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.

Meiotic Nuclear Architecture in Distinct Mole Vole Hybrids with Robertsonian Translocations: Chromosome Chains, Stretched Centromeres, and Distorted Recombination

Genome functioning in hybrids faces inconsistency. This mismatch is manifested clearly in meiosis during chromosome synapsis and recombination. Species with chromosomal variability can be a model for exploring genomic battles with high visibility due to the use of advanced immunocytochemical methods. We studied synaptonemal complexes (SC) and prophase I processes in 44-chromosome intraspecific (Ellobius tancrei × E. tancrei) and interspecific (Ellobius talpinus × E. tancrei) hybrid mole voles heterozygous for 10 Robertsonian translocations. The same pachytene failures were found for both types of hybrids. In the intraspecific hybrid, the chains were visible in the pachytene stage, then 10 closed SC trivalents formed in the late pachytene and diplotene stage. In the interspecific hybrid, as a rule, SC trivalents composed the SC chains and rarely could form closed configurations. Metacentrics involved with SC trivalents had stretched centromeres in interspecific hybrids. Linkage between neighboring SC trivalents was maintained by stretched centromeric regions of acrocentrics. This centromeric plasticity in structure and dynamics of SC trivalents was found for the first time. We assume that stretched centromeres were a marker of altered nuclear architecture in heterozygotes due to differences in the ancestral chromosomal territories of the parental species. Restructuring of the intranuclear organization and meiotic disturbances can contribute to the sterility of interspecific hybrids, and lead to the reproductive isolation of studied species.

Meiotic nuclear architecture in distinct mole vole hybrids with Robertsonian translocations: chromosome chains, stretched centromeres, and distorted recombination

Genome functioning in hybrids faces inconsistency. This mismatch is manifested clearly in meiosis during chromosome synapsis and recombination. Species with chromosomal variability can be a model for exploring genomic battles with high visibility due to the use of advanced immunocytochemical methods. We studied synaptonemal complexes (SC) and prophase I processes in 44-chromosome intraspecific (Ellobius tancrei × E. tancrei) and interspecific (Ellobius talpinus × E. tancrei) hybrid mole voles heterozygous for 10 Robertsonian translocations. The same pachytene failures were found for both types of hybrids. In the intraspecific hybrid, the chains were visible in the pachytene stage, then 10 closed SC trivalents formed in the late pachytene and diplotene stage. In the interspecific hybrid, as a rule, SC trivalents composed the SC chains and rarely could form closed configurations. Metacentrics involved with SC trivalents had stretched centromeres in interspecific hybrids. Linkage between neighboring SC trivalents was maintained by stretched centromeric regions of acrocentrics. This centromeric plasticity in structure and dynamics of SC trivalents was found for the first time. We assume that stretched centromeres were a marker of altered nuclear architecture in heterozygotes due to differences in the ancestral chromosomal territories of the parental species. Restructuring of the intranuclear organization and meiotic disturbances can contribute to the sterility of interspecific hybrids, and lead to the reproductive isolation of studied species.Author summaryMeiosis is essential for sexual reproduction to produce haploid gametes. Prophase I represents a crucial meiotic stage because key processes such as chromosomal pairing, synapsis and desynapsis, recombination, and transcriptional silencing occur at this time. Alterations in each of these processes can activate meiotic checkpoints and lead to the elimination of meiocytes. Here we have shown that two groups of experimental hybrids, intraspecific and interspecific—which were heterozygous for 10 identical Robertsonian translocations—had pachytene irregularities and reduced recombination. However, intraspecific and interspecific hybrids exhibited different patterns of synaptonemal complex (SC) trivalent behavior. In the former, open SC trivalents comprised SC chains due to heterosynapsis of short arms of acrocentrics in early and mid-pachytene and were then able to form 2–4 and even 7 and 10 closed SC trivalents in the late pachytene and diplotene stages. In the second mole voles, SC trivalents had stretched centromeres of the metacentrics, and chains of SC trivalents were formed due to stretched centromeres of acrocentrics. Such compounds could not lead to the formation of separate closed SC trivalents. The distant ancestral points of chromosome attachment with a nuclear envelope in the heterozygous nuclei probably lead to stretching of SC trivalents and their centromeric regions, which can be regarded as an indicator of the reorganization of the intranuclear chromatin landscape. These abnormalities, which were revealed in in prophase I, contribute to a decrease the fertility of intraspecific mole voles and promote the sterility of interspecific mole voles.

Karyotype variability of the Ukrainian Mountain-Carpathian sheep breed

The main purpose of this work was to describe the karyotype variability of the Ukrainian Mountain-Carpathian sheep breed. Cytogenetic studies were carried out on a group of 25 sheep from that breed. The cultivation of lymphocytes, preparing the cytogenetic samples, classification and registration of chromosome aberrations were held using conventional methods. It was established that the number and structure of the chromosomes of sheep of the Ukrainian Mountain-Carpathian breed correspond to the norm typical for this species of animals. Chromosomal variability of the studied population includes 19.22% of numerical and structural aberrations. By the number and structure of the chromosome set the Ukrainian Mountain-Carpathian sheep breed does not differ from other breeds of sheep. Accurate identification of individual chromosomes with routine coloring allows using cytogenetic studies in breeding practice in sheep breeding.

ZZ/ZW Sex Determination with Multiple Neo-Sex Chromosomes is Common in Madagascan Chameleons of the Genus Furcifer (Reptilia: Chamaeleonidae)

Chameleons are well-known, highly distinctive lizards characterized by unique morphological and physiological traits, but their karyotypes and sex determination system have remained poorly studied. We studied karyotypes in six species of Madagascan chameleons of the genus Furcifer by classical (conventional stain, C-banding) and molecular (comparative genomic hybridization, in situ hybridization with rDNA, microsatellite, and telomeric sequences) cytogenetic approaches. In contrast to most sauropsid lineages, the chameleons of the genus Furcifer show chromosomal variability even among closely related species, with diploid chromosome numbers varying from 2n = 22 to 2n = 28. We identified female heterogamety with cytogenetically distinct Z and W sex chromosomes in all studied species. Notably, multiple neo-sex chromosomes in the form Z1Z1Z2Z2/Z1Z2W were uncovered in four species of the genus (F. bifidus, F. verrucosus, F. willsii, and previously studied F. pardalis). Phylogenetic distribution and morphology of sex chromosomes suggest that multiple sex chromosomes, which are generally very rare among vertebrates with female heterogamety, possibly evolved several times within the genus Furcifer. Although acrodontan lizards (chameleons and dragon lizards) demonstrate otherwise notable variability in sex determination, it seems that female heterogamety with differentiated sex chromosomes remained stable in the chameleons of the genus Furcifer for about 30 million years.

THE CONNECTION OF THE KARIOTYPE AND REVERSING ABILITY COWS OF THE UKRAINIAN BLACK AND WHEAT DAIRY BREEDS

The aim of research: Studing cariotype conducted cows of Ukrainian Black-and-White dairy breeds and installed corelation conection between cariotype instability and reproduction ability. Methods of research: Сytogenetic – analysis of metaphase plates, peripheral blood cells cows of Ukrainian Black-and-White dairy breeds, micronucleus test-reaction of the organism on mutagenic factors of different nature, zootechnical – analysis of reproductive properties of animals Ukrainian Black-and-White dairy breeds, statistical. Research result: Cariotype analis of Ukrainian Black-and-White dairy breeds (30 heads) farm husbandry “Progress +” showed the following results: control of spontaneous mytagenesis in cows wich was reserch showing quantitative and structural chromosomal aberation. Quantative chromosomal aberationwas find as aneuploidy. Aneuploidy was equal to 7,4% which does not exceed the limits of spontaneous chromosomal variability(1,5–8,3%), what is normal for animals of milk production breeds. Cellular frequency with asynchronous difference centroid chromosomal areas i population of cows at husbandry “Progress +” was 1,05% and did not exceed the spontaneous cytogenetic variability characteristic for the species Bostaurus. The share of metaphase plates with structural chromosomal abnormalities (chromosomal breaks) 2,6% equal to the level of spontaneous chromosomal variability for cows (0,17–11,1%). Cellular cell with micro nucleus and dual core lymphocytes was within the spontaneous level, characteristic of mammals, which were kept in the absence of direct genotoxic effects and amounted to 3.7‰ and 2.3‰, respectively. To install associate conection between chromosomal abnormalities and the reproductive ability of the studied cows was carried out a correlation analysis. Received coefficient between dual-core lymphocytes and age 1 calving (r = -0,9585) indicates a negative correlation with the strength of communication according to the Student's criteria isreliable at P > 0.99. Conclusions: Quantitative chromosomal aberrations (aneuploidy) were 7.4% which does not exceed the limit of spontaneous chromosomal variability, characteristic for animals breeds of milk production. The frequency of cells with asynchronous difference is established centroid chromosomal areas – 1,05% and a fraction of metaphase plates – 2,6% which corresponds to the level of spontaneous chromosomal variability in cattle. Detected сell frequency with micro nucleus and dual core lymphocytes which were within the spontaneous level, characteristic of mammals which are kept in the absence of direct genotoxic effects and amounted to 3.7‰ and 2.3‰. Was detected a negative correlation relationship between dual-core lymphocytes and age of the 1 calving (r = -0.9585, P > 0.99).

Aneuvis: Web-based exploration of numerical chromosomal variation in single cells

MotivationAberrations in chromosomal copy number are one of the most common molecular features observed in cancer. Quantifying the degree of numerical chromosomal variation in single cells across a population of cells is of interest to researchers studying whole chromosomal instability (W-CIN). W-CIN, a state of high numerical chromosomal variation, contributes to treatment resistance in cancer.ResultsHere, we introduce aneuvis, a web application that allows users to determine whether numerical chromosomal variation exists between experimental treatment groups. The web interface allows users to upload molecular cytogenetic or processed whole-genome sequencing data in a cell-by-chromosome matrix format and automatically generates visualizations and summary statistics that reflect the degree of numeric chromosomal variability. Aneuvis is the first user-friendly web application to help researchers identify the genetic and environmental perturbations that promote numerical chromosomal variation.Availability and ImplementationAneuvis is freely available as a web application at https://dpique.shinyapps.io/aneuvis/. Website implemented using Shiny version 1.0.5 with all major browsers supported. All source code for the application is available at https://github.com/dpique/aneuvis.