Cytoskeletal dynamics of Apedinella radians (Pedinellophyceae) I. Pre-division development and the formation of spine-scales and body scales

Specific events preceding cell division in the unicellular phytoflagellate Apedinella radians (Pedinellophyceae) were investigated ultrastructurally and by immunofluorescence microscopy. These events include the sequential formation and secretion of a duplicate set of elongate spine-scales, the duplication and development of basal bodies/flagella, the generation of two new dictyosomes at the future sites of spindle poles, and the constriction (not division) of chloroplasts. Actin and microtubules are involved in spine-scale formation, while actin alone appears to play a role during body scale formation. Both scale types are formed intracellularly within specialized vesicles located adjacent to the posterior cell membrane. The length of spine-scales is not limited by cell size, as they form within cell extensions. Following secretion, spine-scales remain attached below the equator of the cell, and are not deployed to their interphase positions until after the completion of cell division.