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A detailed study of the expression pattern of embryonic fibroblast growth factor (eFGF) during early Xenopus development has been undertaken using whole-mount DIG in situ hybridization. We show that the zygotic expression of eFGF is activated in the mesoderm of the early gastrula and is first visualized as a ring around the blastopore, with significantly higher levels of expression on the dorsal side of the embryo. As gastrulation proceeds, eFGF transcripts become increasingly abundant in the dorsal blastopore lip. In the early neurulaeFGF expression can be detected in the extreme posterior of the embryo around the closed blastopore and in the cells of the notochord. This latter result is significant and represents the first report of a Xenopus FGF that is expressed in the notochord. In addition, we show that during gastrula and neurula stages, expression of eFGF closely follows the expression of the Xenopus brachyury (Xbra) gene. During later development eFGF expression is localized to the tail-bud region and a stripe at the mid-brain/hind-brain junction. These data provide further evidence that FGFs play an important role in regulating the expression of brachyury in the developing mesoderm.
Fig. 1. eFGF and Xbra expression during development. IA,B,C,E,F,H,I,J,K and LI Embryos hybridized to eFGF antisense RNA. ID and GI Embryos
hybridized to Xbra antisense RNA IA and BI Vegetal views (dorsal is to the top) of stage 10.5 embryos showing eFGF expression in the mesoderm
of the marginal zone around the blastopore. The arrow indicates the position of the dorsal lip (bp) The specimen in (B) has been cleared. IC) shows
the cut surface of a stage 10.5 embryo that has been manually dissected along the dorsoventral midline ra reveal staining in the deep layers of the
marginal zone (dorsal is to the right and animal ra the rap) showing that there is a higher level of eFGF expression in the dorsal marginal zone (dmz)
than in the ventral marginal zone (vmz) (note the animal hemisphere has collapsed onto the vegetal yolk mass during processing). (DI Dorsovegetal
view of Xbra staining In the blastopore region and involuting dorsal mesoderm of a stage 1 7.5 embryo. IE) Oorsovegetal view showing high levels of
eFGF expression in the involuting dorsal mesoderm of a stage 17.5 embryo above the dorsal lip (dl) of the blastopore. (FI Posterior view of a stage
13 embryo (dorsal to the top) showing eFGF expression in the notochord (nee) and around the blastopore (bp). tG and H) Dorsal views of stage 13
embryos (anterior to the rap) showing expression of Xbra and eFGF respectively. in the notochord and posterior around the closed blastopore (bpJ.
(I) Posterior dorsal view of a cleared stage 23 embryo (anterior is into the page) showing eFGF expression in tail-bud (rib) and in the posterior notochord
(nee). {JI Side view of a cleared stage 23 embryo (anterior to the right) showing that eFGF expression is restricted to the extreme posterior of
the developing axis. The arrow shows the posItion Df the proctodeum (pcd). (K) Side view of the tail forming region from a cleared stage 31 embryo
showing eFGF expression in the chordoneural hinge (cnh) and posterior wall (pw) of the neuroenteric canal (nee). (L) Side view of a cleared stage 31
embryo showing a prominent stnpe of eFGF expression at the midbrain/hindbrain junction (mhj) (note the staining in the brain and branchial arch cavities
is background).
