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Fig. 7. TC/TC conceptuses exhibit defects in
heart and yolk sac. (A) Equivalent sections (insets in a and b) of
+/+ (a) and TC/TC (b) 6-s hearts show a
reduction in the pericardial cavity (pc) and both myocardial (my) and
endocardial (ec) layers in TC/TC. A few
Flk1-positive cells (arrowheads) were observed in the
TC/TC mutant endocardium. Scale bar in b: 100
µm for a,b. (B) Yolk sacs were isolated from EHF-stage conceptuses
(a) and cultured for 24 hours to produce yolk sac spheres. 1 and 2 indicate
the level of cuts made in the conceptus to isolate the yolk sac (see Materials
and methods). (b) Histological section through a +/+ yolk sac sphere. (c-g)
Higher magnification of yolk sac vasculature in +/+ (c),
TC/TC (d,e) and TC/+ (f,g)
spheres. Flk1-positive endothelium (arrows) was discontinuous and the endoderm
layer was not uniformly thick in TC/TC yolk
sacs (compare d and e with wild type in c). Presumptive hematopoietic
precursor cells (black arrowheads) were present between
TC/TC yolk sac layers, but remained in a tight
cluster and contained pyknotic cells (red arrowheads). (f,g) Two different
regions of the same TC/+ sphere reveal an intermediate
phenotype (see text). Abbreviations as in
Fig. 1. ht, heart; en, endoderm
of foregut; se, surface ectoderm; mt, mesothelium; `x', former exocoelomic
cavity of the intact conceptus. Scale bar in d: 100 µm for c-g; 400 µm
for b.
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