Chromosomal markers in the genus karenia: Towards an understanding of the evolution of chromosomes, life cycle patterns and phylogenetic relationships in dinoflagellates

Dinofagellates are a group of protists whose genome is unique among eukaryotes in terms of base composition, chromosomal structure and gene expression. Even after decades of research, the structure and behavior of their amazing chromosomes—which without nucleosomes exist in a liquid crystalline state—are still poorly understood. We used fow cytometry and fuorescence in situ hybridization (FISH) to analyze the genome size of three species of the toxic dinofagellate genus Karenia as well the organization and behavior of the chromosomes in diferent cell-cycle stages. FISH was also used to study the distribution patterns of ribosomal DNA (45S rDNA), telomeric and microsatellites repeats in order to develop chromosomal markers. The results revealed several novel and important features regarding dinofagellate chromosomes during mitosis, including their telocentric behavior and radial arrangement along the nuclear envelope. Additionally, using the (AG)10 probe we identifed an unusual chromosome in K. selliformis and especially in K. mikimotoi that is characterized by AG repeats along its entire length. This feature was employed to easily diferentiate morphologically indistinguishable life-cycle stages. The evolutionary relationship between Karenia species is discussed with respect to diferences in both DNA content and the chromosomal distribution patterns of the DNA sequences analyzed.Dinofagellates are a group of protists whose genome is unique among eukaryotes in terms of base composition, chromosomal structure and gene expression. Even after decades of research, the structure and behavior of their amazing chromosomes—which without nucleosomes exist in a liquid crystalline state—are still poorly understood. We used fow cytometry and fuorescence in situ hybridization (FISH) to analyze the genome size of three species of the toxic dinofagellate genus Karenia as well the organization and behavior of the chromosomes in diferent cell-cycle stages. FISH was also used to study the distribution patterns of ribosomal DNA (45S rDNA), telomeric and microsatellites repeats in order to develop chromosomal markers. The results revealed several novel and important features regarding dinofagellate chromosomes during mitosis, including their telocentric behavior and radial arrangement along the nuclear envelope. Additionally, using the (AG)10 probe we identifed an unusual chromosome in K. selliformis and especially in K. mikimotoi that is characterized by AG repeats along its entire length. This feature was employed to easily diferentiate morphologically indistinguishable life-cycle stages. The evolutionary relationship between Karenia species is discussed with respect to diferences in both DNA content and the chromosomal distribution patterns of the DNA sequences analyzed