R. Weinberger et al., THE MOLECULAR COMPOSITION OF NEURONAL MICROFILAMENTS IS SPATIALLY ANDTEMPORALLY REGULATED, The Journal of neuroscience, 16(1), 1996, pp. 238-252
The actin-based microfilament system is thought to play a critical rol
e in neuronal development. We have determined specific changes in the
composition of microfilaments accompanying neuronal morphogenesis. By
using specific antibodies against the isoforms for tropomyosin (Tm) (T
m-5 and TmBr-1/ -3) and actin (beta- and gamma-actin), we found that d
uring early morphogenesis in vivo immature growing axons contain beta-
and gamma-actin and Tm-5. In particular, Tm-5 is exclusively located
in the immature axonal processes relative to the neuronal cell body. I
n contrast, beta-actin and Tm-5 are absent in mature, quiescent axons.
This developmental loss from axons is associated with an approximatel
y twofold downregulation of beta-actin and Tm-5 levels in the brain; g
amma-actin levels do not change, and this molecule is widely distribut
ed throughout neurons during development. The loss of beta-actin and T
m-5 from axons is accompanied by a progressive appearance of TmBr-1/-3
. This apparent replacement of Tm-5 with TmBr-1/-3 occurs over a 2 d t
ime period during rat embryonic hindbrain development and is conserved
in evolution between birds and mammals. The loss of Tm-5 from axons i
nvolves a redistribution of this molecule to the cell soma and dendrit
es. These findings suggest that specialized microfilament domains are
associated with the development and maintenance of neuronal polarity.
We conclude that these Tm isoforms and p-actin are subject to specific
patterns of segregation associated with axonal development and neuron
al differentiation. This provides a potential molecular basis for the
temporal and spatial specificity of microfilament function during neur
onal differentiation.