XB-IMG-74596
Xenbase Image ID: 74596
|
Fig. 3. The endogenous mesoderm-inducing signals are blocked by Cer-S in Nieuwkoop animal-vegetal conjugates. (A) Experimental design. (B) Microinjection of tALK4 mRNA (500 pg into each animal blastomere at 8-cell stage) blocks the response of animal caps to endogenous mesoderm-inducing signals (compare lanes 3 and 4). Caps were in contact with endoderm for 2 hours and are compared to control animal caps incubated without endoderm (lane 2). EF1α is a control for RNA recovery. (C) Lanes 1-4, Nieuwkoop recombinants of uninjected animal caps with vegetal pole explants injected with follistatin (2 ng) or cer-S (600 pg) mRNA. Note in lane 4 that cer-S blocks dorsal (gsc, chd), ventral (Xwnt-8) and pan-mesodermal (Xbra) markers, whereas in lane 3 follistatin mRNA has only a slight dorsalizing effect (total conjugates n=45, two experiments). This amount of follistatin mRNA was sufficient to abolish the activity of activin mRNA in co-injection assays (not shown). Lane 5, dorsal endoderm (Nieuwkoop center) induces preferentially the organizer markers gsc and chd (n=16, three independent experiments). Lane 7, ventral endoderm induces ventral markers Xwnt-8 and the pan-mesodermal marker Xbra (n=17). Lanes 6 and 8, cer-S mRNA in the endodermal fragment prevents both dorsal and ventral mesoderm inductions (n=15 each). Conjugates were prepared between stage 8 and 8.5 and harvested for RNA after two hours. (D-G) External and histological morphology of vegetal fragments conjugated in the presence of control conditioned medium or of 20 nM Cer-S (Piccolo et al., 1999) protein and cultured until stage 36. Note that sections of the control contain muscle (mu), notochord (no) and some neural tissue (ne), whereas in the protein-treated sample the animal cap remains as atypical epidermis (ae) and endoderm (en) Image published in: Agius E et al. (2000) Copyright © 2000. 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 |