December 1, 2000;
A novel member of the Xenopus Zic family, Zic5, mediates neural crest development.
We characterized Xenopus Zic5
which belongs to a novel class of the Zic family. Zic5
is more specifically expressed in the prospective neural crest than other Zic genes. Overexpression of Zic5
in embryos led to ectopic expression of the early neural crest markers, Xsna
, with the loss of epidermal marker expression. In Zic5
-overexpressing animal cap explants, there was marked induction of neural crest markers, without mesodermal and anterior
neural markers. This was in contrast to other Xenopus Zic genes, which induce both anterior
and the neural crest markers in the same assay. Injection of a dominant-negative form of Zic5
can block neural crest formation in vivo. These results indicate that Zic5
expression converts cells from an epidermal fate to a neural crest cell fate. This is the first evidence for neural crest tissue
inductive activity separate from anterior
inductive activity in a Zic family gene.
[+] show captions
Fig. 3. Spatial expression patterns of Zic5 in Xenopus embryos. Series of embryos were hybridized with digoxigenin-labeled antisense Zic5. (A,B) late gastrula stage (stage 11.5). (C,D) Stage 13. (A,C) Dorsal view. (B,D) Lateral view. In the late blastula and early neurula, Zic5 expression was restricted to the prospective neural fold (black arrow head) and anterior neural plate (white arrowhead). (E,F) Stages 14–15. (E) Dorsal view. (F) Lateral view. The staining was seen as four longitudinal lines, which represent the neural plate edges and a part of the neural fold (E, white and black arrowheads). Arrows indicate the neural plate border region of the prospective rhombencephalon. (G,H) Stages 21–22. The black arrowhead, white arrowhead and arrow indicate the telencephalon, diencephalon and mesencephalon, respectively. (G) Anterior view. (H) Lateral view. (I) Stage 30. (J) Magnified views in the head region of (I). (K) Stage 30. Transverse section through the head of the same embryo as in (I,J). bp, blastopore; ov, optic vesicle; tel, telencephalon; di/mi, diencephalon and midbrain boundary; rh, rhombencephalon; e, eye; nt, neural tube.
Fig. 4. Comparison of expression of the Zic family and a neural crest marker in the gastrula and neurula stage. Whole-mount in situ hybridization was performed to demonstrate the spatio-temporal expression of Zic1 (A,B), Zic2 (C,D), Zic3 (E,F), Zic5 (G,H), and Xslu (I,J) at stage 13 (A,C,E,G,I), and stage 16 (B,D,F,H,J). All panels show dorsal views.
Fig. 6. Zic5 expression induces neural crest markers, and suppresses an epidermal marker in early stage embryos. A total of 250 pg of MT-Zic5 mRNA and 100 pg of nls-lacZ mRNA was injected into one blastomere of two-cell stage embryos. Blue staining showed lacZ expression domain and purple staining showed marker gene expression. Whole-mount in situ hybridization was performed with a neural crest marker, Xslu (A–C), Xsna (D–F), probe and an epidermal marker, XK81 probe (G–I). (A,D,G) Dorsal view. (B,E,H) Injected side view. (C,F,I) Uninjected side view. Xslu and Xsna expressing regions show lateral expansion of the injected side (A,B,D,E). XK81 staining in the epidermis is reduced on the injected side (G,H).