[The peculiarities of the chromosome organization in meiosis].

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.

[Morphological manifestation of a unique DNA segment in human meiotic prophase I].

The commercial sample of human DNA fragment from the choromosome 17 was used as the probe for FISH to study of the mode of its attachment to the lateral elements of synaptonemal complex (SC) in human spermatocytes. It was a 160 kb probe from the band 17p1.2, containing RAI1 gene with D17S620 marker (the probe for deletion causing Smith-Magenis syndrome). The probe made lateral chromatin protrusions, contacting with SC stained with anty-SYCP3. Different morphological configuration of lateral chromatin protrusions where observed. They depended on substages of meiotic prophase I. At zygotene, FISH probe form two sticks, c. a. 6 micro long, which was perpendicular to SC longitudinal axe, one stick at each SC side. At early pachytene, each stick transforms into a globule, one globule at each SC side again. At late pachytene each globule transformed into two crumbly globules containing short threads and clumps. At diplotene, globules finally transformed into thin DNA (chromatin) loops up to 10 micro long from the base to top with periodical thickenings (beads) along their length. As the result of this dynamics of transformation, two chromatin loops with beads were found on each side of SC of the chromosome 17. These loops most probably were the loops of sister chromatides, the full set of chromatide loops at the particular SC (bivalent) site being four in number, i. e. representing of two pair of chromatides. This study is the first one in which lateral chromatin loops in human mail meiotic prophase I are visualized as true open loop instead of that usually postulated "loops" after observation of condensed road-like or brush-like chromatin protrusion attached to the lateral elements of synaptonemal complexes. Open configuration of the loops, presumably, depends on activation of transcription during late pachytene-early diplotene. They resemble lateral loops of mini lampbrush chromosomes.

[DNA repeated sequences may be involved in the synaptonemal complexes formation].

Synatonemal complexes (SCs) are the intranuclear structures which facilitate reversible lateral synapsis of the homologous chromosomes in the course of meiosis. It is still unclear which DNA nucleotide sequences are responsible for the chromatin attachment to the SC lateral elements. Considering the features of the dispersed repeated sequences (RS) it is worth to assume their participation in the structure functional organization of the meiotic chromosome. Using numerical analysis we have investigated the relationship between RS and the distribution of events of the meiotic recombination in mouse chromosome 1. Using in situ hybridization on spread mouse spermatocytes, we have demonstrated the arrangement of different types of RS relative to SCs. Hybridization signals of B1(Alu), B2, and minisatellite probes were localizating predominantly in the SCs regions. Our results allow us to suggest the model of the meiotic chromosome organization with the RS as the sequences, participating in the attachment of chromatin loops and SCs.

[Semisterile meiotic mutant sy11 with heterologous chromosome synapsis in rye Secale cereale L].

A study was made of the expression and inheritance of the sy11 mutation, which alters homologous chromosome synapsis in meiotic prophase I of rye. The abnormal phenotype proved to be determined by a recessive allele of a single sy11 gene. Univalents and multivalents were observed in homozygotes for the mutant allele. Analysis of the synaptonemal complex revealed a combination of homologous and nonhomologous synapsis in the mutant. The nonhomologous synapsis frequency significantly decreased in the course of meiotic prophase I in the mutant. The number of chiasmata per bivalent in metaphase I was 1.1 x 0.01 versus 1.8 x 0.01 in wild-type plants, and the number of univalents was 2.7 x 0.06 versus 0.5 x 0.05 in wild-type plants. As a result, a broad range of abnormalities was observed at subsequent stages of meiosis and led to the formation of defective microspores. Mutant plants were semisterile.

[How do chromosomes attach to synaptonemal complexes?].

Fluorochrome-labeled oligonucleotides (n = 44) corresponding to mouse genome repetitive sequences were hybridized in situ with pachytene nuclei of mouse spermatocytes. Signals of the repetitive sequences MaLR, MER, and (GT)22 were found to be dispersed through chromatin, and signals of BI 1 repeats and minisatellites were mostly attached to synaptonemal complexes immunostained with anti-SYCP3 antibodies. These results suggest that B 1 repeats and minisatellites are candidates for sequences anchoring chromatin to synaptonemal complexes.

[Impairment of homologous chromosome synapsis in meiosis in rye Secale cereale L. caused by a recessive mutation of the sy18 gene].

AExpression and inheritance of the sy18 mutation causing impairment of synapsis homology were studied. It was established that the abnormal phenotype is determined by a recessive allele of the sy18 gene. Univalents and multivalents are observed in homozygotes for this mutant allele. According to the electron microscopic analysis of synaptonemal complexes in mutants, homologous synapsis occurs together with nonhomologous synapsis. The sy18 gene was found to have no allelism with asynaptic genes sy1 and sy9 and with genes sy10 and sy19 causing, like sy18, disturbances in synapsis homology.

[Evolution of meiosis of unicellulate and multicellular eucaryotes. Aromorphosis at the cellular level].

An attempt was undertaken to apply the concept elaborated for the evolution of multicellular organisms to that of unicellular eucaryotes. The latter's meiosis was formed on the basis of combination on three intracellular processes: 1) homologous DNA recombination, 2) chromosome disjunction with the assistance of mitotic apparatus, and 3) formation of "linear" chromosome elements consisting of specific proteins. Mechanism of homologous chromosome recombination was inherited from the archibacteria, while both the mitotic apparatus and "linear" chromosome elements emerged de novo. These elements appeared (resulting from appearance of the meiosis-specific proteins) as a complication of cohesion filaments, arising at the boundary between the sister chromatids after DNA replication. Homologous chromosome recombination made it possible for the chromosomes of diploid organisms to join pairwise by means of Holliday structures, while temporary blocking of hydrolysis of the linear elements at centromeres made it possible for the kinetochores to acquire unipolarity and for the sister chromatids to move to the same pole. All these provided for reduction of the chromosome number. Such a type of the reduction of chromosome number was retained by the extant imperfect ascomycetes Schizosaccharomyces pombe and Aspergillus nidulans, and by the infusorian Tetrahyrmena thermophila. It was the derivative of specific proteins, i.e. synaptonemal complexes (SCs). that appeared to be aromorphosis; they came to existence due to the pairwise joining of the chromosome "linear" elements by means of protein "zipper". The SCs join homologous chromosomes temporarily at the prophase of meiotic reduction division, thus optimizing condition for the crossing over and chiasma formation. The latter and the kinetochore unipolarity both provide for the chromosome disjunction. Kinetochore unipolarity is caused by the protein shugoshin which appears at meiotic prophase I and blocks cohesin hydrolysis at centromeres when anaphase I begins. This type of reductional division became the basis of the classical meiosis in the overwhelming majority of unicellular and multicellular organisms over all eucaryote kingdoms.

[The SCAR DNA sequence family is enrichment in the evolution-conserved sequences].

Synaptonemal complex (SC) is a specific structure for prophase I of meiosis. Recently we have described synaptonemal complex tightly associated regions of DNA (SCARs DNA) as a particular family of genomic DNA. Now we reveal the evolutionary conservation of SCAR DNA sequences of vertebrates. This data correlates with universal morphology of SCs and similar processes proceed in prophase I of meiosis at representatives of different taxa.

[Expression and inheritance of a desynaptic phenotype with impaired homologous synapsis in rye].

The cytological phenotype was studied in a desynaptic form isolated from a population of rye cultivar Vyatka. The primary defect of desynaptic plants was identified as nonhomologous (heterologous) chromosome synapsis, which was observed by electron microscopy of synaptonemal complexes (SCs) in meiotic prophase I. Synapsis defects involved switches of synapsing axial elements to nonhomologous partners, asynapsis in the switching region, and foldbacks formed by the SC lateral elements. Defective bivalent formation was observed at later stages: the univalent number varied and multivalent chromosome associations were observed in single cells in metaphase I. The desynaptic phenotype was controlled by two recessive genes, sy8a and sy8b, which acted and were inherited independently. In a hybrid combination with line Ku-2/63, the desynaptic phenotype was suppressed by the dominant allele of a third gene for inhibitor I; the segregation in hybrid families corresponded to 57:7.

[Abnormal meiosis in bisporic mutants of white button mushroom Agaricus bisporus (Lange) Imbach].

A formerly developed method of obtaining spread preparations of mushroom basidial nuclei was applied to study of meiotic prophase I in bisporic white button mushroom (Agaricus bisporus) strains. Meiotic recombination and assemblage of axial structures (axial elements and synaptonemal complexes) of chromosomes in meiotic prophase I are interrelated. It is known that the frequency of meiotic recombination is reduced in the bisporic A. bisporus variety. We showed that formation of axial structures of meiotic chromosomes in bisporic strains of this mushroom was disrupted. The phenotypes of disruptions in spread prophase nuclei are diverse. In leptotene and early zygotene, many nuclei contain abnormal, often short, and, as a rule, few chromosomal axial elements. The abnormalities in the formation of synaptonemal complexes at the zygotene-diplotene stage are of the same kind and even more pronounced. We discovered an important feature of meiosis in A. bisporus associated with fruit-body morphogenesis. Meiosis starting in basidia (meiocytes) of young closed fruit bodies is accompanied by disruption of chromatin condensation in prophase I and, probably, is arrested. After indusium breakage, the course of meiosis normalizes. Preparations with clearly observable chromosomal axial structures can be obtained only at this stage of fruit-body development.

[Genetic collection of meiotic mutants of rye Secale cereale L].

Genetic collection of meiotic mutants of winter rye Secale cereale L. (2n = 14) was created. Mutations were detected in inbred F2 generations after self-fertilization of the F1 hybrids, obtained by individual crossing of rye plants (cultivar Vyatka) or weedy rye with plants from autofertile lines. The mutations cause partial or complete plant sterility and are maintained in collection in a heterozygous state. Genetic analysis accompanied by cytogenetic study of meiosis has revealed six mutation types. (1) Nonallelic asynaptic mutations sy1 and sy9 caused the formation of only axial chromosome elements in prophase and anaphase. The synaptonemal complexes (SCs) were absent, the formation of the chromosome "bouquet" was impaired, and all chromosomes were univalent in meiotic metaphase I in 96% (sy1) and 67% (sy2) of cells. (2) Weak asynaptic mutation sy3, which hindered complete termination of synapsis in prophase II. Subterminal asynaptic segments were always observed in the SC, and at least one pair of univalents was present in metaphase I, but the number of cells with univalents did not exceed 2%. (3) Mutations sy2, sy6, sy7, sy8, sy10, and sy19, which caused partially nonhomologous synapsis: change in pairing partners and fold-back chromosome synapsis in prophase I. In metaphase I, the number of univalents varied and multivalents were observed. (4) Mutation mei6, which causes the formation of ultrastructural protrusions on the lateral SC elements, gaps and branching of these elements. (5) Allelic mutations mei8 and mei10, which caused irregular chromatin condensation along chromosomes in prophase I, sticking and fragmentation of chromosomes in metaphase I. (6) Allelic mutations mei5 and mei10, which caused chromosome hypercondensation, defects of the division spindle formation, and random arrest of cells at different meiotic stages. However, these mutations did not affect the formation of microspore envelopes even around the cells, whose development was blocked at prophase I. Analysis of cytological pictures of meiosis in double rye mutants reveled epistatic interaction in the mutation series sy9 > sy1 > sy3 > sy19, which reflects the order of switching these genes in the course of meiosis. The expression of genes sy2 and sy19 was shown to be controlled by modifier genes. Most meiotic mutations found in rye have analogs in other plant species.

[Developing and testing a method of in silico identification and characterization of meiotic DNA].

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.

[In silico identification and characterization of meiotic DNA: AluJb possibly participates in the attachment of chromatin loops to synaptonemal complex].

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.

[Similarity of domain organization of proteins in phylogenetically distant organisms as a basis of meiosis conservatism]. / Skhodstvo domennoi organizatsii belkov u filogeneticheski dalekikh organizmov kak osnova konservatizma meioza.

The cytological mechanism of meiosis is very conservative in all eukaryotes. Some meiosis-specific structural proteins of yeasts, nematode Caenorhabditis elegans, Drosophila, and mammals, which play identical roles in cells during meiosis, do not have homology of the primary structure, but their domain organization and conformation are similar. The enzymes of meiotic recombination in yeasts and plants have similar epitopes. These facts suggest that the similarity of the higher level of organization of the meiosis-specific proteins allows these proteins to form similar subcellular structures and produce similar cytological picture of meiosis and similar functions of these subcellular structures. Finally, this leads to a conservative scheme of meiosis in evolutionally distant eukaryotes.

[Localization of DNA sequences tightly associated with synaptonemal complex in compositional fractions of golden hamster]. / Lokalizatsiia posledovatel'nostei DNK, prochno assotsirovannykh s sinaptonemym kompleksom, v kompozitsionnykh fraktsiiakh zolotistogo khomiachka.

The synaptonemal complex isolated from the spermatocyte nuclei by exhaustive hydrolysis of the latter by DNase II contains tightly associated DNA sequences (SCAR DNA). Here we studied the compositional properties of a cloned family of SCAR DNA of golden hamster, namely we performed the localization of 27 SCAR DNA clones on compositionally fractionated genomic DNA from golden hamster. We observed that sequences of the SCAR DNA family are mainly localized in the GC-poor isochore families L1 and L2, that showed 63% hybridization signals. This means that 37% of signals is referred to the GC-rich isochores, indicating the presence of SCAR DNA overall the genome, even if each isochore family presents differences in density and sequence type. Moreover, the SCAR DNA sequences containing regions of homology with LINE/SINE repeats were observed in all the isochore families. The compositional localization of SCAR DNA is in agreement with the hypothesis that SC and SCAR DNA participate in the chromatin organization during the meiosis prophase I, which should result in the attachment of chromatin loops to lateral elements of SC along the whole length of the latter.

[Variation and evolution of meiosis]. / Izmenchivost' i évoliutsiia meioza.

Meiosis arose in the evolution of primitive unicellular organisms as a part of sexual process. One type of meiosis, the so-called classical type, predominates in all kingdoms of eukaryotes. Meiosis is controlled by hundreds of genes, both shared with mitosis and specifically meiotic ones. In a wide range of taxa, which in some cases include kingdoms, meiotic genes and features obey Vavilov's law of homologous variation series. Synaptonemal complexes (SCs) temporarily binding homologous chromosomes at prophase I, ensure precise and equal crossing over and interference. SC proteins have 60-80% homology within the class of mammals but differ from the corresponding proteins in fungi and plants. Thus, nonhomologous SC proteins perform similar functions in different taxa. Some recombination enzymes in fungi and insects have common epitopes. The molecular mechanism of recombination is inherited by eukaryotes from prokaryotes and operates in special compartments: SC recombination nodules. Chiasmata, i.e., physical crossovers of nonsister chromatids, are preserved in bivalents until metaphase I due to local cohesion of sister chromatids in the remaining SC fragments. Owing to chiasmata, homologous chromosomes participate in meiosis I in pairs rather than individually, which, along with unipolarity of kinetochores (only in meiosis 1), ensures segregation of homologous chromosomes. The appearance of SC and chiasmata played a key role in the evolution of unicellular organisms since it promoted the development of a progressive type of meiosis. Some lower eukaryotes retain primitive meiosis types. These primitive modes of meiosis also occur in the sex of some insects that is heterozygous for sex chromosomes. I suggest an explanation for these cases. Mutations at meiotic genes impair meiosis; however, due to the preservation of archaic meiotic genes in the genotype, bypass metabolic pathways arise, which provide partial rescue of the traits damaged by mutations. Individual blocks of genetic program of meiotic regulation have probably evolved independently.

[Comparative genomics and proteomics of Drosophila, Brenner's nematode, and Arabidopsis: identification of functionally similar genes and proteins of meiotic chromosome synapsis]. / Sravnitel'naia genomika i proteomika Drozofily, nematody Brennera i Arabidopsisa. Identifikatsiia funktsional'no skhodnykh genov i belkov sinapsisa meioticheskikh khromosom.

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).

[Synaptonemal complex proteins: specific proteins of meiotic chromosomes]. / Belki sinaptonemnogo kompleksa--spetsificheskie belki meioticheskikh khromosom.

The review considers proteins of the synaptonemal complex (SC), a specific structure formed between homologous chromosomes in maturing germline cells during meiotic prophase I. The structure and functions are described for proteins that form ultrastructural SC elements in mammals, in yeast, and in higher plants. The roles of cohesions and of the SC proteins in meiotic sister-chromatid cohesion are considered. Though still scarce, data are summarized on the SC self-assembly and dissociation and on the molecular composition of SC-associated recombination nodules, which provide a compartment for meiotic recombination enzymes. The accumulating data on the SC molecular components and on their structure, properties, and interactions improve the understanding of the SC function.