Euglena gracilis A Model for Flagellar Surface Assembly, with Reference to Other Cells That Bear Flagellar Mastigonemes and Scales

The flagella of euglenoids consist of a rich assemblage of surface appendages precisely positioned with respect to each other and to axonemal components. The presence of these appendages (mastigonemes or flagellar hairs) and the occurrence of flagellar scales in certain “green” flagellates provide visible evidence that the flagellar surface in these forms is constructed and maintained to a large extent independently from the adjacent cell surface. Thus, flagellar assembly may require both the specific targeting of some proteins to and the exclusion of other proteins from the flagellar surface. In the case of some green flagellates, for example, there may be two layers of geometrically arranged scales on the flagella, each layer may consist of a different kind of scale, the layers do not intermix, and the flagellar scales differ markedly from the scales (up to three different kinds) found on the cell body. Organisms with scales and mastigonemes have served as useful models in helping to understand how flagellar surfaces are assembled and how surface molecules are stabilized or held in position along a presumably fluid flagellar membrane.