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The formulation of the nervous system in vertebrate embryos involves extensive morphogenetic movements that include the folding of the neural tube and the migration of neural crest cells. Changes in cell shape and cell movements underlie neural morphogenesis but the molecular mechanisms involved in these processes in vivo are not well understood. Here, we show that a new member of the hepatocyte growth factor family, which we name Livertine, is expressed in frog embryos in neural cells including neural crest and midline neural plate cells which are undergoing pronounced morphogenetic movements. The ectopic expression of Livertine perturbs gastrulation and leads to positional changes in injected cells without apparently changing cell type. These results suggest that one of the normal functions of Livertine is the control of neural morphogenesis in the vertebrate embryo.
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9025073
???displayArticle.link???Mech Dev
Fig. 2. Expression of Livertine in the neural ectoderm of gastrula and neurula stage frog embryos. (A-C) Whole-mount in situ hybridization pictures of
the expression of Livertine in early gastrula (stage -10.5-11; A), late-gastrola (stage -12.5; B) and late gaswala/early neurula (stage -13-14; C) frog
embryos. In all cases dorsal side is up and arrows point to the sites of expression. Note the decreasing size of the blastopore (bp) during gastrulation, a,
anterior; p, posterior; md, midline neural plate (np) cells. (D,E) Expression of L/vert/ne in the superficial layer of the neural plate seen in a side view of
a whole-mount (D) at stage 11-11.5 and in cross section through the anterior region of a stage -14 embryo (E). Arrows point to sites of expression and
the brackets show the position of the different tissues, bp, blastopore; d, deep layer of the neural plate; en, endoderm of the archenteron (ar) roof; me,
axial mesoderm; n, notochord; ne, neural ectoderm; s, superficial layer of the neural plate; so, somite. (F) Dorsolateral view of the expression of Livertine
in the ectoderm (ec) of an early exogastrula (stage -15) in cells occupying the position characteristic for the notoplate, a, anterior in the ectoderm;
m, mesoderm; p, posterior in the ectoderm. Scale bar: (A,B,C,F) 240tim; (D) 60/~m; (E) 100#m.
Fig. 3. Expression of Livertine in late neurula, tailbud and tadpole stage embryos. (A) Livertine mRNA is detected in the migrating neural crest (nc) of
the head, in the eye (e) and in the dorsal neural tube (dnt). Expression in the crest is detected in the mandibular, hyoid and branchial groups (from
anterior to posterior, left to right, respectively). These three groups can be clearly seen in the bottom embryo (stage -20). Dorsal side is up for the
embryo on top (stage -22) and the embryo on the bottom is a more lateral view. (B) Expression of Livertine in the bead of a stage -30 tadpole showing
its mRNA in cells of the branchial arches (ba), frontonasal process (fn), the retina of the eye (e), the telencephalon (t), ventraldiencephalon (vdi) and
ventralmidbrain (vmb). (C) Unilateral view of a cross section of the head of a stage -36 tadpole showing the expression of Livertine in the ventraldiencephalon (vdi) and in the ciliary marginal zone (CMZ) of the retina. (D) Cross section through the posterior spinal cord of a stage -36 tadpole
showing the presence of Livertine in the cells of the floor plate (fp) and in those of the dorsal neural tube (dnt). The notochord (n) is unlabeled. (E)
Side view of the tail of a stage -30--32 embryo showing the expression of Livertine in the newly formed floor plate (fp), dorsal neural tube (dnt) and in
the ventralfin (vf). Expression is also detected throughout the neural tube (nt) in the most posterior region, n: notocbord. (F) Side view of the trunk of
a stage ~36 embryo showing the expression of Livertine in the mesenehymal cells of the dorsal fin (df). These cells are scattered throughout the fin.
Note also the absence of expression in the floor plate (fp). Brackets denote the position of tissues behind the segmented somites, dnt, dorsal neural
tube; n, notochord; nt, neural tube. (G) Side view of the hindbrain (hb) at larval stages (stage ,-40) showing expression of Livertine at rhombomere
centers. Numbers denote rhombomeres. The dark spots anterior to rhombomere 1 and adjacent to rhombomere 6 are pigment cells. Scale bar: (A)
450#m; (B) 170/~m; (C,D) 50#m; (E,F) 70#m; (G) 540#m.
Fig. 4. Morphological defects observed in embryos injected with Livertine. (A) Side view of a stage -36 tadpole injected with plasmids driving the
expression of Livertine into dorsal blastomeres at the 4-cell stage. The arrow points to the head region which is deformed and small, a, anterior; p,
posterior. (B) Cross section through the hindbrain region of an embryo similar to that shown in (A) displaying a ventrally displaced notochord (n). The
arrow points to the presence of axons at the ventral midline of the neural tube. The ventral displacement of the notochord lead to the absence of floor
plate differentiation anteriorly. This was confirmed by labeling with anti-HNF-3fl antibodies (not shown), ov, otic vesicle. (C) Embryos injected with
Livertine (bottom) showing the presence of an open blastopore (arrow). The embryo on top is a normal uninjected control. The middle row shows
dorsal views whereas the bottom row shows side views of affected embryos injected with Livertine. Head and tail structures were sometimes detected.
Scale bar: (A) 260/zm; (B) 60/~m; (C) 440/~m.
Fig. 5. Effects of Livertine of cell position. (A,B) Pattern of RLDx fluorescent labeling in embryos (stage -14-15) injected with RLDx alone into
blastomere B1 at the 32-ceil stage (A) and in those similarly injected with RLDx and Livertine mRNA (B). In both cases dorsal views are shown. Note
the greater scattering of cells (arrows) detected in embryos injected with Livertine. (B) Pattern offl-gal expression in embryos (early stage 9) injected
with plasmids driving the expression of LacZ only (C) or LacZ plus Livertine (D) into a small area of the animal pole at the 2-4-cell stage. In both
cases views of the animal pole are shown. Some embryos show damage in their ventral sides that occurred during preparation for photography. Note
the greater dispersion offl-gal + cells in Livertine injected embryos. Scale bar: (A,B) 330/.tm; (C,D) 720/~m.
mst1 (macrophage stimulating 1) gene expression in the hindbrain of a Xenopus laevis embryo, assayed via in situ hybridization, NF stage 40, anteriorright, dorsal up.
Key: hb=hindbrain, 1-7 =rhombomeres R1-R7 ( rhombomere R8, posterior to R7 is not numbered)
