Fig. 4

Overexpression of slit2 mRNA impairs migration of the prechordal mesodermal cells and the ventral diencephalic cells in the zebrafish embryo. (A–F) The retarded migration of the prechordal plate cells in the slit2-overexpressing embryos (D–F) in comparison to normal embryos (A–C) at 100% epiboly. The positions of the mesodermal cells were examined by comparing the expression patterns of the prechordal plate mesoderm markers, zfz8b (A, D) and ,em>hlx1 (B, E), and the chordal mesoderm marker ntl (C, F) relative to the neural plate markers dlx3 (A, B, D, E), and pax2 (A, C, D, F), which are expressed in the anterior margin of the neural plate and in the midbrain/hindbrain boundary (MHB), respectively. In the slit2-overexpressing embryos, the zfz8b- and hlx1-positive prechordal mesodermal cells are prominently displaced caudally and are improperly located between the anterior margin of the neural plate and MHB. The chordal mesoderm is wider and flatter in the slit2-overexpressing embryo than in the normal embryo. (G–K) The retarded migration of the ventral diencephalic cells both in the slit2-overexpressing and cyc^tz219 mutant embryos at 100% epiboly. The position of the fkh5-positive diencephalic cells relative to the dlx3-positive anterior margin of the neural plate is displaced caudally in the slit2-overexpressing embryo (K) in comparison to the normal embryo (H), as in the cyc^tz219 mutant (I). The opl-positive cells are normally distributed in the slit2-overexpressing embryo (J) as in the normal embryo (G). (L) Schematic of the normal expression patterns of the marker genes used in this figure. np, neural plate; ms, chordal and prechordal mesoderm. Bars, 200 μm.