Luminal material in microtubules of frog olfactory axons: structure and distribution.

Abstract

The substructure and distribution of luminal material in microtubules of olfactory axons were studied in the bullfrog, Rana catesbeiana . By using numerous fixation methods, with and without osmium tetroxide, the luminal component was shown not to be an artifact of fixation. The material consists of globular elements 4-5 nm in diameter loosely arranged within the lumen in a discontinuous column . Counts of microtubules showing luminal material were obtained for axons in the proximal and distal ends of the olfactory nerve, and it was found that 16-18% more of the microtubules in the distal regions showed the luminal component . This raises the possibility that the material might be translocated within the microtubule lumen and tends to accumulate as it moves distally toward the axon terminal. In contrast to those of the olfactory axons, microtubules assembled in vitro from frog brain tubulin did not show luminal material . When microtubules in olfactory axons were depolymerized in situ by cold and calcium treatment and then induced to reassemble, most of those that were formed de novo showed empty lumina . Such evidence suggests that the luminal material is not an integral component of the microtubule . The hypothesis is discussed that material may be translocated within the lumina of microtubules. Furthermore, in the case of neuronal microtubules, the possibility is raised that they may serve as conduits for their own wall subunits .

Molecular Basis for Age-Dependent Microtubule Acetylation by Tubulin Acetyltransferase

“…Future experiments will clarify how TAT access is modulated by the presence of luminal particles. Interestingly, these particles disappear from the lumen of neuronal microtubules upon rapid disassembly and reassembly (Burton, 1984), suggesting a microtubule-age dependent accumulation process. In addition to providing a molecular basis for age dependent microtubule acetylation, our studies are also applicable to the microtubule binding behavior of other proteins with luminal localization found in neuronal microtubules and axonemes.…”

Ultrastructural studies of microtubules and microtubule organizing centers of the vertebrate olfactory neuron

“…3). One of the characteristics of axonal microtubules is the frequency with which one sees dense particles in their electron-lucent central regions (Burton, 1984), and this region, which is 12-15 nm across, is often referred to as the "lumen" of the microtubule. There can be no question that much translocation occurs along the outer surface of microtubules (5 in Fig.…”

“…The luminal material seen in microtubules of bullfrog olfactory axons is in the form of short strings of beaded elements 4-5 nm in diameter, and when these microtubules are induced to depolymerize and then repolymerize, the newly formed microtubules appear empty (Burton, 1984). This may indicate a rather loose association between the beaded elements and the walls of the microtubules.…”

Improved ultrastructural preservation of rat ciliary body after high pressure freezing and freeze substitution: A perspective view based upon comparison with tissue processed according to a conventional protocol or by osmium tetroxide/microwave fixation

“…High pressure freezing and freeze substitution of rat ciliary body and its iridial extension resulted in excellent preservation of intracellular components, the demonstration of central densities or cores in the microtubules not only of axons and glial cells, as previously described (Burton, 1984(Burton, , 1992Rodriguez Echandia et al, 19681, but also in other cells, such as ciliary epithelium, fibrocytes, and lymphocytes, being particularly noteworthy.…”