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Fig. 5. Apod mRNA can induce mesoderm. Apod mRNA (500 pg) was ectopically expressed in the whole embryo by injection of synthetic mRNA into the animal pole region of two-cell embryos. These were reared until uninjected siblings had reached stage 26. Embryos ectopically expressing Apod failed to gastrulate and developed as exogastrulae (A). Apod-injected and uninjected embryos were sectioned and then analysed for the expression of Xbra by in situ hybridisation at stage 10.25 (B,C, respectively). The ectopic expression of mesodermal markers in the animal cap region of the embryo suggests that Apod is able to induce mesoderm. To further characterise Apod mesoderm- inducing properties, the indicated amounts of Apod mRNA were injected into the animal pole region of embryos at the 2-cell stage. At stage 9, animal caps were isolated and cultured as explants until sibling embryos had reached stage 10.25. Total RNA was extracted from the equivalent of two embryos and analysed for the expression of mesodermal markers by RNase protection (D). Apod mRNA is able to strongly induce Xwnt-8, Xbrachyury (Xbra), Eomesodermin (Eomes) and Mix.1. At high Apod mRNA concentrations there is a weak activation of goosecoid (gsc). Siamois (Sia) is not activated. Histological examination shows that whereas uninjected controls form atypical epidermis (E), Apod-injected animal caps form mesoderm of ventral character as judged by the presence of mesenchyme and vesicles (F). Immunostaining of explants in E and F with the muscle- specific 12/101 antibody showed no muscle (see also Table 1). Image published in: Stennard F et al. (1996) Copyright © 1996. Image reproduced with permission of the publisher and the copyright holder. This is an Open Access article distributed under the terms of the Creative Commons Attribution License. Larger Image Printer Friendly View

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