Fig. 6. Expression of (A,B) Ag-pnr and (C) Ag-ASH in segregating sensory organ precursors. Precursors arise as the domains of expression fade and can be seen as spaced single cells. Precursors of bristles of the acrostichal (AC) and dorsocentral (DC) rows arise first, indicated by arrowheads; they are large and arranged in poorly defined rows. Scale precursors in the vicinity of the AC and DC rows arise at the same time, indicated by the arrow in C. The scale precursors are smaller. The triangular domain of expression is visible at the bottom in B. The epithelium is somewhat creased at these stages distorting the spatial arrangements. Precursors of bristles and scales at other positions arise slightly later. Within the rows and at different spatial locations, there is no apparent order to precursor segregation: the distribution of stained cells is variable between individuals. LSH, persistent larval sensory hair. (D) A fourth instar larva stained with anti-HRP to visualise the neurons. (Precursor segregation is accomplished before pupation in some individuals). Neurons corresponding to some of the AC and DC bristles have appeared in this individual, as well as some of the lateral antealar (AA) neurons. LSN, larval sensory neurons.

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