ARGYROPHILIC PROTEINS IN DINOFLAGELLATES - AN ULTRASTRUCTURAL, CYTOCHEMICAL AND IMMUNOCYTOCHEMICAL STUDY

Dinoflagellate protists constitute an original eukaryotic phylum and h ave an ancestor in common with ciliates. They are important tools in s tudies of structure and function of the nucleus because they present a mixing of prokaryotic characteristics such as chromatin devoid of his tones and nucleosomes, eukaryotic characteristics such as the presence of a nuclear membrane, nucleoli and AgNOR-like proteins and original characteristics of their own. Among them are the permanent compaction of the chromosomes, the presence of a nuclear envelope during the whol e cell cycle, rare bases in their DNA, as well as an original mitosis. We have studied the distribution of the nuclear argyrophilic proteins (AgP) in three genera of Dinoflagellates (Prorocentrum, Crypthecodini um and Amphidinium) by means of light microscopy (LM) and electron mic roscopy (EM), using cytochemical silver staining and immunocytochemica l reactions following various preparation procedures. By means of the silver staining reaction, we determined by LM the distribution of nucl eoli in the three non-synchronized cell populations and localized by E M the presence of AgP. These are always found in the nucleolar fibrill o-granular compartment (FG) and partly in the chromosomes and in the n ucleolar UCh (unwound region of the nucleolar chromosome corresponding to the NOR); the chromosomes and the UCh are always stained in P mica ns, under special conditions in C cohnii but never in A carterae. To d etermine whether these nucleolar and chromosomal proteins are similar or different, we modified the conditions of the silver staining reacti on by acidic, alkaline or enzymatic pretreatments and changes in the r eaction's temperature. Our results suggested that these proteins belon g to different groups. We have characterized one of these proteins usi ng a mammalian anti-B23 Ab in P micans cells. Positive labeling was mo stly detected in chromosomes and UCh and in a smaller amount in the nu cleolar FG and G compartments, co-locating with end-products of the si lver staining reaction. This suggests that: i) one among the dinoflage llate chromosomal AgP is analogous to the B23 mammalian protein; and i i) this B23-like protein is probably a DNA partner.