Figure 5

A.m.H overexpression antagonizes Notch signaling in the process of bristle and wing development. A) Scheme of bristle organ development. After being singled out from a proneural cluster by lateral inhibition, a sensory organ precursor (SOP) divides unequally to produce two daughter cells (pIIa, pIIb), destined for outer and inner cell fate, respectively. pIIa gives rise to shaft and socket cells, and pIIb eventually to neuron and thecogen. A Notch signal is required for proper designation of cells depicted in red color. B) Thorax of a wild type fly. Note typical arrangement of macrochaete and regular spacing of microchaete, each consisting of a shaft and a socket. B') The underlying cell pair consists of a thecogen (red) and a neuron (light blue). Size bar; 10 μm. C) Early heat induction (black dash; about 5 days after egg deposition) of hs-AmH during larval to pupal transition interferes with lateral inhibition. As a result ectopic SOPs form, each giving rise to a complete bristle organ. Accordingly, additional thecogen/neuron pairs are detected inside (C'; size as in B'). The resultant flies are furry compared to the wild type. D) Later heat shock (blue dash; about 5 days 18 hours after egg deposition) leads to a transformation of outer pIIa to inner pIIb cell fate. Accordingly, neither shafts nor sockets develop, and the flies have bald patches. D') As expected, additional inner cell pairs of thecogen (red) and neuron (light blue) develop (arrow). Moreover, a transformation of thecogen to neuron is observed, giving rise to a neuron doublet (arrowhead). Same size as in B'. E) Heat shock at an even later phase (red dash; about 6 days after egg deposition) causes socket to shaft transformation most easily seen on the head. Consequently, two shafts arise from a bristle organ (black arrowhead). A partial transformation of the socket gives the appearance of a triple shaft (white arrowhead). E') Transformation of inner cell types, thecogen to neuron, is observed as well. In extreme cases, all four bristle cells are transformed to neurons (light blue), giving rise a neuron quadruple (arrow). Size is as in B'. F) The wing of a control fly shows the five longitudinal veins that end thinly at the margin (see enlargement F'). Mechano- and chemosensory bristles cover the anterior, and hairs the posterior wing margin in a regular pattern (anterior is up). G) Heat induction of hs-AmH affects the veins, now ending in typical deltas (arrowhead; see enlargement G'), and the bristles as described above, leaving the impression of a 'sloppy' margin (arrow). In addition, the wing is elongated along the proximo-distal axis, giving it a more lanceolate overall appearance.