Abstract
Developmental signaling pathways often activate their own inhibitors. Such inhibitory feedback has been suggested to restrict the spatial and temporal extent of signaling or mitigate signaling fluctuations, but these models are difficult to rigorously test. Here, we determine whether the ability of the mesendoderm inducer Nodal to activate its inhibitor Lefty is required for development. We find that zebrafish lefty mutants exhibit excess Nodal signaling and increased specification of mesendoderm, resulting in embryonic lethality. Strikingly, development can be fully restored without feedback: Lethal patterning defects in lefty mutants can be rescued by ectopic expression of lefty far from its normal expression domain or by spatially and temporally uniform exposure to a Nodal inhibitor drug. While drug-treated mutants are less tolerant of mild perturbations to Nodal signaling levels than wild type embryos, they can develop into healthy adults. These results indicate that patterning without inhibitory feedback is functional but fragile.
Highlights
Feedback inhibition is a common feature of developmental pathways across phyla (Freeman, 2000; Freeman and Gurdon, 2002; Meinhardt, 2009; Piddini and Vincent, 2009; Ribes and Briscoe, 2009; Rogers and Schier, 2011)
Complete lefty loss causes lethal expansion of Nodal signaling and mesendoderm To determine the consequences of removing feedback inhibition, we first used TALENs to generate null lefty1 and lefty2 alleles in zebrafish (Figure 1C–T) (Bedell et al, 2012; Reyon et al, 2012; Sander et al, 2011; Sanjana et al, 2012). lefty1a145 contains a 13-base-pair deletion that removes the translational start site and part of the predicted signal sequence (Figure 1C), and lefty2a146 contains an 11-base-pair deletion that results in a stop codon after amino acid 18 (Figure 1D)
Lefty morphants display disrupted gastrulation and do not survive past 24 hr, whereas lefty double mutants successfully gastrulate and survive past 24 hr (Figure 1—figure supplement 2). These differences are not caused by compensation in lefty1-/-;lefty2-/- mutants but by off-target morpholino effects: lefty1-/-;lefty2-/mutants injected with lefty1/2 morpholinos display disrupted gastrulation and die by 24 hr (Figure 1—figure supplement 2)
Summary
Feedback inhibition is a common feature of developmental pathways across phyla (Freeman, 2000; Freeman and Gurdon, 2002; Meinhardt, 2009; Piddini and Vincent, 2009; Ribes and Briscoe, 2009; Rogers and Schier, 2011). Feedback inhibitors contribute to patterning processes in tissues ranging from the mouse neural tube (Ribes and Briscoe, 2009) and the zebrafish hindbrain (White and Schilling, 2008), to the Drosophila wing (Gerlitz and Basler, 2002; Piddini and Vincent, 2009; Zeng et al, 2000) and eye (Freeman, 1997). Directly testing the role of feedback per se has remained challenging: Eliminating inhibitors removes feedback, but it increases signaling levels. Experiments that decouple inhibitor activation and inhibition while maintaining near-normal signaling levels are required to unambiguously test the role of feedback in developmental patterning
Sign-in/Register to view highlights & summary Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
