XB-ART-14978Mech Dev April 1, 1998; 73 (1): 73-83.
The Xenopus Emx genes identify presumptive dorsal telencephalon and are induced by head organizer signals.
We have isolated and studied the expression pattern of Xemx1 and Xemx2 genes in Xenopus laevis. Xemx genes are the homologues of mouse Emx genes, related to Drosophila empty spiracles. They are expressed in selected regions of the developing brain, particularly in the telencephalon, and, outside the brain, in the otic vesicles, olfactory placodes, visceral arches and the developing excretory system. We also report on experiments concerning the tissue and molecular signals responsible for their activation in competent ectoderm. Xemx genes are activated in ectoderm conjugated with head organizer tissue, but not with tail organizer tissue. Furthermore, they are not activated in animal cap either by noggin or by Xnr3, thus suggesting that a different inducer or the integration of several signals may be responsible for their activation.
PubMed ID: 9545539
Article link: Mech Dev
Species referenced: Xenopus
Genes referenced: dlx5 emx1l emx2 nodal3.1 nodal3.2 nog otx2
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|Fig. 2. Whole-mount in situ hybridization on stage-14 Xenopus embryos showing expression of: (a) Xemx1; (b) Xemx2; (c) Xemx1 (blue stain, triangle) and Xdll-3 (magenta stain, arrowhead); (d) Xemx2 (blue stain, triangle) and Xdll-3 (magenta stain, arrowhead).|
|Fig. 3. Whole-mount in situ hybridization showing expression of Xemx1 (a–d) and Xemx2 (e–i) during tailbud and tadpole stages. (a,e) Stage 21/22, (f) stage 30/31, (b,c,g,h) stage 37, (d,i) stage 40. Triangles in (c,d,h) show Xemx gene expression in the dorsal telencephalic region. Arrows in (f–i) show Xemx2 labeling of the olfactory placodes. Arrowheads in (g–i) point to mesencephalic Xemx2 expression. In (d), an arrow and an arrowhead point to Xemx1 expression in the diencephalon and in the mesencephalon, respectively. p, pronephros; va, visceral arches.|
|Fig. 4. Expression of Xemx1 (a–c) and Xemx2 (d–f) as detected in transverse sections of stage 33 (a,d) and stage 37 (b,c,e,f) Xenopus embryos following whole-mount in situ hybridization. Sections show expression within telencephalon (a,d), diencephalon (b,e) and mesencephalon (c,f). d, diencephalon; dt, dorsal telencephalon; h, hypothalamus; lt, lamina terminalis; m, mesencephalon; op, olfactory placode; t, thalamus; va, visceral arches.|
|Fig. 5. Expression of Xemx1 (a–c) and Xemx2 (d–f) as detected in frontal sections of stage 33 Xenopus embryos following whole-mount in situ hybridization. Left-to-right sections show expression at progressively more dorsal levels. Arrowheads in (a,d) point to Xemx gene expression in the olfactory region. ov, otic vesicle. Other abbreviations as in Fig. 4.|
|Fig. 6. In situ hybridization of stage 30/31 embryos with Xemx1 and Xotx-b (right embryo) or with Xemx2 and Xotx-b (left embryo) probes. Xotx-b is specifically expressed in the epiphysis (arrowhead) and in the eye (arrow). A clear gap is visible in between Xotx-b labeling of the epiphysis and the posterior border of Xemx gene expression.|
|Fig. 7. Expression of Xemx2 as detected in transverse (a) and frontal (b) sections of stage 30/31 Xenopus embryo following whole-mount in situ hybridization. Comparison of (a) with Fig. 4a,d and of (b) with Fig. 5b,e shows that between stage 30/31 and stage 33 Xemx2 expression becomes restricted to the ventricular zone of the dorsal telencephalon, while that of Xemx1 embraces the whole neuroepithelium. Abbreviations as in Fig. 4.|
|Fig. 8. Induction of Xemx gene activities in conjugates of organizer tissue and ectodermal explants. (a) The head-inducing activity of the early blastopore lip is shown by induction of secondary heads in host embryos. (b) Xemx1 (upper embryo) and Xemx2 (lower embryo) expression in stage 24 embryos. (c) The tail-inducing activity of a late blastopore lip is shown by induction of secondary tails in host embryos. (d–g) Results of whole-mount in situ hybridization performed on animal cap/head organizer conjugates (d,e) or animal cap/tail organizer conjugates (f,g) grown to stage 24, using either an Xemx1 (d,f) or an Xemx2 (e,g) probe, respectively. The signal is detectable as a blue stain on the sandwiches.|
|Fig. 9. Neural induction assays on animal caps. Animal caps injected with either noggin (a,b,c) or Xnr3 (d,e,f) mRNA were tested by in situ hybridization as for Xotx2 (positive control, a and d), Xemx1 (b,e) and Xemx2 (c,f) expression. The blue stain shows activation of Xotx2 only (a,d).|