doi: 10.1242/10.1242/jcs.00065
The growth of Drosophila bristles and laterals is not restricted to the tip or base
Xiaoyin Fei*,
Biao He
and
Paul N. Adler
Biology Department and Cancer Center, University of Virginia,
Charlottesville, VA 22903, USA
* Present address: University of North Carolina Medical School, Chapel Hill, NC
27514, USA
Present address: Thoracic Oncology Laboratory, UCSF Cancer Center, University
of Califonia, San Francisco, CA 94115, USA
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Fig. 1. Graphs of lateral growth in vivo. The upper panel shows growth as a
function of time for a lateral that was followed for 18 hours. The lateral
extended from less than 10 µm to more than 80 µm during this time
period. The lower panel shows the width of this lateral at three distances
from the base of the lateral. Rectangles are for a point 5 µm from the
base, triangles 15 µm from the base and ovals 35 µm from the base. This
lateral was nicely oriented parallel to the plan of focus and it did not move
much during the experiment allowing it to be followed for longer than most.
Some of the scatter in the data is probably due to slight variations in the
orientation of the lateral, which both altered its length and made it
difficult to measure being slightly out of focus.
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Fig. 2. Lateral tip shape changes during elongation. Growing laterals of various
lengths are shown. (A) 3 µm lateral; (B) 9 µm lateral; (C) 17 µm
lateral; (D) 29 µm lateral; (E) 40 µm lateral; (F) the distal part of a
71 µm lateral; (G) the distal part of a 123 µm lateral. The line drawing
in panel A is a tracing of the outline of the lateral in that panel. The
remaining line drawings were made by uniformly stretching the line drawing
from A proportional to the growth of the lateral in the panel. Note that
simply stretching approximates the change in shape seen with growth. Panels D,
E and F are from a time-lapse series of a single lateral as are panels B and
C. Panels A and G are from the same experiment and were chosen to widen the
range of lengths.
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Fig. 3. Early stages of lateral growth. Panels A-D show a time-lapse series just
prior to the start of outgrowth. The lateral is shown at 25 (A), 26 (B), 27
(C) and 28 (D) hours after white pupae formation (awp). Panels E-I show a time
lapse series for the early stages of lateral outgrowth. The lateral is shown
at 28 (E), 29.5 (F), 31 (G), 33 (H) and 35 (I) hours awp. Panel J is a cartoon
representation of the early stages in lateral outgrowth. From top to bottom of
panel J are drawings representing aristae at 20, 25, 28, 31 and 35 hours awp.
Note, as lateral development proceeds the cells become highly elongated along
the proximal distal axis and the nuclei move proximally
(He and Adler, 2001 ). The
distorted shape of the 35 hour cell is meant to represent this.
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Fig. 4. Bristle pictures. Shown are ocellar bristles from Oregon R
(Ore R, wild-type, injected with saline), Ore R injected
with vinblastine (VB), Ore R injected with latrunculin A (Lat-A),
Sb/+ and Sb +/+ Bsb2 flies. All micrographs are
at the same magnification (x360). Note the multiply split bristle that
resulted from latrunculin A injection. Note the very short and fat bristles
that resulted from VB injection. In the extreme VB-induced phenotype panel
note that all that is left of some bristles is a pigmented `blob'
(arrows).
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Fig. 7. FRAP of GFP-actin. Maximum projections of confocal stacks of scutellar
bristles from a hs-GAL4/+; UAS-GFP-actin pupa are shown.
Panel A shows the bristles immediately after bleaching. The other micrographs
are equivalent images taken with a 1 hour interval. Panels A, C and E contain
an insert showing a higher magnification view of the bleached/non-bleached
boundary. Note that the distinction between the bleached and unbleached region
remains obvious for the entire 5 hour experiment. The retrograde movement of
the actin is also obvious. Panel G is a plot of the distance from the distal
edge of the proximal unbleached region to the boundary of the socket cell (see
arrow). This approach was taken as the actin bundles extend down into the cell
and their proximal end was sometimes out of the range of z sections we
obtained. The measurements in G are for the bristle on the right. This
distance decreased over time and provides a measure of the retrograde movement
of actin filaments. Note that the bleached/unbleached border becomes uneven
over time due to the differential retrograde movement of individual actin
bundles. Panel H is a plot of the fluorescence intensity at locations
approximately 5 µm either distal or proximal to the bleached/unbleached
border. Note that the proximal region of these bristles was substantially
brighter than the distal region, which may be a consequence of the heat shock
hours prior to the start of the experiment. There is a slight decrease in the
intensity of the bright proximal unbleached region and a slight increase in
the intensity of the bleached regions over time.
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Fig. 6. FRAP of tubulin-GFP. Maximum projections of confocal stacks of a scutellar
bristle from a UAS-GFP-tubulin/+; neur-GAL4/+ pupa are
shown. Prior to bleaching (A) the entire bristle shows strong fluorescence.
The bristle immediately after bleaching is shown in B and the recovery of
fluorescence is shown in micrographs taken at 5 minute intervals. Panels B, D
and H also contain an insert showing the bleach/non-bleached boundary at a
higher magnification. Shown below is a graph plotting fluorescence intensity
as a function of time. The intensity was measured from the maximal projections
(with no other manipulation) as locations approximately 5 µm proximal or
distal to either the proximal or distal bleached/unbleached border. Note the
gradual increase in fluorescence in the bleached region and the gradual
decline of fluorescence in the unbleached region.
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Fig. 8. The movement of central cytoplasm in developing bristles. Shown is a
hs-GAL4/+; UAS-GFP-tubulin/+ pupae. At the start of the experiment
the distal segment of the bristle was bleached. The arrow points to the distal
tip of the bristle and the arrowhead to a faintly fluorescent region in the
proximal central region of the bristle. Below is a graph that plots the length
of the bristle (rectangles) and the distance from the distal edge of the
faintly fluorescent region to the tip of the bristle (ovals) as a function of
time. The bristle grows more than 20 µm during the experiment. The faintly
fluorescent region moves distally at a slightly faster rate than the tip so
that the distance from the faint region to the tip decreases slowly over
time.
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© The Company of Biologists Ltd 2002
growth is
restricted to the distal tip (represented by filled areas). This leads to no
movement of the branch-points but an increase in the lengths of the arms. In
ß growth is restricted to the base of the lateral. This leads to an
increase in the distance from the base of the lateral to the proximal
branch-point. No increase is seen in the length of the arms or of the distance
between the branch-points. In 
growth is distributed throughout the
lateral and there is an increase in the distance of the branch points to the
base, between the two branch points and in the lengths of the arms. In 
growth takes place at both the base and at the distal tip. There is an
increase in the distance from the base to the branch points but no increase in
the distance between the branch points. There is an increase in the lengths of
the arms. Our observations routinely fit the model shown in