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This study carried out a detailed step‐by‐step PBE/TZVP level analysis of the inclusion of Fe(III)/Fe(II) aqua complexes into the cavity of cucurbit[6]urils (CB[6]). The structural characteristics of all intermediate stable structures formed during the inclusion process from the bulk of aqueous solution to the inclusion compound were obtained. To account for solvation effects, a molecular‐continuum model was used in which six water molecules of the first coordination sphere of aqua complexes and 12 water molecules of the second coordination sphere were taken into account, while the interaction of such a supermolecule with a dielectric medium was accounted within the continuum model (PCM) [Correction added on 9 June 2023, after first online publication. The word molecular continual has been changed to molecular‐continuum in the sentence.]. The process of incorporation of the aqua complex into the cavity was found to be accompanied by a partial desolvation of the second coordination sphere of the aqua complex and a change in the structure of the first coordination sphere. Additionally, the standard electrode potential of the half‐reaction Fe3+(aq) + e = Fe2+(aq) was estimated for all adducts formed in the reaction. [ABSTRACT FROM AUTHOR]

Nonhomologous chromosome interactions take place in both somatic and meiotic cells. Prior to this study, we had discovered special contacts through the SYCP3 (synaptonemal complex protein 3) filament between the short arms of nonhomologous acrocentrics at the pachytene stage in the Alay mole vole, and these contacts demonstrate several patterns from proximity to the complete fusion stage. Here, we investigated the nonhomologous chromosome contacts in meiotic prophase I. It turned out that such contacts do not introduce changes into the classic distribution of DNA double-strand breaks. It is noteworthy that not all meiotic contacts were localized in the H3k9me3-positive heterochromatic environment. Both in the mid zygotene and in the early-mid diplotene, three types of contacts (proximity, touching, and anchoring/tethering) were observed, whereas fusion seems to be characteristic only for pachytene. The number of contacts in the mid pachytene is significantly higher than that in the zygotene, and the distance between centromeres in nonhomologous contacts is also the smallest in mid pachytene for all types of contacts. Thus, this work provides a new insight into the behavior of meiotic contacts during prophase I and points to avenues of further research.

The evolution of proteins can be accompanied by changes not only to their amino acid sequences, but also their structural and spatial molecular organization. Comparison of the protein conservation within different taxonomic groups (multifunctional, or highly specific) allows to clarify their specificity and the direction of evolution. Two multifunctional enzymes, cyclin-dependent kinase 2 (CDK2) and BRCA1 ubiquitin ligase, that are partners in some mitotic and meiotic processes were investigated in the present work. Two research methods, bioinformatics and immunocytochemical, were combined to examine the conservation levels of the two enzymes. It has been established that CDK2 is a highly conserved protein in different taxonomic lineages of the eukaryotic tree. Immunocytochemically, a conserved CDK2 pattern was revealed in the meiotic autosomes of five rodent species and partially in domestic turkey and clawed frog. Nevertheless, variable CDK2 distribution was detected at the unsynapsed segments of the rodent X chromosomes. BRCA1 was shown to be highly conserved only within certain mammalian taxa. It was also noted that in those rodent nuclei, where BRCA1 specifically binds to antigens, asynaptic regions of sex chromosomes were positive. BRCA1 staining was not always accompanied by specific binding, and a high nonspecificity in the nucleoplasm was observed. Thus, the studies revealed different conservation of the two enzymes at the level of protein structure as well as at the level of chromosome behavior. This suggests variable rates of evolution due to both size and configuration of the protein molecules and their multifunctionality., Competing Interests: The authors declare there are no competing interests., (©2021 Matveevsky and Grishaeva.)

Cyclin-dependent kinases (CDKs) are crucial regulators of the eukaryotic cell cycle. The critical role of CDK2 in the progression of meiosis was demonstrated in a single mammalian species, the mouse. We used immunocytochemistry to study the localization of CDK2 during meiosis in seven rodent species that possess hetero- and homomorphic male sex chromosomes. To compare the distribution of CDK2 in XY and XX male sex chromosomes, we performed multi-round immunostaining of a number of marker proteins in meiotic chromosomes of the rat and subterranean mole voles. Antibodies to the following proteins were used: RAD51, a member of the double-stranded DNA break repair machinery; MLH1, a component of the DNA mismatch repair system; and SUN1, which is involved in the connection between the meiotic telomeres and nuclear envelope, alongside the synaptic protein SYCP3 and kinetochore marker CREST. Using an enhanced protocol, we were able to assess the distribution of as many as four separate proteins in the same meiotic cell. We showed that during prophase I, CDK2 localizes to telomeric and interstitial regions of autosomes in all species investigated (rat, vole, hamster, subterranean mole voles, and mole rats). In sex bivalents following synaptic specificity, the CDK2 signals were distributed in three different modes. In the XY bivalent in the rat and mole rat, we detected numerous CDK2 signals in asynaptic regions and a single CDK2 focus on synaptic segments, similar to the mouse sex chromosomes. In the mole voles, which have unique XX sex chromosomes in males, CDK2 signals were nevertheless distributed similarly to the rat XY sex chromosomes. In the vole, sex chromosomes did not synapse, but demonstrated CDK2 signals of varying intensity, similar to the rat X and Y chromosomes. In female mole voles, the XX bivalent had CDK2 pattern similar to autosomes of all species. In the hamster, CDK2 signals were revealed in telomeric regions in the short synaptic segment of the sex bivalent. We found that CDK2 signals colocalize with SUN1 and MLH1 signals in meiotic chromosomes in rats and mole voles, similar to the mouse. The difference in CDK2 manifestation at the prophase I sex chromosomes can be considered an example of the rapid chromosome evolution in mammals.

Darevskia rostombekowi, the most outstanding of the seven known parthenogenetic species in the genus Darevskia, is the result of an ancestral cross between two bisexual species Darevskia raddei and Darevskia portschinskii. The chromosomal set of this species includes a unique submetacentric autosomal chromosome; the origin of this chromosome was unresolved as only acrocentric chromosomes are described in the karyotypes of Darevskia genus normally. Here, we applied a suite of molecular cytogenetic techniques, including the mapping of telomeric (TTAGGG) n repeats using fluorescence in situ hybridization (FISH), comparative genomic hybridization (CGH), and whole-chromosome painting (WCP) in both D. rostombekowi and parental (D. portschinskii and D. raddei) species. The obtained results in total suggest that a de novo chromosomal rearrangement via Robertsonian translocation (centric fusion) between two maternal (D. raddei) acrocentric chromosomes of different size was involved in the formation of this unique submetacentric chromosome present in the parthenogenetic species D. rostombekowi. Our findings provide new data in specific and rapid evolutional processes of a unisexual reptile species karyotype.

An approach for estimating at the DFT level of the standard redox potentials of the inclusion compounds based on Fe(III) and Fe(II) aqua complexes inside the cavities of cucurbit[ n]urils ( n = 6-8) has been proposed. These inclusion compounds were established to have compositions which can be described by the formulas [Fe(H 2 O) 6 ] 3+/2+ @CB[6] and [Fe(H 2 O) 6 ·4H 2 O] 3+/2+ @CB[7,8]. Redox potentials E 0 relative to the standard hydrogen electrode for the half-reaction Fe(III)/Fe(II) in the CB[ n] cavities calculated at the PBE/TZVP level within the molecular-continuum solvation model are 1.607, 0.949, and 0.847 V for n = 6, 7, and 8, respectively. The obtained values indicate a relative increase of the oxidative ability of Fe(III) aqua-ions in the cavities of the examined CB[ n], especially in CB[6], compared to the calculated value ( E 0 = 0.786 V) for the same half-reaction in the bulk of aqueous solution. Possible causes of the detected trend are discussed. The calculations also showed that the Fe(III) aqua complex inside the CB[6] changes its magnetic properties, transforming into a low-spin state with a total spin S = 1/2, whereas for all other systems high-spin states in accord with the classical ligand field theory are realized.

According to the synthesis of 30 years of multidisciplinary studies, parthenogenetic species of rock lizards of genus Darevskia were formed as a result of different combination patterns of interspecific hybridization of the four bisexual parental species: Darevskia raddei , D. mixta , D. valentini , and D. portschinskii . In particular, D. portschinskii and D. raddei are considered as the parental species for the parthenogenetic species D. rostombekowi . Here for the first time, we present the result of comparative immunocytochemical study of primary spermatocyte nuclei spreads from the leptotene to diplotene stages of meiotic prophase I in two species: D. portschinskii and D. raddei . We observed similar chromosome lengths for both synaptonemal complex (SC) karyotypes as well as a similar number of crossing over sites. However, unexpected differences in the number and distribution of anti-centromere antibody (ACA) foci were detected in the SC structure of bivalents of the two species. In all examined D. portschinskii spermatocyte nuclei, one immunostained centromere focus was detected per SC bivalent. In contrast, in almost every studied D. raddei nuclei we identified three to nine SCs with additional immunostained ACA foci per SC bivalent. Thus, the obtained results allow us to identify species-specific karyotype features, previously not been detected using conventional mitotic chromosome analysis. Presumably the additional centromere foci are result of epigenetic chromatin modifications. We assume that this characteristic of the D. raddei karyotype could represent useful marker for the future studies of parthenogenetic species hybrid karyotypes related to D. raddei ., Competing Interests: The authors declare that they have no competing interests.

Meiotic and mitotic chromosomes differ in a number of features. 1. At the early prophase I of meiosis, chromosomes acquire proteinaceous axial elements (AEs) which were absent at mitosis. In addition to somatic cohesins, AEs contain meiosis-specific cohesins REC8, SMC1beta, STAG3. 2. At the middle prophase I, proteinaceous lateral elements (LEs) of synaptonemal complexes (SC) are shaped on a basis of AEs. Proteins of LEs are not conserved, but in Saccharomyces cerevisiae and Arabidopsis thaliana they contain functional domains with conserved secondary structure. Proteins or functional domains similar to SC proteins have been found in green and brown algae, some of lower fungi and in Coelenterata amongs about 679 hundreds of proteins of primitive eukaryotes studied with bioinformatic methods. 3. During the pachytene and diplotene stages of meiosis, chromosomes of spermatocytes and mother pollen cells acquire the structure resembling in miniature the structure of amphibian and avian lamp brush chromosomes. Lateral chromatin loops of 90, 160 and more than 480 Kb in size are observed in human spermatocytes during the diplotene stage. Taken together, these findings support the idea of considerable conservation of the scheme of molecular and ultrastructural organization of meiotic chromosomes in a variety of eukaryotic organisms.

Earlier, using bioinformatic methods, we reported the identification of repeated DNA sequences (RS), presumably responsible for the attachment of chromatin loops to the lateral elements of synaptonemal complex in meiotic chromosomes. In the present study, consensus sequences for this class of RS were identified. It was demonstrated that at least part of these sequences belonged to the AluJb subfamily of Alu sequences. The Alu copies distribution along the major human histocompatibility complex (MHC) and their spatial separation from the sites of meiotic recombination was examined. It was demonstrated that simple sequences, like (GC/CA)n, were flanking meiotic recombination sites. A model of the RS organization in meiotic chromosome, most efficiently linking experimental data on the meiotic recombination in MHC and the in silico data on the RS localization (the coefficient of multiple correlation, r = 0.92) is suggested.

A method of in silico search for specific repetitive DNA sequences related to the synaptonemal complex (meiDNA) in mammalian genomes was developed. A study of the distribution of these repeats over chromosomes revealed their scarcity on the Y chromosome and a decrease in recombination frequency in regions enriched in meiDNA. The results are discussed in context of the model of the looplike meiotic chromosome organization during the formation of the synaptonemal complex.

The mutagenic effect of low-dose gamma-irradiation was studied in Drosophila melanogaster systems of hybrid dysgenesis by estimating polytene chromosome rearrangements, recombination frequency, and viability at the embryonic and postembryonic developmental stages. A dose of gamma-irradiation which had no effect detectable by routine line crossing proved to significantly reduce the number of recombinants in the H-E and P-M systems and mortality at postembryonic stages. However, this combined effect was obtained if irradiation followed transposition, i.e., it depended on the application sequence of the mutagenic factors. The reverse order of the mutagenic treatment led to summation of the effects: as compared to either control, the frequencies of the dominant allele mutations as well as the larval and pupal mortality in F2 increased significantly (at the level of 99.9%). This allowed us to estimate the contribution of extremely low-dose gamma-irradiation into the mutagenic effect, which was impossible under routine conditions.

The published principles of computer analysis of genomes and protein sets in taxonomically distant eukaryotes are expounded. The authors developed a search strategy to identify in genomes of such organisms genes and proteins nonhomologous in primary structure but having similar functions in cells dividing by meiosis. This strategy based on the combined principles of genomics, proteomics, and morphometric analysis of subcellular structures was applied to a computer search for genes encoding the proteins of synaptonemal complexes in genomes of Drosophila melanogaster, the nematode Caenorhabditis elegans, and the plant Arabidopsis thaliana. These proteins proved to be functionally similar to their counterparts in yeast Saccharomyces cerevisiae (protein Zip1p) and mammals (protein SCP1).

From data on the molecular organization of transverse filament proteins of the synaptonemal complex (SC)--Zip1 in yeast and SCP1 in mammals--and on the width of the central SC space in these organisms and in Drosophila, the putative molecular structure and size of a transverse filament protein of the SC in Drosophila has been inferred. Using genetic and molecular databases and software from the Internet, we carried out in silico screening for a candidate gene for the Drosophila transverse filament protein. The search in the 250-bp region overlapping the locus of this gene (sections 88E-89B) and containing 78 predicted genes has revealed only one gene, CG17604, whose protein meets all requirements for the transverse filament protein of the SC. It was suggested that gene CG17604 is gene c(3)G. In this case, gene c(3)G must be localized in section 89A7-8 of the cytological map of Drosophila melanogaster.

By the beginning of 2000, more than 80 genes specifically controlling meiosis and meiotic recombination in Drosophila melanogaster have been described. Meiosis in Drosophila is different from the classical model. In females, these differences concern cytological features of prophase I, which have no principal genetic significance. Drosophila males lack lateral synapsis of chromosomes, recombination and chiasmata, and their chromosomes segregate in meiosis I following the "touch-and-go" principle. Meiotic genes in Drosophila can be classified according to their functions as affecting prerequisites for recombination and crossing over, controlling chromosome segregation in meiosis I separately in males and females and controlling sister-chromatid segregation in meiosis II in both sexes. Some meiotic genes are pleiotropic. There are meiotic genes controlling mitosis, and vice versa. Some genes for DNA repair in somatic cells are also involved in meiosis. Meiotic genes in Drosophila are compared with their counterparts in other organisms.

Chromosome synapsis in meiosis is performed through the formation of a synaptonemal complex (SC). The SC aggregates homologues until the diplotene stage, when the function of physical binding is carried out by a chiasmata. SC formation is controlled by specific genes. Regularities of SC formation in animals and plants are being studied at the Laboratory of Cytogenetics, Vavilov Institute of General Genetics, the Russian Academy of Sciences. It was shown that, in Drosophila melanogaster, the presence or absence of SC in meiosis is determined by balance between autosomes and sex chromosomes. i.e., SC is formed according to regularities in sex determination. The dose of the 8C-11A segment of X chromosome plays a key role in this process. Eight mutations in synaptic genes that affect SC formation were studied in rye Secale cereale. SC variants occurring in heteromorphic sex chromosomes were analyzed in the Ellobius genera and in B-chromosomes of Apodemus peninsulae. It was shown that, in addition to homologous synapsis, non-homologous synapsis of aberrant chromosomes occurs in rye and mouse heterozygotes at chromosome rearrangements. Twice as many heterozygous chromosome rearrangements were revealed, when the SC was studied at pachytene instead of diakinesis and metaphase I. Simple methods of SC investigations extended the capabilities of cytogenetic analysis of meiosis and provided new perspectives for studying the action of meiotic gen.

Three families of mobile elements that induce P-M, H-E, and I-R hybrid dysgenesis in Drosophila melanogaster were activated by crossing files of different cytotypes. Manifestation of gonadal sterility in F1 hybrid progeny was dependent on the temperature of development. The systems differed significantly in lethality of F2 hybrids at various stages of ontogeny (embryos, larvae, pupae, and adult flies). The highest embryo lethality was found in the P-M system at the cleavage stage. In the I-R and H-E systems, the peak of embryonic death corresponded to the stages of blastoderm and organogenesis, respectively. Experimental results are discussed in view of molecular and cytological characteristics of interacting strains and existing hypotheses for regulation xof transposition of P, hobo, and I mobile elements.

Comparative analysis was carried out with respect to the results of combined effects of gamma-irradiation and transposition of mobile elements in Drosophila, depending on the succession of their application. As turned out, introduction of the P and hobo elements into the M' line, prior to irradiation, resulted in decreased number of unfertilized eggs and reduced the proportion of flies killed at the larval and pupal stages. However, opposite effects were shown, when the P element was introduced following irradiation: the number of unfertilized eggs and that of the flies killed at the larval and pupal stages has significantly increased, as compared to the control. Interaction between the processes induced at the level of DNA repair both by gamma-irradiation and the P' elements' transposition is suggested.