In hb knock-down embryos, posterior gt fails to retract from the posterior pole (24/35) or does not retract fully (4/35).
In D. melanogaster tll hkb double mutants, posterior hb is absent or strongly reduced (Casanova, 1990), posterior gt fails to retract (Brönner and Jäckle, 1991), abdominal kni expands to the posterior (Brönner and Jäckle, 1991), and so does Kr if combined with a posterior system mutant background (Weigel et al., 1990).
In the absence of Fra, detection of Netrin-dependent chemoattraction is compromised and many posterior commissures fail to form.
However, as described herein, we observed the opposite: fra commissural defects are dramatically enhanced as both anterior and posterior commissures fail to form and this is associated with a large number of CNS axons projecting beyond the CNS/PNS border.
In Drosophila, Netrins are midline attractants detected by Frazzled, a receptor expressed on most CNS neurons and in its absence many posterior commissures fail to form [5], [6], [13].
To quantify the midline crossing defects, we scored the number of segments in which the EW axons, which normally cross the midline in the posterior commissure, fail to cross.
In D. melanogaster hkb mutants, the posterior hb domain fails to retract from the posterior pole (Casanova, 1990; Brönner and Jäckle, 1991), hkb represses gt when over-expressed (gt is unaltered in hkb mutants) (Brönner et al., 1994), and Kr expands further in a tll hkb compared to tll background when combined with a posterior system mutant (Weigel et al., 1990).
Further the biophysical characteristics of osk motion in the Stau (Figure 3C)) retained its posterior bias, which failed to the "captured" at the posterior.
Similarly, in kni RNAi embryos, the anterior boundary of the posterior gt domain is slightly displaced towards the posterior (24/30), while the posterior boundary of this domain fails to retract from the pole (18/30) or does not fully retract (6/30).
Therefore the polygon of pointwise posterior distributions can fail to convey the region of high posterior concentration, as represented by the mode.
