August 5, 2013;
Development: scaling to size by protease inhibition.
The dorsal half of bisected Xenopus laevis embryos can regenerate a well-proportioned organism on a smaller scale. A new study indicates that the removal of ventral tissue
generates a steeper Chordin
gradient by reducing Sizzled
, a secreted inhibitor of Tolloid
[+] show captions
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 . Crescent is a Sizzled homolog
expressed in the Spemann Organizer . (C) A simplified pathway in which Chordin and
Sizzled regulate each other . The in situ hybridization in the background illustrates that
chd and szl mRNAs are expressed at opposite poles of the mid-gastrula . The arrows indicate
direct protein�protein interactions in black, transcriptional regulation by BMP signaling in
blue, and diffusion (flux) of Chordin/BMP in red.
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.
Inomata, Scaling of dorsal-ventral patterning by embryo size-dependent degradation of Spemann's organizer signals. 2013, Pubmed