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Fig. 3. Posterior crossvein formation requires BMPs and BMP transport
components. (A,B) pMad accumulation in the longitudinal
veins (LVs) and posterior crossvein (PCV) at 26 (A) and 36 (B) hours
post-puparium formation (ppf). Note that at 26 hours ppf pMad accumulates at
the PCV in a wide domain that then refines considerably by 36 hours ppf.
(C) dpp mRNA expression in the LVs, but not in the PCV, at 24
hours ppf. (D) cv-2 mRNA expression at 24 and 29 hours ppf.
Note the sharpening in the cv-2 mRNA profile as time progresses.
(E) A schematic representation of one possible patterning mechanism.
Dpp is only produced in the LVs, whereas Gbb is uniformly expressed. The
Dpp/Gbb heterodimers formed in the LVs preferentially bind to a complex of Sog
and Cv (also known as Tsg2). Tlr cleaves Sog to release the heterodimer for
signaling. Initial low signal levels, together with other unknown positional
cues, induce cv-2 transcription (yellow) in a zone that will form the
PCV. Cv-2 protein accumulates on the cell surface and creates a
positive-feedback loop that presents BMP ligand to the signaling receptors.
(F-I) Expression patterns of sog (F), cv (G) and
tlr (H) mRNA, and Tkv protein (I) in 19-24 hour ppf wings. (J)
Uniform overexpression of sog (UAS-sog), cv
(EP(X)1349) and cv-2 (EP(2)1103) in the posterior
of the wing with en-gal4 does not disrupt PCV formation. (C,F,I)
Reproduced, with permission, from Ralston and Blair
(Ralston and Blair, 2005);
(D,H,J) reproduced, with permission, from Ralston (A. Ralston, PhD thesis,
University of Wisconsin, 2004); (G) reproduced, with permission, from Shimmi
et al. (Shimmi et al.,
2005a).
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