RESUMO
Satellite DNAs (satDNAs) constitute one of the main components of eukaryote genomes and are involved in chromosomal organization and diversification. Although largely studied, little information was gathered about their evolution on holocentric species, i.e., diffuse centromeres, which, due to differences in repeat organization, could result in different evolutionary patterns. Here, we combined bioinformatics and cytogenetic approaches to evaluate the evolution of the satellitomes in Mahanarva holocentric insects. In two species, de novo identification revealed a high number of satDNAs, 110 and 113, with an extreme monomer length range of 18-4228 bp. The overall abundance of satDNAs was observed to be 6.67% in M. quadripunctata and 1.98% in M. spectabilis, with different abundances for the shared satDNAs. Chromosomal mapping of the most abundant repeats of M. quadripunctata and M. spectabilis on other Mahanarva reinforced the dynamic nature of satDNAs. Variable patterns of chromosomal distribution for the satDNAs were noticed, with the occurrence of clusters on distinct numbers of chromosomes and at different positions and the occurrence of scattered signals or nonclustered satDNAs. Altogether, our data demonstrated the high dynamism of satDNAs in Mahanarva with the involvement of this genomic fraction in chromosome diversification of the genus. The general characteristics and patterns of evolution of satDNAs are similar to those observed on monocentric chromosomes, suggesting that the differential organization of genome compartments observed on holocentric chromosomes compared with monocentric chromosomes does not have a large impact on the evolution of satDNAs. Analysis of the satellitomes of other holocentric species in a comparative manner will shed light on this issue.
Assuntos
Centrômero , DNA Satélite , Animais , DNA Satélite/genética , Mapeamento Cromossômico , Centrômero/genética , Genômica , Insetos/genética , Evolução MolecularRESUMO
Moths of the family Crambidae include a number of pests that cause economic losses to agricultural crops. Despite their economic importance, little is known about their genome architecture and chromosome evolution. Here, we characterized the chromosomes and repetitive DNA of the sugarcane borer Diatraea saccharalis using a combination of low-pass genome sequencing, bioinformatics, and cytogenetic methods, focusing on the sex chromosomes. Diploid chromosome numbers differed between the sexes, i.e., 2n = 33 in females and 2n = 34 in males. This difference was caused by the occurrence of a WZ1Z2 trivalent in female meiosis, indicating a multiple sex-chromosome system WZ1Z2/Z1Z1Z2Z2. A strong interstitial telomeric signal was observed on the W chromosome, indicating a fusion of the ancestral W chromosome with an autosome. Among repetitive DNAs, transposable elements (TEs) accounted for 39.18% (males) to 41.35% (females), while satDNAs accounted for only 0.214% (males) and 0.215% (females) of the genome. FISH mapping revealed different chromosomal organization of satDNAs, such as single localized clusters, spread repeats, and non-clustered repeats. Two TEs mapped by FISH were scattered. Although we found a slight enrichment of some satDNAs in the female genome, they were not differentially enriched on the W chromosome. However, we found enriched FISH signals for TEs on the W chromosome, suggesting their involvement in W chromosome degeneration and differentiation. These data shed light on karyotype and repetitive DNA dynamics due to multiple chromosome fusions in D. saccharalis, contribute to the understanding of genome structure in Lepidoptera and are important for future genomic studies.
Assuntos
Mariposas , Saccharum , Feminino , Masculino , Animais , Saccharum/genética , Evolução Molecular , Cromossomos Sexuais/genética , Cariótipo , Elementos de DNA Transponíveis , Mariposas/genéticaRESUMO
Achiasmatic male meiosis in scorpions is characterized by a high frequency of gaps, asynaptic regions and multivalent associations. Here, we performed an immunocytogenetic analysis to investigate recombination, and synapsis and chromatin-remodeling events during meiosis of the scorpion Tityus silvestris Our results demonstrate that the synaptonemal complex (SC) begins its organization in the zygotene stage and persists until metaphase I. The advancement of the synaptic process is related to the epigenetic modification histone H3 lysine 27 trimethylation (H3K27m3). The distribution and dynamics patterns of variant γH2AX and recombinase Rad51 during achiasmatic meiosis suggests formation and repair of DNA double-strand breaks (DSBs) during early stages of prophase I. The epigenetic modifications, histone H3 lysine 4 trimethylation (H3K4m3) and histone H3 lysine 9 acetylation (H3K9ac), showed a dispersed distribution along the bivalents, suggesting that transcriptional activity is maintained constitutively during prophase I. However, H3K9ac modifications are absent in constitutive heterochromatin carrying the 45S rDNA in pachytene and post-pachytene stages. Collectively, our data demonstrate that T. silvestris exhibits adaptations to the achiasmatic mode, and suggest that epigenetic modifications may act in the regulation of these mechanisms to favor the normal continuation of meiosis in this scorpion.
RESUMO
Spittlebugs, which belong to the family Cercopidae (Auchenorrhyncha, Hemiptera), form a large group of xylem-feeding insects that are best known for causing damage to plantations and pasture grasses. The holocentric chromosomes of these insects remain poorly studied in regards to the organization of different classes of repetitive DNA. To improve chromosomal maps based on repetitive DNAs and to better understand the chromosomal organization and evolutionary dynamics of multigene families in spittlebugs, we physically mapped the U1 snRNA gene with fluorescence in situ hybridization (FISH) in 10 species of Cercopidae belonging to three different genera. All the U1 snDNA clusters were autosomal and located in interstitial position. In seven species, they were restricted to one autosome per haploid genome, while three species of the genus Mahanarva showed two clusters in two different autosomes. Although it was not possible to precisely define the ancestral location of this gene, it was possible to observe the presence of at least one cluster located in a small bivalent in all karyotypes. The karyotype stability observed in Cercopidae is also observed in respect to the distribution of U1 snDNA. Our data are discussed in light of possible mechanisms for U1 snDNA conservation and compared with the available data from other species.
Assuntos
Hemípteros/genética , RNA Nuclear Pequeno/genética , Animais , Mapeamento Cromossômico , Cromossomos de Insetos , DNA/química , Hibridização in Situ Fluorescente , Masculino , Sequências Repetitivas de Ácido NucleicoRESUMO
Satellite DNA repeats (or satDNA) are fast-evolving sequences usually associated with condensed heterochromatin. To test whether the chromosomal organisation of centromeric and non-centromeric satDNA differs in species with holocentric chromosomes, we identified and characterised the major satDNA families in the holocentric Cyperaceae species Rhynchospora ciliata (2n = 10), R. globosa (2n = 50) and R. tenuis (2n = 2x = 4 and 2n = 4x = 8). While conserved centromeric repeats (present in R. ciliata and R. tenuis) revealed linear signals at both chromatids, non-centromeric, species-specific satDNAs formed distinct clusters along the chromosomes. Colocalisation of both repeat types resulted in a ladder-like hybridisation pattern at mitotic chromosomes. In interphase, the centromeric satDNA was dispersed while non-centromeric satDNA clustered and partly colocalised to chromocentres. Despite the banding-like hybridisation patterns of the clustered satDNA, the identification of chromosome pairs was impaired due to the irregular hybridisation patterns of the homologues in R. tenuis and R. ciliata. These differences are probably caused by restricted or impaired meiotic recombination as reported for R. tenuis, or alternatively by complex chromosome rearrangements or unequal condensation of homologous metaphase chromosomes. Thus, holocentricity influences the chromosomal organisation leading to differences in the distribution patterns and condensation dynamics of centromeric and non-centromeric satDNA.
Assuntos
Centrômero/genética , DNA Satélite , Magnoliopsida/genética , Cromossomos de Plantas , Heterocromatina/genética , Hibridização in Situ FluorescenteRESUMO
To complement the epidemiological data and assist in the prophylaxis of Chagas disease in the State of São Paulo, we examined entomological lifting conducted in 40 municipalities of the Western region of the state from 2004 to 2008, highlighted the main vector species in this region, and reanalyzed the cytogenetic characteristics of Rhodnius neglectus from 3 different Brazilian states (Formoso/GO, Frutal/MG, Guaíra/SP, and Pitangueiras/SP). The municipalities of Castilho and Santo Antônio do Acaranguá registered the highest relative amounts of notifications. The main species notified in Western São Paulo were Triatoma sordida and R. neglectus. We collected a large number of T. sordida in 2005 and noted the absence of notification of infected insects in 2008. We observed no variation in chromosomal characteristics of R. neglectus of different states. These data are complementary to the survey presented from 1990 to 1999,as the vector species were the same (T. sordida and R. neglectus),with emphasis on T. sordida. We corroborate the future colonization domiciliary initially proposed for T. sordida in the region and under score the importance of vector control programs in the prophylaxis of Chagas disease. Furthermore, we observed that the populations of R. neglectus in Brazil showed no intraspecific variation and we corroborated the chromosomal patterns originally described. These data are important for understanding the evolution of these hematophagous insects, which are vectors of Chagas disease...