Mesokaryote

The first investigations of the dinoflagellate nucleus, during the 1950s-1960s, revealed a fine nucleus and chromosome structure that was completely different from other nucleated organisms or eukaryotes, lacking histones and with a permanently condensed chromatin. The traits considered by Dodge to define Mesocaryota were: lack of detectable histones; absence of a mitotic spindle; continuous DNA synthesis; chromatin fibrils arranged in arched swirls as in bacterial nucleoids; and chromosomes permanently condensed persistently adhered to the nuclear envelope, which remains intact throughout mitosis (i.e., it is a closed mitosis). The mesokaryote hypothesis was disproven in the following decades through more detailed observations of the criteria listed above. For example, detailed studies on the parasitic Syndinium demonstrated the presence of an unconventional type of basic histone-like proteins and of an extranuclear mitotic spindle in dinoflagellates, similarly to 'higher' eukaryotes. == References ==