Biology Reference
In-Depth Information
Fig. 18.2 Distribution of
microtubules in cultured
embryonic rat hippocampal
neurons in the context of
dendritic development. a A
dendrite-bearing neuron
immunostained for
microtubules. The image is
presented in a quantitative
scale in which white indicates
the highest intensity, black
indicates the least, and shades
of gray indicate intermediate
levels. The cell body contains
high levels of microtubules
within a discrete region. This
region is continuous with
high levels of polymer within
the developing dendrites.
Adapted from Sharp et al.
(
1995
). Bar, 20 lm.
b Schematic illustration of a
dendrite-bearing neuron,
depicting a stream of
microtubules emerging from
the centrosome and flowing
into the developing dendrites.
The centrosome itself
occupies a location that is
roughly central in reference
to developing dendrites
minus ends of microtubules (Corthesy-Theulaz et al.
1992
). As a general but not
universal principle, very little gamma-tubulin is located in cells anywhere except
the centrosome (or other microtubule-organizing centers) and de novo nucleation
of microtubules is suppressed in the cytoplasm relative to nucleation from such
structures (Alberts et al.
2007
). Nucleation from structural templates also serves
the purpose of constraining the lattice of the microtubule to a consistent number of
protofilaments (typically 13 in most vertebrate cells) (Evans et al.
1985
) although
there are other factors that influence protofilament number as well (Fourniol et al.
2010
; Moores et al.
2004
).
The centrosome is generally positioned in the center of the cell (hence the name
centrosome) and this location is determined by a balance of forces that act upon the
microtubules that emanate from the centrosome while remaining attached to it
(Euteneuer and Schliwa
1992
; Vallee and Stehman
2005
). Without the attached
microtubules, there is nothing for molecular motors to pull on in order to center the
