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Figure 1. Extracellular protein interactions in Xenopus dorsal-ventral patterning.
(A) Chordin inhibits BMPs, which activate expression of Sizzled, an inhibitor of Tolloid
proteases that degrades Chordin. (B) The dorsal-ventral network consists of many components
under opposite transcriptional control by BMPs [7]. Crescent is a Sizzled homolog
expressed in the Spemann Organizer [13]. (C) A simplified pathway in which Chordin and
Sizzled regulate each other [8]. The in situ hybridization in the background illustrates that
chd and szl mRNAs are expressed at opposite poles of the mid-gastrula [4]. The arrows indicate
direct protein�protein interactions in black, transcriptional regulation by BMP signaling in
blue, and diffusion (flux) of Chordin/BMP in red. |
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Figure 2. Chordin and Sizzled are key
regulators of dorsal-ventral patterning.
Depletion of Chordin or Sizzled with morpholinos
(MOs) results in identical high-BMP
phenotypes marked by an expanded ventral
domain of sizzled mRNA expression. |
