Gaginskaya E.R., Kasyanov V.L., Kogan G.L.
Ribosomal gene amplification and extrachromosomal nucleoli formation in oocytes of starfish Henricia hayashi Djakonov (Echinasteridae: Echinorerm)
Tsitologiia — 1987. — V. 29, — P. 1233–1238.

The amplification of rRNA genes was shown in oocytes of the starfish H. hayashi. Ag-NOR staining and in situ hybridization technique were used for studying the nucleolar apparatus in growing oocytes. A clone of 18S and 28S rDNA of D. melanogaster was taken as a probe for rDNA. The probe was nick-translated according to Rigby et al. (1977). Growth and following fragmentation of rDNA bodies and NOR complexes proceed by proposed cascade mechanism and lead to arising of multiple extrachromosomal nucleoli in the oocyte nucleus. In every discribed NOR structures amplified rRNA genes were found. The extra nucleoli are shown to contain Ag+ nucleolar organizers.