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Fig. 4. A transplantation technique using SOX32 to target reagents to specific
germ layers. (A) Genetic pathway leading to endoderm formation.
SOX32 acts downstream of Nodals, their receptors (TAR) and receptor co-factors
(OEP) in endodermal specification. (B) Lateral view of foxa3
expression in a 24 hpf control embryo. Endodermal foxa3 expression
extends from slightly anterior of the AP level of somite one (arrowhead)
towards the posterior, there is also expression in the posterior tip of the
notochord. (C) foxa3 is not expressed in the endoderm of
SOX32-MO injected embryos, while notochordal expression in the tail is
retained. (D) Schematic of the transplantation technique using
sox32 to target donor cells to the endoderm. Donor cells from embryos
co-injected with SOX32 and GFP mRNA are placed along the blastoderm margin of
a SOX32-MO injected host. Following gastrulation, all endoderm is derived from
donor cells, which distribute along the ventral AP axis and exhibit
regionalized expression of an array of endoderm-specific markers, including
insulin (blue arrowhead). (E-H) Transplanted specimens in dorsal view
at 24 hpf. (E) insulin expression (arrowhead) in donor-derived
endoderm (green). (F) Normal 24 hpf foxa3 expression
(arrowhead) in donor-derived endoderm (green). (G) Normal pharyngeal
nkx2.3 expression. (H) nkx2.3 expression in
donor-derived endoderm; donor tissue has contributed to only the right side in
this example but AP patterning is normal.
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