[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.