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Fig. 4. Two different MT subsets coexist inside the oocyte. Optical planes
from confocal Z-sectioning of oocytes stained with anti-Khc according to the
sectioning experimental setup presented in A. The numbers 1-5 represent
the position of representative optical sections in a wild-type oocyte (1
represents the most proximal plane close to the cortex, and 5 the most distal
plane). (B) Stage 6, (C) stage 7, (D) stage 8 and (E) stage 9 oocytes. Two MT
subsets can be distinguished according to orientation and stage-dependent
changes. The DV subset: throughout oogenesis, cortical MTs oriented along the
DV axis could be observed. At the proximal and distal cortices, MTs running
parallel to the DV axis can be seen from stage 7 on (C1, C5; D1, D5; E1, E5;
white arrowheads) and to a lesser extent in stage 6 (B1, B5; white
arrowheads). The AP subset: (B) Before oocyte repolarization at stage
6, MTs extend along the cortex and fold back slightly at the anterior (B2 and
B3, red arrowheads). The nucleus is encapsulated by MTs and short fibers point
from the nucleus toward the anterior (B3 and B4, arrows). (C) By stage
7, long MTs are rolled up in the shape of a `diaphragm' in the center of the
oocyte (C2-C4). MT bundles emanating from the perinuclear region project
toward the cortex (C2, arrow). The center of the cytoplasm contains only a few
MT fibers. (D) In stage 8, the `diaphragm' has opened and MT bundles
project from the anterior in the AP direction (D2, arrow). MTs bundle at the
posterior and join the center (D3, arrow). Transverse sections of MTs appear
as dots on the ventral side of the oocyte (D3, arrowhead). Free MT ends are
found in the center of the oocyte (D4, arrowheads). (E) In stage 9, the
central MTs originate from the anterior and the oocyte nucleus (E2 and E3,
arrows). One or two thick bundles that resemble a `horseshoe'-like pattern
orient in the AP direction (E4, arrows). (B6,C6,D6,E6) Schematic
representations of the MT distribution at mid-oogenesis. (B6) MT distribution
before repolarization is shown in blue. After repolarization, the invariant DV
subset is depicted in black, the dynamic AP subset in red. (C6) Stage 7
(`diaphragm' state). (D6) Stage 8 (`open diaphragm' state). (E6) Stage 9
(`horseshoe' state). (F-H) Living egg chambers expressing Tau-GFP. (F)
The cortical DV (arrowhead) subset can be detected in living stage 8 oocyte.
(G) Stage 10A oocyte, in which two MT bundles in AP orientation can be seen in
the center (arrows). (H) Stage 11: thin bundles of MTs can be detected in the
DV orientation (arrowhead) close to the cortex. Red dotted lines mark the
outline of the oocyte. Asterisk, location of oocyte nucleus. Scale bar: 20
µm.
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