THE DINOFLAGELLATE NUCLEUS AND CHROMOSOMES - MESOKARYOTE CONCEPT RECONSIDERED

This review considers the literature data which appeared mainly during the latest 12 years. Chromosome structure in dinoflagellates and new models of chromosome organization are reviewed. The chromosomes are no longer considered to be polytene. The existence of eukaryotic-type ce ll cycle in dinoflagellates contradicts the mesokaryote concept. Mitos is in dinoflagellates (class Dinoflagellatea) is usually extranuclear closed pleuromitosis with the spindle microtubules hidden inside chann els which pierce the dividing nucleus, but it can be also closed intra nuclear (in Oxyrrhis, belonging to class Protalveolatea). Sequencing o f both large and small subunit ribonuclear RNA (or the corresponding g enes coding for them) has demonstrated late emergence of dinoflagellat es among eukaryotes and their clustering with ciliates and sporozoans; the dinoflagellates thus cannot any more be considered mesokaryotes, meant as a sister group to all eukaryotes. The dinoflagellates frequen tly harbour eukaryotic photosynthetic symbionts which show various deg rees of integration into the dinoflagellate cell.