Chromosomal variations of Lycoris species revealed by FISH with rDNAs and centromeric histone H3 variant associated DNAs

Lycoris species have various chromosome numbers and karyotypes, but all have a constant total number of chromosome major arms. In addition to three fundamental types, including metacentric (M-), telocentric (T-), and acrocentric (A-) chromosomes, chromosomes in various morphology and size were also observed in natural populations. Both fusion and fission translocation have been considered as main mechanisms leading to the diverse karyotypes among Lycoris species, which suggests the centromere organization playing a role in such arrangements. We detected several chromosomal structure changes in Lycoris including centric fusion, inversion, gene amplification, and segment deletion by using fluorescence in situ hybridization (FISH) probing with rDNAs. An antibody against centromere specific histone H3 (CENH3) of L. aurea (2n = 14, 8M+6T) was raised and used to obtain CENH3-associated DNA sequences of L. aurea by chromatin immunoprecipitation (ChIP) cloning method. Immunostaining with anti-CENH3 antibody could label the centromeres of M-, T-, and A-type chromosomes. Immunostaining also revealed two centromeres on one T-type chromosome and a centromere on individual mini-chromosome. Among 10,000 ChIP clones, 500 clones which showed abundant in L. aurea genome by dot-blotting analysis were FISH mapped on chromosomes to examine their cytological distribution. Five of these 500 clones could generate intense FISH signals at centromeric region on M-type but not T-type chromosomes. FISH signals of these five clones rarely appeared on A-type chromosomes. The five ChIP clones showed similarity in DNA sequences and could generate similar but not identical distribution patterns of FISH signals on individual chromosomes. Furthermore, the distinct distribution patterns of FISH signals on each chromosome generated by these five ChIP clones allow to identify individual chromosome, which is considered difficult by conventional staining approaches. Our results suggest a different organization of centromeres of the three chromosome types in Lycoris species.

Spatial population structure: patterns of adaptation in populations of the water hyacinth grasshopper Cornops aquaticum (Bruner 1906)

The water hyacinth grasshopper Cornops aquaticum (Bruner 1906) constitutes an appropriate model to assess phenotypic and karyotypic variability in the context of differentiation and adaptation of insect populations because it occurs over a wide latitudinal range. This study represents a general analysis of phenotype, karyotype and molecular variation in native populations of C. aquaticum in South America. This is also relevant because this insect is considered a promising biological control agent of water hyacinth, a native South American aquatic plant but a pest in South Africa. Along Paraná and Uruguay River Basins, body size correlated negatively with latitude, and positively so with temperature and rainfall in both sexes. To test whether the chromosomal and phenotypic patterns were adaptive, we compared them with neutral microsatellite loci variation in populations from the medium and lower course of the Paraná River. Firstly, the lack of pairwise association between karyotype and phenotype distance matrixes with that of neutral loci suggested non-neutrality. Secondly, phenotypic differentiation for all morphometric traits (PST) was significantly larger than molecular differentiation (FST), indicating a prevailing divergence selection effect on the observed phenotypic patterns. Finally, the phenotypic and genotypic spatial structures – inferred from Bayesian approaches – were discordant: neutral genetic structure clustered together most populations except for the two southernmost, downstream ones, whereas phenotypic spatial structure groups together all the deltaic populations and singles out the two northernmost ones. The results suggest directional selection leading to higher centric fusion frequencies in the downstream populations and favouring morphometric optimal differences in relation to the environment.

Tempo and mode in karyotype evolution revealed by a probabilistic model incorporating both chromosome number and morphology

Karyotype, including the chromosome and arm numbers, is a fundamental genetic characteristic of all organisms and has long been used as a species-diagnostic character. Additionally, karyotype evolution plays an important role in divergent adaptation and speciation. Centric fusion and fission change chromosome numbers, whereas the intra-chromosomal movement of the centromere, such as pericentric inversion, changes arm numbers. A probabilistic model simultaneously incorporating both chromosome and arm numbers has not been established. Here, we built a probabilistic model of karyotype evolution based on the “karyograph”, which treats karyotype evolution as a walk on the two-dimensional space representing the chromosome and arm numbers. This model enables analysis of the stationary distribution with a stable karyotype for any given parameter. After evaluating their performance using simulated data, we applied our model to two large taxonomic groups of fish, Eurypterygii and series Otophysi, to perform maximum likelihood estimation of the transition rates and reconstruct the evolutionary history of karyotypes. The two taxa significantly differed in the evolution of arm number. The inclusion of speciation and extinction rates demonstrated possibly high extinction rates in species with karyotypes other than the most typical karyotype in both groups. Finally, we made a model including polyploidization rates and applied it to a small plant group. Thus, the use of this probabilistic model can contribute to a better understanding of tempo and mode in karyotype evolution and its possible role in speciation and extinction.

Chromosomal Polymorphism and Speciation: The Case of the Genus Mazama (Cetartiodactyla; Cervidae)

Chromosomal polymorphism plays a major role in speciation processes in mammals with high rates of karyotypic evolution, as observed in the family Cervidae. One remarkable example is the genus Mazama that comprises wide inter- and intra-specific chromosomal variability. To evaluate the impact of chromosomal polymorphisms as reproductive barriers within the genus Mazama, inter-specific hybrids between Mazama gouazoubira and Mazama nemorivaga (MGO × MNE) and intra-specific hybrids between cytotypes of Mazama americana (MAM) differing by a tandem (TF) or centric fusion (Robertsonian translocations—RT) were evaluated. MGO × MNE hybrid fertility was evaluated by the seminal quality and testicular histology. MAM hybrids estimation of the meiotic segregation products was performed by sperm-FISH analysis. MGO × MNE hybrids analyses showed different degrees of fertility reduction, from severe subfertility to complete sterility. Regarding MAM, RT, and TF carriers showed a mean value for alternate segregation rate of 97.74%, and 67.23%, and adjacent segregation rate of 1.80%, and 29.07%, respectively. Our results suggested an efficient post-zygotic barrier represented by severe fertility reduction for MGO × MNE and MAM with heterozygous TF. Nevertheless, RT did not show a severe effect on the reproductive fitness in MAM. Our data support the validity of MGO and MNE as different species and reveals cryptic species within MAM.

TBP-Related Factor 2 as a Trigger for Robertsonian Translocations and Speciation

Robertsonian (centric-fusion) translocation is the form of chromosomal translocation in which two long arms of acrocentric chromosomes are fused to form one metacentric. These translocations reduce the number of chromosomes while preserving existing genes and are considered to contribute to speciation. We asked whether hypomorphic mutations in genes that disrupt the formation of pericentromeric regions could lead to centric fusion. TBP-related factor 2 (Trf2) encodes an alternative general transcription factor. A decrease of TRF2 expression disrupts the structure of the pericentromeric regions and prevents their association into chromocenter. We revealed several centric fusions in two lines of Drosophila melanogaster with weak Trf2 alleles in genetic experiments. We performed an RNAi-mediated knock-down of Trf2 in Drosophila and S2 cells and demonstrated that Trf2 upregulates expression of D1—one of the major genes responsible for chromocenter formation and nuclear integrity in Drosophila. Our data, for the first time, indicate that Trf2 may be involved in transcription program responsible for structuring of pericentromeric regions and may contribute to new karyotypes formation in particular by promoting centric fusion. Insight into the molecular mechanisms of Trf2 function and its new targets in different tissues will contribute to our understanding of its phenomenon.

Protective Effect of Costus Speciosus Rhizome Extract Against Cytotoxicity Induced by Tramadol in Mice

Tramadol is a centrally acting analgesic generally used to treat moderate to severe pain. This study was designed to evaluate the protective effect of Costus speciosus rhizome extract (CSRE) against the chromosomal ’aberration’s tramadol-induced in mice bone marrow. Sixty male albino mice were examined in this study and separated into four groups which are as follows: Control group; CSRE group (which have been supplied with 200 mg/kg per day); Tramadol group (Supplied with 40 mg/kg); and CSRE + Tramadol group ( which were given Tramadol for a period of 4 weeks and then given CSRE for a further 4 weeks, applying the same dosage. Microscopic examination of the bone marrow showed a significant increase in structural chromosomal aberrations (centromeric attenuation, gap chromosome, ring chromosome, end to end association, and centric fusion) in addition to numerical chromosomal aberrations (polyploidy and endomitosis) in the treated mice with Tramadol comparable to mice in the control group. The administration of Tramadol disrupted oxidants-antioxidants balance, which is proven by the increased malondialdehyde (MDA) and the reduced superoxide dismutase (SOD), catalase (CAT), and glutathione (GSH). Interestingly, in contrast, CSRE administration has shown attenuate in the numerical chromosomal aberrations and biochemical modification caused by Tramadol. This study demonstrated that CSRE supplementation is improved the tramadol-induced cytotoxicity injury through its antioxidant activity.

Chromosome synapsis, recombination and epigenetic modification in rams heterozygous for metacentric chromosome 3 of the domestic sheep Ovis aries and acrocentric homologs of the argali Ovis ammon

Hybridization of domestic animal breeds with their wild relatives is a promising method for increasing the genetic diversity of farm animals. Resource populations derived from the hybridization of various breeds of domestic sheep with mouflon and argali are an important source of breeding material. The karyotypes of argali and domestic sheep differ for a Robertsonian translocation, which occurred in the common ancestor of mouflon and domestic sheep (Ovis aries) due to the centric fusion of chromosomes 5 and 11 of the argali (O. ammon) into chromosome 3 of sheep. It is known that heterozygosity for translocation can lead to synapsis, recombination and chromosome segregation abnormalities in meiosis. Meiosis in the heterozygotes for translocation that distinguishes the karyotypes of sheep and argali has not yet been studied. We examined synapsis, recombination, and epigenetic modification of chromosomes involved in this rearrangement in heterozygous rams using immunolocalization of key proteins of meiosis. In the majority of cells, we observed complete synapsis between the sheep metacentric chromosome and two argali acrocentric chromosomes with the formation of a trivalent. In a small proportion of cells at the early pachytene stage we observed delayed synapsis in pericentromeric regions of the trivalent. Unpaired sites were subjected to epigenetic modification, namely histone H2A.X phosphorylation. However, by the end of the pachytene, these abnormalities had been completely eliminated. Asynapsis was replaced by a nonhomologous synapsis between the centromeric regions of the acrocentric chromosomes. By the end of the pachytene, the γH2A.X signal had been preserved only at the XY bivalent and was absent from the trivalent. The translocation trivalent did not differ from the normal bivalents of metacentric chromosomes for the number and distribution of recombination sites as well as for the degree of centromeric and crossover interference. Thus, we found that heterozygosity for the domestic sheep chromosome 3 and argali chromosomes 5 and 11 does not cause significant alterations in key processes of prophase I meiosis and, therefore, should not lead to a decrease in fertility of the offspring from interspecific sheep hybridization.

Intrapopulation Chromosomal Polymorphism in Mazama gouazoubira (Cetartiodactyla; Cervidae): The Emergence of a New Species?

Mazama gouazoubira is a small deer species widely distributed in South America. Previous studies have shown that this species presents intraspecific chromosomal polymorphisms, which could affect fertility due to the effects of chromosomal rearrangements on gamete formation. Important aspects regarding the karyotype evolution of this species and the genus remain undefined due to the lack of information concerning the causes of this chromosomal variation. Nineteen individuals belonging to the Mazama gouazoubira population located in the Pantanal were cytogenetically evaluated. Among the individuals analyzed, 9 had B chromosomes and 5 carried a heterozygous centric fusion (2n = 69 and FN = 70). In 3 individuals, the fusion occurred between chromosomes X and 16, in 1 individual between chromosomes 7 and 21, and in another individual between chromosomes 4 and 16. These striking polymorphisms could be explained by several hypotheses. One is that the chromosome rearrangements in this species are recent and not fixed in the population yet, and another hypothesis is that they represent a balanced polymorphism and that heterozygotes have an adaptive advantage. On the other hand, these polymorphisms may negatively influence fertility and raise questions about sustainability or reproductive isolation of the population.