Microdensitometer-computer correlation analysis of two distinct, spatially segregated classes of microtubule bridges in Allogromia pseudopodia.
Previous video-light microscopic studies have shown that the microtubule bundles in the pseudopodia of foraminiferan protists display several types of movements in vivo, including active bending, zipping/splaying, and axial translocations. To gain insight into the types and arrangement of microtubule-associated proteins (e.g., mechanoenzymes, crosslinkers) in such a highly dynamic system, we employed microdensitometric-computer correlation methods to analyze, quantitatively, intermicrotubule bridges in thin-section electron micrographs of Allogromia laticollaris and Allogromia sp. (strain NF). Two distinct bridges occupying mutually exclusive zones between adjacent microtubules were identified. Type I bridges displayed a single axial repeat (34 nm for A. laticollaris and 28 nm for Allogromia sp.) and Type II bridges showed a typical 12-dimer helical superlattice pattern. In A. laticollaris, the two types of bridges were morphologically distinct: Type I bridges were aligned perpendicular to the microtubule wall and were 23-nm wide with an electron-lucent core; Type II bridges were irregular filaments projecting from the microtubules at various angles. When compared with the known distribution of microtubule-associated proteins in other systems, our findings indicate that, in vivo, Allogromia pseudopodial microtubules are decorated with MAP2-like bridges interrupted by discrete clusters of a dynein-like component.
Jensen
C G
CG
Department of Anatomy, School of Medicine, University of Auckland, New Zealand.
Bollard
S M
SM
Jensen
L C
LC
Travis
J L
JL
Bowser
S S
SS
D000818:Animals; D003198:Computer Simulation; D003720:Densitometry; D056890:Eukaryota / Q000648:ultrastructure*; D008854:Microscopy, Electron; D008870:Microtubules / Q000648:ultrastructure*