13 resultados para instar
em National Center for Biotechnology Information - NCBI
Resumo:
Many insects feed on blood or tissue from mammalian hosts. One potential strategy for the control of these insects is to vaccinate the host with antigens derived from the insect. The larvae of the fly Lucilia cuprina feed on ovine tissue and tissue fluids causing a cutaneous myiasis associated with considerable host morbidity and mortality. A candidate vaccine antigen, peritrophin 95, was purified from the peritrophic membrane, which lines the gut of these larvae. Serum from sheep vaccinated with peritrophin 95 inhibited growth of first-instar L. cuprina larvae that fed on this serum. Growth inhibition was probably caused by antibody-mediated blockage of the normally semipermeable peritrophic membrane and the subsequent development of an impervious layer of undefined composition on the gut lumen side of the peritrophic membrane that restricted access of nutrients to the larvae. The amino acid sequence of peritrophin 95 was determined by cloning the DNA complementary to its mRNA. The deduced amino acid sequence codes for a secreted protein containing a distinct Cys-rich domain of 317 amino acids followed by a mucin-like domain of 139 amino acids. The Cys-rich domain may be involved in binding chitin. This report describes a novel immunological strategy for the potential control of L. cuprina larvae that may have general application to the control of other insect pests.
Resumo:
Null mutations at the misato locus of Drosophila melanogaster are associated with irregular chromosomal segregation at cell division. The consequences for morphogenesis are that mutant larvae are almost devoid of imaginal disk tissue, have a reduction in brain size, and die before the late third-instar larval stage. To analyze these findings, we isolated cDNAs in and around the misato locus, mapped the breakpoints of chromosomal deficiencies, determined which transcript corresponded to the misato gene, rescued the cell division defects in transgenic organisms, and sequenced the genomic DNA. Database searches revealed that misato codes for a novel protein, the N-terminal half of which contains a mixture of peptide motifs found in α-, β-, and γ-tubulins, as well as a motif related to part of the myosin heavy chain proteins. The sequence characteristics of misato indicate either that it arose from an ancestral tubulin-like gene, different parts of which underwent convergent evolution to resemble motifs in the conventional tubulins, or that it arose by the capture of motifs from different tubulin genes. The Saccharomyces cerevisiae genome lacks a true homolog of the misato gene, and this finding highlights the emerging problem of assigning functional attributes to orphan genes that occur only in some evolutionary lineages.
Resumo:
The XPD/ERCC2/Rad3 gene is required for excision repair of UV-damaged DNA and is an important component of nucleotide excision repair. Mutations in the XPD gene generate the cancer-prone syndrome, xeroderma pigmentosum, Cockayne’s syndrome, and trichothiodystrophy. XPD has a 5′- to 3′-helicase activity and is a component of the TFIIH transcription factor, which is essential for RNA polymerase II elongation. We present here the characterization of the Drosophila melanogaster XPD gene (DmXPD). DmXPD encodes a product that is highly related to its human homologue. The DmXPD protein is ubiquitous during development. In embryos at the syncytial blastoderm stage, DmXPD is cytoplasmic. At the onset of transcription in somatic cells and during gastrulation in germ cells, DmXPD moves to the nuclei. Distribution analysis in polytene chromosomes shows that DmXPD is highly concentrated in the interbands, especially in the highly transcribed regions known as puffs. UV-light irradiation of third-instar larvae induces an increase in the signal intensity and in the number of sites where the DmXPD protein is located in polytene chromosomes, indicating that the DmXPD protein is recruited intensively in the chromosomes as a response to DNA damage. This is the first time that the response to DNA damage by UV-light irradiation can be visualized directly on the chromosomes using one of the TFIIH components.
Resumo:
In a screen for genes expressed in the Drosophila embryonic salivary gland, we identified a tryptophanyl-tRNA synthetase gene that maps to cytological position 85D (WRS-85D). WRS-85D expression is dependent on the homeotic gene Sex combs reduced (Scr). In the absence of Scr function, WRS-85D expression is lost in the salivary gland primordia; conversely, ectopic expression of Scr results in expression of WRS-85D in new locations. Despite the fact that WRS-85D is a housekeeping gene essential for protein synthesis, we detected both WRS-85D mRNA and protein at elevated levels in the developing salivary gland. WRS-85D is required for embryonic survival; embryos lacking the maternal contribution were unrecoverable, whereas larvae lacking the zygotic component died during the third instar larval stage. We showed that recombinant WRS-85D protein specifically charges tRNATrp, and WRS-85D is likely to be the only tryptophanyl-tRNA synthetase gene in Drosophila. We characterized the expression patterns of all 20 aminoacyl-tRNA synthetases and found that of the four aminoacyl-tRNA synthetase genes expressed at elevated levels in the salivary gland primordia, WRS-85D is expressed at the highest level throughout embryogenesis. We also discuss the potential noncanonical activities of tryptophanyl-tRNA synthetase in immune response and regulation of cell growth.
Resumo:
The process of wing patterning involves precise molecular mechanisms to establish an organizing center at the dorsal–ventral boundary, which functions to direct the development of the Drosophila wing. We report that misexpression of dLMO, a Drosophila LIM-only protein, in specific patterns in the developing wing imaginal disc, disrupts the dorsal–ventral (D-V) boundary and causes errors in wing patterning. When dLMO is misexpressed along the anterior–posterior boundary, extra wing outgrowth occurs, similar to the phenotype seen when mutant clones lacking Apterous, a LIM homeodomain protein known to be essential for normal D-V patterning of the wing, are made in the wing disc. When dLMO is misexpressed along the D-V boundary in third instar larvae, loss of the wing margin is observed. This phenotype is very similar to the phenotype of Beadex, a long-studied dominant mutation that we show disrupts the dLMO transcript in the 3′ untranslated region. dLMO normally is expressed in the wing pouch of the third instar wing imaginal disc during patterning. A mammalian homolog of dLMO is expressed in the developing limb bud of the mouse. This indicates that LMO proteins might function in an evolutionarily conserved mechanism involved in patterning the appendages.
Resumo:
The discovery that several inherited human diseases are caused by mtDNA depletion has led to an increased interest in the replication and maintenance of mtDNA. We have isolated a new mutant in the lopo (low power) gene from Drosophila melanogaster affecting the mitochondrial single-stranded DNA-binding protein (mtSSB), which is one of the key components in mtDNA replication and maintenance. lopo1 mutants die late in the third instar before completion of metamorphosis because of a failure in cell proliferation. Molecular, histochemical, and physiological experiments show a drastic decrease in mtDNA content that is coupled with the loss of respiration in these mutants. However, the number and morphology of mitochondria are not greatly affected. Immunocytochemical analysis shows that mtSSB is expressed in all tissues but is highly enriched in proliferating tissues and in the developing oocyte. lopo1 is the first mtSSB mutant in higher eukaryotes, and its analysis demonstrates the essential function of this gene in development, providing an excellent model to study mitochondrial biogenesis in animals.
Resumo:
The Drosophila dribble (dbe) gene encodes a KH domain protein, homologous to yeast KRR1p. Expression of dbe transcripts is ubiquitous during embryogenesis. Overexpressed Dribble protein is localized in the nucleus and in some cell types in a subregion of the nucleolus. Homozygous dbe mutants die at first instar larval stage. Clonal analyses suggest that dbe+ is required for survival of dividing cells. In dbe mutants, a novel rRNA-processing defect is found and accumulation of an abnormal rRNA precursor is detected.
Resumo:
This work illustrates potential adverse effects linked with the expression of proteinase inhibitor (PI) in plants used as a strategy to enhance pest resistance. Tobacco (Nicotiana tabacum L. cv Xanthi) and Arabidopsis [Heynh.] ecotype Wassilewskija) transgenic plants expressing the mustard trypsin PI 2 (MTI-2) at different levels were obtained. First-instar larvae of the Egyptian cotton worm (Spodoptera littoralis Boisd.) were fed on detached leaves of these plants. The high level of MTI-2 expression in leaves had deleterious effects on larvae, causing mortality and decreasing mean larval weight, and was correlated with a decrease in the leaf surface eaten. However, larvae fed leaves from plants expressing MTI-2 at the low expression level did not show increased mortality, but a net gain in weight and a faster development compared with control larvae. The low MTI-2 expression level also resulted in increased leaf damage. These observations are correlated with the differential expression of digestive proteinases in the larval gut; overexpression of existing proteinases on low-MTI-2-expression level plants and induction of new proteinases on high-MTI-2-expression level plants. These results emphasize the critical need for the development of a PI-based defense strategy for plants obtaining the appropriate PI-expression level relative to the pest's sensitivity threshold to that PI.
Resumo:
Mutations in 12 genes regulating Drosophila melanogaster mushroom body (MB) development were each studied in two genetic backgrounds. In all cases, brain structure was qualitatively or quantitatively different after replacement of the "original" genetic background with that of the Canton Special wild-type strain. The mushroom body miniature gene (mbm) was investigated in detail. mbm supports the maintenance of MB Kenyon cell fibers in third instar larvae and their regrowth during metamorphosis. Adult mbm1 mutant females are lacking many or most Kenyon cell fibers and are impaired in MB-mediated associative odor learning. We show here that structural defects in mbm1 are apparent only in combination with an X-linked, dosage-dependent modifier (or modifiers). In the Canton Special genetic background, the mbm1 anatomical phenotype is suppressed, and MBs develop to a normal size. However, the olfactory learning phenotype is not fully restored, suggesting that submicroscopic defects persist in the MBs. Mutant mbm1 flies with full-sized MBs have normal retention but show a specific acquisition deficit that cannot be attributed to reductions in odor avoidance, shock reactivity, or locomotor behavior. We propose that polymorphic gene interactions (in addition to ontogenetic factors) determine MB size and, concomitantly, the ability to recognize and learn odors.
Resumo:
Previously, we reported on the discovery and characterization of a mammalian chromatin-associated protein, CHD1 (chromo-ATPase/helicase-DNA-binding domain), with features that led us to suspect that it might have an important role in the modification of chromatin structure. We now report on the characterization of the Drosophila melanogaster CHD1 homologue (dCHD1) and its localization on polytene chromosomes. A set of overlapping cDNAs encodes an 1883-aa open reading frame that is 50% identical and 68% similar to the mouse CHD1 sequence, including conservation of the three signature domains for which the protein was named. When the chromo and ATPase/helicase domain sequences in various CHD1 homologues were compared with the corresponding sequences in other proteins, certain distinctive features of the CHD1 chromo and ATPase/helicase domains were revealed. The dCHD1 gene was mapped to position 23C-24A on chromosome 2L. Western blot analyses with antibodies raised against a dCHD1 fusion protein specifically recognized an approximately 210-kDa protein in nuclear extracts from Drosophila embryos and cultured cells. Most interestingly, these antibodies revealed that dCHD1 localizes to sites of extended chromatin (interbands) and regions associated with high transcriptional activity (puffs) on polytene chromosomes from salivary glands of third instar larvae. These observations strongly support the idea that CHD1 functions to alter chromatin structure in a way that facilitates gene expression.
Resumo:
The regulatory protein calmodulin is a major mediator of calcium-induced changes in cellular activity. To analyze the roles of calmodulin in an intact animal, we have generated a calmodulin null mutation in Drosophila melanogaster. Maternal calmodulin supports calmodulin null individuals throughout embryogenesis, but they die within 2 days of hatching as first instar larvae. We have detected two pronounced behavioral abnormalities specific to the loss of calmodulin in these larvae. Swinging of the head and anterior body, which occurs in the presence of food, is three times more frequent in the null animals. More strikingly, most locomotion in calmodulin null larvae is spontaneous backward movement. This is in marked contrast to the wild-type situation where backward locomotion is seen only as a stimulus-elicited avoidance response. Our finding of spontaneous avoidance behavior has striking similarities to the enhanced avoidance responses produced by some calmodulin mutations in Paramecium. Thus our results suggest evolutionary conservation of a role for calmodulin in membrane excitability and linked behavioral responses.
Resumo:
In a search for retinoid X receptor-like molecules in Drosophila, we have identified an additional member of the nuclear receptor superfamily, XR78E/F. In the DNA-binding domain, XR78E/F is closely related to the mammalian receptor TR2, as well as to the nuclear receptors Coup-TF and Seven-up. We demonstrate that XR78E/F binds as a homodimer to direct repeats of the sequence AGGTCA. In transient transfection assays, XR78E/F represses ecdysone signaling in a DNA-binding-dependent fashion. XR78E/F has its highest expression in third-instar larvae and prepupae. These experiments suggest that XR78E/F may play a regulatory role in the transcriptional cascade triggered by the hormone ecdysone in Drosophila.
Resumo:
We have designed a rapid cloning and screening strategy to identify new members of the nuclear hormone receptor superfamily that are expressed during the onset of Drosophila metamorphosis. Using this approach, we isolated three Drosophila genes, designated DHR38, DHR78, and DHR96. All three genes are expressed throughout third-instar larval and prepupal development. DHR38 is the Drosophila homolog of NGFI-B and binds specifically to an NGFI-B response element. DHR78 and DHR96 are orphan receptor genes. DHR78 is induced by 20-hydroxyecdysone (20E) in cultured larval organs, and its encoded protein binds to two AGGTCA half-sites arranged as either direct or palindromic repeats. DHR96 is also 20E-inducible, and its encoded protein binds selectively to the hsp27 20E response element. The 20E receptor can bind to each of the sequences recognized by DHR78 and DHR96, indicating that these proteins may compete with the receptor for binding to a common set of target sequences.