1. Lefty Proteins Are Long-Range Inhibitors of Squint-Mediated Nodal Signaling 
Yu Chen, Alexander F Schier 
Current Biology 
Volume 12, Issue 24, Pages (December 2002)
DOI: /S (02)

2. Figure 1
The Expanded Range of Nodal Signaling upon the Blockage of lefty Is Mediated by Sqt but not Cyc
lefty was blocked by injection of 5 ng each of lefty1 and lefty2 morpholinos (lefty MO) into embryos at the one-cell stage [13]. The specificity of the morpholinos has been previously validated [13]. ntl, bik, and gsc expression at the germ ring stage is visualized by in situ staining, shown in blue. (A–J) Dorsal ntl expression in embryos of various genotypes without lefty MO (A–E) or with lefty MO (F–J). The ntl expression domain is expanded in lefty MO-injected wild-type embryos (F); this expansion depends on Nodal signaling because it does not occur in cyc;sqt double mutants (I) and maternal-zygotic one-eyed pinhead (MZoep) mutants (J). Similar expansion is also observed in cyc mutants injected with lefty MO (H). In contrast, no expansion of the ntl expression domain was observed in sqt mutants (G). Similar results are seen for bik (K–T) and gsc (A′–J′) expression without (K–O and A′–E′) or with (P–T and F′–J′) lefty MO. Embryos were genotyped as described previously [6].
Current Biology  , DOI: ( /S (02) )

3. Figure 2 One Form of the Reaction-Diffusion Model
The activator activates both its own production and production of the inhibitor. The inhibitor blocks activator autoregulation and acts long-range to restrict the effects of the activator.
Current Biology  , DOI: ( /S (02) )

4. Figure 3 Lefty Can Act at a Distance
lefty1 mRNA was coinjected with fluorescein-dextran into a single cell in wild-type embryos at the 128-cell stage; embryos were fixed 3 hr later at the germ ring stage. ntl and bik expression is shown in blue, whereas the cells injected with the mRNA are marked by the brown staining produced by detection of the lineage tracer fluorescein-dextran with an anti-fluorescein antibody. (A) ntl expression in a wild-type embryo at the germ ring stage. (B and B′) Single-cell injection with 6 pg lefty1 mRNA. Dorsal ntl expression, which depends on Nodal signaling, is severely reduced (n = 10/10). (C) bik expression in a wild-type embryo at the germ ring stage. (D and D′) Single-cell injection with 6 pg lefty1 mRNA. bik expression is abolished (n = 7/7). The focus in (B) and (D) is on the expression domains of ntl and bik in marginal cells, whereas the focus in (B′) and (D′) is on the injected cells.
Current Biology  , DOI: ( /S (02) )

5. Figure 4
Lefty Regulates the Range of Sqt Activity Prior to Regulating sqt Expression
ntl and sqt expression was examined at different developmental stages in wild-type embryos (A-D and I–L) and lefty MO-injected embryos (E–H and M–P). The ntl expression domain in the lefty MO-injected embryos is expanded from the dome stage (E–H), whereas sqt expression in these embryos is only increased after 30% epiboly (N–P).
Current Biology  , DOI: ( /S (02) )

6. Figure 5
Lefty Blocks the Range of Sqt Activity in cyc;sqt Mutant Embryos, in which Nodal Autoregulation Is Blocked
sqt mRNA (0.8 pg) along with fluorescein-dextran (brown) was injected into a single cell of wild-type ([A], n = 10/10; [E], n = 12/12), lefty MO-injected wild-type ([C], n = 22/22; [G], n = 20/20), cyc;sqt double mutant ([B], n = 6/6; [F], n = 6/6), and lefty MO-injected cyc;sqt double mutant ([D], n = 6/7; [H], n = 5/5) embryos at the 128-cell stage; cyc;sqt double mutants (B, D, F, and H) were distinguished from sibling embryos by the loss of ntl expression on the dorsal side (B and D) and by the lack of gsc expression (F and H). Note that although there is similar expansion of the ectopic ntl domains in (C) and (D), the additional expansion of the marginal ntl domain in (C) results in an embryo that expresses ntl in most of the cells. In contrast, there is a gap between the expanded ectopic ntl domain and the dorsal margin in (D) because ntl is not expressed in the dorsal margin of cyc;sqt double mutant embryos.
Current Biology  , DOI: ( /S (02) )