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. 2022 Apr 1;11:e74509. doi: 10.7554/eLife.74509

Figure 4. Bicoid thresholds measurements by the Bcd-only synthetic reporters.

(A) Modeling the pattern shifts between Bcd-2X and Bcd-1X embryos. Top: The Bcd concentration gradient along the AP axis with its exponential decay length λ. At the anterior pole, Bcd concentration is cA in Bcd-2X embryos (solid green line) and cA/2 in Bcd-1X embryos (solid yellow line). The distance between any two nuclei columns in Bcd-2X and Bcd-1X that have the same Bcd concentration (blue horizontal arrow) is given by -λln2. Middle: along the AP axis, expression pattern of a Bcd-dependent reporter in Bcd-2X embryos (f2X(x), solid green line) and in Bcd-1X embryos (f1X(x) solid yellow line). Δ(x) : the shift in position (blue horizontal arrows) from a nuclei column in Bcd-2X embryos at position x to one at Bcd-1X embryos with the same expression level, such that f2Xx=f1X(x-Δx). Bottom: Cartoon of log-probability map of the shift Δx based on the expression patterns in Bcd-2X and Bcd-1X (i.e. f1X(x) and f2X(x)). Its value logp(Δ(x)) is represented on the grey scale. The blue vertical arrows denoting the shift correspond to the horizontal arrows with similar shade observed in the middle panel. If the Bcd gradient is the only source of positional information for the expression patterns, then the best fit value of Δ(x) given the probability map is Δ~=-λln2 (horizontal blue dashed line). (B–D and F) Expression patterns of B6 (B), B9 (C), Z2B6 (D) and hb-P2 (F) reporters in embryos from wild-type (Bcd-2X, solid green lines with shaded errors) and Δbcd/+ (Bcd-1X, solid yellow lines with shaded errors) females. In each panel, the numbers of embryos for each construct and condition are also shown. Prediction of Bcd-1X patterns from the Bcd-2X patterns assuming a fitted constant shift (values in panel G) are shown as dashed black lines. (E) Log-probability map (logp(Δx)) of the shift Δx (in %EL) at a given nuclei position in Bcd-2X embryos (x, in %EL), extracted from combined B6, B9, and Z2B6 reporters’ data. The horizontal cyan dashed line represents the best fit value Δ~ = 10.5 %EL from the log-probability map. (G) Comparison of the shift, with 95% confidence interval, in nuclei position from wild-type embryos to embryos from Δbcd/ + females (left bars) and from wild-type embryos to embryos from bcdE1/ + females (right bars) fitted individually to B6, B9, Z2B6 and hb-P2 reporters’ data.

Figure 4.

Figure 4—figure supplement 1. Comparison of fraction of expressing nuclei between nuclear cycles and between Bcd-2X and bcdE1/ + flies.

Figure 4—figure supplement 1.

A) Boundary position of fraction of expressing nuclei along AP axis as a function time in nc12 (red) and nc13 (purple), shown for hb-P2 and synthetic reporters, shown with 95% confidence interval. The hb-P2 reporter reach position of expression boundary very rapidly therefore, the position of the boundary is the same at nc12 and nc13 for the hb-P2 reporter even though nc12 is very short. In contrast, positions of the Bcd-only reporters are different at the end of nc12 and nc13. This also true for H6B6 and Z2B6. (B) Expression patterns of hb-P2 and synthetic reporters in embryos from wild-type (Bcd-2X, solid green lines with shaded errors) and bcdE1/+ (solid yellow lines with shaded errors) females. Projection of bcdE1/ + pattern (black dashed) from the Bcd-2X pattern assuming a fitted constant shift Δ~ = 9.0% ± 0.5 %EL for hb-P2 (n2x = 5 embryos, nbcdE1/+ = 4 embryos), Δ~ = 8.5% ± 1.0 %EL for B6 (n2x = 5, nbcdE1/+ = 4), Δ~ = 8.0% ± 0.5 %EL for B9 (n2x = 6, nbcdE1/+ = 6), Δ~ = 7.0% ± 0.5 %EL for B12 (n2x = 4, nbcdE1/+ = 6), Δ~ = 7.0% ± 0.5 %EL for H6B6 (n2x = 7, nbcdE1/+ = 5), Δ~ = 7.5% ± 1.0 %EL for Z2B6 (n2x = 3, nbcdE1/+ = 5). (C) Comparison of the best fitted shift constant from Bcd-2X to bcdE1/ + flies for hb-P2 and synthetic reporters.