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Fig. 1. X-Gal staining and Islet1 in situ hybridisation or
immunofluorescence in Mlc1v-nlacZ-24 and Mlc3f-nlacZ-2E
mouse embryos between the 4- and 7-somite stages. (A-F) X-Gal
staining for β-gal (blue) and whole-mount in situ hybridisation for
Islet1 (Isl1) transcripts (purple) on
Mlc1v-nlacZ-24 (A,C,E) and Mlc3f-nlacZ-2E (B,D,F) embryos.
β-gal activity in the Mlc1v-nlacZ-24 line marks the AHF and its
myocardial derivatives, whereas in the Mlc3f-nlacZ-2E line it marks
differentiated myocardial cells. Islet1 is transcribed in splanchnic
mesoderm. Labelling by the Islet1 probe, rostral to the heart-forming
region, under the head folds, marks neurectoderm of the future central nervous
system. Islet1 is also expressed in endoderm. Embryos at the 4-(A,B),
6-(C,D) and 7-(E,F) somite stages. Lines in A,C,E indicate plane of sections
in A' and A'', C' and C'', E'. (A'') Merge of
Hoechst and Islet1 immunofluorescence. (C',C'') Merge of Hoechst,
β-gal and Islet1 immunofluorescence. The arrow in C' points to a
double-positive cell co-expressing Mlc1v-nlacZ-24/Fgf10 and
Islet1. PC, pharyngeal cavity. The arrows in C'' indicate the
Islet1-positive mesoderm near the intraembryonic coelomic cavity. The
arrows in E indicate the sinus venosus (sv) and the underlying endoderm (En).
The arrowhead in E' indicates the heart tube that is negative for
β-gal, and the arrow points to the endoderm adjacent to the foregut,
which is also positive for Islet1 transcripts. CC, cardiac crescent;
HT, heart tube; NT, neural tube. Black rectangles in A,B,C,D indicate the
regions used for explants. L, left side of embryo; R, right side of embryo.
Beneath is shown a schematic summary of expression of Islet1 and the
Mlc1v-nlacZ-24 (Fgf10) transgene in the second heart field
(SHF) and anterior heart field (AHF), respectively, and of myosin in
cardiomyocytes of the cardiac crescent (CC) and heart tube (HT); p,
posterior.
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