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Fig. 1. During gastrulation in zebrafish, cxcr4a is expressed in the
endoderm, and sdf1a and sdf1b are expressed in the
mesoderm. (A-D) cxcr4a expression was examined by
whole-mount in situ hybridization in cas mutant embryos and embryos
injected with either cas or nlacZ mRNA at the 80% epiboly
stage (8.3 hpf). Lateral views, dorsal to the right (A,B), and dorsal views,
anterior to the top (C,D). The salt-and-pepper endodermal expression of
cxcr4a is absent in the cas mutant, whereas expression in
others tissues is still detectable on the dorsal side (arrow in B) and is
faintly detectable (arrowheads in B) in other regions of the cas
mutant. Although the overexpression of nlacZ mRNA does not affect the
salt-and-pepper expression of cxcr4a, cas mRNA injection increases
the number of cxcr4a-expressing cells (arrow in D). (E-P)
sdf1a and sdf1b expression was examined in wild-type (WT)
and cas mutant embryos. Lateral views with dorsal to the right
(except for G,H,M,N). (E,F,K,L) At the 80% epiboly stage, neither
sdf1a nor sdf1b expression is altered in the cas
mutant embryos. (G,M) Optical cross-sections (OS) of 80% epiboly stage embryos
show that expression of both sdf1a and sdf1b is present in
the hypoblast layer, but not in the epiblast layer (the epiblast layer is
indicated by the red dashed lines). Dorsal views, anterior to top. (H,N)
Confocal images of sagittal sections of 80% epiboly stage embryos by confocal
laser-scanning reflection microscopy
(Jékely and Arendt,
2007 ). Expression of both sdf1a and sdf1b (red)
is restricted to the hypoblast layer (arrowheads). y, yolk. (I,J,O,P) The
expression of sdf1a and sdf1b in WT embryos at 90% epiboly
(9 hpf) and tail bud (TB; 10 hpf) stages. As gastrulation proceeds, both
sdf1a- and sdf1b-expressing cells move to the dorsal side of
the embryo. (Q-S) sox17 expression in endodermal cells at 80%
epiboly, 90% epiboly and TB stages in WT embryos. Lateral views, dorsal to the
right. The regions of sox17-expressing endodermal cells from 80%
epiboly to TB stages (red dashed lines in Q-S) are comparable to those of
sdf1a- and sdf1b-expressing cells (red dashed lines in
E,I,J,K,O,P).
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A/p2, where
A=area and p=perimeter. Note that the differences between the misMO1 and
cxcr4aMO1 values, as well as the differences between the misMO1 and
sdf1MOs values, are statistically significant
(*P<0.01, Student's t-test). Error bars
represent the standard error. (E) Schematic representation of the
methods used to measure the angles of the filopodial processes relative to the
direction of migration of the endodermal cells. ±180° indicates
opposing the direction of migration. (F) Rose diagrams representing the
orientation of filopodial processes relative to the direction of migration.
The orientation of the filopodia from 4-5 randomly chosen cells was measured
at two consecutive time points (time interval, 10 minutes) from 9-10
independent movies in misMO1- (n=100 cells), cxcr4aMO1-
(n=99 cells) and sdf1MOs- (n=87 cells) injected
embryos. (G-I) The migration tracks of 10-11 individual endodermal
cells over a period of 30 minutes. The direction of migration is to the right
and the cell position was determined every 30 seconds. Scale bars: 20
µm.