Fig. 2.

NC induction by DLMZ and IM. (A) Early NC induction. The prospective mesoderm was dissected out from stage 10.25 embryos and divided in dorsal marginal zone (DMZ), dorsolateral marginal zone (DLMZ) and lateral marginal zone (LMZ). This tissue was then conjugated with an animal cap taken from a stage 9 embryo and cultured until the equivalent of stage 15 when the expression of the NC marker Snail2 was analysed. (a) Conjugates with DMZ. (b) Conjugates with DLMZ. (c) Conjugates with LMZ. (B) Early NC induction by late mesoderm. Different regions of mesoderm (named 1-4) were dissected from a stage 16 neurula embryo previously injected with FDX and grafted into the blastocoel cavity of a stage 10 gastrula embryo. The grafted embryos were cultured until stage 16 when the expression of Snail2 and Sox3 was analysed. (a-h) Control explants of mesoderm were fixed immediately to analyse the expression of Snail2 and Sox3; no expression of these markers was observed. Purple, in situ hybridisation; blue, grafted tissue. (i-l) Lateral view of grafted embryos showing expression of Snail2. Dorsal is towards the top; anterior towards the right. Only embryos in which the grafted tissue was located in ventral epidermis were analysed. (m-p) Higher magnification of the graft showing expression of Snail2. (q-t) Section through the graft showing expression of Snail2. (u-x) Section through the graft showing expression of Sox3. (C) Late NC maintenance. NC explants were dissected from a stage 16 neurula embryo; NC was fixed immediately or cultured alone or together with the underlying IM until the equivalent of stage 23. The expression of Snail2 was analysed. (a) NC dissected from a stage 16 embryo and fixed immediately. (b) NC cultured until the equivalent of stage 23. (c) NC cultured with the underlying mesoderm (IM).