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Fig. 6. Double homozygous mutant embryos fail to form a primitive streak and its
derivatives. Histological and wholemount in situ analysis of marker gene
expression in normal and
Lrp5-/-;Lrp6-/- mutant embryos at
7.0-7.5 dpc. Where possible, anterior is towards the left. For some mutant
embryos, the orientation is ambiguous. (A,B) Sagittal histological sections
stained with Hematoxylin and Eosin. In the normal embryo (A), mesoderm (me) is
apparent between the embryonic ectoderm (ee) and either the visceral endoderm
(ve) or definitive endoderm (de), and the amnion (am) has formed. In the
mutant embryo (B), no mesoderm or definitive endoderm is detected. (C,D)
Analysis of Bmp4 expression. A control embryo (C) shows expression in
the extra-embryonic mesoderm, whereas the mutant embryo (D) shows expression
in only a faint proximal ring (arrow). (E,F) Analysis of Fgf8
expression. A control embryo (E) shows expression at the primitive streak that
is absent in the mutant embryo (F). (G,H) Analysis of T expression. A
control embryo (G) shows expression at primitive streak that is lost in the
mutant embryo (H). (I,J) Analysis of Tbx6 expression. A control
embryo (I) shows expression at the primitive streak that is missing in the
mutant embryo (J). (K,L) Analysis of Wnt3 expression. A control
embryo (K) shows expression in the primitive streak and nascent mesoderm that
is lost in the mutant embryo (L). (M,N) Analysis of Lhx1 expression.
A control embryo (M) shows expression in the primitive streak, nascent
mesoderm, and the AVE. The mutant embryo (N) shows expression in a small
distal patch (arrow) that most probably corresponds to the AVE. (O,P) Analysis
of Hex expression. A control embryo (O) shows expression in the ADE.
The mutant embryo (P) shows reduced expression that most probably corresponds
to the AVE. (Q,R) Analysis of Cer1 expression. A control embryo (Q)
shows expression in the AVE and definitive endoderm. The mutant embryo (R)
shows reduced expression that most probably corresponds to the AVE. (S,T)
Analysis of Hesx1 expression. A control embryo (S) shows expression
in the anterior axial mesendoderm and overlying anterior neurectoderm. The
mutant embryo (T) shows greatly expanded expression that likely corresponds to
anterior neurectoderm. Photos taken at the same magnification are grouped as
follows: A,B; C,D,G,H,K-T; E,F,I,J.
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