Lifting the Curtain? The Microtubular Cytoskeleton of Oxyrrhis marina (Dinophyceae) and its Rearrangement during Phagocytosis.

The cortical microtubular cytoskeleton of the colorless, phagotrophic dinoflagellate Oxyrrhis marina has been investigated by immunofluorescence and transmission electron microscopy. It consists of two systems, an anterior system comprising microtubular bands (of 2-4 microtubules each) which extend from a focal point at the cell apex to about three-quarters of the cell length where they either become transversely oriented (on the ventral right surface of the cell) or abut transversely oriented microtubules (on the dorsal and ventral left cell surface); and a posterior system in which microtubular bands extend from a focal point near the basal apparatus posteriorly around the antapex of the cell to become transversely oriented in the region where they meet the abutting anterior microtubular bands. The peripheral cytoskeleton of Oxyrrhis contains no continuous pole-to-pole microtubules and is thus basically similar to that of other dinoflagellates. Upon phagotrophic feeding the peripheral microtubular cytoskeleton undergoes reversible rearrangements. The non-permanent cytostome is located at the right ventral surface of the cell between the ventral ridge microtubules (vrm) and the groove of the longitudinal flagellum. During phagocytosis the anteriorly focused microtubular bands of the peripheral cytoskeleton near the right ventral surface of the cell are 'lifted' or 'pushed' towards the vrm to enable uptake of food organisms of diverse size and shape. Within minutes after phagocytosis the microtubular bands are relocated to their former position. We conclude that the organization of a peripheral microtubular cytoskeleton from two opposite focal points provided the dinoflagellates with the flexibility needed to evolve the multitude of phagocytotic mechanisms that characterize this group of protists today.