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Fig. 4. mRNA expression patterns during early embryogenesis. (A-U) Longitudinal
median sections of developing wild-type seeds. Bound probe is stained brown.
The clonal boundary resulting from the division of the zygote is marked (black
arrowheads). The demarcation line between the apical and central domain of the
early embryo is indicated (open arrowheads). The white asterisks indicate
brown color of the seed coat independent of the staining reaction. (A-G) In
situ hybridization with a WOX2 antisense probe. (A) WOX2
mRNA is detected in the zygote. (B) After the first zygotic division,
WOX2 expression is restricted to the apical daughter cell, and absent
from the basal one. (C) WOX2 mRNA is expressed in all cells of the
4-cell embryo proper (unspecified arrow), but not in the suspensor. (D)
WOX2 mRNA is expressed in the apical domain of the 8-cell embryo, but
not in the central domain, the suspensor or the hypophysis. (E-F) At the
16-cell stage (E) and in early globular embryos (F), WOX2 mRNA
remains restricted to the apical embryo domain. (G) In heart stage embryos,
WOX2 expression is only weakly detected in epidermal cells of the
central domain (arrow). (H-N) Hybridization with a WOX9 antisense
probe. (H) No expression is detectable in the zygote. (I) WOX9 mRNA
is detected only in the basal daughter cell of the zygote. (J) At the 4-cell
stage, WOX9 expression is restricted to the hypophysis. (K) In 8-cell
embryos, WOX9 mRNA is expressed in the central embryo domain and in
the hypophysis. (L) In 16-cell embryos, WOX9 mRNA expression is
restricted to epidermal cells of the central domain and to the hypophysis
(arrows). (M) In mid globular embryos, WOX9 expression is detected in
epidermal cells of the central domain, but not in the hypophysis (arrow). (N)
In heart stage embryos, WOX9 mRNA is only detected in a ring of
epidermal cells (arrow). (O-U) Hybridization with a WOX8 antisense
probe. (O) WOX8 mRNA is detected in the zygote. (P) After the first
division of the zygote WOX8 mRNA is exclusively found in the basal
daughter cell but not in the apical one. (Q,R) WOX8 expression marks
all suspensor cells of the 4- and 8-cell embryo, but is not expressed in the
embryo proper (unspecified arrow in Q). (S) At the 16-cell stage,
WOX8 mRNA is detected in all suspensor cells, including the
hypophysis. (T) In mid globular embryos, continuous strong WOX8
expression is detected in the suspensor, but there is no expression in the
derivatives of the hypophysis. (U) In heart stage embryos, WOX8 is
expressed in the suspensor and surrounding endosperm cells. a, apical daughter
cell of the zygote; ad, apical domain of the early embryo; b, basal daughter
cell of the zygote; cd, central domain of the early embryo; en, endosperm; hy,
hypophysis; su, suspensor; z, zygote. Scale bars: 10 µm (A-T): 20 µm
(U).
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