germline, the lineage that passes genetic information across generations. New TE insertions can disrupt genes and impair the functionality and viability of germ cells. However, we found that in P-M hybrid dysgenesis in Drosophila, a sterility syndrome triggered by the P-element DNA transposon, germ cells harbor unexpectedly few new TE insertions despite accumulating DNA double-strand breaks (DSBs) and inducing cell cycle arrest. Using an engineered CRISPR-Cas9 system, we show that generating DSBs at silenced P-elements or other noncoding sequences is sufficient to induce germ cell loss independently of gene disruption. Indeed, we demonstrate that both developing and adult mitotic germ cells are sensitive to DSBs in a dosage-dependent manner. Following the mitotic-to-meiotic transition, however, germ cells become more tolerant to DSBs, completing oogenesis regardless of the accumulated genome damage. Our findings establish DNA damage tolerance thresholds as crucial safeguards of genome integrity during germline development.

Transposon and Transgene Tribulations in Mosquitoes: A Perspective of piRNA Proportions

Mosquitoes, like Drosophila, are dipterans, the order of "true flies" characterized by a single set of two wings. Drosophila are prime model organisms for biomedical research, while mosquito researchers struggle to establish robust molecular biology in these that are arguably the most dangerous vectors of human pathogens. Both insects utilize the RNA interference (RNAi) pathway to generate small RNAs to silence transposons and viruses, yet details are emerging that several RNAi features are unique to each insect family, such as how culicine mosquitoes have evolved extreme genomic feature differences connected to their unique RNAi features. A major technical difference in the molecular genetic studies of these insects is that generating stable transgenic animals are routine in Drosophila but still variable in stability in mosquitoes, despite genomic DNA-editing advances. By comparing and contrasting the differences in the RNAi pathways of Drosophila and mosquitoes, in this review we propose a hypothesis that transgene DNAs are possibly more intensely targeted by mosquito RNAi pathways and chromatin regulatory pathways than in Drosophila. We review the latest findings on mosquito RNAi pathways, which are still much less well understood than in Drosophila, and we speculate that deeper study into how mosquitoes modulate transposons and viruses with Piwi-interacting RNAs (piRNAs) will yield clues to improving transgene DNA expression stability in transgenic mosquitoes.

Historical DNA Manipulation Overview

The history of DNA manipulation for the creation of genetically modified animals began in the 1970s, using viruses as the first DNA molecules microinjected into mouse embryos at different preimplantation stages. Subsequently, simple DNA plasmids were used to microinject into the pronuclei of fertilized mouse oocytes and that method became the reference for many years. The isolation of embryonic stem cells together with advances in genetics allowed the generation of gene-specific knockout mice, later on improved with conditional mutations. Cloning procedures expanded the gene inactivation to livestock and other non-model mammalian species. Lentiviruses, artificial chromosomes, and intracytoplasmic sperm injections expanded the toolbox for DNA manipulation. The last chapter of this short but intense history belongs to programmable nucleases, particularly CRISPR-Cas systems, triggering the development of genomic-editing techniques, the current revolution we are living in.

Mutants of the white ABCG Transporter in Drosophila melanogaster Have Deficient Olfactory Learning and Cholesterol Homeostasis

Drosophila's white gene encodes an ATP-binding cassette G-subfamily (ABCG) half-transporter. White is closely related to mammalian ABCG family members that function in cholesterol efflux. Mutants of white have several behavioral phenotypes that are independent of visual defects. This study characterizes a novel defect of white mutants in the acquisition of olfactory memory using the aversive olfactory conditioning paradigm. The w¹¹¹⁸ mutants learned slower than wildtype controls, yet with additional training, they reached wildtype levels of performance. The w¹¹¹⁸ learning phenotype is also found in the w^apricot and w^coral alleles, is dominant, and is rescued by genomic white and mini-white transgenes. Reducing dietary cholesterol strongly impaired olfactory learning for wildtype controls, while w¹¹¹⁸ mutants were resistant to this deficit. The w¹¹¹⁸ mutants displayed higher levels of cholesterol and cholesterol esters than wildtype under this low-cholesterol diet. Increasing levels of serotonin, dopamine, or both in the white mutants significantly improved w¹¹¹⁸ learning. However, serotonin levels were not lower in the heads of the w¹¹¹⁸ mutants than in wildtype controls. There were also no significant differences found in synapse numbers within the w¹¹¹⁸ brain. We propose that the w¹¹¹⁸ learning defect may be due to inefficient biogenic amine signaling brought about by altered cholesterol homeostasis.

The fushi tarazu zebra element is not required for Drosophila viability or fertility

Expression of genes in precisely controlled spatiotemporal patterns is essential for embryonic development. Much of our understanding of mechanisms regulating gene expression comes from the study of cis-regulatory elements (CREs) that direct expression of reporter genes in transgenic organisms. This reporter-transgene approach identifies genomic regions sufficient to drive expression but fails to provide information about quantitative and qualitative contributions to endogenous expression, although such conclusions are often inferred. Here we evaluated the endogenous function of a classic Drosophila CRE, the fushi tarazu (ftz) zebra element. ftz is a pair-rule segmentation gene expressed in seven stripes during embryogenesis, necessary for formation of alternate body segments. Reporter transgenes identified the promoter-proximal zebra element as a major driver of the seven ftz stripes. We generated a precise genomic deletion of the zebra element (ftzΔZ) to assess its role in the context of native chromatin and neighboring CREs, expecting large decreases in ftz seven-stripe expression. However, significant reduction in expression was found for only one stripe, ftz stripe 4, expressed at ∼25% of wild type levels in ftzΔZ homozygotes. Defects in corresponding regions of ftzΔZ mutants suggest this level of expression borders the threshold required to promote morphological segmentation. Further, we established true-breeding lines of homozygous ftzΔZ flies, demonstrating that the body segments missing in the mutants are not required for viability or fertility. These results highlight the different types of conclusions drawn from different experimental designs and emphasize the importance of examining transcriptional regulatory mechanisms in the context of the native genomic environment.

Epithelial Function in the Drosophila Malpighian Tubule: An In Vivo Renal Model

The insect renal (Malpighian) tubule has long been a model system for the study of fluid secretion and its neurohormonal control, as well as studies on ion transport mechanisms. To extend these studies beyond the boundaries of classical physiology, a molecular genetic approach together with the 'omics technologies is required. To achieve this in any vertebrate transporting epithelium remains a daunting task, as the genetic tools available are still relatively unsophisticated. Drosophila melanogaster, however, is an outstanding model organism for molecular genetics. Here we describe a technique for fluid secretion assays in the D. melanogaster equivalent of the kidney nephron. The development of this first physiological assay for a Drosophila epithelium, allowing combined approaches of integrative physiology and functional genomics, has now provided biologists with an entirely new model system, the Drosophila Malpighian tubule, which is utilized in multiple fields as diverse as kidney disease research and development of new modes of pest insect control.

The Drosophila DAXX-Like Protein (DLP) Cooperates with ASF1 for H3.3 Deposition and Heterochromatin Formation

Histone variants are nonallelic isoforms of canonical histones, and they are deposited, in contrast to canonical histones, in a replication-independent (RI) manner. RI deposition of H3.3, a histone variant from the H3.3 family, is mediated in mammals by distinct pathways involving either the histone regulator A (HIRA) complex or the death-associated protein (DAXX)/α-thalassemia X-linked mental retardation protein (ATRX) complex. Here, we investigated the function of the Drosophila DAXX-like protein (DLP) by using both fly genetic approaches and protein biochemistry. DLP specifically interacts with H3.3 and shows a prominent localization on the base of the X chromosome, where it appears to act in concert with XNP, the Drosophila homolog of ATRX, in heterochromatin assembly and maintenance. The functional association between DLP and XNP is further supported by a series of experiments that illustrate genetic interactions and the DLP-XNP-dependent localization of specific chromosomal proteins. In addition, DLP both participates in the RI deposition of H3.3 and associates with anti-silencing factor 1 (ASF1). We suggest, in agreement with a recently proposed model, that DLP and ASF1 are part of a predeposition complex, which is recruited by XNP and is necessary to prevent DNA exposure in the nucleus.

Modeling congenital disease and inborn errors of development in Drosophila melanogaster

Fly models that faithfully recapitulate various aspects of human disease and human health-related biology are being used for research into disease diagnosis and prevention. Established and new genetic strategies in Drosophila have yielded numerous substantial successes in modeling congenital disorders or inborn errors of human development, as well as neurodegenerative disease and cancer. Moreover, although our ability to generate sequence datasets continues to outpace our ability to analyze these datasets, the development of high-throughput analysis platforms in Drosophila has provided access through the bottleneck in the identification of disease gene candidates. In this Review, we describe both the traditional and newer methods that are facilitating the incorporation of Drosophila into the human disease discovery process, with a focus on the models that have enhanced our understanding of human developmental disorders and congenital disease. Enviable features of the Drosophila experimental system, which make it particularly useful in facilitating the much anticipated move from genotype to phenotype (understanding and predicting phenotypes directly from the primary DNA sequence), include its genetic tractability, the low cost for high-throughput discovery, and a genome and underlying biology that are highly evolutionarily conserved. In embracing the fly in the human disease-gene discovery process, we can expect to speed up and reduce the cost of this process, allowing experimental scales that are not feasible and/or would be too costly in higher eukaryotes.

Use of electroporation as an option to transform the horn fly, Haematobia irritans: a species recalcitrant to microinjection

The horn fly, Haematobia irritans, is a serious pest of cattle in North America. The control of horn flies has primarily relied on insecticides. However, the heavy use of insecticides has led to the development of insecticide resistance in horn flies. Novel methods to control horn flies are greatly needed. Transgenic technology is an effective tool to genetically modify insects and may lead to novel methods of pest control based on genomic approaches. Here we report a piggyBac-mediated transformation of the horn fly via electroporation. Transformation with a DsRed fluorescent marker protein coding region was verified by PCR analysis of individual fly bodies and pupal cases and sequencing of PCR products. However, Southern blot analysis failed to indicate the DsRed gene was integrated into the horn fly genome. Thus, the electroporation protocol may have caused the DsRed gene to be integrated into bacterial symbionts of the horn fly.

Light, heat, action: neural control of fruit fly behaviour

The fruit fly Drosophila melanogaster has emerged as a popular model to investigate fundamental principles of neural circuit operation. The sophisticated genetics and small brain permit a cellular resolution understanding of innate and learned behavioural processes. Relatively recent genetic and technical advances provide the means to specifically and reproducibly manipulate the function of many fly neurons with temporal resolution. The same cellular precision can also be exploited to express genetically encoded reporters of neural activity and cell-signalling pathways. Combining these approaches in living behaving animals has great potential to generate a holistic view of behavioural control that transcends the usual molecular, cellular and systems boundaries. In this review, we discuss these approaches with particular emphasis on the pioneering studies and those involving learning and memory.

Tools for Targeted Genome Engineering of Established Drosophila Cell Lines

We describe an adaptation of φC31 integrase-mediated targeted cassette exchange for use in Drosophila cell lines. Single copies of an attP-bounded docking platform carrying a GFP-expression marker, with or without insulator elements flanking the attP sites, were inserted by P-element transformation into the Kc167 and Sg4 cell lines; each of the resulting docking-site lines carries a single mapped copy of one of the docking platforms. Vectors for targeted substitution contain a cloning cassette flanked by attB sites. Targeted substitution occurs by integrase-mediated substitution between the attP sites (integrated) and the attB sites (vector). We describe procedures for isolating cells carrying the substitutions and for eliminating the products of secondary off-target events. We demonstrate the technology by integrating a cassette containing a Cu(2+)-inducible mCherry marker, and we report the expression properties of those lines. When compared with clonal lines made by traditional transformation methods, which lead to the illegitimate insertion of tandem arrays, targeted insertion lines give more uniform expression, lower basal expression, and higher induction ratios. Targeted substitution, though intricate, affords results that should greatly improve comparative expression assays-a major emphasis of cell-based studies.

Functional Requirements for Fab-7 Boundary Activity in the Bithorax Complex

Chromatin boundaries are architectural elements that determine the three-dimensional folding of the chromatin fiber and organize the chromosome into independent units of genetic activity. The Fab-7 boundary from the Drosophila bithorax complex (BX-C) is required for the parasegment-specific expression of the Abd-B gene. We have used a replacement strategy to identify sequences that are necessary and sufficient for Fab-7 boundary function in the BX-C. Fab-7 boundary activity is known to depend on factors that are stage specific, and we describe a novel ∼700-kDa complex, the late boundary complex (LBC), that binds to Fab-7 sequences that have insulator functions in late embryos and adults. We show that the LBC is enriched in nuclear extracts from late, but not early, embryos and that it contains three insulator proteins, GAF, Mod(mdg4), and E(y)2. Its DNA binding properties are unusual in that it requires a minimal sequence of >65 bp; however, other than a GAGA motif, the three Fab-7 LBC recognition elements display few sequence similarities. Finally, we show that mutations which abrogate LBC binding in vitro inactivate the Fab-7 boundary in the BX-C.

Insulin-independent role of adiponectin receptor signaling in Drosophila germline stem cell maintenance

Adipocytes have key endocrine roles, mediated in large part by secreted protein hormones termed adipokines. The adipokine adiponectin is well known for its role in sensitizing peripheral tissues to insulin, and several lines of evidence suggest that adiponectin might also modulate stem cells/precursors. It remains unclear, however, how adiponectin signaling controls stem cells and whether this role is secondary to its insulin-sensitizing effects or distinct. Drosophila adipocytes also function as an endocrine organ and, although no obvious adiponectin homolog has been identified, Drosophila AdipoR encodes a well-conserved homolog of mammalian adiponectin receptors. Here, we generate a null AdipoR allele and use clonal analysis to demonstrate an intrinsic requirement for AdipoR in germline stem cell (GSC) maintenance in the Drosophila ovary. AdipoR null GSCs are not fully responsive to bone morphogenetic protein ligands from the niche and have a slight reduction in E-cadherin levels at the GSC-niche junction. Conversely, germline-specific overexpression of AdipoR inhibits natural GSC loss, suggesting that reduction in adiponectin signaling might contribute to the normal decline in GSC numbers observed over time in wild-type females. Surprisingly, AdipoR is not required for insulin sensitization of the germline, leading us to speculate that insulin sensitization is a more recently acquired function than stem cell regulation in the evolutionary history of adiponectin signaling. Our findings establish Drosophila female GSCs as a new system for future studies addressing the molecular mechanisms whereby adiponectin receptor signaling modulates stem cell fate.

Structure-function analysis of the C-clamp of TCF/Pangolin in Wnt/ß-catenin signaling

The evolutionarily conserved Wnt/ß-catenin (Wnt/ß-cat) pathway plays an important role in animal development in metazoans. Many Wnt targets are regulated by members of the TCF/LEF1 (TCF) family of transcription factors. All TCFs contain a High Mobility Group (HMG) domain that bind specific DNA sequences. Invertebrate TCFs and some vertebrate TCF isoforms also contain another domain, called the C-clamp, which allows TCFs to recognize an additional DNA motif known as the Helper site. While the C-clamp has been shown to be important for regulating several Wnt reporter genes in cell culture, its physiological role in regulating Wnt targets is less clear. In addition, little is known about this domain, except that two of the four conserved cysteines are functionally important. Here, we carried out a systematic mutagenesis and functional analysis of the C-clamp from the Drosophila TCF/Pangolin (TCF/Pan) protein. We found that the C-clamp is a zinc-binding domain that is sufficient for binding to the Helper site. In addition to this DNA-binding activity, the C-clamp also inhibits the HMG domain from binding its cognate DNA site. Point mutations were identified that specifically affected DNA-binding or reduced the inhibitory effect. These mutants were characterized in TCF/Pan rescue assays. The specific DNA-binding activity of the C-clamp was essential for TCF/Pan function in cell culture and in patterning the embryonic epidermis of Drosophila, demonstrating the importance of this C-clamp activity in regulating Wnt target gene expression. In contrast, the inhibitory mutation had a subtle effect in cell culture and no effect on TCF/Pan activity in embryos. These results provide important information about the functional domains of the C-clamp, and highlight its importance for Wnt/ß-cat signaling in Drosophila.

Torso-like functions independently of Torso to regulate Drosophila growth and developmental timing

Activation of the Drosophila receptor tyrosine kinase Torso (Tor) only at the termini of the embryo is achieved by the localized expression of the maternal gene Torso-like (Tsl). Tor has a second function in the prothoracic gland as the receptor for prothoracicotropic hormone (PTTH) that initiates metamorphosis. Consistent with the function of Tor in this tissue, Tsl also localizes to the prothoracic gland and influences developmental timing. Despite these commonalities, in our studies of Tsl we unexpectedly found that tsl and tor have opposing effects on body size; tsl null mutants are smaller than normal, rather than larger as would be expected if the PTTH/Tor pathway was disrupted. We further found that whereas both genes regulate developmental timing, tsl does so independently of tor. Although tsl null mutants exhibit a similar length delay in time to pupariation to tor mutants, in tsl:tor double mutants this delay is strikingly enhanced. Thus, loss of tsl is additive rather than epistatic to loss of tor. We also find that phenotypes generated by ectopic PTTH expression are independent of tsl. Finally, we show that a modified form of tsl that can rescue developmental timing cannot rescue terminal patterning, indicating that Tsl can function via distinct mechanisms in different contexts. We conclude that Tsl is not just a specialized cue for Torso signaling but also acts independently of PTTH/Tor in the control of body size and the timing of developmental progression. These data highlight surprisingly diverse developmental functions for this sole Drosophila member of the perforin-like superfamily.

The human THAP9 gene encodes an active P-element DNA transposase

The human genome contains ~50 genes that were derived from transposable elements or transposons, and many are now integral components of cellular gene expression programs. The human THAP9 gene is related to the Drosophila P-element transposase. Here, we show that human THAP9 can mobilize Drosophila P-elements in both Drosophila and human cells. Chimeric proteins formed between the Drosophila P-element transposase N-terminal THAP DNA binding domain and the C-terminal regions of human THAP9 can also mobilize Drosophila P elements. Our results indicate that human THAP9 is an active DNA transposase that, although "domesticated," still retains the catalytic activity to mobilize P transposable elements across species.

Conservation and variation in Hox genes: how insect models pioneered the evo-devo field

Evolutionary developmental biology, or evo-devo, broadly investigates how body plan diversity and morphological novelties have arisen and persisted in nature. The discovery of Hox genes in Drosophila, and their subsequent identification in most other metazoans, led biologists to try to understand how embryonic genes crucial for proper development have changed to promote the vast morphological variation seen in nature. Insects are ideal model systems for studying this diversity and the mechanisms underlying it because phylogenetic relationships are well established, powerful genetic tools have been developed, and there are many examples of evolutionary specializations that have arisen in nature in different insect lineages, such as the jumping leg of orthopterans and the helmet structures of treehoppers. Here, we briefly introduce the field of evo-devo and Hox genes, discuss functional tools available to study early developmental genes in insects, and provide examples in which changes in Hox genes have contributed to changes in body plan or morphology.

A modular toolset for recombination transgenesis and neurogenetic analysis of Drosophila

Transgenic Drosophila have contributed extensively to our understanding of nervous system development, physiology and behavior in addition to being valuable models of human neurological disease. Here, we have generated a novel series of modular transgenic vectors designed to optimize and accelerate the production and analysis of transgenes in Drosophila. We constructed a novel vector backbone, pBID, that allows both phiC31 targeted transgene integration and incorporates insulator sequences to ensure specific and uniform transgene expression. Upon this framework, we have built a series of constructs that are either backwards compatible with existing restriction enzyme based vectors or utilize Gateway recombination technology for high-throughput cloning. These vectors allow for endogenous promoter or Gal4 targeted expression of transgenic proteins with or without fluorescent protein or epitope tags. In addition, we have generated constructs that facilitate transgenic splice isoform specific RNA inhibition of gene expression. We demonstrate the utility of these constructs to analyze proteins involved in nervous system development, physiology and neurodegenerative disease. We expect that these reagents will facilitate the proficiency and sophistication of Drosophila genetic analysis in both the nervous system and other tissues.

The Drosophila melanogaster host model

The deleterious and sometimes fatal outcomes of bacterial infectious diseases are the net result of the interactions between the pathogen and the host, and the genetically tractable fruit fly, Drosophila melanogaster, has emerged as a valuable tool for modeling the pathogen-host interactions of a wide variety of bacteria. These studies have revealed that there is a remarkable conservation of bacterial pathogenesis and host defence mechanisms between higher host organisms and Drosophila. This review presents an in-depth discussion of the Drosophila immune response, the Drosophila killing model, and the use of the model to examine bacterial-host interactions. The recent introduction of the Drosophila model into the oral microbiology field is discussed, specifically the use of the model to examine Porphyromonas gingivalis-host interactions, and finally the potential uses of this powerful model system to further elucidate oral bacterial-host interactions are addressed.

Regulation of cyclin A localization downstream of Par-1 function is critical for the centrosome orientation checkpoint in Drosophila male germline stem cells

Male germline stem cells (GSCs) in Drosophila melanogaster divide asymmetrically by orienting the mitotic spindle with respect to the niche, a microenvironment that specifies stem cell identity. The spindle orientation is prepared during interphase through stereotypical positioning of the centrosomes. We recently demonstrated that GSCs possess a checkpoint ("the centrosome orientation checkpoint") that monitors correct centrosome orientation prior to mitosis to ensure an oriented spindle and thus asymmetric outcome of the division. Here, we show that Par-1, a serine/threonine kinase that regulates polarity in many systems, is involved in this checkpoint. Par-1 shows a cell cycle-dependent localization to the spectrosome, a germline-specific, endoplasmic reticulum-like organelle. Furthermore, the localization of cyclin A, which is normally localized to the spectrosome, is perturbed in par-1 mutant GSCs. Interestingly, overexpression of mutant cyclin A that does not localize to the spectrosome and mutation in hts, a core component of the spectrosome, both lead to defects in the centrosome orientation checkpoint. We propose that the regulation of cyclin A localization via Par-1 function plays a critical role in the centrosome orientation checkpoint.

Identification of a classical bipartite nuclear localization signal in the Drosophila TEA/ATTS protein scalloped

Drosophila melanogaster wing development has been shown to rely on the activity of a complex of two proteins, Scalloped (Sd) and Vestigial (Vg). Within this complex, Sd is known to provide DNA binding though its TEA/ATTS domain, while Vg modulates this binding and provides transcriptional activation through N- and C-terminal activation domains. There is also evidence that Sd is required for the nuclear translocation of Vg. Indeed, a candidate sequence which shows consensus to the bipartite family of nuclear localization signals (NLSs) has been identified within Sd previously, though it is not known if it is functional, or if additional unpredicted signals that mediate nuclear transport exist within the protein. By expressing various enhanced green fluorescent protein (eGFP) tagged constructs within Drosophila S2 cells, we demonstrate that this NLS is indeed functional and necessary for the proper nuclear localization of Sd. Additionally, the region containing the NLS is critical for the wildtype function of ectopically expressed Sd, in the context of wing development. Using site-directed mutagenesis, we have identified a group of five amino acids within this NLS which is critical for its function, as well as another group of two which is of lesser importance. Together with data that suggests that this sequence mediates interactions with Importin-α3, we conclude that the identified NLS is likely a classical bipartite signal. Further dissection of Sd has also revealed that a large portion of the C-terminal domain of the protein is required its proper nuclear localization. Finally, a Leptomycin B (LB) sensitive signal which appears to facilitate nuclear export is identified, raising the possibility that Sd also contains a nuclear export signal (NES).

The Drosophila jing gene is a downstream target in the Trachealess/Tango tracheal pathway

Primary branching in the Drosophila trachea is regulated by the Trachealess (Trh) and Tango (Tgo) basic helix-loop-helix-PAS (bHLH-PAS) heterodimers, the POU protein Drifter (Dfr)/Ventral Veinless (Vvl), and the Pointed (Pnt) ETS transcription factor. The jing gene encodes a zinc finger protein also required for tracheal development. Three Trh/Tgo DNA-binding sites, known as CNS midline elements, in 1.5 kb of jing 5′ cis-regulatory sequence (jing1.5) previously suggested a downstream role for jing in the pathway. Here, we show that jing is a direct downstream target of Trh/Tgo and that Vvl and Pnt are also involved in jing tracheal activation. In vivo lacZ enhancer detection assays were used to identify cis-regulatory elements mediating embryonic expression patterns of jing. A 2.8-kb jing enhancer (jing2.8) drove lacZ expression in all tracheal cell lineages, the CNS midline and Engrailed-positive segmental stripes, mimicking endogenous jing expression. A 1.3-kb element within jing2.8 drove expression that was restricted to Engrailed-positive CNS midline cells and segmental ectodermal stripes. Surprisingly, jing1.5-lacZ expression was restricted to tracheal fusion cells despite the presence of consensus DNA-binding sites for bHLH-PAS, ETS, and POU domain transcription factors. Given the absence of Trh/Tgo DNA-binding sites in the jing1.3 enhancer, these results are consistent with previous observations suggesting a combinatorial basis to Trh-/Tgo-mediated transcriptional regulation in the trachea.

Staying alive: dalmation mediated blocking of apoptosis is essential for tissue maintenance

In an EMS screen for mutations disrupting tracheal development, we identified new alleles of the dalmation (dmt) gene, which had previously been shown to affect peripheral nervous system (PNS) development. Here, we demonstrate that dmt loss results in programmed cell death, disrupting PNS patterning and leading to large gaps in the salivary duct and trachea. Dmt loss results in increased expression of the proapoptotic regulator genes head involution defective (hid) and reaper (rpr), and deletion of these genes or tissue-specific expression of the baculoviral apoptotic inhibitor P35 rescues the dmt defects. dmt is also required to protect cells from irradiation induced expression of hid and rpr during the irradiation resistant stage, which begins as cells become irreversibly committed to their final fates. Thus, we propose that Dmt keeps cells alive by blocking activation of hid and rpr as cells become irreversibly committed.

Inheritance and expression of foreign genes in transgenic soybean plants

DNA-coated gold particles were introduced into meristems of immature soybean seeds using electric discharge particle acceleration to produce transgenic fertile soybean plants. The lineages of integrated foreign DNA in two independently transformed plants were followed in the first (R(1)) and second (R(2)) generation of self-pollinated progeny. One plant (4615) was transformed with the Escherichia coli genes for beta-glucuronidase and neomycin phosphotransferase II; the other (3993) was transformed only with the gene for beta-glucuronidase. Segregation ratios for the introduced gene(s) were approximately 3:1 for plant 4615 and 1:1 for plant 3993 in the R(1) generation. DNA analysis showed 100% concordance between presence of the foreign gene sequences and enzyme activity. Moreover, all copies of the foreign genes are inherited as a unit in each plant. Plant 3993 segregated in a 1:1 ratio in the R(2) generation. R(1) plants derived from plant 4615, which expressed both genes, gave either 100% or 3:1 expression of both genes in the R(2) generation, demonstrating recovery of both homozygous and heterozygous R(1) plants. Our results show that foreign DNA introduced into soybean plants using electric discharge particle acceleration can be inherited in a Mendelian manner. Results also demonstrate cotransformation of tandem markers and show that both markers are inherited as closely linked genes in subsequent generations. These results indicate that whole plants can be derived from single transformed cells by a de novo organogenic pathway.

Interaction between eye pigment genes and tau-induced neurodegeneration in Drosophila melanogaster

Null mutations in the genes white and brown, but not scarlet, enhance a rough eye phenotype in a Drosophila melanogaster model of tauopathy; however, adding rosy mutations suppresses these effects. Interaction with nucleotide-derived pigments or increased lysosomal dysregulation are potential mechanisms. Finally, tau toxicity correlates with increased GSK-3β activity, but not with tau phosphorylation at Ser202/Thr205.

The Drosophila copper transporter Ctr1C functions in male fertility

Living organisms have evolved intricate systems to harvest trace elements from the environment, to control their intracellular levels, and to ensure adequate delivery to the various organs and cellular compartments. Copper is one of these trace elements. It is at the same time essential for life but also highly toxic, not least because it facilitates the generation of reactive oxygen species. In mammals, copper uptake in the intestine and copper delivery into other organs are mediated by the copper importer Ctr1. Drosophila has three Ctr1 homologs: Ctr1A, Ctr1B, and Ctr1C. Earlier work has shown that Ctr1A is an essential gene that is ubiquitously expressed throughout development, whereas Ctr1B is responsible for efficient copper uptake in the intestine. Here, we characterize the function of Ctr1C and show that it functions as a copper importer in the male germline, specifically in maturing spermatocytes and mature sperm. We further demonstrate that loss of Ctr1C in a Ctr1B mutant background results in progressive loss of male fertility that can be rescued by copper supplementation to the food. These findings hint at a link between copper and male fertility, which might also explain the high Ctr1 expression in mature mammalian spermatozoa. In both mammals and Drosophila, the X chromosome is known to be inactivated in the male germline. In accordance with such a scenario, we provide evidence that in Drosophila, the autosomal Ctr1C gene originated as a retrogene copy of the X-linked Ctr1A, thus maintaining copper delivery during male spermatogenesis.

Functional dissection of Timekeeper (Tik) implicates opposite roles for CK2 and PP2A during Drosophila neurogenesis

Repression by E(spl)M8 during inhibitory Notch (N) signaling (lateral inhibition) is regulated, in part, by protein kinase CK2, but the involvement of a phosphatase has been unclear. The studies we report here employ Tik, a unique dominant-negative (DN) mutation in the catalytic subunit of CK2, in a Gal4-UAS based assay for impaired lateral inhibition. Specifically, overexpression of Tik elicits ectopic bristles in N(+) flies and suppresses the retinal defects of the gain-of-function allele N(spl). Functional dissection of the two substitutions in Tik (M(161)K and E(165)D), suggests that both mutations contribute to its DN effects. While the former replacement compromises CK2 activity by impairing ATP-binding, the latter affects a conserved motif implicated in binding the phosphatase PP2A. Accordingly, overexpression of microtubule star (mts), the PP2A catalytic subunit closely mimics the phenotypic effects of loss of CK2 functions in N(+) or N(spl) flies, and elicits notched wings, a characteristic of N mutations. Our findings suggest antagonistic roles for CK2 and PP2A during inhibitory N signaling.

On the mechanism underlying the divergent retinal and bristle defects of M8* (E(spl)D) in Drosophila

Our results, using endogenous mutants and Gal4-UAS driven transgenes, implicate multisite phosphorylation in repression by E(spl)M8. We propose that these phosphorylations occur in the morphogenetic furrow (MF) to reverse an auto-inhibited state of M8, enabling repression of Atonal during R8 specification. Our studies address the paradoxical behavior of M8*, the truncated protein encoded by E(spl)D. We suggest that differences in N signaling in the bristle versus the eye underlie the antimorphic activity of M8* in N(+) (ectopic bristles) and hypermorphic activity in N(spl) (reduced eye). Ectopic M8* impairs eye development (in N(spl)) only during establishment of the atonal feedback loop (anterior to the MF), but is ineffective after this time point. In contrast, a CK2 phosphomimetic M8 lacking Groucho (Gro) binding, M8SDDeltaGro, acts antimorphic in N(+) and suppresses the eye/R8 and bristle defects of N(spl), as does reduced dosage of E(spl) or CK2. Multisite phosphorylation could serve as a checkpoint to enable a precise onset of repression, and this is bypassed in M8*. Additional implications are discussed.

The non-conserved C-terminal segments of Sine Oculis Homeobox (SIX) proteins confer functional specificity

The Sine Oculis Homeobox (SIX) proteins play critical roles in organogenesis and are defined by the presence of two evolutionarily conserved functional motifs: a homeobox DNA binding domain and the SIX protein-protein interaction domain. Members of this transcription factor family can be divided into three subgroups: Six1/2, Six4/5, and Six3/6. This partitioning is based mainly on protein sequence similarity and genomic architecture, and not on specificities of DNA binding or binding partners. In fact, it is well demonstrated that members of the different subgroups can bind to and activate common transcriptional targets as well as form biochemical complexes with communal binding partners. Here we report that the C-terminal segment, which is not conserved across different SIX subfamilies, may serve to functionally distinguish individual SIX proteins. In particular, we have dissected the C-terminal region of Optix, the Drosophila ortholog of mammalian Six3/6, and identified three regions that distinguish Optix from Sine Oculis, the fly homolog of Six1/2. Two of these regions have been preserved in all Six3/6 family members while the third section is present only within Optix proteins in the Drosophilids. The activities of these regions are required, in unison, for Optix function. We suggest that biochemical/functional differences between members of large protein families as well as proteins encoded by duplicate genes can, in part, be attributed to the activities of nonconserved segments. Finally, we demonstrate that a subset of vertebrate SIX proteins has retained the ability to function during normal fly eye development but have lost the ability to induce the formation of ectopic eyes.

Human copper transporter Ctr1 is functional in Drosophila, revealing a high degree of conservation between mammals and insects

Living cells have to carefully control the intracellular concentration of trace metals, especially of copper, which is at the same time essential but owing to its redox activity can also facilitate generation of reactive oxygen species. Mammals have two related copper transporters, Ctr1 and Ctr2, with Ctr1 playing the major role. The fruit fly Drosophila has three family members, termed Ctr1A, Ctr1B, and Ctr1C. Ctr1A is expressed throughout development, and a null mutation causes lethality at an early stage. Ctr1B ensures efficient copper uptake in the intestinal tract, whereas Ctr1C is mainly expressed in male gonads. Ectopic expression of Ctr1 transporters in Drosophila causes toxic effects due to excessive copper uptake. Here, we compare the effects of human Ctr1 (hCtr1) with those of the Drosophila homologs Ctr1A and Ctr1B in two overexpression assays. Whereas the overexpression of Drosophila Ctr1A and Ctr1B results in strong phenotypes, expression of hCtr1 causes only a very mild phenotype, indicating a low copper-import efficiency in the Drosophila system. However, this can be boosted by coexpressing the human copper chaperone CCS. Surprisingly, hCtr1 complements a lethal Ctr1A mutation at least as well as Ctr1A and Ctr1B transgenes. These findings reveal a high level of conservation between the mammalian and insect Ctr1-type copper importers, and they also demonstrate that the Drosophila Ctr1 proteins are functionally interchangeable.

A novel system for the launch of alphavirus RNA synthesis reveals a role for the Imd pathway in arthropod antiviral response

Alphaviruses are RNA viruses transmitted between vertebrate hosts by arthropod vectors, primarily mosquitoes. How arthropods counteract alphaviruses or viruses per se is not very well understood. Drosophila melanogaster is a powerful model system for studying innate immunity against bacterial and fungal infections. In this study we report the use of a novel system to analyze replication of Sindbis virus (type species of the alphavirus genus) RNA following expression of a Sindbis virus replicon RNA from the fly genome. We demonstrate deficits in the immune deficiency (Imd) pathway enhance viral replication while mutations in the Toll pathway fail to affect replication. Similar results were observed with intrathoracic injections of whole virus and confirmed in cultured mosquito cells. These findings show that the Imd pathway mediates an antiviral response to Sindbis virus replication. To our knowledge, this is the first demonstration of an antiviral role for the Imd pathway in insects.

ISOGENIC AUTOSOMES TO BE APPLIED IN OPTIMAL SCREENING FOR NOVEL MUTANTS WITH VIABLE PHENOTYPES INDROSOPHILA MELANOGASTER

Most insertional mutagenesis screens of Drosophila performed to date have not used target chromosomes that have been checked for their suitability for phenotypic screens for viable phenotypes. To address this, we have generated a selection of stocks carrying either isogenized second chromosomes or isogenized third chromosomes, in a genetic background derived from a Canton-S wild-type strain. We have tested these stocks for a range of behavioral and other viable phenotypes. As expected, most lines are statistically indistinguishable from Canton-S in most phenotypes tested. The lines generated are now being used as target chromosomes in mutagenesis screens, and the characterization reported here will facilitate their use in screens of these lines for behavioral and other viable phenotypes.

mars and tousled-like kinase act in parallel to ensure chromosome fidelity in Drosophila

Background

High levels of Hepatoma Up-Regulated Protein (HURP) and Tousled-Like Kinase (TLK) transcripts are found in hepatocellular carcinoma. HURP overexpression induces anchorage-independent growth of 293-T cells and enhances a rough-eye phenotype resulting from tlk overexpression in Drosophila. In addition, both HURP and Mars, a Drosophila HURP sequence homologue, promote polymerization of mitotic spindles. Thus, the genetic interaction of mars with tlk might be required for accurate chromosome segregation.

Methods

To reveal whether chromosome fidelity was decreased, the frequency of gynandromorphy, an individual with both male and female characteristics, and of non-disjunction were measured in the progeny from parents with reduced mars and/or tlk activities and analyzed by Student's t-test. To show that the genetic interaction between mars and tlk is epistatic or parallel, a cytological analysis of embryos with either reduced or increased activities of mars and/or tlk was used to reveal defects in mitotic-spindle morphology and chromosome segregation.

Results

A significant but small fraction of the progeny from parents with reduced mars activity showed gynandromorphy and non-disjunction. Results of cytological analysis revealed that the decrease in chromosome fidelity was a result of delayed polymerization of the mitotic spindle, which led to asynchronous chromosome segregation in embryos that had reduced mars activity. By removing one copy of tousled-like kinase (tlk) from flies with reduced mars activity, chromosome fidelity was further reduced. This was indicated by an increased in the non-disjunction rate and more severe asynchrony. However, the morphology of the mitotic spindles in the embryos at metaphase where both gene activities were reduced was similar to that in mars embryos. Furthermore, tlk overexpression did not affect the morphology of the mitotic spindles and the cellular localization of Mars protein.

Conclusion

Chromosome fidelity in progeny from parents with reduced mars and/or tlk activity was impaired. The results from cytological studies revealed that mars and tlk function in parallel and that a balance between mars activity and tlk activity is required for cells to progress through mitosis correctly, thus ensuring chromosome fidelity.

Insights into the Malpighian tubule from functional genomics

Classical physiological study of the Malpighian tubule has led to a detailed understanding of fluid transport and its control across several species. With the sequencing of the Drosophila genome, and the concurrent development of post-genomic technologies such as microarrays,proteomics, metabolomics and systems biology, completely unexpected roles for the insect Malpighian tubule have emerged. As the insect body plan is simpler than that of mammals, tasks analogous to those performed by multiple mammalian organ systems must be shared out among insect tissues. As well as the classical roles in osmoregulation, the Malpighian tubule is highly specialized for organic solute transport, and for metabolism and detoxification. In Drosophila, the adult Malpighian tubule is the key tissue for defence against insecticides such as DDT; and it can also detect and mount an autonomous defence against bacterial invasion. While it is vital to continue to set insights obtained in Drosophila into the context of work in other species, the combination of post-genomic technologies and physiological validation can provide insights that might not otherwise have been apparent for many years.

The Torso signaling pathway modulates a dual transcriptional switch to regulate tailless expression

The Torso (Tor) signaling pathway activates tailless (tll) expression by relieving tll repression. None of the repressors identified so far, such as Capicuo, Groucho and Tramtrack69 (Ttk69), bind to the tor response element (tor-RE) or fully elucidate tll repression. In this study, an expanded tll expression pattern was shown in embryos with reduced heat shock factor (hsf) and Trithorax-like (Trl) activities. The GAGA factor, GAF encoded by Trl, bound weakly to the tor-RE, and this binding was enhanced by both Hsf and Ttk69. A similar extent of expansion of tll expression was observed in embryos with simultaneous knockdown of hsf, Trl and ttk69 activities, and in embryos with constitutively active Tor. Hsf is a substrate of mitogen-activated protein kinase and S378 is the major phosphorylation site. Phosphorylation converts Hsf from a repressor to an activator that works with GAF to activate tll expression. In conclusion, the GAF/Hsf/Ttk69 complex binding to the tor-RE remodels local chromatin structure to repress tll expression and the Tor signaling pathway activate tll expression by modulating a dual transcriptional switch.

Kinetic and mechanical analysis of live tube morphogenesis

Ribbon is a nuclear Broad Tramtrack Bric-a-brac (BTB) -domain protein required for morphogenesis of the salivary gland and trachea. We recently showed that ribbon mutants exhibit decreased Crumbs and Rab11-coincident apical vesicles and increased apical Moesin activity and microvillar structure during tube elongation. To learn how these molecular and morphological changes affect the dynamics of tubulogenesis, we optimized an advanced two-photon microscope to enable high-resolution live imaging of the salivary gland and trachea. Live imaging revealed that ribbon mutant tissues exhibit slowed and incomplete lumenal morphogenesis, consistent with previously described apical defects. Because Moesin activity correlates with cortical stiffness, we hypothesize that ribbon mutants suffer from increased apical stiffness during morphogenesis. We develop this hypothesis through mechanical analysis, using the advantages of live imaging to construct computational elastic and analytical viscoelastic models of tube elongation, which suggest that ribbon mutant tubes exhibit three- to fivefold increased apical stiffness and twofold increased effective apical viscosity.

Coincidence of P-insertion sites and breakpoints of deletions induced by activating P elements in Drosophila

We isolated a set of seven deletions in the 67B region by activating a nearby P-element insertion. The structures of the deletions were characterized by cloning and sequencing. The results showed that the P-induced deletions occurred nonrandomly in the genomic sites. One breakpoint of the deletions was located precisely at the end of the starting element, i.e., at the end of the inverted terminal repeats. The other breakpoint was nearby the retained starting element and coincided with preferential P-element insertion sites that harbor transcription initiation activities. It is known that P elements induce male recombination near the starting elements, giving rise to deletions with one breakpoint precisely located at an inverted terminal repeat of the retained starting element. Database analyses further revealed that deletions generated in P-induced male recombination also contained the other breakpoint in genomic regions that coincided with preferential P-insertion sites. The results suggest that nonrandom distribution of the deletion breakpoints is characteristic of the mechanism by which P elements induce deletions near the starting elements.

Perspectives on the state of insect transgenics

Genetic transformation is a critical component to the fundamental genetic analysis of insect species and holds great promise for establishing strains that improve population control and behavior for practical application. This is especially so for insects that are disease vectors, many of which are currently subject to genomic sequence analysis, and intensive population control measures that must be improved for better efficacy and cost-effectiveness. Transposon-mediated germ-line transformation has been the ultimate goal for most fundamental and practical studies, and impressive strides have been made in recent development of transgene vector and marker systems for several mosquito species. This has resulted in rapid advances in functional genomic sequence analysis and new strategies for biological control based on conditional lethality. Importantly, advances have also been made in our ability to use these systems more effectively in terms of enhanced stability and targeting to specific genomic loci. Nevertheless, not all insects are currently amenable to germ-line transformation techniques, and thus advances in transient somatic expression and paratransgenesis have also been critical, if not preferable for some applications. Of particular importance is how this technology will be used for practical application. Early ideas for population replacement of indigenous pests with innocuous transgenic siblings by transposon-vector spread, may require reevaluation in terms of our current knowledge of the behavior of transposons currently available for transformation. The effective implementation of any control program using released transgenics, will also benefit from broadening the perspective of these control measures as being more mainstream than exotic.

Metabolomic profiling of Drosophila using liquid chromatography Fourier transform mass spectrometry

Hydrophilic interaction chromatography (HILIC) interfaced with an Orbitrap Fourier transform mass spectrometer (FT-MS) was used to carry out metabolomic profiling of the classical Drosophila mutation, rosy (ry). This gene encodes a xanthine oxidase/dehydrogenase. In addition to validating the technology by detecting the same changes in xanthine, hypoxanthine, urate and allantoin that have been reported classically, completely unsuspected changes were detected in each of the tryptophan, arginine, pyrimidine and glycerophospholipid metabolism pathways. The rosy mutation thus ramifies far more widely than previously detected.

LTR retrotransposons and the evolution of dosage compensation in Drosophila

Background

Dosage compensation in Drosophila is the epigenetic process by which the expression of genes located on the single X-chromosome of males is elevated to equal the expression of X-linked genes in females where there are two copies of the X-chromosome. While epigenetic mechanisms are hypothesized to have evolved originally to silence transposable elements, a connection between transposable elements and the evolution of dosage compensation has yet to be demonstrated.

Results

We show that transcription of the Drosophila melanogaster copia LTR (long terminal repeat) retrotransposon is significantly down regulated when in the hemizygous state. DNA digestion and chromatin immunoprecipitation (ChIP) analyses demonstrate that this down regulation is associated with changes in chromatin structure mediated by the histone acetyltransferase, MOF. MOF has previously been shown to play a central role in the Drosophila dosage compensation complex by binding to the hemizygous X-chromosome in males.

Conclusion

Our results are consistent with the hypothesis that MOF originally functioned to silence retrotransposons and, over evolutionary time, was co-opted to play an essential role in dosage compensation in Drosophila.

Enhancer blocking and transvection at the Drosophila apterous locus

Intra- and interchromosomal interactions have been implicated in a number of genetic phenomena in diverse organisms, suggesting that the higher-order structural organization of chromosomes in the nucleus can have a profound impact on gene regulation. In Drosophila, homologous chromosomes remain paired in somatic tissues, allowing for trans interactions between genes and regulatory elements on the two homologs. One consequence of homolog pairing is the phenomenon of transvection, in which regulatory elements on one homolog can affect the expression of a gene in trans. We report a new instance of transvection at the Drosophila apterous (ap) locus. Two different insertions of boundary elements in the ap regulatory region were identified. The boundaries are inserted between the ap wing enhancer and the ap promoter and have highly penetrant wing defects typical of mutants in ap. When crossed to an ap promoter deletion, both boundary inserts exhibit the interallelic complementation characteristic of transvection. To confirm that transvection occurs at ap, we generated a deletion of the ap wing enhancer by FRT-mediated recombination. When the wing-enhancer deletion is crossed to the ap promoter deletion, strong transvection is observed. Interestingly, the two boundary elements, which are inserted approximately 10 kb apart, fail to block enhancer action when they are present in trans to one another. We demonstrate that this is unlikely to be due to insulator bypass. The transvection effects described here may provide insight into the role that boundary element pairing plays in enhancer blocking both in cis and in trans.

rosy Function is required for juvenile hormone effects in Drosophila melanogaster

Application of a high dose of juvenile hormone (JH) III or its mimics (JHM) to Drosophila at the white puparium stage causes the formation of a pupal-like abdomen with few or no short bristles. We report here that the rosy (ry) gene encoding the enzyme xanthine dehydrogenase (XDH), which catalyzes the final two-step oxidation in purine catabolism, is required for this effect of JH on the epidermis. In ry506 (null allele) homozygotes or hemizygotes, JH III or pyriproxifen (a JHM) had little effect on abdominal bristle or cuticle formation, but disrupted the development of the central nervous system as in wild-type flies. Wild-type ry rescued the JH sensitivity of the abdominal epidermis in ry506 mutants. Inhibition of XDH activity phenocopied the ry null mutant's insensitivity to JH. Larvae fed on hypoxanthine or xanthine showed a decreased JH sensitivity. ry506 clones were sensitive to JH, indicating that ry is required non-cell autonomously for the JH effects. Normally JH applied at pupariation causes the aberrant reexpression of the transcription factor broad in the abdominal epidermis during adult development, but in the ry506 mutant most of the cells in the dorsal tergite showed no broad reexpression, indicating that ry is upstream of broad in the JH signaling pathway.

The use of P-element transposons to generate transgenic flies

The development of a technique to stably integrate exogenous DNA into the germline of Drosophila melanogaster marked a milestone in the ability to study gene function in the fly. On the molecular level germline transformation mainly relies on a particular transposable element, the D. melanogaster P-element. Based on certain features of the P-element, vectors have been designed for diverse applications like gene disruption, chromosome engineering, gene tagging, and inducible gene expression/repression. Despite the fact that an increasing number of other transposons have been utilized for germline transformation of Drosophila most transformation vectors are still P-element based. Technically, microinjection serves as the method of choice to physically introduce transgenes into preblastoderm Drosophila embryos. Besides an appropriate technical equipment including suitable microcapillaries in conjunction with a micromanipulator, a microinjector, and a microscope, proper handling of the Drosophila embryos before and after microinjection is the key step to the generation of transgenic flies. Pioneer work in Drosophila also served as a general guideline for the transformation of other insect species including those with medical and agricultural importance.

Hip, an HP1-interacting protein, is a haplo- and triplo-suppressor of position effect variegation

The Drosophila heterochromatin protein 1 (HP1) regulates epigenetic gene silencing and heterochromatin formation by promoting and maintaining chromatin condensation. Here we report the identification and characterization of an HP1-interacting protein (Hip). Hip interacts with HP1 in vitro and is associated with HP1 in vivo. This interaction is mediated by at least three independent but similar HP1-binding modules of the Hip protein. Hip and HP1 completely colocalize in the pericentric heterochromatin, and both haplo- and triplo-dosage mutations act as dominant suppressors of position effect variegation. These findings identify a player in heterochromatinization and suggest that Hip cooperates with HP1 in chromatin remodeling and gene silencing.

Meiotic pairing and disjunction of mini-X chromosomes in drosophila is mediated by 240-bp rDNA repeats and the homolog conjunction proteins SNM and MNM

In most eukaryotes, segregation of homologous chromosomes during meiosis is dependent on crossovers that occur while the homologs are intimately paired during early prophase. Crossovers generate homolog connectors known as chiasmata that are stabilized by cohesion between sister-chromatid arms. In Drosophila males, homologs pair and segregate without recombining or forming chiasmata. Stable pairing of homologs is dependent on two proteins, SNM and MNM, that associate with chromosomes throughout meiosis I until their removal at anaphase I. SNM and MNM localize to the rDNA region of the X-Y pair, which contains 240-bp repeats that have previously been shown to function as cis-acting chromosome pairing/segregation sites. Here we show that heterochromatic mini-X chromosomes lacking native rDNA but carrying transgenic 240-bp repeat arrays segregate preferentially from full-length sex chromosomes and from each other. Mini-X pairs do not form autonomous bivalents but do associate at high frequency with the X-Y bivalent to form trivalents and quadrivalents. Both disjunction of mini-X pairs and multivalent formation are dependent on the presence of SNM and MNM. These results imply that 240-bp repeats function to mediate association of sex chromosomes with SNM and MNM.