[Show abstract][Hide abstract] ABSTRACT: While a number of studies have identified host factors that influence endosymbiont titer, little is known concerning environmental influences on titer. Here we examined nutrient impact on maternally transmitted Wolbachia endosymbionts in Drosophila. We demonstrate that Drosophila reared on sucrose- and yeast-enriched diets exhibit increased and reduced Wolbachia titers in oogenesis, respectively. The yeast-induced Wolbachia depletion is mediated in large part by the somatic TOR and insulin signaling pathways. Disrupting TORC1 with the small molecule rapamycin dramatically increases oocyte Wolbachia titer, whereas hyper-activating somatic TORC1 suppresses oocyte titer. Furthermore, genetic ablation of insulin-producing cells located in the Drosophila brain abolished the yeast impact on oocyte titer. Exposure to yeast-enriched diets altered Wolbachia nucleoid morphology in oogenesis. Furthermore, dietary yeast increased somatic Wolbachia titer overall, though not in the central nervous system. These findings highlight the interactions between Wolbachia and germline cells as strongly nutrient-sensitive, and implicate conserved host signaling pathways by which nutrients influence Wolbachia titer.
[Show abstract][Hide abstract] ABSTRACT: Author Summary
During cell division, chromosomes acquire their characteristic X-shaped morphology by having well-resolved chromosome arms while still remaining connected at the heterochromatic regions around the centromere. This connection is mediated by the cohesin complex, a “molecular glue” that keeps the two DNA molecules stuck together and ensures that the chromosomes are properly segregated. However, it is unclear how important it is for efficient chromosome segregation that these cohesive forces are specifically positioned near the centromere. In this study, we tested several strains of the fruit fly Drosophila melanogaster carrying chromosomal rearrangements in which long stretches of heterochromatin from near the centromere have been misplaced within distant euchromatic regions. We find that such inappropriately located heterochromatin is enough to promote increased levels of cohesin complex loading and the formation of additional constrictions, regardless of proximity to the centromere. Importantly, we further show that as cell division proceeds and the sister chromatids move to opposite poles of the cell, the presence of ectopic heterochromatin (and hence ectopic cohesion) leads to significant chromosome stretching due to impaired resolution of the ectopic cohesion sites. These results highlight the possibility that chromosome rearrangements involving heterochromatin regions near the centromeres, often seen in many cancers, can induce additional errors in cell division and thereby compromise genetic stability.
[Show abstract][Hide abstract] ABSTRACT: During spermiogenesis, histones are massively replaced with protamines. A previous report showed that Drosophila males homozygous for a genomic deletion covering several genes including the protamine-like genes Mst35Ba/b are surprisingly fertile. Here, we have precisely deleted the Mst35B locus by homologous recombination and we confirm the dispensability of Mst35Ba/b for fertility.
[Show abstract][Hide abstract] ABSTRACT: Author Summary
Filarial nematodes are responsible for a number of neglected tropical diseases. The vast majority of these human parasites harbor the bacterial endosymbiont Wolbachia. Wolbachia are essential for filarial nematode survival and reproduction, and thus are a promising anti-filarial drug target. Understanding the molecular and cellular basis of Wolbachia-nematode interactions will facilitate the development of a new class of drugs that specifically disrupt these interactions. Here we focus on Wolbachia segregation patterns and interactions with the host cytoskeleton during early embryogenesis. Our studies indicate that centrosomes are maternally inherited in filarial nematodes resulting in a posterior microtubule-organizing center of maternal origin, unique to filarial nematodes. This microtubule-organizing center facilitates the concentration of Wolbachia at the posterior pole. We find that the microtubule motor dynein is required for the proper posterior Wolbachia localization. In addition, we demonstrate that Wolbachia rely on polarity signals in the egg for their preferential localization at the posterior pole. Conversely, Wolbachia are required for normal embryonic axis determination and Wolbachia removal leads to distinct anterior-posterior embryonic polarity defects. To our knowledge, this is the first example of a bacterial endosymbiont required for normal host embryogenesis.
[Show abstract][Hide abstract] ABSTRACT: The model organism Drosophila melanogaster is particularly well suited for live image analysis. The availability of GFP transgenic flies and a wide array of fluorescent probes, in conjunction with laser scanning confocal microscopy, allow us to image multiple aspects of the cell cycle simultaneously. Confocal microscopy provides the sensitivity and resolution to observe the dynamics of specific cellular events in real time. For example, GFP-histone and rhodamine-labeled tubulin enable one to follow specific nuclear and cytoskeletal events including nuclear envelope formation, nuclear envelope breakdown, spindle formation, centrosome duplication, separation and migration, chromosomes condensation, and segregation. This analysis permits a detailed morphological and temporal description of nuclear and cytoskeletal events in normal or drug-injected embryos.
[Show abstract][Hide abstract] ABSTRACT: Wolbachia, a maternally inherited endosymbiont of arthropods, is commonly known for its extreme reproductive manipulations of its hosts, and, more recently, for its potential use in reducing insect-borne diseases. Twenty years ago, a cytoplasmic incompatibility (CI)-inducing strain of Wolbachia, wRi, was shown to decrease the fecundity of infected Drosophila simulans females in California, making it an apparent parasite of this species, at least under laboratory conditions. However, extensive field surveys have documented the rapid spread of wRi-infected D. simulans through North America, Europe and Australia. To better understand this symbiont-host interaction, we assayed variation in levels of CI and fecundity effects in a natural orchard population. We found that multiple lines of wRi conferred significantly lower CI in their isofemale line than a control line. We also found an isofemale line, “Y36”, of D. simulans that showed severely decreased fecundity when uninfected, or when infected with wRi from other isofemale lines. To learn more about the cell biology of this aberrant line, we researched its cell localization patterns in D. simulans, compared to lines with no obvious fitness effects of infection. We found that Y36 showed higher concentration outside of cells in the brain than control lines, which primarily concentrate in the gonads. Our results suggest that, in wRi alone, there can be a wide variety of cell localization patterns, fitness effects, and more generally, host-symbiont relationships. In conclusion, we believe that this variation points to the untapped potential for naturally occurring variants of Wolbachia that could be useful in disease research.
Entomological Society of America Annual Meeting 2013; 11/2013
[Show abstract][Hide abstract] ABSTRACT: The maternally inherited bacterium Wolbachia infects the germline of most arthropod species. Using D. simulans and D. melanogaster, we demonstrate that localization of Wolbachia to the fat bodies and adult brain is likely also a conserved feature of Wolbachia infection. Examination of three Wolbachia strains (WMel , WRiv , WPop ) revealed that the bacteria preferentially concentrate in the central brain with low titers in the optic lobes. Distribution within regions of the central brain is largely determined by the Wolbachia strain, while the titer is influenced by both, the host species and the bacteria strain. In neurons of the central brain and ventral nerve cord, Wolbachia preferentially localize to the neuronal cell bodies but not to axons. All examined Wolbachia strains are present intracellularly or in extracellular clusters, with the pathogenic WPop strain exhibiting the largest and most abundant clusters. We also discovered that 16 of 40 lines from the Drosophila Genetic Reference Panel are Wolbachia infected. Direct comparison of Wolbachia infected and cured lines from this panel reveals that differences in physiological traits (chill coma recovery, starvation, longevity) are likely due to host line influences. In addition, a tetracycline-induced increase in Drosophila longevity was detected many generations after treatment.
[Show abstract][Hide abstract] ABSTRACT: Among all organisms, Drosophila melanogaster has the most extensive well-characterized collection of large-scale chromosome rearrangements. Compound chromosomes, rearrangements in which homologous chromosome arms share a centromere, have proven especially useful in genetic-based surveys of the entire genome. However, their potential has not been fully realized because compound autosome stocks are refractile to standard genetic manipulations: if outcrossed, they yield inviable aneuploid progeny. Here we describe two strategies, cold-shock and use of the bubR1 mutant alleles, to produce nullo gametes through nondisjunction. These gametes are complementary to the compound chromosome-bearing gametes and thus produce viable progeny. Using these techniques, we created a compound chromosome two C(2)EN stock bearing a red fluorescent protein-histone transgene, facilitating live analysis of these unusually long chromosomes.
[Show abstract][Hide abstract] ABSTRACT: Chromosome segregation must be coordinated with cell cleavage to ensure correct transmission of the genome to daughter cells. Here we identify a novel mechanism by which Drosophila melanogaster neuronal stem cells coordinate sister chromatid segregation with cleavage furrow ingression. Cells adapted to a dramatic increase in chromatid arm length by transiently elongating during anaphase/telophase. The degree of cell elongation correlated with the length of the trailing chromatid arms and was concomitant with a slight increase in spindle length and an enlargement of the zone of cortical myosin distribution. Rho guanine-nucleotide exchange factor (Pebble)-depleted cells failed to elongate during segregation of long chromatids. As a result, Pebble-depleted adult flies exhibited morphological defects likely caused by cell death during development. These studies reveal a novel pathway linking trailing chromatid arms and cortical myosin that ensures the clearance of chromatids from the cleavage plane at the appropriate time during cytokinesis, thus preserving genome integrity.
The Journal of Cell Biology 11/2012; 199(5):745-53. DOI:10.1083/jcb.201208041 · 9.69 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Early Drosophila embryogenesis is characterized by shifting from astral microtubule-based to central spindle-based positioning of cleavage furrows. Before cellularization, astral microtubules determine metaphase furrow position by producing Rappaport-like furrows, which encompass rather than bisect the spindle. Their positioning is explained by our finding that the conserved central spindle components centralspindlin (mKLP1 and RacGAP50C), Polo, and Fascetto (Prc1) localize to the astral microtubule overlap region. These components and the chromosomal passenger complex localize to the central spindle, though no furrow forms there. We identify the maternally supplied RhoGEF2 as a key factor in metaphase furrow positioning. Unlike the zygotic, central spindle-localized RhoGEF (Pebble), RhoGEF2 localizes to metaphase furrows, a function distinct from RhoGEF/Pebble and likely due to the absence of a RacGAP50C binding domain. Accordingly, we find that ectopic activation of Rho GTPase generates furrows perpendicular to the central spindle during syncytial divisions. Whereas metaphase furrow formation is myosin independent, these ectopic furrows, like conventional furrows, require myosin as well as microtubules. These studies demonstrate that early Drosophila embryogenesis is primed to form furrows at either overlapping astral microtubules or the central spindle. We propose that the shift to the latter is driven by a corresponding shift from RhoGEF2 to Pebble in controlling furrow formation.
Current biology: CB 09/2012; 22(21). DOI:10.1016/j.cub.2012.08.046 · 9.92 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Wolbachia endosymbionts carried by filarial nematodes give rise to the neglected diseases African river blindness and lymphatic filariasis afflicting millions worldwide. Here we identify new Wolbachia-disrupting compounds by conducting high-throughput cell-based chemical screens using a Wolbachia-infected, fluorescently labeled Drosophila cell line. This screen yielded several Wolbachia-disrupting compounds including three that resembled Albendazole, a widely used anthelmintic drug that targets nematode microtubules. Follow-up studies demonstrate that a common Albendazole metabolite, Albendazole sulfone, reduces intracellular Wolbachia titer both in Drosophila melanogaster and Brugia malayi, the nematode responsible for lymphatic filariasis. Significantly, Albendazole sulfone does not disrupt Drosophila microtubule organization, suggesting that this compound reduces titer through direct targeting of Wolbachia. Accordingly, both DNA staining and FtsZ immunofluorescence demonstrates that Albendazole sulfone treatment induces Wolbachia elongation, a phenotype indicative of binary fission defects. This suggests that the efficacy of Albendazole in treating filarial nematode-based diseases is attributable to dual targeting of nematode microtubules and their Wolbachia endosymbionts.
[Show abstract][Hide abstract] ABSTRACT: Spatially and temporally dependent optical aberrations induced by the inhomogeneous refractive index of live samples limit the resolution of live dynamic imaging. We introduce an adaptive optical microscope with a direct wavefront sensing method using a Shack-Hartmann wavefront sensor and fluorescent protein guide-stars for live imaging. The results of imaging Drosophila embryos demonstrate its ability to correct aberrations and achieve near diffraction limited images of medial sections of large Drosophila embryos. GFP-polo labeled centrosomes can be observed clearly after correction but cannot be observed before correction. Four dimensional time lapse images are achieved with the correction of dynamic aberrations. These studies also demonstrate that the GFP-tagged centrosome proteins, Polo and Cnn, serve as excellent biological guide-stars for adaptive optics based microscopy.
[Show abstract][Hide abstract] ABSTRACT: Parasitic filarial nematodes that belong to the Onchocercidae family live in mutualism with Wolbachia endosymbionts. We developed whole-mount techniques to follow the segregation patterns of Wolbachia through the somatic and germline lineages of four filarial species. These studies reveal multiple evolutionarily conserved mechanisms that are required for Wolbachia localization to the germline. During the initial embryonic divisions, Wolbachia segregate asymmetrically such that they concentrate in the posteriorly localized P(2) blastomere, a precursor to the adult germline and hypodermal lineages. Surprisingly, in the next division they are excluded from the germline precursor lineage. Rather, they preferentially segregate to the C blastomere, a source of posterior hypodermal cells. Localization to the germline is accomplished by a distinct mechanism in which Wolbachia invade first the somatic gonadal cells close to the ovarian distal tip cell, the nematode stem cell niche, from the hypodermis. This tropism is associated with a cortical F-actin disruption, suggesting an active engulfment. Significantly, germline invasion occurs only in females, explaining the lack of Wolbachia in the male germline. Once in the syncytial environment of the ovaries, Wolbachia rely on the rachis to multiply and disperse into the germ cells. The utilization of cell-to-cell invasion for germline colonization may indicate an ancestral mode of horizontal transfer that preceded the acquisition of the mutualism.
Biology Open 06/2012; 1(6):536-47. DOI:10.1242/bio.2012737 · 2.42 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Defects in DNA replication and chromosome condensation are common phenotypes in cancer cells. A link between replication and condensation has been established, but little is known about the role of checkpoints in monitoring chromosome condensation. We investigate this function by live analysis, using the rapid division cycles in the early Drosophila embryo. We find that S-phase and topoisomerase inhibitors delay both the initiation and the rate of chromosome condensation. These cell cycle delays are mediated by the cell cycle kinases chk1 and wee1. Inhibitors that cause severe defects in chromosome condensation and congression on the metaphase plate result in delayed anaphase entry. These delays are mediated by wee1 and are not the result of spindle assembly checkpoint activation. In addition, we provide the first detailed live analysis of the direct effect of widely used anticancer agents (aclarubicin, ICRF-193, VM26, doxorubicin, camptothecin, aphidicolin, hydroxyurea, cisplatin, mechlorethamine and x-rays) on key nuclear and cytoplasmic cell cycle events.
Molecular biology of the cell 01/2012; 23(6):1047-57. DOI:10.1091/mbc.E11-10-0832 · 5.98 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: RNA interference (RNAi) is an efficient reverse genetics technique for investigating gene function in eukaryotes. The method has been widely used in model organisms, such as the free-living nematode Caenorhabditis elegans, where it has been deployed in genome-wide high throughput screens to identify genes involved in many cellular and developmental processes. However, RNAi techniques have not translated efficiently to animal parasitic nematodes that afflict humans, livestock and companion animals across the globe, creating a dependency on data tentatively inferred from C. elegans.
We report improved and effective in vitro RNAi procedures we have developed using heterogeneous short interfering RNA (hsiRNA) mixtures that when coupled with optimized immunostaining techniques yield detailed analysis of cytological defects in the human parasitic nematode, Brugia malayi. The cellular disorganization observed in B. malayi embryos following RNAi targeting the genes encoding γ-tubulin, and the polarity determinant protein, PAR-1, faithfully phenocopy the known defects associated with gene silencing of their C. elegans orthologs. Targeting the B. malayi cell junction protein, AJM-1 gave a similar but more severe phenotype than that observed in C. elegans. Cellular phenotypes induced by our in vitro RNAi procedure can be observed by immunofluorescence in as little as one week.
We observed cytological defects following RNAi targeting all seven B. malayi transcripts tested and the phenotypes mirror those documented for orthologous genes in the model organism C. elegans. This highlights the reliability, effectiveness and specificity of our RNAi and immunostaining procedures. We anticipate that these techniques will be widely applicable to other important animal parasitic nematodes, which have hitherto been mostly refractory to such genetic analysis.
[Show abstract][Hide abstract] ABSTRACT: Although much is known about interactions between bacterial endosymbionts and their hosts, little is known concerning the host factors that influence endosymbiont titer. Wolbachia endosymbionts are globally dispersed throughout most insect species and are the causative agent in filarial nematode-mediated disease. Our investigation indicates that gurken (grk), a host gene encoding a crucial axis determinant, has a cumulative, dosage-sensitive impact on Wolbachia growth and proliferation during Drosophila oogenesis. This effect appears to be mediated by grk mRNA and its protein-binding partners Squid and Hrp48/Hrb27C, implicating the grk mRNA-protein (mRNP) complex as a rate-limiting host factor controlling Wolbachia titer. Furthermore, highly infected flies exhibit defects that match those occurring with disruption of grk mRNPs, such as nurse cell chromatin disruptions and malformation of chorionic appendages. These findings suggest a feedback loop in which Wolbachia interaction with the grk mRNP affects both Wolbachia titer and grk mRNP function.
[Show abstract][Hide abstract] ABSTRACT: Filarial nematodes maintain a mutualistic relationship with the endosymbiont Wolbachia. Depletion of Wolbachia produces profound defects in nematode development, fertility and viability and thus has great promise as a novel approach for treating filarial diseases. However, little is known concerning the basis for this mutualistic relationship. Here we demonstrate using whole mount confocal microscopy that an immediate response to Wolbachia depletion is extensive apoptosis in the adult germline, and in the somatic cells of the embryos, microfilariae and fourth-stage larvae (L4). Surprisingly, apoptosis occurs in the majority of embryonic cells that had not been infected prior to antibiotic treatment. In addition, no apoptosis occurs in the hypodermal chords, which are populated with large numbers of Wolbachia, although disruption of the hypodermal cytoskeleton occurs following their depletion. Thus, the induction of apoptosis upon Wolbachia depletion is non-cell autonomous and suggests the involvement of factors originating from Wolbachia in the hypodermal chords. The pattern of apoptosis correlates closely with the nematode tissues and processes initially perturbed following depletion of Wolbachia, embryogenesis and long-term sterilization, which are sustained for several months until the premature death of the adult worms. Our observations provide a cellular mechanism to account for the sustained reductions in microfilarial loads and interruption of transmission that occurs prior to macrofilaricidal activity following antibiotic therapy of filarial nematodes.
[Show abstract][Hide abstract] ABSTRACT: During early embryogenesis, nuclei divide within a syncytium without cytokinesis. However, actin-based furrows form during metaphase in order to separate neighboring nuclei. Regulation of these "metaphase furrows" has been shown to be similar to that of cytokinetic furrows. In order to find novel components or regulators of these structures, our lab has generated a class of temperature sensitive mutations that affect their formation and maintenance. One of the genes generated, ts161 (which we’ve named push pop), fails to form furrows during cycle 14 and therefore never cellularize. push pop is a homologue of the mammalian folypolyglutamate synthase (FPGS) which is an enzyme occurring early in the folate pathway. The folate pathway is required for purine synthesis and methylation of both DNA and proteins. Folate deficiencies have been shown to cause neural tube closure defects such as spina bifida. Our results indicate a possible role for folate derivatives in the organization of cytoskeletal elements. Furthermore, the folic acid pathway may in fact coordinate nuclear and cytoplasmic events during the cell cycle.
2011 Society for Advancement of Hispanics/Chicanos and Native Americans in Science National Conference; 10/2011