Fig. 3. Amos expression during olfactory precursor formation. (A-L) Time course of Amos protein expression relative to olfactory precursor formation. In all cases we concentrate on precursors in the third segment, although a large number of chordotonal precursors are also visible in the surrounding second segment (carets; see also the summary in Fig. 4). (A,E,I) At 0 hours APF, the first wave of precursors appear (arrow). (B,F,J) At 4 hours APF, the second wave of precursors appears in a highly characteristic pattern (bracket). (C,G,K) At 8 hours APF, the third wave of precursors accumulate between the rows of the second wave, eventually obscuring any clear pattern by 16 hours APF (D,H,L). (A-D) Amos expression is detected throughout this time, but the expression is ectodermal from 0-4 hours APF, and then it co-labels with some of the precursors between 4-16 hours APF. Amos continues to be expressed in some cells at 16 hours APF, and these cells seem to be a mixture of ectodermal cells and precursors.