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Fig. 8. BMP-4 and Xbra affect Hox expression independently but cooperatively. Arrowheads in all panels point to the site of injection. (A–D) Vegetal views
(organiser is up) of gastrula stage embryos after injection of BMP-4 morpholino (BMP4MO1) (A, B) or control morpholino (C, D). Whilst Hoxd-1 was
downregulated in BMP4MO1-injected embryos (A), Xbra expression was still present (B). (E–H) Vegetal views (organiser is up) of gastrula stage embryos
after injection of noggin (nog) or chordin (chd) mRNA. Both of these BMP inhibitors downregulated Hoxd-1 expression (E, G) but not Xbra expression (F, H).
(I, J) To see whether Xbra had an effect on the BMP pathway, the BMP-4 target gene Xvent-2 was analysed after animal injection of Xbra. The expression
pattern was unchanged (I, J) (lateral views, organiser to the right). (K–N) Views of an uninjected embryo from the non-organiser side (K), an embryo injected
with Xbra alone (L), an embryo injected with BMP4MO1 (M) and an embryo injected with BMP4MO1 and Xbra (N). The Xbra coinjection did not rescue the
Hoxd-1 downregulation by BMP4MO1. (O) Lightcycler PCR was performed to demonstrate that the upregulation of Hoxd-1 expression by Xbra in animal cap
sandwiches (Xbra + conMO AC) can be reduced by coinjection of a BMP-4 morpholino (Xbra + BMP4MO1 AC). The graph shows Hoxd-1 levels normalised
to odc levels and expressed as a percentage of endogenous expression in whole embryos (WE). Noninjected cap sandwiches (ni AC) are also shown. Error bars
indicate standard deviation (n = 3). |
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Fig. 4. The constitutively active BMP receptor, ALK-6, ventralises and posteriorises embryos. (A, B) Embryos were injected with the constitutively active human BMP receptor (Alk-6) at stage 1. Phenotypic analysis shows the expected effects of head reduction and shortened trunks in Alk-6-injected embryos (B) compared to noninjected (ni) controls (A). (C–N) Marker analysis of Alk-6-injected embryos. In situ hybridisations were performed on noninjected embryos (C, F, I, L) and embryos injected with 600 pg Alk-6 (D, G, J, M) or 1.2 ng Alk-6 (E, H, K, N) using probes for the anterior gene, otx-2 (C, D, E), the organiser gene, chordin (F, G, H), the posterior gene, Hoxb-9 (I, J, K) and the ventral gene, Xvent-2 (L– N). Expression of otx-2 and chordin was reduced, whereas expression of Hoxb-9 and Xvent-2 was expanded. Embryos are shown from the anterior (C– E), from the dorsal site with anterior to the right (F–K) or from the lateral side with anterior to the right (L – N). |
