[Structural changes of the nucleolar organizing regions in rhabdomyosarcoma RA-23 tumor cells induced by okadaic acid].

It has been recently shown that okadaic acid (OA), an inhibitor of dephosphorilation, is capable of inducing changes in the nucleolar organizer regions (AgNORs) of some mammalian cells. Our work was focused on studying the structural changes in AgNORs of tumour cells of rat rhabdomyosarcoma RA-23 by their exposure to 100 nM OA. A standard silver staining procedure of interphase AgNORs in tumour cells was used. We measured no less than 100 tumour cells in each clone. In the examined tumour cell populations, the index of interphase AgNORs varied from 1.54 to 4.35. A clear structure and form of AgNORs was not observed in 30% okadaic acid-treated tumour cells, as opposed to 10% of the control ones. AgNORs in these cells looked like a mixture of thin threads encompassing some dark dots lying, mostly, separately. Additional procedures of tumour cell staining with Giemsa and fluorescent dye Hoechst 33,258, respectively, revealed that such structures were not chromosomes. Meanwhile, the frequency of cells at the stage of prophase exceeded 3%, as opposed to the control, where the frequency of cells at this stage was less than 0.5%. Thus, we can conclude that we have detected specific changes in AgNORs and chromatin structure of okadaic acid-treated tumour cells.