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Fig. 8. Ectopic expression of UAS-Alk and UAS-jeb in the mesoderm
gives rise to different phenotypes. Wild-type embryos are shown in A,D,G and
L. (B,E,H) UAS-jeb is ectopically expressed with a twi-GAL4
driverline. (C,F,I,J,K,M) UAS-Alk is ectopically expressed with a
twi-GAL4 (C,F,I,M) or bap-GAL4 driver line (J,K). Founder
cells (f) are marked by rP298-lacZ expression (green in A,B,J,K).
(D-F) Fusion-competent myoblasts (fcms) are visualised by sns in situ
hybridisation. (B) Ectopic expression of UAS-jeb converts all cells
of the visceral mesoderm to founder cells. (E) sns expression is
absent in these cells of the visceral mesoderm. (H) The somatic mesoderm shows
no defects, as indicated by ß3tubulin antibody staining. (C) No visceral
founder cells can be detected by Fas3 staining of stage 11 embryos in which
UAS-Alk is ectopically expressed in the entire mesoderm. (F)
sns in situ hybridisation indicates that through the overexpression
of UAS-Alk the fcms of the somatic mesoderm are missing in stage 11
and only the band of the fcms of the visceral mesoderm remains. (I) The dorsal
and ventral somatic muscles in stage 16 show a fusion defect phenotype with
thin projections (arrow) and unfused myoblasts (arrowhead) as indicated by
ß3tubulin staining. When UAS-Alk is expressed only in the
visceral mesoderm with a bap-GAL4 driverline, which also carries
rP298-lacZ as founder cell marker, the founder cells of the visceral
mesoderm are still present and seem to be doubled in number (J,K). In contrast
to a single row in the wild type (A), a second row of founder cells is present
in these stage 11 embryos. The bands of both halves of the embryo are shown
(J,K). In the wild type, jeb is expressed in a continuous band in the
mesoderm (L), whereas upon overexpression of UAS-Alk in the entire
mesoderm the signal is reduced (M).
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