Direct and Long-Range Action of a Wingless Morphogen Gradient

TLDR

Wingless (Wg) is a Wnt family protein that functions as both a short‑range inducer and a long‑range organizer in Drosophila development. The study aims to assess the consequences of ectopically expressing wild‑type Wg, membrane‑tethered Wg, and constitutively active Armadillo, and to compare these with loss of endogenous Wg or Arm activity. The authors performed ectopic expression of these constructs and compared the resulting transcriptional effects to those observed when endogenous Wg or Arm activity was removed. Wild‑type Wg acts as a long‑range gradient morphogen, up‑regulating target gene transcription in a concentration‑dependent manner, whereas membrane‑tethered Wg and constitutively active Armadillo exert only short‑range or autonomous effects, supporting direct long‑range action of Wg during development.

Abstract

Wingless (Wg), a founding member of the Wingless/Int-1 (Wnt) family of secreted proteins, acts as a short-range inducer and as a long-range organizer during Drosophila development. Here, we determine the consequences of ectopically expressing (i) a wild-type form of Wg, (ii) a membrane-tethered form of Wg, and (iii) a constitutively active form of the cytosolic protein Armadillo (Arm), which normally acts to transduce Wg, and we compare them with the effects of removing endogenous Wg or Arm activity. Our results indicate that wild-type Wg acts at long range, up-regulating the transcription of particular target genes as a function of concentration and distance from secreting cells. In contrast, tethered Wg and Arm have only short-range or autonomous effects, respectively, on the transcription of these genes. We interpret these findings as evidence that Wg can act directly and at long range as a gradient morphogen during normal development.