DYNAMICS OF STRUCTURAL CHANGES OF PARAMECIUM CAUDATUM AND BURSARIA TRUNCATELLA
MACRONUCLEAR CHROMATIN AND NUCLEOLI UNDER HYPOTONIC CONDITIONS
O. G. Leonova, 1 Yu. L. Ivanova, 1 B. P. Karadjan, 2
V. I. Popenko 1 *
1 Engelhardt Institute of Molecular Biology RAS, Moscow, and 2
Institute of Cytology RAS, St. Petersburg, Russia;
* e-mail: popenko@eimb.ru
Dynamics of structural changes of nucleoli, complex nucleolar aggregates and chromatin bodies in macronuclei (Ma)
of ciliates Paramecium caudatum and Bursaria truncatella under hypotonic conditions was studied. It was shown that after a
3 min hypotonic treatment nuclei swelled and became highly vacualated. 3D-reconstruction showed that such nucleoli were formed by
nucleolonema-like threads about 100-200 nm in thickness. Intranucleolar chromatin bodies decompacted, but remained bound with
fibrillar component of the nucleolus by thin fibres about 10 nm thick. After 6 min hypotonic treatment the nucleolar material loosened and
had a "gauze", or network-like appearence. After 10 min hypotonic treatment nucleoli dissociated completely. It was shown that a
transition of chromatin bodies from completely compact to partially and fully decompacted state occurred cooperatively in different regions
of Ma. In partucular, chromatin bodies in the central part of complex nucleolar aggregates decompacted much faster than those in the Ma
karyoplasm. It evidences for a specific, well-ordered chromatin organizaton in Ma. Prolonged hypotonic treatment led to a complete
dissociation of Ma components; fibres 6-10 nm thick were solely observed in such preparations. Such fibres may represent remnant
structures of the nuclear matrix. Dynamics of Ma chromatin bodies decompaction correlates well with that of chromomeres in the nuclei
of higher eukaryotes. Our data confirm that chromatin 100-200 nm bodies in the ciliate Ma are analogues of chromomeres - looped
discrete chromatin domains, observed in the nuclei of higher eukaryotes.
Key words: ciliates, macronuclei, hypotonic treatment, chromatin, nucleoli, 3D-reconstruction
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