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A Guide to the Russian Academy of Sciences - University of Texas ...

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High value <strong>of</strong> DNA supercoiling density -0.075 was found in<br />

transcriptionally hyperactive Balbiani ring 2, <strong>the</strong> value is above <strong>the</strong><br />

threshold <strong>of</strong> formation <strong>of</strong> noncanonical forms in <strong>to</strong>rsionally stressed<br />

DNA. On <strong>the</strong> contrary, DNA in transcriptionally inactive bands <strong>of</strong><br />

polytene chromosomes was found <strong>to</strong> be practically under no <strong>to</strong>rsional<br />

tension, but <strong>to</strong>pologically closed. Never<strong>the</strong>less, DNA <strong>of</strong> temporary<br />

inactive polytene nuclei (after brief heat shock and during <strong>the</strong> last<br />

larval molt <strong>of</strong> Chironomus larvae) was found <strong>to</strong> be under negative<br />

<strong>to</strong>rsional tension.<br />

Several synaptic (as1, as2 etc.) mutants and mutants affecting segregation<br />

<strong>of</strong> chromosomes and spindle structure (ms3, ms28, dv) in maize<br />

were analysed. New mutations (ms, ms3, pam) affecting cell cycle<br />

regulation were found and analyzed. Perinuclear ring <strong>of</strong><br />

microtubules - a new cy<strong>to</strong>skeletal structure was found in plant<br />

meiotic cells. Its reorganization <strong>to</strong> meiotic spindle was described.<br />

Unknown stage <strong>of</strong> cy<strong>to</strong>kinesis - a stage <strong>of</strong> crosswise dyad which is<br />

indicative <strong>of</strong> double-step simultaneous cy<strong>to</strong>kinesis has been noted.<br />

Cy<strong>to</strong>genetic analysis <strong>of</strong> reorganization <strong>of</strong> <strong>the</strong> mink embryonic genome<br />

during diapause has been carried out. Seasonal delay in implantation<br />

(embryonic diapause) is known widely spread in <strong>the</strong> animal world<br />

and being <strong>of</strong> adaptive value. It was found that <strong>the</strong> diapausing<br />

blas<strong>to</strong>cyst size growth is realized due <strong>to</strong> <strong>the</strong> increase in <strong>the</strong> number<br />

<strong>of</strong> trophoblast cells without classic mi<strong>to</strong>tic divisions. Giant polytene<br />

(up <strong>to</strong> 512n) nuclei divide by <strong>the</strong> "hidden" segregation <strong>of</strong> <strong>the</strong>ir<br />

genomes. The resulting new cells posess most high functional<br />

activity which is supposed <strong>to</strong> provide successful implantation and<br />

placentation <strong>of</strong> embryo.<br />

Participation in State and International Programs:<br />

RFBR<br />

New Trends in Genetics<br />

Joint project "DNA <strong>to</strong>pology in chromatin and chromosomes" with Pr<strong>of</strong>.<br />

Dr. M.Lezzi (Institut f. Zellbiologie, ETH, Zurich, Switzerland).<br />

Subjects <strong>of</strong> Scientific Collaboration:<br />

Study <strong>of</strong> DNA <strong>to</strong>pology in metaphase chromosomes, inactive nuclei <strong>of</strong><br />

lymphocytes, sperm heads et al. Study <strong>of</strong> changes in DNA <strong>to</strong>pology during<br />

cell cycle, during cell differentiation, after lymphocyte activation<br />

etc.<br />

Study <strong>of</strong> genetical control and cellular mechanisms <strong>of</strong> meiosis in higher<br />

plants. Light and EM analysis and comparison <strong>of</strong> morphological and<br />

biochemical phenotypes <strong>of</strong> <strong>the</strong> mutants.<br />

Cy<strong>to</strong>genetical investigations <strong>of</strong> embryonic genome activity during<br />

seasonal delayed implantation in mammal.<br />

6. Labora<strong>to</strong>ry <strong>of</strong> Cells Differentiation.<br />

Staff:<br />

Sergei I. Baiborodin, Ph.D., Executive Head <strong>of</strong> <strong>the</strong> Labora<strong>to</strong>ry<br />

Vic<strong>to</strong>ria I. Deribas, Ph.D.<br />

1017

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