A house fly gene homologous to the zinc finger proto-oncogene Gfi-1

Transcriptional dynamics during Heliothis zea nudivirus 1 infection in an ovarian cell line from Helicoverpa zea

Nudiviruses (family Nudiviridae) are double-stranded DNA viruses that infect various insects and crustaceans. Among them, Heliothis zea nudivirus 1 (HzNV-1) represents the rare case of a lepidopteran nudivirus inducing a sexual pathology. Studies about molecular pathological dynamics of HzNV-1 or other nudiviruses are scarce. Hence, this study aims to provide a transcriptomic profile of HzNV-1 in an ovary-derived cell line of Helicoverpa zea (HZ-AM1), during early (3, 6 and 9 h post-infection) and advanced (12 and 24 h post-infection) stages of infection. Total RNA was extracted from both virus- and mock-infected cells, and RNA-seq analysis was performed to examine both virus and host transcriptional dynamics. Hierarchical clustering was used to categorize viral genes, while differential gene expression analysis was utilized to pinpoint host genes that are significantly affected by the infection. Hierarchical clustering classified the 154 HzNV-1 genes into four temporal phases, with early phases mainly involving transcription and replication genes and later phases including genes for virion assembly. In addition, a novel viral promoter motif was identified in the upstream region of early-expressed genes. Host gene analysis revealed significant upregulation of heat shock protein genes and downregulation of histone genes. The identification of temporal patterns in viral gene expression enhances the molecular understanding of nudivirus pathology, while the identified differentially expressed host genes highlight the key pathways most hijacked by HzNV-1 infection.

Standing genetic variation in laboratory populations of insecticide-susceptible Phlebotomus papatasi and Lutzomyia longipalpis (Diptera: Psychodidae: Phlebotominae) for the evolution of resistance

Insecticides can exert strong selection on insect pest species, including those that vector diseases, and have led to rapid evolution of resistance. Despite such rapid evolution, relatively little is known about standing genetic variation for resistance in insecticide-susceptible populations of many species. To help fill this knowledge gap, we generated genotyping-by-sequencing data from insecticide-susceptible Phlebotomus papatasi and Lutzomyia longipalpis sand flies that survived or died from a sub-diagnostic exposure to either permethrin or malathion using a modified version of the Centers for Disease Control and Prevention bottle bioassay. Multi-locus genome-wide association mapping methods were used to quantify standing genetic variation for insecticide resistance in these populations and to identify specific alleles associated with insecticide survival. For each insecticide treatment, we estimated the proportion of the variation in survival explained by the genetic data (i.e., "chip" heritability) and the number and contribution of individual loci with measurable effects. For all treatments, survival to an insecticide exposure was heritable with a polygenic architecture. Both P. papatasi and L. longipalpis had alleles for survival that resided within many genes throughout their genomes. The implications for resistance conferred by many alleles, as well as inferences made about the utility of laboratory insecticide resistance association studies compared to field observations, are discussed.

CYP-mediated permethrin resistance in Aedes aegypti and evidence for trans-regulation

Aedes aegypti poses a serious risk to human health due to its wide global distribution, high vector competence for several arboviruses, frequent human biting, and ability to thrive in urban environments. Pyrethroid insecticides remain the primary means of controlling adult A. aegypti populations during disease outbreaks. As a result of decades of use, pyrethroid resistance is a global problem. Cytochrome P450 monooxygenase (CYP)-mediated detoxification is one of the primary mechanisms of pyrethroid resistance. However, the specific CYP(s) responsible for resistance have not been unequivocally determined. We introgressed the resistance alleles from the resistant A. aegypti strain, Singapore (SP), into the genetic background of the susceptible ROCK strain. The resulting strain (CKR) was congenic to ROCK. Our primary goal was to determine which CYPs in SP are linked to resistance. To do this, we first determined which CYPs overexpressed in SP are also overexpressed in CKR, with the assumption that only the CYPs linked to resistance will be overexpressed in CKR relative to ROCK. Next, we determined whether any of the overexpressed CYPs were genetically linked to resistance (cis-regulated) or not (trans-regulated). We found that CYP6BB2, CYP6Z8, CYP9M5 and CYP9M6 were overexpressed in SP as well as in CKR. Based on the genomic sequences and polymorphisms of five single copy CYPs (CYP4C50, 6BB2, 6F2, 6F3 and 6Z8) in each strain, none of these genes were linked to resistance, except for CYP6BB2, which was partially linked to the resistance locus. Hence, overexpression of these four CYPs is due to a trans-regulatory factor(s). Knowledge on the specific CYPs and their regulators involved in resistance is critical for resistance management strategies because it aids in the development of new control chemicals, provides information on potential environmental modulators of resistance, and allows for the detection of resistance markers before resistance becomes fixed in the population.

Molecular mechanisms of metabolic resistance to synthetic and natural xenobiotics

Xenobiotic resistance in insects has evolved predominantly by increasing the metabolic capability of detoxificative systems and/or reducing xenobiotic target site sensitivity. In contrast to the limited range of nucleotide changes that lead to target site insensitivity, many molecular mechanisms lead to enhancements in xenobiotic metabolism. The genomic changes that lead to amplification, overexpression, and coding sequence variation in the three major groups of genes encoding metabolic enzymes, i.e., cytochrome P450 monooxygenases (P450s), esterases, and glutathione-S-transferases (GSTs), are the focus of this review. A substantial number of the adaptive genomic changes associated with insecticide resistance that have been characterized to date are transposon mediated. Several lines of evidence suggest that P450 genes involved in insecticide resistance, and perhaps insecticide detoxification genes in general, may share an evolutionary association with genes involved in allelochemical metabolism. Differences in the selective regime imposed by allelochemicals and insecticides may account for the relative importance of regulatory or structural mutations in conferring resistance.

A genetic screen in Drosophila for genes interacting with senseless during neuronal development identifies the importin moleskin

Senseless (Sens) is a conserved transcription factor required for normal development of the Drosophila peripheral nervous system. In the Drosophila retina, sens is necessary and sufficient for differentiation of R8 photoreceptors and interommatidial bristles (IOBs). When Sens is expressed in undifferentiated cells posterior to the morphogenetic furrow, ectopic IOBs are formed. This phenotype was used to identify new members of the sens pathway in a dominant modifier screen. Seven suppressor and three enhancer complementation groups were isolated. Three groups from the screen are the known genes Delta, lilliputian, and moleskin/DIM-7 (msk), while the remaining seven groups represent novel genes with previously undefined functions in neural development. The nuclear import gene msk was identified as a potent suppressor of the ectopic interommatidial bristle phenotype. In addition, msk mutant adult eyes are extremely disrupted with defects in multiple cell types. Reminiscent of the sens mutant phenotype, msk eyes demonstrate reductions in the number of R8 photoreceptors due to an R8 to R2,5 fate switch, providing genetic evidence that Msk is a component of the sens pathway. Interestingly, in msk tissue, the loss of R8 fate occurs earlier than with sens and suggests a previously unidentified stage of R8 development between atonal and sens.

Role of the transcriptional repressor mdGfi-1 in CYP6D1v1-mediated insecticide resistance in the house fly, Musca domestica

Gfi-1 is a C(2)H(2)-type zinc finger protein that is a transcriptional repressor in vertebrates and has been implicated in control of CYP6D1 expression in house flies (Musca domestica). A 15 bp insert, which disrupts a putative mdGfi-1 binding site in the CYP6D1v1 promoter has been implicated as a cause of increased expression of CYP6D1, and thus insecticide resistance. Using electrophoretic mobility shift assays we demonstrate that the CYP6D1 promoter from susceptible strains binds mdGfi-1. The 15 bp insert that interrupts the mdGfi-1-binding site in insecticide-resistant strains reduces the amount of mdGfi-1 binding by 9- to 20-fold, consistent with the role of mdGfi-1 in resistance. Partial sequences of mdGfi-1 (spanning the first intron) from individual houseflies from 11 different strains revealed the presence of 23 alleles. There was no consistent difference in the mdGfi-1 alleles between susceptible and CYP6D1-mediated insecticide-resistant strains, indicating that mdGfi-1 alleles were not likely involved in resistance. Polymorphisms were used to map mdGfi-1 to autosome 1. Quantitative real time PCR (qRT-PCR) revealed Gfi-1 expression was higher in the thorax compared to the head and abdomen, and varied between life stages and between strains. However, similar levels of mdGfi-1 were detected in susceptible and resistant adults suggesting that altered levels of mdGfi-1 were not likely a cause of insecticide resistance. The significance of these results to understanding insecticide resistance is discussed.

Gfi-1 oncoproteins in hematopoiesis

The family of Gfi-1 zinc finger transcriptional repressor oncoproteins consists of Gfi-1 and Gfi-1B. Recent gene targeting experiments and mutational screening in humans have revealed an essential role for Gfi-1 and Gfi-1B in hematopoiesis. Mice lacking Gfi-1 are unexpectedly neutropenic. Neutrophil differentiation is abolished and T lymphocyte differentiation is partially blocked in these mice. Heterozygous germline mutations of Gfi-1 causes severe congenital neutropenia (SCN) in humans. Ela2, whose germline mutation is the major contributor to hereditary neutropenias, is repressed in vivo by Gfi-1. Gfi-1B disruption is embryonic lethal due to a block of erythropoiesis. Gfi-1B is required for both erythroid and megakaryocyte development. The ongoing identification of repressed target genes and interacting transcriptional cofactors is helping to unravel the central contributions of these two hematopoietic factors.