Analysis by polarizing microscopy of chromosomal structure among dinoflagellates and its phylogenetic involvement

Abstract

Dinoflagellate chromosomes are highly interesting because of their condensed state, their lack of histone, and their ultrastructure reminiscent of that of bacterial nucleoid. With the use of a highly sensitive resolution polarization microscope coupled with electron microscope observations, and by studying and comparing a great variety of species, we confirm the intrinsic nature of birefringence and bring new data about the evolution of interphasic chromosomes among dinoflagellates. Three types are observed: the A-type, characterized by positive birefringence, condensed state, and lack of basic proteins; the B-type, with a half positive-half negative birefringence corresponding to a neck lace chromosome shape and possessing no or very few basic proteins; and the C-type, which has a negative birefringence because of its loosely gathered filament bundle possessing few basic proteins.