In the history of cytoskeleton research, primitive eukaryotes have always attracted the interest of individual scientists, for the simple reason that the variety of cell architectural blueprints at this basic evolutionary level is much higher than in the advanced, phylogenetically younger organisms. I.e., among lower organisms, there is an impressive number of examples with fundamentally different cell architectures, mechanisms of cell shape control, and locomotion. Studying any of these features in detail could provide invaluable informations on the basic mechanisms of cytoskeletal dynamics.
Pioneering research with new organisms could be a difficult task initially, however, many well known examples attest to the success of such an undertaking. For example, who would have anticipated that the egg of the brown alga (Fucus) would help us understanding the polarity axis determination in plants or that the giant internodal cells of the green fresh water alga (Nitella) would open new ways for the development of in vitro motility assays to study organelle movement along actin cables. Other successful algal, protistan and metazoan models for instance are Chlamydomonas, Dictyostelium, Physarum, Trypanosoma and gamete cells from the lower metazoans, amphibians and mammals.
The marine green alga Acetabularia is one of these primitive eukaryotes with unique, very interesting features. This giant, unicellular organism has originally been introduced to the cell biology laboratory by Hämmerling in the 1930s and has since been used by several labs for studying principle biological phenomena such as nucleus-cytoplasm interactions and cell morphogenesis. In the past 7 to 8 years our lab has put considerable energy into developing Acetabularia as an experimental model organism for the study of cytoskeleton structure and dynamics in plants.
Since the work of Noburo Kamiya in the 1960s, it has been known that the cytoplasm in this organism is engaged in a bidirectional type of streaming along multiple parallel tracks made of actin cables. The inhibitory effects of cytochalasin B on streaming suggested early on, that the tracks were made of actin filaments. However, methods for the visualization of the actin cytoskeleton had not been available at that time. It was not before the beginning of the 1980s that methods for the staining of cytoskeletal elements were introduced for plant cells and it was only in 1986 that a modification of this method was successfully employed on Acetabularia (Menzel 1986). A recent improvement of this method (Sawitzky et al. 1996) has enabled us to cut down on sample preparation time and to visualize the actin cytoskeleton in the finest extremities of the cell.