Changes In Chromosome Number Research Articles

Karyological studies of four species of Lady’s Slipper Orchids (Paphiopedilum) collected in the Bogor Botanical Garden, Indonesia

Paphiopedilum is one of the most widely grown and hybridized of all orchid genera due to its distinctive flower morphology. This genus consists of 139 accepted species and is native to southern China to tropical Asia. Karyological studies on the genus Paphiopedilum have been reported by many cytologists in different countries. However, many Indonesian members of Paphiopedilum have remained comparatively limited in investigated cytologically. This study aimed to analyze karyological characters of four species of Paphiopedilum collected in the Bogor Botanical Garden, Indonesia, namely P. armeniacum, P. hirsutissimum, P. primulinum, and P. superbiens. Karyological studies were conducted by root tips squash method. The results showed that four species of Paphiopedilum have a basic chromosome number of x = 15. They are diploid with 2n=30, instead of the common diploid chromosome number of Paphiopedilum (2n = 26). Paphiopedilum hirsutissimum and P. primulinum possess 16 m + 14 sm chromosome formulae. Whereas Paphiopedilum armeniacum and P. superbiens revealed 16 m + 14 sm and 18 m + 12 sm chromosome formulae, respectively.A Robertsonian change in chromosome number generated by the fission of chromosomes would best explain the origin of the new diploid chromosome number and karyotypes of these species.

Evolutionary patterns of variations in chromosome counts and genome sizes show positive correlations with taxonomic diversity in tropical gingers.

Cytogenetic traits such as an organism's chromosome number and genome size are taxonomically critical as they are instrumental in defining angiosperm diversity. Variations in these traits can be traced to evolutionary processes such as polyploidization, although geographic variations across cytogenetic traits remain underexplored. In the pantropical monocot family Zingiberaceae (~1500 species), cytogenetic traits have been well documented; however, the role of these traits in shaping taxonomic diversity and biogeographic patterns of gingers is not known. A time-calibrated Bayesian phylogenetic tree was constructed for 290 taxa covering three of the four subfamilies in Zingiberaceae. We tested models of chromosome number and genome size evolution within the family and whether lineage age, taxonomic diversity, and distributional range explain the variations in the cytogenetic traits. Tests were carried out at two taxonomic ranks: within Zingiberaceae and within genus Hedychium using correlations, generalized linear models and phylogenetic least square models. The most frequent changes in chromosome number within Zingiberaceae were noted to be demi-polyploidization and polyploidization (~57% of the time), followed by ascending dysploidy (~27%). The subfamily Zingiberoideae showed descending dysploidy at its base, while Alpinioideae showed polyploidization at its internal nodes. Although chromosome counts and genome sizes did not corroborate with each other, suggesting that they are not equivalent; higher chromosome number variations and higher genome size variations were associated with higher taxonomic diversity and wider biogeographic distribution. Within Zingiberaceae, multiple incidences of polyploidization were discovered, and cytogenetic events appear to have reduced the genome sizes and increased taxonomic diversity, distributional ranges and invasiveness.

Complete telomere-to-telomere genomes uncover virulence evolution conferred by chromosome fusion in oomycete plant pathogens

Variations in chromosome number are occasionally observed among oomycetes, a group that includes many plant pathogens, but the emergence of such variations and their effects on genome and virulence evolution remain ambiguous. We generated complete telomere-to-telomere genome assemblies for Phytophthora sojae, Globisporangium ultimum, Pythium oligandrum, and G. spinosum. Reconstructing the karyotype of the most recent common ancestor in Peronosporales revealed that frequent chromosome fusion and fission drove changes in chromosome number. Centromeres enriched with Copia-like transposons may contribute to chromosome fusion and fission events. Chromosome fusion facilitated the emergence of pathogenicity genes and their adaptive evolution. Effectors tended to duplicate in the sub-telomere regions of fused chromosomes, which exhibited evolutionary features distinct to the non-fused chromosomes. By integrating ancestral genomic dynamics and structural predictions, we have identified secreted Ankyrin repeat-containing proteins (ANKs) as a novel class of effectors in P. sojae. Phylogenetic analysis and experiments further revealed that ANK is a specifically expanded effector family in oomycetes. These results revealed chromosome dynamics in oomycete plant pathogens, and provided novel insights into karyotype and effector evolution.

A macroevolutionary role for chromosomal fusion and fission in Erebia butterflies.

The impact of large-scale chromosomal rearrangements, such as fusions and fissions, on speciation is a long-standing conundrum. We assessed whether bursts of change in chromosome numbers resulting from chromosomal fusion or fission are related to increased speciation rates in Erebia, one of the most species-rich and karyotypically variable butterfly groups. We established a genome-based phylogeny and used state-dependent birth-death models to infer trajectories of karyotype evolution. We demonstrated that rates of anagenetic chromosomal changes (i.e., along phylogenetic branches) exceed cladogenetic changes (i.e., at speciation events), but, when cladogenetic changes occur, they are mostly associated with chromosomal fissions rather than fusions. We found that the relative importance of fusion and fission differs among Erebia clades of different ages and that especially in younger, more karyotypically diverse clades, speciation is more frequently associated with cladogenetic chromosomal changes. Overall, our results imply that chromosomal fusions and fissions have contrasting macroevolutionary roles and that large-scale chromosomal rearrangements are associated with bursts of species diversification.

Drift drives the evolution of chromosome number I: The impact of trait transitions on genome evolution in Coleoptera.

Chromosomal mutations such as fusions and fissions are often thought to be deleterious, especially in heterozygotes (underdominant), and consequently are unlikely to become fixed. Yet, many models of chromosomal speciation ascribe an important role to chromosomal mutations. When the effective population size (Ne) is small, the efficacy of selection is weakened, and the likelihood of fixing underdominant mutations by genetic drift is greater. Thus, it is possible that ecological and phenotypic transitions that modulate Ne facilitate the fixation of chromosome changes, increasing the rate of karyotype evolution. We synthesize all available chromosome number data in Coleoptera and estimate the impact of traits expected to change Ne on the rate of karyotype evolution in the family Carabidae and 12 disparate clades from across Coleoptera. Our analysis indicates that in Carabidae, wingless clades have faster rates of chromosome number increase. Additionally, our analysis indicates clades exhibiting multiple traits expected to reduce Ne, including strict inbreeding, oligophagy, winglessness, and island endemism, have high rates of karyotype evolution. Our results suggest that chromosome number changes are likely fixed by genetic drift despite an initial fitness cost and that chromosomal speciation models may be important to consider in clades with very small Ne.

Interstitial telomere sequences in Original Article chromosomes of Baikal planarians

The presence of internal telomeric sequences (ITSs) in chromosomes typically indicates instances of genome reorganization. Changes in morphology and chromosome number can be sources of intraspecific polymorphism and also lead to speciation. Both variants are found in flatworms, but ITSs are rare in chromosomes, as is common in other invertebrate animals. Out of 23 flatworm species ITSs has been identified in only three parasitic species. Using FISH with telomeric probes, we found that ITSs are also present in the chromosomes of the endemic Baikal planarians Baikalobia Kenk, 1930 (Tricladida, Continenticola, Dendrocoelidae). This is the first time that ITSs has been identified in free-living flatworms. Like Shistosoma Weinland, 1858, the appearance of ITSs in the Baikal planarians could be associated with the process of speciation. There is no data yet on ITSs in other dendrocoelids, and the question remains whether ITSs are a specific feature of Baikal planarians or a special feature of all dendrocoelids.

Repositioning of centromere-associated repeats during karyotype evolution in Oryzias fishes.

The karyotype, which is the number and shape of chromosomes, is a fundamental characteristic of all eukaryotes. Karyotypic changes play an important role in many aspects of evolutionary processes, including speciation. In organisms with monocentric chromosomes, it was previously thought that chromosome number changes were mainly caused by centric fusions and fissions, whereas chromosome shape changes, that is, changes in arm numbers, were mainly due to pericentric inversions. However, recent genomic and cytogenetic studies have revealed examples of alternative cases, such as tandem fusions and centromere repositioning, found in the karyotypic changes within and between species. Here, we employed comparative genomic approaches to investigate whether centromere repositioning occurred during karyotype evolution in medaka fishes. In the medaka family (Adrianichthyidae), the three phylogenetic groups differed substantially in their karyotypes. The Oryzias latipes species group has larger numbers of chromosome arms than the other groups, with most chromosomes being metacentric. The O. javanicus species group has similar numbers of chromosomes to the O. latipes species group, but smaller arm numbers, with most chromosomes being acrocentric. The O. celebensis species group has fewer chromosomes than the other two groups and several large metacentric chromosomes that were likely formed by chromosomal fusions. By comparing the genome assemblies of O. latipes, O. javanicus, and O. celebensis, we found that repositioning of centromere-associated repeats might be more common than simple pericentric inversion. Our results demonstrated that centromere repositioning may play a more important role in karyotype evolution than previously appreciated.

Chromosomal instability-induced cell invasion through caspase-driven DNA damage

Chromosomal instability (CIN), an increased rate of changes in chromosome structure and number, is observed in most sporadic human carcinomas with high metastatic activity. Here, we use a Drosophila epithelial model to show that DNA damage, as a result of the production of lagging chromosomes during mitosis and aneuploidy-induced replicative stress, contributes to CIN-induced invasiveness. We unravel a sub-lethal role of effector caspases in invasiveness by enhancing CIN-induced DNA damage and identify the JAK/STAT signaling pathway as an activator of apoptotic caspases through transcriptional induction of pro-apoptotic genes. We provide evidence that an autocrine feedforward amplification loop mediated by Upd3-a cytokine with homology to interleukin-6 and a ligand of the JAK/STAT signaling pathway-contributes to amplifying the activation levels of the apoptotic pathway in migrating cells, thus promoting CIN-induced invasiveness. This work sheds new light on the chromosome-signature-independent effects of CIN in metastasis.

Drivers of diversification in Linum (Linaceae) by means of chromosome evolution: correlations with biogeography, breeding system and habit.

Chromosome evolution leads to hybrid dysfunction and recombination patterns and has thus been proposed as a major driver of diversification in all branches of the tree of life, including flowering plants. In this study we used the genus Linum (flax species) to evaluate the effects of chromosomal evolution on diversification rates and on traits that are important for sexual reproduction. Linum is a useful study group because it has considerable reproductive polymorphism (heterostyly) and chromosomal variation (n = 6-36) and a complex pattern of biogeographical distribution. We tested several traditional hypotheses of chromosomal evolution. We analysed changes in chromosome number across the phylogenetic tree (ChromEvol model) in combination with diversification rates (ChromoSSE model), biogeographical distribution, heterostyly and habit (ChromePlus model). Chromosome number evolved across the Linum phylogeny from an estimated ancestral chromosome number of n = 9. While there were few apparent incidences of cladogenesis through chromosome evolution, we inferred up to five chromosomal speciation events. Chromosome evolution was not related to heterostyly but did show significant relationships with habit and geographical range. Polyploidy was negatively correlated with perennial habit, as expected from the relative commonness of perennial woodiness and absence of perennial clonality in the genus. The colonization of new areas was linked to genome rearrangements (polyploidy and dysploidy), which could be associated with speciation events during the colonization process. Chromosome evolution is a key trait in some clades of the Linum phylogeny. Chromosome evolution directly impacts speciation and indirectly influences biogeographical processes and important plant traits.

Dramatic difference in rate of chromosome number evolution among sundew (Drosera L., Droseraceae) lineages.

Chromosome number change is a driver of speciation in eukaryotic organisms. Carnivorous sundews in the plant genus Drosera L. exhibit single chromosome number variation both among and within species, especially in the Australian Drosera subg. Ergaleium D.C., potentially linked to atypical centromeres that span much of the length of the chromosomes. We critically reviewed literature on chromosome counts in Drosera, verified the taxonomy and quality of the original counts, and reconstructed dated phylogenies. We used the BiChrom model to test whether rates of single chromosome number increase, decrease, and chromosome number doubling differed between D. subg. Ergaleium and the other subgenera and between self-compatible and self-incompatible lineages. The best model for chromosome evolution among subgenera had equal rates of chromosome number doubling but higher rates of single chromosome number change in D. subg. Ergaleium than the other subgenera. Contrary to expectation, self-incompatible lineages had a significantly higher rate of single chromosome loss than self-compatible lineages. We found no evidence for an association between differences in single chromosome number changes and diploidization after polyploidy or centromere type. This study presents an exemplar for critically examining published cytological data and rigorously testing factors that may impact the rates of chromosome number evolution.

Meiotic behavior of two grapevine somatic mutants with ornamental potential

‘Niagara Steck’ and ‘Niagara Variegada’ are two grapevine varieties that arose spontaneously as somatic mutants of ‘Niagara Rosada’. Berries characterize ‘Niagara Steck’ at young stages exhibiting a remarkable brown reticulated structure on the epidermis which develops into a brown-bronze russet-like structure as the berries ripe. The mature berries have strongly acidic flesh. ‘Niagara Variegada’ shows notable variegation in leaves and berries. Meiotic studies were carried out to ascertain if the mutant phenotypes could be related to any change in chromosome number, structure or other irregularity. Floral buds of both varieties at different developmental stages were collected and fixed for cytological analyses. Chromosome counts at diakinesis/metaphase I showed n=19 bivalents for both varieties. Univalent, trivalent, tetravalent chromosomes or chain configuration were not recorded ruling out the possibility of any alteration in the chromosome number or structure in both mutant varieties. However, low percentages of meiotic irregularities were recorded such as chromosome stickiness, laggards, non-oriented chromosomes, precocious chromosome segregation, tetrads with one microcyte, microspore fusion, and tetrad degeneration. The total percentage of abnormalities was higher in ‘Niagara Variegada’ (19.68%) than in ‘Niagara Steck’ (14.40%) which may have contributed to a lower percentage of pollen fertility (79.80%) when compared to ‘Steck’ (90.74%). The aforementioned varieties can be propagated by hardwood cuttings and constitute an interesting option for ornamentation of home backyards, patios, and gardens with the advantage that ‘Niagara Variegada’ bearing sweet edible berries.

O-181 Utilisation of monopronucleated (1PN) embryos and potential clinical benefits for patients

Abstract Study question Is it beneficial to culture 1PN embryos for clinical use? Summary answer Culturing 1PN embryos to blastocyst for potential clinical use is beneficial to all patients, especially those with low prognosis. What is known already 1PN embryos are those with only a single pronucleus visible at the time of fertilisation check. It is generally assumed that such embryos are haploid, having only 23 chromosomes in each of their cells. Given that haploid embryos are not viable, current guidelines recommend only transfering embryos where two pronuclei are visualised. Embryo biopsy at the blastocyst stage, followed by testing with next-generation sequencing (NGS), combined with analysis of DNA polymorphisms, can reveal whether 1PN embryos are truly haploid, or whether normal fertilsation has occurred. Previous studies have shown that in some cases a diploid chromosome number may be present. Study design, size, duration A new clinical policy was put into practice to culture all 1PN embryos to day 5/6. This is an ongoing study initiated in April 2022. The data reported are from an eight month period, up until December 2022. During this time, we cultured 288 1PN embryos from 203 patients. Trophectoderm biopsy specimens were shipped to a specialist genetics laboratory where they underwent PGT-A using a method that assesses chromosome copy number and polymorphisms in tandem. Participants/materials, setting, methods If embryos were assessed at fertilisation check and found to be 1PN they were not discarded, but rather they were maintained in culture. If any such embryos successfully produced a blastocyst the patients received counselling from their fertility consultant and an embryologist, giving them the options to either go ahead with transfer (only IVF derived), have the embryos genetic status clarified using PGT-A, freeze without testing, or to discard the embryo. Main results and the role of chance Of the 288 1PN embryos cultured (IVF and ICSI derived) 85 displayed signs of blastulation (29.5%). 134 of these were derived from ICSI with 20 forming blastocysts (14.9%). 154 were derived from IVF with 65 forming blastocysts (42.2%). Three IVF derived 1PN embryos have been transferred. Currently one is an ongoing singleton pregnancy, one is an ongoing twin pregnancy and the third has resulted in a live birth. 35 embryos were biopsied and underwent genetic testing to confirm their ploidy status. Six of these were ICSI derived, four of which were found to be haploid and two diploid. The other 29 tested embryos were derived from IVF. Of these, 27 were found to be diploid (93.1%) and two were shown to be triploid (6.9%). None were confirmed as haploid. Traditionally, PGT-A methods using NGS examine relative chromosome copy number, but in cases of haploidy/triploidy all of the chromosomes are decreased/increased in number, meaning there is no change in the relative number of individual chromosomes. We established embryo ploidy status using an advanced PGT method, genotyping thousands of polymorphisms scattered across the genome, which are essential for accurate diagnosis of haploidy/triploidy. Limitations, reasons for caution The sample size for genetically tested ICSI derived 1PN’s is currently too small to clearly determine whether culture and testing of these embryos is beneficial to the patient. Patients who decided to transfer an embryo categorised as 1PN were made fully aware of the potential risks in doing so. Wider implications of the findings These findings show that the culture of 1PN embryos is clinically beneficial to a large number of patients, especially those with poor prognosis who would otherwise have had a failed cycle. Genetic testing demonstrates that IVF derived 1PN embryos that reach the blastocyst stage are likely to have fertilised normally. Trial registration number *

Confinement plus myosin-II suppression maximizes heritable loss of chromosomes, as revealed by live-cell ChReporters.

The mechanical environment of a cell can have many effects, but whether it impacts the DNA sequence of a cell has remained unexamined. To investigate this, we developed a live-cell method to measure changes in chromosome numbers. We edited constitutive genes with GFP or RFP tags on single alleles and discovered that cells that lose Chromosome reporters (ChReporters) become non-fluorescent. We applied our new tools to confined mitosis and to inhibition of the putative tumor suppressor myosin-II. We quantified compression of mitotic chromatin in vivo and demonstrated that similar compression in vitro resulted in cell death, but also rare and heritable ChReptorter loss. Myosin-II suppression rescued lethal multipolar divisions and maximized ChReporter loss during three-dimensional (3D) compression and two-dimensional (2D) lateral confinement, but not in standard 2D culture. ChReporter loss was associated with chromosome mis-segregation, rather than just the number of divisions, and loss in vitro and in mice was selected against in subsequent 2D cultures. Inhibition of the spindle assembly checkpoint (SAC) caused ChReporter loss in 2D culture, as expected, but not during 3D compression, suggesting a SAC perturbation. Thus, ChReporters enable diverse studies of viable genetic changes, and show that confinement and myosin-II affect DNA sequence and mechano-evolution.

A non-homogeneous model of chromosome-number evolution to reveal shifts in the transition patterns across the phylogeny.

Changes in chromosome numbers, including polyploidy and dysploidy events, play a key role in eukaryote evolution as they could expediate reproductive isolation and have the potential to foster phenotypic diversification. Deciphering the pattern of chromosome-number change within a phylogeny currently relies on probabilistic evolutionary models. All currently available models assume time homogeneity, such that the transition rates are identical throughout the phylogeny. Here, we develop heterogeneous models of chromosome-number evolution that allow multiple transition regimes to operate in distinct parts of the phylogeny. The partition of the phylogeny to distinct transition regimes may be specified by the researcher or, alternatively, identified using a sequential testing approach. Once the number and locations of shifts in the transition pattern are determined, a second search phase identifies regimes with similar transition dynamics, which could indicate on convergent evolution. Using simulations, we study the performance of the developed model to detect shifts in patterns of chromosome-number evolution and demonstrate its applicability by analyzing the evolution of chromosome numbers within the Cyperaceae plant family. The developed model extends the capabilities of probabilistic models of chromosome-number evolution and should be particularly helpful for the analyses of large phylogenies that include multiple distinct subclades.

Disentangling Crocus Series Verni and Its Polyploids.

Spring crocuses, the eleven species within Crocus series Verni (Iridaceae), consist of di- and tetraploid cytotypes. Among them is a group of polyploids from southeastern Europe with yet-unclear taxonomic affiliation. Crocuses are generally characterized by complex dysploid chromosome number changes, preventing a clear correlation between these numbers and ploidy levels. To reconstruct the evolutionary history of series Verni and particularly its polyploid lineages associated with C. heuffelianus, we used an approach combining phylogenetic analyses of two chloroplast regions, 14 nuclear single-copy genes plus rDNA spacers, genome-wide genotyping-by-sequencing (GBS) data, and morphometry with ploidy estimations through genome size measurements, analysis of genomic heterozygosity frequencies and co-ancestry, and chromosome number counts. Chromosome numbers varied widely in diploids with 2n = 8, 10, 12, 14, 16, and 28 and tetraploid species or cytotypes with 2n = 16, 18, 20, and 22 chromosomes. Crocus longiflorus, the diploid with the highest chromosome number, possesses the smallest genome (2C = 3.21 pg), while the largest diploid genomes are in a range of 2C = 7-8 pg. Tetraploid genomes have 2C values between 10.88 pg and 12.84 pg. Heterozygosity distribution correlates strongly with genome size classes and allows discernment of di- and tetraploid cytotypes. Our phylogenetic analyses showed that polyploids in the C. heuffelianus group are allotetraploids derived from multiple and partly reciprocal crosses involving different genotypes of diploid C. heuffelianus (2n = 10) and C. vernus (2n = 8). Dysploid karyotype changes after polyploidization resulted in the tetraploid cytotypes with 20 and 22 chromosomes. The multi-data approach we used here for series Verni, combining evidence from nuclear and chloroplast phylogenies, genome sizes, chromosome numbers, and genomic heterozygosity for ploidy estimations, provides a way to disentangle the evolution of plant taxa with complex karyotype changes that can be used for the analysis of other groups within Crocus and beyond. Comparing these results with morphometric analysis results in characters that can discern the different taxa currently subsumed under C. heuffelianus.

Evolution of genome size and GC content in the tribe Carduinae (Asteraceae)

Genome size and GC content are basic species-specific attributes often delimiting genera or higher taxa, which enable the identification of polyploidy, hybridization and other modes of genome or karyotype evolution. The evolution of these genomic traits can often occur as a result of the selective pressure of the environment. Here, we reconstruct the evolution of these genomic traits in subtribe Carduinae (Asteraceae) in the context of changes in chromosome numbers. Using flow cytometry, genome size and GC content were estimated for 119 taxa and mapped onto a phylogenetic tree constructed using sequences from seven genetic markers. In addition, the genomic data were compared with the length of stomatal guard cells and achene size (length, weight) to evaluate the extent to which genomic characters could evolve adaptively in this subtribe. We found strong phylogenetic signals for the analysed genomic and phenotypic traits, which delimited most Carduinae genera or clades in agreement with the reconstructed phylogeny. Monoploid genome size was positively correlated with genomic GC content and stomatal guard cell length. In Cirsium, whose species were the focus of the majority of the analyses, the large-genomed subgen. Lophiolepis had smaller guard cells, which might be related to it occurring in more xeric habitats compared to subgen. Cirsium. In contrast, the achenes of the large-genomed subgen. Lophiolepis were larger, possibly in response to the summer drought, whereas achene weight and length were independent of genome size across the subtribe. Thus, genome size in the subtribe Carduinae might evolve under weak environmental control, at least under that mediated by the size of guard cells or achenes. Achene size was related positively to GC content, which could have evolved adaptively in response to summer drought. In Carduus and the North American Cirsium taxa, there is an increase in average chromosome size with reduction in monoploid chromosome number, suggesting descending dysploidy associated with chromosomal fusion. Polyploidy is relatively rare in this subtribe and was confirmed only in five of the species studied, including Cirsium vulgare, an invasive species that likely originated via distant (intersubgeneric) hybridization, as suggested by its intermediate genomic and achene features combined with the conflict between its morphology and phylogenetic position. Phylogenetic reconstruction, differences in genomic parameters, as well as stomatal guard cell and achene sizes support the separation of a monophyletic Lophiolepis from the remainder of Cirsium. Genome and achene size results also indicate that the early diverging Cirsium italicum can be separated from the rest of the monophyletic Lophiolepis+Picnomon+Notobasis clade.

Using ChromEvol to Determine the Mode of Chromosomal Evolution.

The ChromEvol software was the first to implement a likelihood-based approach, using probabilistic models that depict the pattern of chromosome number change along a specified phylogeny. The initial models have been completed and expanded during the last years. New parameters that model polyploid chromosome evolution have been implemented in ChromEvol v.2. In recent years, new and more complex models have been developed. The BiChrom model is able to implement two distinct chromosome models for the two possible trait states of a binary character of interest. ChromoSSE jointly implements chromosome evolution, speciation, and extinction. In the near future, we will be able to study chromosome evolution with increasingly complex models.

Inferring Chromosome Number Changes Along a Phylogeny Using chromEvol.

Chromosome numbers have long been used for the identification of key genomic events such as polyploidy and dysploidy. These inferences are often challenging, particularly when applied to large phylogenies, or clades in which more than a few chromosome number transitions had occurred. Here we describe the chromEvol computational framework that infers shifts in chromosome numbers along a phylogeny using probabilistic models of chromosome number change. Given chromosome count data and an associated phylogeny, chromEvol identifies such patterns by fitting probabilistic models of chromosome number evolution to the data. We describe the chromEvol workflow using available online tools, including the specification of the desired models, the examination of model fit to the data, and the inference of ploidy levels. The pipeline can be used by the wide scientific community and requires no previous computational or programming skills.

EXPRESSION OF H/ACA snoRNA IN CELL LINES WITH CHROMOSOMAL ABNORMALITIES AFTER IRRADIATION

The H/ACA snoRNA family is involved in pseudouridine biogenesis. It prevents genetic changes in cells and makes them more stable due to ribosomal RNA characteristics. Therefore, the study of H/ACA snoRNA expression in cell lines with chromosomal disorders after irradiation is of particular interest.
 The purpose of the study is to analyze the effect of chromosomal disorders on H/ACA snoRNA expression in radioresistant K562 and radiosensitive HL-60 cell lines after radiation exposure.
 Materials and Methods. K562 and HL-60 cell lines were exposed to radiation (4 Gy). H/ACA snoRNA expression was analyzed by NGS sequencing (1, 4, and 24 hours after irradiation).
 Results. The authors revealed differences in H/ACA snoRNA expression by chromosomes in the studied cell lines, as well as the impact of chromosomal abnormalities on H/ACA snoRNA expression after radiation exposure. Changes in the copy number of normal chromosomes lead to minor changes in H/ACA snoRNA expression. Marker chromosomes disrupt H/ACA snoRNA expression. Thus, is becomes impossible to use H/ACA snoRNAs located in abnormal chromosomes as radioresistance markers. Moreover, marker chromosomes decrease the number of H/ACA snoRNAs expressed in K562, despite the greater amount of genetic material.

An Approximate Bayesian Computation Approach for Modeling Genome Rearrangements.

The inference of genome rearrangement events has been extensively studied, as they play a major role in molecular evolution. However, probabilistic evolutionary models that explicitly imitate the evolutionary dynamics of such events, as well as methods to infer model parameters, are yet to be fully utilized. Here, we developed a probabilistic approach to infer genome rearrangement rate parameters using an Approximate Bayesian Computation (ABC) framework. We developed two genome rearrangement models, a basic model, which accounts for genomic changes in gene order, and a more sophisticated one which also accounts for changes in chromosome number. We characterized the ABC inference accuracy using simulations and applied our methodology to both prokaryotic and eukaryotic empirical datasets. Knowledge of genome-rearrangement rates can help elucidate their role in evolution as well as help simulate genomes with evolutionary dynamics that reflect empirical genomes.