Evidence for the existence of microtubule protein in the extracellular space of marine sponges.
The medulla region of sponges (= mesohyl) is only rarely dispersed with cells (approximately 25% of the total tissue volume). In vivo studies with a series of anti-cytoskeletal drugs revealed that taxol caused a significant contraction of intact specimens. Therefore, we investigated the possibility that microtubules are one component of the dynamic extracellular network in sponges, especially in the mesohyl. Using the sponge Geodia cydonium we found that most cells are not intracellulary stained in indirect immunofluorescence microscopy. However, all cells were brightly stained by the monoclonal antibody (mAb) at their plasma membranes. After incubating cryostat sections with a buffer, containing ATP, large (length up to 75 mum) aster- to filamentous-like structures became visible in the extracellular space of the mesohyl region. By three cycles of assembly and disassembly microtubules could be isolated from the extracellular material which were composed of alpha- and beta-tubulin (M(r): 55,000), several polypeptides within the M(r) range 55,000-82,000 (presumably tau proteins) and one protein of an M(r) higher than 100,000. Electron microscopical analysis revealed morphologically intact microtubules with typical side projections (very probably composed of microtubule-associated protein). Some aspects of the possible involvement of microtubules in the extracellularly localized displacement and motion network are discussed.
Reuter
P
P
Institut für Physiologische Chemie, Universität, Duesbergweg, 6500 Mainz, West Germany.
Dorn
A
A
Batel
R
R
Schröder
H C
HC
Müller
W E
WE