Figure 1.

The non-neuronal locus mir-279/996 restricts neural fate in PNS organs. (A) Summary of mechanosensory bristle development. Spatially patterned activity of basic helix-loop-helix activators Achaete (Ac) and Scute (Sc) defines a PNC, among which Notch signaling (schematized by red repression lines) restricts neural competence to single SOP cells. The SOP undergoes a fixed set of asymmetric cell divisions to generate the four cells of the mature sensory organ (ne, neuron; sha, shaft cell; she, sheath cell; so, socket cell); a fifth glial-like cell undergoes apoptosis. Each of the cell divisions in the sensory organ lineage is made asymmetric by Notch signaling (schematized by red repression lines). Developmental times for microchaete bristle lineage stages are labeled in hours APF, and cell-specific markers used in this study are marked. (B) Examples of triple labeling of mature sensory organ cell types with distinctive markers. Bars, 10 µm. (C) The expression of a tub-GFP-miR-279 activity sensor is elevated in Elav+ neurons in the notum. In C′, examples of large DPax2+ shaft cell nuclei are labeled with red arrowheads, and small DPax2+ sheath cell nuclei are labeled with arrows. In C′′, examples of individual neuronal nuclei are labeled as 1N. (D) Expression of tub-GFP-miR-279 in mir-279/996 mutant is generally up-regulated in epidermal cells in the notum but is substantially higher in multiple sensory organ cells. This is associated with a profound cell specification defect, because most sensory organs contain two Elav+ neurons and are lacking the small DPax2+ nucleus (the sheath, which is the sister cell of the neuron). Examples of sensory organ clusters with only DPax2+ shaft cells (D′, red arrowheads,) and double neurons (2N; D′′, blue arrowheads) are indicated; a triple neuron (3N) cluster is highlighted by dotted lines. Bars: (C and D, main panels) 50 µm; (insets) 10 µm.