Journal of Neuroscience, Vol 7, 1461-1469, Copyright © 1987 by Society for Neuroscience
The molecular structure of microtubule-associated protein 1A (MAP1A) in vivo and in vitro. An immunoelectron microscopy and quick-freeze, deep- etch study
Y Shiomura and N Hirokawa
We studied the distribution of microtubule-associated protein 1A (MAP1A) in
Purkinje cell dendrites by means of electronmicroscopic
immunocytochemistry, using a monoclonal antibody (McAb) against MAP1A; this
was combined with the observation of the 3-dimensional cytoskeletal
ultrastructure in dendrites via the quick-freeze, deep- etch technique
(QF-DE). We prepared a McAb against rat brain MAP1. This McAb recognized
MAP1A on a nitrocellulose filter through use of the immunoblotting method,
and stained immunofluorescently Purkinje cell perikarya, dendrites, and
axons. Using the McAb, we labeled rat cerebellum extracted with Triton
X-100 and simultaneously fixed with aldehyde, followed by gold-labeled
rabbit anti-mouse IgG. Gold particles were attached to the filamentous,
fuzzy materials, mostly those connected to microtubules (MTs), but were
hardly localized on those attached to neurofilaments (NFs). The
3-dimensional cytoskeletal ultrastructure of fresh Purkinje cell dendrites
was revealed by QF-DE. In Purkinje cell dendrites, MT was a predominant
cytoskeletal element, whereas only a few NFs were found. Fine, elaborate
cross-bridges filled up the interstices among MTs, and between MTs and
other cellular components. Cross-bridges linking MTs to one another were
composed mainly of a fine filamentous structure, frequently branching and
anastomosing at several sites, and appeared somewhat granular. We ensured
that the cross-bridges observed in saponin-extracted tissues were not a
result of artifactual condensations or precipitations of soluble proteins
during deep etching. The molecular structure of MAP1A was further
investigated by the rotary shadowing technique. The affinity-purified MAP1A
was a long, thin, filamentous, and very flexible molecule.(ABSTRACT
TRUNCATED AT 250 WORDS)