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Fig. 4. pbl mutant embryos have a mesodermal cell migration defect. (A,B)
Transverse sections of in situ hybridisations with a twi antisense
RNA probe. (A) In late stage 10 wild-type embryos, the mesodermal cells have
dissociated and migrated dorsally to form a uniform layer beneath the ectoderm
(arrows indicate dorsalmost mesodermal cells, which lie adjacent to the
dorsalmost epidermal cells). (B) In a similarly staged
pbl2/pbl3 mutant embryo, the mesodermal cells
appear aggregated and have failed to complete dorsolateral migration (arrows
indicate the dorsalmost epidermal cells). (C) A stage 10, wild-type embryo
stained for F-Actin. Mesodermal cells have formed a monolayer beneath the
ectoderm. (D,E) Equivalently staged pbl2/pbl3
embryos, in which mesoderm spreading is defective. (F) A stage 10
pbl2/pbl3 embryo expressing GFP-Actin driven by
twi-GAL4 visualised with an anti-GFP antibody. Similar to D,E, the
spreading of the mesoderm is defective. (G) A stage 10,
pbl2/pbl3 embryo co-expressing wild-type PBL
and GFP-Actin with twi-GAL4 visualised with an anti-GFP antibody. The
dissociation and migration of the mesodermal cells has been rescued, such that
the mesodermal cells form a uniform layer beneath the ectoderm similar to wild
type. (G') The same embryo showing multinucleate cells in the ectoderm
(arrows).