Proc Natl Acad Sci U S A
June 21, 2011;
Negative feedback in the bone morphogenetic protein 4 (BMP4) synexpression group governs its dynamic signaling range and canalizes development.
What makes embryogenesis a robust and canalized process is an important question in developmental biology. A bone
morphogenetic protein (BMP) morphogen gradient plays a key role in embryonic development, and we are beginning to understand how the self-regulating properties of its signaling circuitry ensure robust embryonic patterning. An unexplored question is why the BMP signaling circuit is organized as a modular synexpression group, with a prevalence of feedback inhibitors. Here, we provide evidence from direct experimentation and mathematical modeling that the synexpressed feedback inhibitors BAMBI
, and SMAD7
(i) expand the dynamic BMP signaling range essential for proper embryonic patterning and (ii) reduce interindividual phenotypic and molecular variability in Xenopus embryos. Thereby, negative feedback linearizes signaling responses and confers robust patterning, thus promoting canalized development. The presence of negative feedback inhibitors in other growth factor synexpression groups suggests that these properties may constitute a general principle.
Proc Natl Acad Sci U S A
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Fig. 4. Bambi and smad6/7 negative feedback canalize development. (A) Phenotypes of stage-36/7 X. laevis embryos injected with the indicated MOs. (B) (Upper) Representative body and tail length of stage-36/7 X. laevis embryos injected with MOs as in A. (Lower) Average coefficient of variation of body and tail length of stage 36/7 X. laevis embryos injected as indicated in A of (n = 3) biological replicates with 15–30 embryos per replicate. (C) Eye morphology of stage-36/7 tadpoles from embryos injected as indicated. (D) Quantification of the relative eye size. Graph shows average eye area (Left) and coefficient of variation (Right) of three biological replicates with 15–30 embryos per replicate. (E) qPCR expression analysis of the indicated genes from individual X. laevis embryos of stage 10.5, which were injected at the four-cell stage with the indicated MOs (n = 9–10 embryos per sample). (F) Coefficient of variation of early BMP4 marker gene expression from individual stage 10.5 X. laevis embryos as in C (n = 2). Error bars, SD; *P < 0.05 and **P < 0.01 (unpaired t test).
Fig. S1. The Xenopus laevis BMP4 synexpression group. (A) Schematic model of the Xenopus laevis BMP4 synexpression group embedded into the BMP4/7 signal transduction pathway. Members of the BMP4 synexpression group are drawn in red while non- synexpressed pathway components are in yellow. (B) In situ hybridization of bmp4 and synexpression group members ventx2, bambi, and smad7 in tailbud stage X. laevis embryos; dorsal eye (de), heart field (he), proctodeum (pr). The figure is partially reproduced and adapted from (1) with permission of EMBO Journal.
Fig. S8. Bambi knock down increases variability of the myf5 expression domain width. (A) In situ hybridization of myf5 in midgastrula X. laevis embryos injected equatorially with either 40ng control, 40ng BAMBI MO, or 20/20ng Chordin/Noggin MOs per embryo equatorially at the 2-4 cells stage. (B) Morphometric analysis of myf5 expression domain- width of embryos injected with MOs as in (A). Error bars indicate s.d.; gray boxes represent 50-percentile spread; (AU) arbitrary units; Coefficient of variation (COV).