View larger version (88K):
[in this window]
[in a new window]
|
Fig. 4. Elimination of suboptimal stem cells and the accumulation of
pre-cancerous mutations. (A) Germaria of 1-week-old flies
homozygous for dmycP0 stained with anti-Hts (red) and
anti-pMad (green) to identify GSCs (arrows). Note that
dmycP0 mutant GSCs display a normal morphology.
(B-D) Mosaic niches containing dmycP0 mutant
(βGal-negative) and control GSCs (dmycP0/+;
βGal-positive, red) were generated and differentiating progeny was
followed over time. GSCs were identified by the presence of a round fusome
(anti-Hts staining, green) and their proximity to the terminal filament, or,
alternatively, by the lack of Bam expression (blue, see F). Four days after
clone induction (ACI), mosaic stem cell niches are observed (B). However, stem
cell niches become depleted of dmycP0 mutant GSCs over
time, visualized by βGal-negative cells distal from the niche. (C,D)
dmycP0 mutant cystoblasts (C) and cysts (D) 1 week and 2
weeks ACI, respectively, derived from formerly mosaic niches.
(E,F) GSC-GSC interaction is non-apoptotic. (E) Mosaic
germarium, containing control [dmycP0/+; βGal
positive (red)] and dmycP0 mutant GSCs, was stained with
anti-active Caspase 3 (green). Inset shows positive control staining (arrow)
for the same antibody in wild-type GSCs from heat-stressed flies (nuclei
stained with DAPI, red). (F) Competition between GSCs proceeds in the absence
of a fully active apoptotic pathway, i.e. in a background of dIAP-1
overexpression. Mosaic germarium, containing control
[dmycP0/+; βGal-positive (red)] and
dmycP0 mutant GSCs. Bam-GFP is shown in blue.
(G,H) Expression of tkvACT in the germline
prevents both loss of dmycP0 GSCs from the niche (black)
under competition with control dmycP0/+ GSCs (βGal,
red) (G) and differentiation of Dpmyc/+ stem cells (βGal, red)
when in competition with 4xdmyc mutant GSCs (black; H; note Hts
staining, green). (I) Mosaic niche containing
savshrp6B21 mutant (black) and control
savshrp6B21/+ (GFP-positive, green) GSCs. GSC progeny was
analyzed 2 weeks ACI. Anti-Hts, red. The savshrp6B21
mutant GSC gave rise to more offspring (see
Table 2), but did not expel the
control GSC. (J) Mosaic niche containing control
(bam 86/+) stem cells
(GFP-positive, green) and bam86
mutant (black) GSCs and their progeny 2 weeks ACI. Anti-Hts, red.
Bam86 mutant `GSC-like' cells
accumulate in the niche. (K-M) Diagrams illustrating the methods by
which tumor-promoting mutations may be established within a stem cell-based
adult tissue, i.e. a germarium containing wild-type stem cells (GSC, gray).
GSCs are attached to the cap cells (magenta) and divide asymmetrically to
produce cystoblasts (CB), which in turn will divide to form cysts. Mutations
affecting tumor-promoting genes take place originally in one stem cell but are
inherited by its progeny as shown in red. Mutations may establish within the
tissue by the following strategies. (K) `Settler' strategy. Mutant GSCs (red)
remain in the stem cell niche and produce differentiated progeny, usually at
higher rates than the wild-type GSCs (gray). The number of mutant GSCs does
not change. (L) `Squatter' strategy. Mutations expand among the stem cell
population, which leads to an increasing number of mutant GSCs, without
affecting total GSC numbers as wild-type cells are forced to differentiate and
are being replaced by mutant stem cells. (M) `Plague' strategy. Mutations
expand by increasing total stem cell-like numbers (black asterisks), thereby
producing a `plague of stem cell-like cells'.
|
CiteULike 
Complore 
Connotea 
Del.icio.us 
Digg 
Reddit 
Technorati 
Twitter What's this?
