Ribosomal DNA Organization Patterns within the Dinoflagellate Genus Alexandrium as Revealed by FISH: Life Cycle and Evolutionary Implications.
MetadataShow full item record
AuthorsFigueroa, R.I. (Rosa Isabel); Cuadrado, Á. (Ángeles); Stüken, A. (Anke); Rodríguez, F. (Francisco); Fraga, S. (Santiago)
Nuclear Organizer Regions (NORs)
Dinoflagellates are a group of protists whose genome differs from that of other eukaryotes in terms of size (contains up to 250pg per haploid cell), base composition, chromosomal organization, and gene expression. But rDNA gene mapping of the active nucleolus in this unusual eukaryotic genome has not been carried out thus far. Here we used FISH in dinoflagellate species belonging to the genus Alexandrium (genome sizes ranging from 21 to 170 pg of DNA per haploid genome) to localize the sequences encoding the 18S, 5.8S, and 28S rRNA genes. The results can be summarized as follows: 1) Each dinoflagellate cell contains only one active nucleolus, with no hybridization signals outside it. However, the rDNA organization varies among species, from repetitive clusters forming discrete nuclear organizer regions (NORs) in some to specialized “ribosomal chromosomes” in other species. The latter chromosomes, never reported before in other eukaryotes, are mainly formed by rDNA genes and ...