RESUMO
Multigene families are essential components of eukaryotic genomes and play key roles either structurally and functionally. Their modes of evolution remain elusive even in the era of genomics, because multiple multigene family sequences coexist in genomes, particularly in large repetitive genomes. Here, we investigate how the multigene families 18S rDNA, U2 snDNA, and H3 histone evolved in 10 species of Schistocerca grasshoppers with very large and repeat-enriched genomes. Using sequenced genomes and fluorescence in situ hybridization mapping, we find substantial differences between species, including the number of chromosomal clusters, changes in sequence abundance and nucleotide composition, pseudogenization, and association with transposable elements (TEs). The intragenomic analysis of Schistocerca gregaria using long-read sequencing and genome assembly unveils conservation for H3 histone and recurrent pseudogenization for 18S rDNA and U2 snDNA, likely promoted by association with TEs and sequence truncation. Remarkably, TEs were frequently associated with truncated copies, were also among the most abundant in the genome, and revealed signatures of recent activity. Our findings suggest a combined effect of concerted and birth-and-death models driving the evolution of multigene families in Schistocerca over the last 8 million years, and the occurrence of intra- and interchromosomal rearrangements shaping their chromosomal distribution. Despite the conserved karyotype in Schistocerca, our analysis highlights the extensive reorganization of repetitive DNAs in Schistocerca, contributing to the advance of comparative genomics for this important grasshopper genus.
Assuntos
Evolução Molecular , Rearranjo Gênico , Gafanhotos , Animais , Genoma de Inseto , Gafanhotos/genética , Hibridização in Situ Fluorescente , Cariótipo , Família MultigênicaRESUMO
A common characteristic of sex chromosomes is the accumulation of repetitive DNA, which accounts for their diversification and degeneration. In grasshoppers, the X0 sex-determining system in males is considered ancestral. However, in some species, derived variants like neo-XY in males evolved several times independently by Robertsonian translocation. This is the case of Ronderosia bergii, in which further large pericentromeric inversion in the neo-Y also took place, making this species particularly interesting for investigating sex chromosome evolution. Here, we characterized the satellite DNAs (satDNAs) and transposable elements (TEs) of the species to investigate the quantitative differences in repeat composition between male and female genomes putatively associated with sex chromosomes. We found a total of 53 satDNA families and 56 families of TEs. The satDNAs were 13.5% more abundant in males than in females, while TEs were just 1.02% more abundant in females. These results imply differential amplification of satDNAs on neo-Y chromosome and a minor role of TEs in sex chromosome differentiation. We showed highly differentiated neo-XY sex chromosomes owing to major amplification of satDNAs in neo-Y. Furthermore, chromosomal mapping of satDNAs suggests high turnover of neo-sex chromosomes in R. bergii at the intrapopulation level, caused by multiple paracentric inversions, amplifications, and transpositions. Finally, the species is an example of the action of repetitive DNAs in the generation of variability for sex chromosomes after the suppression of recombination, and helps understand sex chromosome evolution at the intrapopulation level.
Assuntos
DNA Satélite , Evolução Molecular , Gafanhotos , Cromossomos Sexuais , Animais , Feminino , Gafanhotos/genética , MasculinoRESUMO
Supernumerary (B) chromosomes are dispensable genomic elements occurring frequently among grasshoppers. Most B chromosomes are enriched with repetitive DNAs, including satellite DNAs (satDNAs) that could be implicated in their evolution. Although studied in some species, the specific ancestry of B chromosomes is difficult to ascertain and it was determined in only a few examples. Here we used bioinformatics and cytogenetics to characterize the composition and putative ancestry of B chromosomes in three grasshopper species, Rhammatocerus brasiliensis, Schistocerca rubiginosa, and Xyleus discoideus angulatus. Using the RepeatExplorer pipeline we searched for the most abundant satDNAs in Illumina sequenced reads, and then we generated probes used in fluorescent in situ hybridization (FISH) to determine chromosomal position. We used this information to infer ancestry and the events that likely occurred at the origin of B chromosomes. We found twelve, nine, and eighteen satDNA families in the genomes of R. brasiliensis, S. rubiginosa, and X. d. angulatus, respectively. Some satDNAs revealed clustered organization on A and B chromosomes varying in number of sites and position along chromosomes. We did not find specific satDNA occurring in the B chromosome. The satDNAs shared among A and B chromosomes support the idea of putative intraspecific ancestry from small autosomes in the three species, i.e., pair S11 in R. brasiliensis, pair S9 in S. rubiginosa, and pair S10 in X. d. angulatus. The possibility of involvement of other chromosomal pairs in B chromosome origin is also hypothesized. Finally, we discussed particular aspects in composition, origin, and evolution of the B chromosome for each species.
RESUMO
BACKGROUND: Neo-sex chromosome systems arose independently multiple times in evolution, presenting the remarkable characteristic of repetitive DNAs accumulation. Among grasshoppers, occurrence of neo-XY was repeatedly noticed in Melanoplinae. Here we analyzed the most abundant tandem repeats of R. bergii (2n = 22, neo-XYâ) using deep Illumina sequencing and graph-based clustering in order to address the neo-sex chromosomes evolution. RESULTS: The analyses revealed ten families of satDNAs comprising about ~1% of the male genome, which occupied mainly C-positive regions of autosomes. Regarding the sex chromosomes, satDNAs were recorded within centromeric or interstitial regions of the neo-X chromosome and four satDNAs occurred in the neo-Y, two of them being exclusive (Rber248 and Rber299). Using a combination of probes we uncovered five well-defined cytological variants for neo-Y, originated by multiple paracentric inversions and satDNA amplification, besides fragmented neo-Y. These neo-Y variants were distinct in frequency between embryos and adult males. CONCLUSIONS: The genomic data together with cytogenetic mapping enabled us to better understand the neo-sex chromosome dynamics in grasshoppers, reinforcing differentiation of neo-X and neo-Y and revealing the occurrence of multiple additional rearrangements involved in the neo-Y evolution of R. bergii. We discussed the possible causes that led to differences in frequency for the neo-Y variants between embryos and adults. Finally we hypothesize about the role of DNA satellites in R. bergii as well as putative historical events involved in the evolution of the R. bergii neo-XY.
Assuntos
DNA Satélite/genética , Evolução Molecular , Gafanhotos/genética , Análise de Sequência de DNA , Cromossomo X/genética , Cromossomo Y/genética , Animais , Feminino , Hibridização in Situ Fluorescente , Masculino , Metáfase/genéticaRESUMO
B chromosomes, extra elements present in the karyotypes of some eukaryote species, have been described in the grasshopper Xyleus discoideus angulatus. Although some studies have proposed an autosomal origin of the B chromosome in X. d. angulatus, little is known about its repetitive DNA composition and evolutionary dynamics. The aim of the present work was to shed light on the B chromosome evolution in X. d. angulatus by cytogenetic analysis of 27 populations from Pernambuco and Ceará states (Brazil). The frequency of B chromosomes in the different populations was determined, and chromosome measurements and fluorescence in situ hybridization (FISH) with C0t-DNA and telomeric and B chromosome sequences were performed in cells from B-carrying individuals. The results revealed variations in B chromosome prevalence among the populations and showed that some B chromosomes were smaller in certain populations. FISH produced similar patterns for the C0t-DNA probe in all hybridized individuals, whereas telomeric and B chromosome probes, obtained by microdissection, exhibited variations in their distribution. These results indicate the presence of 3 morphotypes of B chromosomes in X. d. angulatus, with variation in repetitive DNA composition during their evolution. In this species, B chromosomes have an intraspecific origin and probably arose from the pericentromeric region of A chromosomes.
Assuntos
Gafanhotos/genética , Animais , Brasil , Centrômero/genética , Mapeamento Cromossômico , Cromossomos/genética , DNA/genética , Evolução Molecular , Variação Genética , Genética Populacional , Genoma de Inseto , Hibridização in Situ Fluorescente , Cariotipagem , Sequências Repetitivas de Ácido Nucleico , Telômero/genética , Cromossomo X/genéticaRESUMO
In an attempt to track the chromosomal differentiation in the Dichroplus elongatus species group, we analyzed the karyotypes of four species with classical cytogenetic and mapping several multigene families through fluorescent in situ hybridization (FISH). We improved the taxon sampling of the D. elongatus species group adding new molecular data to infer the phylogeny of the genus and reconstruct the karyotype evolution. Our molecular analyses recovered a fully resolved tree with no evidence for the monophyly of Dichroplus. However, we recovered several stable clades within the genus, including the D. elongatus species group, under the different strategies of tree analyses (Maximum Parsimony and Maximum Likelihood). The chromosomal data revealed minor variation in the D. elongatus species group's karyotypes caused by chromosome rearrangements compared to the phylogenetically related D. maculipennis species group. The karyotypes of D. intermedius and D. exilis described herein showed the standard characteristics found in most Dichroplini, 2n = 23/24, X0â XXâ, Fundamental number (FN) = 23/24. However, we noticed two established pericentric inversions in D. intermedius karyotype, raising the FN to 27â/28â. A strong variation in the heterochromatic blocks distribution was evidenced at interespecific level. The multigene families' mapping revealed significant variation, mainly in rDNA clusters. These variations are probably caused by micro chromosomal changes, such as movement of transposable elements (TEs) and ectopic recombination. These observations suggest a high genomic dynamism for these repetitive DNA sequences in related species. The reconstruction of the chromosome character "variation in the FN" posits the FN = 23/24 as the ancestral state, and it is hypothesized that variations due to pericentric inversions has arisen independently three times in the evolutionary history of Dichroplus. One of these independent events occurred in the D. elongatus species group, where D. intermedius is the unique case with the highest FN described in the tribe Dichroplini.
Assuntos
Gafanhotos/genética , Cariótipo , Filogenia , Animais , Teorema de Bayes , Evolução Biológica , Mapeamento Cromossômico/métodos , Elementos de DNA Transponíveis , DNA Ribossômico/genética , Evolução Molecular , Feminino , Heterocromatina/metabolismo , Hibridização in Situ Fluorescente , Cariotipagem , Funções Verossimilhança , Masculino , Recombinação Genética , Cromossomos Sexuais , Software , Telômero/ultraestruturaRESUMO
In this study, we describe a strategy to determine the presence of B chromosomes in the living grasshopper Abracris flavolineata by FISH using U2 snDNA as a probe in interphase hemolymph nuclei. In individuals without B chromosomes, (0B) 2 dot signals were noticed, corresponding to A complement U2 snDNA clusters. In +1B and +2B individuals, 4 or 8 additional signals were noticed, respectively. In all cases, the absence or presence of 1 or 2 B chromosomes correlated in hemolymph and in somatic or germline tissues, validating the efficiency of the marker. Our data suggest that the B chromosome of A. flavolineata is present in all somatic tissues. B-carrying individuals showed the same number of B chromosomes in germ and somatic cells, suggesting that the B is mitotically stable. The marker was used to compare B chromosome frequency in the analyzed population with a sample collected previously, in order to test for B frequency changes and differences of B chromosome prevalence among sexes, but no statistically significant differences were noticed. The identification of living animals harboring B chromosomes will be very useful in future studies of B chromosome transmission, as well as in functional studies involving RNA analysis, thus contributing to the understanding of evolutionary history and the possible role of the B chromosome in A. flavolineata.
Assuntos
Cromossomos de Insetos/genética , Gafanhotos/genética , Hibridização in Situ Fluorescente/métodos , RNA Nuclear Pequeno/genética , Animais , Feminino , Hemolinfa/metabolismo , Interfase/genética , MasculinoRESUMO
A large percentage of eukaryotic genomes consist of repetitive DNA that plays an important role in the organization, size and evolution. In the case of crickets, chromosomal variability has been found using classical cytogenetics, but almost no information concerning the organization of their repetitive DNAs is available. To better understand the chromosomal organization and diversification of repetitive DNAs in crickets, we studied the chromosomes of two Gryllidae species with highly divergent karyotypes, i.e., 2n(â) = 29,X0 (Gryllus assimilis) and 2n = 9, neo-X1X2Y (Eneoptera surinamensis). The analyses were performed using classical cytogenetic techniques, repetitive DNA mapping and genome-size estimation. Conserved characteristics were observed, such as the occurrence of a small number of clusters of rDNAs and U snDNAs, in contrast to the multiple clusters/dispersal of the H3 histone genes. The positions of U2 snDNA and 18S rDNA are also conserved, being intermingled within the largest autosome. The distribution and base-pair composition of the heterochromatin and repetitive DNA pools of these organisms differed, suggesting reorganization. Although the microsatellite arrays had a similar distribution pattern, being dispersed along entire chromosomes, as has been observed in some grasshopper species, a band-like pattern was also observed in the E. surinamensis chromosomes, putatively due to their amplification and clustering. In addition to these differences, the genome of E. surinamensis is approximately 2.5 times larger than that of G. assimilis, which we hypothesize is due to the amplification of repetitive DNAs. Finally, we discuss the possible involvement of repetitive DNAs in the differentiation of the neo-sex chromosomes of E. surinamensis, as has been reported in other eukaryotic groups. This study provided an opportunity to explore the evolutionary dynamics of repetitive DNAs in two non-model species and will contribute to the understanding of chromosomal evolution in a group about which little chromosomal and genomic information is known.
Assuntos
Cromossomos de Insetos/genética , Gryllidae/genética , Animais , Mapeamento Cromossômico , DNA/genética , Evolução Molecular , Feminino , Variação Genética , Genoma de Inseto , Hibridização in Situ Fluorescente , Cariótipo , Cariotipagem , Masculino , Família Multigênica , Sequências Repetitivas de Ácido Nucleico , Cromossomos Sexuais/genética , Especificidade da EspécieRESUMO
A common placement for most sex chromosomes that is involved in their evolutionary histories is the accumulation of distinct classes of repetitive DNAs. Here, with the aim of understanding the poorly studied repetitive DNA organization in crickets and its possible role in sex chromosome differentiation, we characterized the chromosomes of the cricket species Cycloptiloides americanus, a species with the remarkable presence of the unusual sex chromosome system X1X20â/X1X1X2X2â. For these proposes, we used C-banding and mapping through the fluorescence in situ hybridization of some repetitive DNAs. The C-banding and distribution of highly and moderately repetitive DNAs (C 0t-1 DNA) varied depending of the chromosome. The greater accumulation of repetitive DNAs in the X2 chromosome was evidenced. The microsatellites were spread along entire chromosomes, but (AG)10 and (TAA)10 were less enriched, mainly in the centromeric areas. Among the multigene families, the 18S rDNA was spread throughout almost all of the chromosomes, except for pair 5 and X2, while the U2 snDNA was placed exclusively in the largest chromosome. Finally, the 5S rDNA was exclusively located in the short arms of the sex chromosomes. The obtained data reinforce the importance of chromosomal dissociation and inversion as a primary evolutionary mechanism to generate neo-sex chromosomes in the species studied, followed by the repetitive DNAs accumulation. Moreover the exclusive placement of 5S rDNA in the sex chromosomes suggests the involvement of this sequence in sex chromosome recognition throughout meiosis and, consequently, their maintenance, in addition to their avoiding degeneration.
Assuntos
Cromossomos de Insetos/genética , Gryllidae/genética , Cromossomos Sexuais/genética , Animais , Mapeamento Cromossômico , DNA Ribossômico/genética , Feminino , Cariótipo , Masculino , Sequências Repetitivas de Ácido NucleicoRESUMO
BACKGROUND: The accumulation of repetitive DNA during sex chromosome differentiation is a common feature of many eukaryotes and becomes more evident after recombination has been restricted or abolished. The accumulated repetitive sequences include multigene families, microsatellites, satellite DNAs and mobile elements, all of which are important for the structural remodeling of heterochromatin. In grasshoppers, derived sex chromosome systems, such as neo-XYâ/XXâ and neo-X1X2Yâ/X1X1X2X2â, are frequently observed in the Melanoplinae subfamily. However, no studies concerning the evolution of sex chromosomes in Melanoplinae have addressed the role of the repetitive DNA sequences. To further investigate the evolution of sex chromosomes in grasshoppers, we used classical cytogenetic and FISH analyses to examine the repetitive DNA sequences in six phylogenetically related Melanoplinae species with X0â/XXâ, neo-XYâ/XXâ and neo-X1X2Yâ/X1X1X2X2â sex chromosome systems. RESULTS: Our data indicate a non-spreading of heterochromatic blocks and pool of repetitive DNAs (C0t-1 DNA) in the sex chromosomes; however, the spreading of multigene families among the neo-sex chromosomes of Eurotettix and Dichromatos was remarkable, particularly for 5S rDNA. In autosomes, FISH mapping of multigene families revealed distinct patterns of chromosomal organization at the intra- and intergenomic levels. CONCLUSIONS: These results suggest a common origin and subsequent differential accumulation of repetitive DNAs in the sex chromosomes of Dichromatos and an independent origin of the sex chromosomes of the neo-XY and neo-X1X2Y systems. Our data indicate a possible role for repetitive DNAs in the diversification of sex chromosome systems in grasshoppers.