Extended Data Figure 8: Temporal development and fitting procedure of Brk data set.

a, b, As can be seen in Fig. 2f, there is a gap in Brk expression in the lateral-most region of the posterior compartment, indicative of Dpp expression from another, laterally located source. Indeed, it has been shown that Dpp is expressed during the third instar larval stage in a posterior, lateral position and exerts a patterning role on the wing imaginal disc. However, this late Dpp expression does not affect the growth properties of wing disc cells⁵⁹. Despite this, the additional Dpp source might complicate the interpretation of our growth analyses. To circumvent this problem, we also measured the growth properties in the anterior compartment in the presence (a) and in the absence of the eGFP::Dpp gradient (b; high uniform levels of Brk are indeed present in all cells outside the source). Indeed, we found that the lateral anterior region still grows despite the absence of the Dpp gradient and the lack of Dpp signalling. c, d, Width of the anterior and posterior compartment respectively in dpp^d8/d12 mutant wing discs rescued with eGFP::Dpp (black, n = 34) and dpp^d8/d12 mutant wing discs co-expressing eGFP::Dpp and morphotrap (red, n = 37, error bars show s.d.). e, The red dots mark the 15 points used as landmarks for the affine transformation. Using affine transformation allowed us to overlay discs of slightly different shapes and sizes when generating the mitotic density maps shown in Fig. 3c, e (see also Methods for details). f, Computation of Brk data set shown for the posterior compartment: (1) The compartment width L_A or L_P was defined as the distance from the A/P boundary to the anterior or posterior edge of the wing tissue, respectively. Brk profiles were measured along a straight line with 30%D offset. (2) Profiles were extracted using WingJ software. (3) The single gradients were fitted to the shown Hill function. The fitting procedure returns the parameter k, which corresponds to the position of half-maximum Brk levels and hence to the width of the medial domain. Therefore, the lateral domain equals L − k.