Microtubules are the main component of the reticulopodial
networks (RPNs) of most foraminifers and the closely related
fresh water organism Reticulomyxa. They share remarkable high
dynamics in the assembly and disassembly of their
microtubule-cytoskeletons. Obviously, they have developed
specific mechanisms for this fast rearrangement, which are at
least ten times faster as in most other organisms . This may
be partly due to the fact, that their microtubular systems reveal
not a complete disassembly into heterodimeric subunits, but only
a partial disassembly into helical filaments respectively
We succeeded in transforming the microtubules of the RPN of Reticulomyxa directly into helical filaments by extracellular application of 20 mM MgCl2. Further investigation showed, that the presence of magnesium in the transformation assay is not essential, since a variety of cations with approximately the same ionic strength led to similar results. The transformation is reversible by rinsing with salt-free media, since cytoplasmic streaming and also organelle transport was immediately reconstituted.
We conclude, that the microtubules of Reticulomyxa can be directly transformed into helical filaments or vice versa, as originally proposed for the foraminiferan Allogromia by Hauser and Schwab , and as recently confirmed by Welnhofer and Travis . Since the reaction is independent of specific ions, we suggest a common pathway for the transformation to helical filaments by the action of cations on microtubules via the cell membrane.
References: 1. Chen, Y. T. & Schliwa, M. Cell Motil. Cytoskel. 17, 214-226 (1990). 2. Hauser, M., Lindenblatt, J. & Hülsmann, N. Eur. J. Protistol. 25, 145-157 (1989). 3. Hauser, M. & Schwab, D. Cytobiologie 9, 263-279 (1974). 4. Welnhofer, E. A. & Travis, J. L. Cell Motil. Cytoskel. 34, 81-94 (1996).