Summary
The nuclear apparatus of the ciliateBlepharisma japonicum (Spirotricha, Heterotricha) consists of one macronucleus, presiding over the phenotypic expression, and a variable number Of micronuclei (from 6 to 30) with a germinal function.Blepharisma, as all other ciliates, can reproduce asexually through binary fission and sexually through conjugation. Its morphology, behaviour and reproductive biology are well known, whereas any information pertaining the biochemical and molecular structure of nuclei is lacking. In the research work of sexual differentiation ofBlepharisma the problem rose about the formation and differentiation of its macronucleus during conjugation.
A preliminary analysis of macronuclear DNA in vegetative cells was carried out by different physical-chemical parameters.
The agarose gel electrophoretic pattern of macronuclear native DNA shows the presence of a unique band with a high molecular weight: this fact seems to avoid the presence of DNA fragmentation during macronuclear differentiation, that on the contrary, occurs in other ciliates, such as Hypotrichs.
CsCl sedimentation profiles show a peak with buoyant density 1,692 g/ml, while Hoechst 33258/CsCl ultracentrifugation separates a light fraction (17.5% of the total DNA) from the main peak.
Thermal denaturation profiles support the presence of a A-T rich family; the thermal transition interval has a low value (Δt=5.3) in comparison to other Eukaryotic DNAs. Reassociation kinetics analysis indicates that 3–4% of DNA reassociates at Cot practically equal to 0 and the remaining fraction at a rate corresponding to single copy sequences. After digestion with restriction enzymes the electrophoretic pattern does not show the presence of highly repetitive sequences.
These findings alignBlepharisma japonicum to the close heterotrichousStentor and toParamecium andTetrahymena for the presence of a single banded macronuclear DNA of high molecular weight.
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Salvini, M., Durante, M. & Nobili, R. Chacterization of macronuclear DNA inBlepharisma japonicum . Protoplasma 117, 82–88 (1983). https://doi.org/10.1007/BF01281787
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DOI: https://doi.org/10.1007/BF01281787