Dorsoventral Patterning of the Zebrafish Embryo
91
Fig. 3A-I. (A-F) Expression patterns of bmp2b, chordino (chd), and bmp4, detected via whole mount in situ hybridization. Dorsal is always to the right, ventral to the left. A,B Initial expression patterns of bmp2b (A lateral view, B animal view) and (C) chordino (animal view) at a late blastula stage, 2 h before
the onset of gastrulation. bmp2b transcripts are uniformly distributed in the
embryo with the exception of the dorsal marginal region, the presumptive Spemann organizer, which shows expression of chordino. Expression pattern of
bmp4 at the onset of gastrulation, lateral view, in a wild-type (D), a chordino
mutant (E), and a swirl/bmp2b mutant (F) embryo. Compared to wild-type
(D), the swirl/bmp2b mutant (F) displays a significant reduction in bmp4 transcription, indicating that bmp4 is a target of Bmp2 signaling, and that bmp4
mRNA levels reflect Bmp2b activity. In the wild-type embryo (D), bmp4 displays a graded expression pattern with mRNA levels progressively dropping
from ventral to dorsal, reflecting a gradient of Bmp2b activity. In the chordino
mutant (E), bmp4 displays a uniform expression throughout the embryo, indicating that instead of the establishment of a gradient of Bmp2b activity, the initial broad and uniform pattern is maintained. G-I Long-range signaling of
Chordino, revealed in a chimeric embryo after transplantation of a few (darkly
labeled) wild-type cells into the Spemann organizer of a chordino mutant embryo (H). Whole mount in situ hybridization of wild-type control (G),
chimeric (H), and chordino mutant control embryo (I) with eve} probe (Joly et
al. 1993), marking presumptive ventral mesodermal cells at a midgastrula
stage, 2 h after the transplantation. View from vegetal pole, dorsal to the right.
The dorsal boundary of the eve} expression domain is marked by arrows. In
the wild-type embryo (G), eve} expression is restricted to the ventral side,
while in the chordino mutant, the eve} expression domain is extended far into
the dorsal side. Transplantation of a few wild-type cells leads to a significant
veutral retraction of the extended eve} expression domain. Lateral regions
many cell diameters away from the wild-type cells, indicate that Chordino signaling has a long-range effect, spreading over approximately a quarter of the
entire dorsolateral axis within 2 h
91
Fig. 3A-I. (A-F) Expression patterns of bmp2b, chordino (chd), and bmp4, detected via whole mount in situ hybridization. Dorsal is always to the right, ventral to the left. A,B Initial expression patterns of bmp2b (A lateral view, B animal view) and (C) chordino (animal view) at a late blastula stage, 2 h before
the onset of gastrulation. bmp2b transcripts are uniformly distributed in the
embryo with the exception of the dorsal marginal region, the presumptive Spemann organizer, which shows expression of chordino. Expression pattern of
bmp4 at the onset of gastrulation, lateral view, in a wild-type (D), a chordino
mutant (E), and a swirl/bmp2b mutant (F) embryo. Compared to wild-type
(D), the swirl/bmp2b mutant (F) displays a significant reduction in bmp4 transcription, indicating that bmp4 is a target of Bmp2 signaling, and that bmp4
mRNA levels reflect Bmp2b activity. In the wild-type embryo (D), bmp4 displays a graded expression pattern with mRNA levels progressively dropping
from ventral to dorsal, reflecting a gradient of Bmp2b activity. In the chordino
mutant (E), bmp4 displays a uniform expression throughout the embryo, indicating that instead of the establishment of a gradient of Bmp2b activity, the initial broad and uniform pattern is maintained. G-I Long-range signaling of
Chordino, revealed in a chimeric embryo after transplantation of a few (darkly
labeled) wild-type cells into the Spemann organizer of a chordino mutant embryo (H). Whole mount in situ hybridization of wild-type control (G),
chimeric (H), and chordino mutant control embryo (I) with eve} probe (Joly et
al. 1993), marking presumptive ventral mesodermal cells at a midgastrula
stage, 2 h after the transplantation. View from vegetal pole, dorsal to the right.
The dorsal boundary of the eve} expression domain is marked by arrows. In
the wild-type embryo (G), eve} expression is restricted to the ventral side,
while in the chordino mutant, the eve} expression domain is extended far into
the dorsal side. Transplantation of a few wild-type cells leads to a significant
veutral retraction of the extended eve} expression domain. Lateral regions
many cell diameters away from the wild-type cells, indicate that Chordino signaling has a long-range effect, spreading over approximately a quarter of the
entire dorsolateral axis within 2 h