[Structure and function of oocyte chromosomes nucleoli and as well as the extra DNA during oogenesis in panoistic and meroistic insects].
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Animals↗
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Results for “Chromosomes, Insect”
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Genomic imprinting during seed development.
Genomic imprinting allows parent-of-origin specific control over gene expression. Although imprinted genes (or entire chromosomes) are homologous sequences that can be inherited from either parent, they are differentially marked by a heritable epigenetic modification (imprint), which can condition their behavior in term of gene expression. Imprinting-based regulation of entire chromosomes is observed in both insects (paternal genome elimination) and mammals (nonrandom X inactivation). Until recently, it was unknown whether plants possessed a similar epigenetic system discriminating between homologous chromosomes from either paternal or maternal origin. There is now experimental evidence for a genome-wide imprinting phenomenon during seed development in Arabidopsis. Genomic imprinting at the gene (or locus) level is observed in both mammals and flowering plants. In maize, only a few allelic variants of several nonessential genes expressed in the endosperm are imprinted. In Arabidopsis, gene-specific imprinting has recently been demonstrated for the MEDEA (and FIS2) gene, which is essential for normal seed development. Unlike the imprinted maize genes, so far all tested MEA alleles are subjected to regulation by imprinting. MEDEA and FIS 2 are members of the FIS class of genes (FERTILIZATION INDEPENDENT SEED) involved in regulation of growth and cell proliferation during seed development. MEDEA shares several paradigmatic features with imprinted mammalian genes. The MEDEA phenotypes provide empirical support for theories of an intragenomic parental conflict during seed development, whereby imprinting is proposed as a means to differentially balance the selfish interests of each sex's genome during the development of the progeny.
Alleles↗
Karyotypic characterization by mitosis, meiosis and C-banding of Eriopis connexa Mulsant (Coccinellidae: Coleoptera: Polyphaga), a predator of insect pests.
Eriopis connexa presents a chromosome number of 2n = 18 + XX for most females analyzed and a meioformula of n = 9 + Xyp for all males. A small metacentric B chromosome restricted to females occurred in 10% of our sample and, when submitted to C-banding, it was shown to be almost completely euchromatic. Chromosome pairs 2 and 3 had satellites and probably contained the nucleolar organizer regions (NORs). C-band analysis also revealed that the constitutive heterochromatin was localized in the centromeres of all chromosomes in the complement.
Animals↗
Mixed Evidence that Dosage Sensitive Genes Drive Global Dosage Compensation in Flour Beetles.
Heteromorphic sex chromosomes create inherent gene dosage differences between males and females because one sex carries a single copy of the X chromosome while the other carries two. Many species have evolved mechanisms that equalize X-linked gene expression between the sexes and, in some cases, restore ancestral autosomal levels, a process known as dosage compensation. Although chromosome-wide compensation is common in male heterogametic (XY) insects, regulatory outcomes vary across taxa and sex chromosome systems, leaving the evolutionary forces shaping sex chromosome regulation unresolved. One hypothesis proposes that the extent to which genes are sensitive to changes in gene dose determines whether complete compensation evolves. We tested predictions of this insensitive sex chromosome hypothesis (ISCH) across five flour beetle species using comparative transcriptomics and genome-wide RNAi-derived measures of gene-by-gene sensitivity. Including an X-autosome fusion in Tribolium confusum allowed direct assessment of expression evolution following a transition from a diploid autosome to a hemizygous Neo-X. Across all five species, we detect complete chromosome-wide dosage compensation and balance between the sexes in somatic tissues, including the Neo-X region. Consistent with ISCH predictions, neither the ancestral Shared-X nor the Neo-X is depleted of genes that are sensitive to RNAi-based expression disruption. However, contrary to expectations, at the level of individual genes, we find little evidence that more sensitive genes exhibit reduced expression divergence. These results suggest that chromosome-wide compensation can be maintained by global regulatory mechanisms that persist through sex chromosome turnover, even when gene-by-gene constraints are weak. Understanding the molecular basis of these mechanisms remains a central challenge in sex chromosome evolution.
Animals↗
The reaction with polytene chromosomes of antibodies raised against Drosophila E75A protein.
The steroid insect molting hormone ecdysone rapidly induces a small number of polytene chromosome puffs in Drosophila. The Ashburner model proposes that the corresponding early genes encode proteins involved in both the induction of the late genes and the repression of the early genes. The Drosophila E75 early gene has been isolated and two of its products, E75A and E75B, have been shown to be members of the steroid receptor superfamily. We have now prepared antisera directed against A- and B-specific regions of the E75 proteins. Antisera and a monoclonal antibody raised against E75A, the major larval protein product of the E75 gene, bind to discrete sites in native salivary gland chromosomes. These sites are closely correlated with early and late ecdysone responsive loci.
Animals↗
Are Cirripedia hopeful monsters? Cytogenetic approach and evidence for a Hox gene cluster in the cirripede crustacean Sacculina carcini.
The "hopeful monster" has haunted evolutionary thinking since Richard Goldschmidt coined the phrase in 1933. The phrase is directly related to genetic mechanisms in development and evolution. Cirripedes are peculiar crustaceans in that they all lack abdomens as adults. In a previous study aimed at describing the repertoire of Hox genes of the Cirripedia, we failed to isolate the abdominal-A gene in three species representative of all three cirripede orders. To address the question of whether the cirripede ancestor could have been a "hopeful monster" arising from a rearrangement of the Hox complex, we have performed a cytogenetic analysis of the Hox complex of the cirripede Sacculina carcini. We present here molecular and cytogenetic evidence for the grouping of the Hox genes on a single chromosome. This is the first direct evidence reported for the grouping of Hox genes on the same chromosome in a non-insect arthropod species.
Animals↗
Specific targeting of insect and vertebrate telomeres with pyrrole and imidazole polyamides.
DNA minor groove-binding compounds (polyamides) that target insect and vertebrate telomeric repeats with high specificity were synthesized. Base pair recognition of these polyamides is based on the presence of the heterocyclic amino acids pyrrole and imidazole. One compound (TH52B) interacts uniquely and with excellent specificity (K(d) = 0.12 nM) with two consecutive insect-type telomeric repeats (TTAGG). A related compound, TH59, displays high specificity (K(d) = 0.5 nM) for tandem vertebrate (TTAGGG) and insect telomeric repeats. The high affinity and specificity of these compounds were achieved by bidentate binding of two flexibly linked DNA-binding moieties. Epifluorescence microscopy studies show that fluorescent derivatives of TH52B and TH59 stain insect or vertebrate telomeres of chromosomes and nuclei sharply. Importantly, the telomere-specific polyamide signals of HeLa chromosomes co-localize with the immunofluorescence signals of the telomere-binding protein TRF1. Our results demonstrate that telomere-specific compounds allow rapid estimation of relative telomere length. The insect-specific compound TH52 was shown to be incorporated rapidly into growing Sf9 cells, underlining the potential of these compounds for telomere biology and possibly human medicine.
Animals↗
Insect control by genetic manipulation of natural populations.
The possible use of chromosome rearrangements is considered as a means for introducing genes into insect populations for their own control. The release of laboratory-constructed strains differing from the field population for a number of chromosome interchanges should create an unstable situation leading to the rapid replacement of the field population. This replacement should allow introduction of genes for insecticide susceptibility, cold sensitivity, or the like. The process would produce sterile hybrids while the genetic displacement occurs which itself will contribute to a reduction in pest numbers.
Animals↗
Double minutes and other chromosomal aberrations in two malignant cell lines of the German cockroach Blattella germanica.
Structural anomalies of mitotic chromosomes from two tumorigenic cell lines of the German cockroach (Blattella germanica) is described. Aberrations, such as unpairable marker chromosomes, double minutes, di- and tricentrics, ring chromosomes, tri- and quadriradials, and chromosome and chromatid gaps and breaks, were observed in varying proportions. This study reports that the double minute chromosomes (DMs) are associated with insect tumor cells, similar to the findings in both murine and human tumor cells.
Animals↗
Sequence and evolution of the gene for the monomeric globin I and its linkage to genes coding for dimeric globins in the insect Chironomus thummi.
We isolated genomic clones containing sequences encoding globins I and IA from a Chironomus thummi thummi genomic library. Three clones contain globin IA (ctt-1A) genes, while one contains a globin I (ctt-1) gene. The coding regions of the four genes are identical except for the single base substitution accounting for the globin I/IA polymorphism. The noncoding DNA flanking the coding region is more than 98% similar, confirming a previous hypothesis that the globin ctt-1 and ctt-1A genes are alleles. Hemoglobins I and IA are monomeric in the insect hemolymph. Earlier in situ hybridization studies suggested that monomeric and dimeric globin genes are clustered at different chromosomal loci. In situ hybridization of ctt-1 DNA to polytene salivary gland chromosomes places the ctt-1 gene on the same band as genes for the dimeric globins II beta and VIIB, forcing revision of the earlier hypothesis that genes for monomeric and dimeric globin genes are at different loci. The evolution of the ctt-1 and ctt-1A alleles and of the two globin gene loci are discussed.
Amino Acid Sequence↗
A paracentric inversion suppresses genetic recombination at the FON3 locus with breakpoints corresponding to sequence gaps on rice chromosome 11L.
Paracentric inversion is known to inhibit genetic recombination between normal and inverted chromosomal segments in heterozygous arrangements. Insect inversion polymorphisms have been studied to reveal adaptive processes for maintaining genetic variation. We report the first paracentric inversion in rice (Oryza sativa), which was discovered in our effort to clone the floral organ number gene FON3. Recombination at the FON3 locus on the long arm of chromosome 11 was severely suppressed over a distance of more than 36 cM. An extensive screening among 8,242 F(2) progeny failed to detect any recombinants. Cytological analysis revealed a loop-like structure on pachytene chromosomes, whereas FISH analysis showed the migration of a BAC clone from a distal location to a position closer to the centromere. Interestingly, the locations where the genetic recombination suppression began were coincided with the positions of two physical gaps on the chromosome 11, suggesting a correlation between the physical gaps, the inversion breakpoints. Transposons and retrotransposons, and tandemly arranged members of gene families were among the sequences immediately flanking the gaps. Taken together, we propose that the genetic suppression at the FON3 locus was caused by a paracentric inversion. The possible genetic mechanism causing such a spontaneous inversion was proposed.
Base Sequence↗
Molecular identification of microorganisms associated with parthenogenesis.
Cytoplasmically interited microorganisms are widespread in insects and have been implicated as causes of female parthenogenesis (females developing from unfertilized eggs) and cytoplasmic incompatibility. Normal sexual reproduction can be restored by treatment with antibiotics. Sequence analysis of the DNA encoding 16S ribosomal RNA has shown that cytoplasmic incompatibility bacteria from diverse insect taxa are closely related (they share >95% sequence sililarity) and belong to the alpha subdivision of Proteobacteria. Here we show that parthenogenesis-associated bacteria from parasitoid Hymenoptera also fall into this bacterial group, having up to 99% sequence similarity to some incompatibility microorganisms. Both incompatibility and parthenogenesis microorganisms alter host chromosome behaviour during early mitotic divisions of the egg. Incompatibility bacteria act by interfering with paternal chromosome incorporation in fertilized eggs, whereas parthenogenesis bacteria prevent segregation of chromosomes in unfertilized eggs. These traits are adaptive for the microorganisms. On the basis of their sequence similarities, we conclude that parthenogenesis bacteria and cytoplasmic incompatibility bacteria form a monophyletic group of microorganisms that 'specialize' in manipulating chromosome behaviour and reproduction of insects.
Animals↗
Chromosome cores and chromatin at meiotic prophase.
We review the synaptonemal complex, SC, of the synapsed homologous chromosomes at meiotic prophase in insects and mammals in terms of its formation, and the association of specific chromatin elements with the synaptonemal complexes. The focus is: (1) The SC as visualized with a variety of techniques; (2) The nature of the chromatin loops where they are associated with the SCs--the bases of the loops may be instrumental in recombinant events judging from the presence of Rad51 protein and late recombination nodules at the SCs; (3) Differences in DNA content of similarly sized loops; (4) Requirements for chromatin attachment to the chromosome cores, requirements that are apparently lacking in foreign DNA inserts; (5) Regulation of loop size by the position along the chromosome; (6) The structural correlates of recombination at the SCs--these comments are based on studies of SC structure, DNA-core protein associations, fluorescent in situ hybridization to visualize specific DNA segments, and fluorescent immunocytology to visualize the chromosome core proteins.
Animals↗
A dense genetic map of the silkworm, Bombyx mori, covering all chromosomes based on 1018 molecular markers.
A dense linkage map was constructed for the silkworm, Bombyx mori, containing 1018 genetic markers on all 27 autosomes and the Z chromosome. Most of the markers, covering approximately 2000 cM, were randomly amplified polymorphic DNAs amplified with primer-pairs in combinations of 140 commercially available decanucleotides. In addition, eight known genes and five visible mutations were mapped. Bombyx homologues of engrailed and invected genes were found to be closely linked, as in Drosophila melanogaster. The average interval between markers was approximately 2 cM, equal to approximately 500 kb. The correspondence of seven linkage groups to counterparts of the conventional linkage map was determined. This map is the first linkage map in insects having a large number of chromosomes (n = 28) that covers all chromosomes without any gaps.
Animals↗
An attempt to produce chromosome translocations in Glossina austeni.
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Animals↗
Genomics. Recycling the Y chromosome.
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Animals↗
Retrotransposable elements on the W chromosome of the silkworm, Bombyx mori.
The sex chromosomes of the silkworm, Bombyxmori, are designated ZW(XY) for females and ZZ(XX) for males. The W chromosome of B. mori does not recombine with the Z chromosome and autosomes and no genes for morphological characters have been mapped to the W chromosome as yet. Furthermore, femaleness is determined by the presence of a single W chromosome, regardless of the number of autosomes or Z chromosomes. To understand these interesting features of the W chromosome, it is necessary to analyze the W chromosome at the molecular biology level. Initially to isolate DNA sequences specific for the W chromosome as randomly amplified polymorphic DNA (RAPD) markers, we compared the genomic DNAs between males and females by PCR with arbitrary 10-mer primers. To the present, we have identified 12 W-specific RAPD markers, and with the exception of one RAPD marker, all of the deduced amino acid sequences of these W-specific RAPD markers show similarity to previously reported amino acid sequences of retrotransposable elements from various organisms. After constructing a genomic DNA lambda phage library of B. mori we obtained two lambda phage clones, one containing the W-Kabuki RAPD sequence and one containing the W-Samurai RAPD sequence and found that these DNA sequences comprised nested structures of many retrotransposable elements. To further analyze the W chromosome, we obtained 14 W-specific bacterial artificial chromosome (BAC) clones from three BAC libraries and subjected these clones to shotgun sequencing. The resulting assembly of sequences did not produce a single contiguous sequence due to the presence of many retrotransposable elements. Therefore, we coupled PCR with shotgun sequencing. Through these analyses, we found that many long terminal repeat (LTR) and non-LTR retrotransposons, retroposons, DNA transposons and their derivatives, have accumulated on the W chromosome as strata. These results strongly indicate that retrotransposable elements are the main structural component of the W chromosome.
Animals↗
Transcription of telomere repeats in protozoa.
The telomerically located variant cell surface glycoprotein (VSG) gene expression sites of the protozoan parasite Trypanosoma brucei are transcribed by an unusual alpha-amanitin resistant RNA polymerase. We show that the telomere GGGTTA repeats located at the chromosome ends of T. brucei and the related protozoan T. equiperdum are also transcribed by alpha-amanitin resistant RNA polymerases. This transcription predominantly proceeds unidirectionally towards the end of the chromosome, in both bloodstream and insect form trypanosomes and results in the generation of heterogeneously sized steady state RNA. We postulate that telomere repeat transcription results from readthrough downstream of telomeric genes. Telomere repeat transcription was found in all seven protozoan species tested, but was alpha-amanitin resistant only in trypanosome species which exhibited antigenic variation. The data indicate that in some trypanosome species a subset of telomeres is transcribed by a different type of RNA polymerase.
Amanitins↗