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Fig. 1. Xhex-expressing SBE is necessary for normal anterior development. Sections transversely and longitudinally through the dorsal lip show Xhex
expression in the outermost cells. A vegetal view of an early stage 10 embryo (A) shows expression of Xhex in the suprablastoporal endoderm (SBE), just
above the dorsal lip (dorsal to top). Transverse (B, TS) and longitudinal (C, LS) sections through dorsal lip region confirm the localization of Xhex transcripts in
the superficial layer. The insert in (C) shows the entire section from which the enlargement is taken. An SBE extirpation and dorsal marginal zone (DMZ)
culture assay (D) was used to investigate the importance of the Xhex-expressing SBE for head organiser formation. Half of the DMZs with the SBE removed
lack cement glands (CG) (E, 49%) while the remainder develop cement glands but are slightly truncated rostrally (F, 51%). Wild-type DMZs (G) and control
embryos (H) develop normal anterior structures including cement glands and eyes. (93%, 179 explants in total from six experiments.) An RTCR assay (I)
shows the loss of anterior pattern: expression of the forebrain marker XBF1 is not detected in SBE-extirpated DMZs which lack visible cement glands, but
expression is normal in those which develop cement glands. Expression of Xotx2 is detected, demonstrating that only the anteriormost development is affected
by lack of an SBE. |
