MORPHOLOGICAL MANIFESTATION OF A UNIQUE DNA SEGMENT IN HUMAN MEIOTIC PROPHASE I
Yu.F. Bogdanov,1 V.E. Spangenberg,1 S.Ya. Dadashev,1 I.I. Vityzeva,2
S.V. Bogoliubov,2 O.L. Kolomiets 1,*
1 N.I. Vavilov Institute of General Genetics RAS, Moscow, and 2 Endocrinology Research Centre, Moscow;
* e-mail: olkolomiets@mail.ru
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 m 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 m 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.
Key words: meiosis, prophase I, synaptonemal complex, fluorescent hybridization in situ, lateral chromatin loops
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