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Fig. 6 Bone morphogenetic protein-4 (BMP4) restores XK81 expression and autoneuralization is induced in dissociated Xenopus gastrula stage animal caps. A: Schematic representation of experiment analyzing the effect of dissociation and BMP4 treatment on gene expression in Xenopus gastrula stage animal caps. Animal caps were dissected from early gastrula (st.10) and either cultured intact or after dissociation for 1 or 3 hr followed by reassociation (see Experimental Procedures section). Explants were cultured for a total of 5 hr (until st.13, equivalent to early neurula) in the presence or absence of BMP4 followed by analysis by reverse transcriptase-polymerase chain reaction (RT-PCR) for expression of XK81, otx2, opl, XVent-1, and EF1a. B: Results of experiment outlined in A. Animal caps were harvested immediately after dissection (lane 1) or after 5 hr in culture (lanes 2-6). Explants cultured for 5 hr were either dissociated into single cells and reassociated after 1 (lanes 2 and 3) or 3 (lanes 4 and 5) hr or left intact (lane 6). Explants were cultured in the presence (lane 3 and 5) or absence (lanes 2, 4, and 6) of 500 ng/ml of BMP4. XK81 is expressed in the Xenopus outer layer, otx2, and opl dorsally and Xvent-1 ventrally in Xenopus. Xenopus EF1a was used as a loading control.