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Cell
1997 Oct 31;913:417-26. doi: 10.1016/s0092-8674(00)80425-0.
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Production of a DPP activity gradient in the early Drosophila embryo through the opposing actions of the SOG and TLD proteins.
Marqués G
,
Musacchio M
,
Shimell MJ
,
Wünnenberg-Stapleton K
,
Cho KW
,
O'Connor MB
.
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During early Drosophila embryogenesis, several zygotic gene products act to establish a posttranscriptional activity gradient of the morphogen DPP. Among these molecules, Tolloid, a putative metalloprotease related to BMP-1, enhances DPP function, while SOG, an ortholog of the Xenopus organizerChordin, inhibits DPP function. Using epistasis tests and a Xenopus secondary axis induction assay, we show that TLD negates the inhibitory effects of SOG/CHD on DPP/BMP-type ligands. In transient transfection assays, we demonstrate that TLD cleaves SOG and that cleavage is stimulated by DPP. We propose that formation of the embryonic DPP activity gradient involves the opposing effects of SOG inhibiting DPP and TLD processing SOG to release DPP from the inhibitory complex.
Figure 4.
Inhibition of SOG/CHD-Mediated Secondary Axis Formation by TLD
(A) Uninjected stage 37 embryos.
(B) Embryos injected with SOG mRNA (2 ng). Secondary axes are present (arrows).
(C) Embryos injected with SOG (2 ng) and TLD mRNA (2 ng). No secondary axis is present.
(D) Histogram showing the induction of secondary axes by Chordin or SOG with various TLD mRNAs. Chordin or SOG mRNA (0.125 mg/ml and 0.25 mg/ml, respectively) was microinjected into two ventral blastomers (4 nl each) together with wild-type or mutant TLD mRNAs. The final concentrations of wild-type TLD and activated TLD were 4 ng, 1.5 ng, and 0.4 ng per embryo. For ActTLD10E95 and pmTLD, 4 ng and 1.6 ng of mRNA was injected. Embryos that survived until the late neurula stage were scored. Combined results from three experiments are shown here. A minimum of 35 (often over 50) embryos were analyzed per injection sample.
(E) Schematic representation of the various forms of TLD products used to make synthetic mRNAs. Abbreviations: TLD, wild-type Tolloid; ActTLD, activated Tolloid; ActTLD10E95, activated form of protease mutant; pmTLD, processing mutant; pp, propeptide; Zn, zinc protease domain; CUB, CUB repeat; E, EGF-repeat; H, HA epitope.
(F) Expression of activated TLD (0.4 ng, 1.5 ng, and 4.0 ng per embryo) does not block secondary axis formation mediated by noggin (100 pg), DN-BMPR (2 ng), and Cm-BMP4 (2 ng) mRNA injected.
