Neurogenic effects A-C. Dorsal thorax preparations revealing pattern of bristles. A. Wildtype. The number and position of macrochaetae is highly stereotyped (arrows). B. Dl overexpression led to a few ectopic macrchaetae (arrows; see also Doherty et al., 1997). Shown is the strongest of our UAS-Dl insertion lines. Genotype is ScaG4>DESI (lineA10). C. Ser overexpression led to extreme neurogenic phenotypes apparently converting all cells in proneural regions to bristle precursors (arrows). Genotype is ScaG4>SESI. D-J Eye imaginal disc epithelia. D, E show eye discs labelled for the R8-specific protein Boss. Ser overexpression led to large clusters of R8-like cells (E) in place of an array of single cells in wildtype (D). F,G,H show eye discs with differentiating photoreceptor cells labelled for the neural-specific ELAV protein. F. In wildtype photoreceptors are progressively added until a total of 8 are differentiating in each cluster. G. Ser overexpression within and anterior to the morphogenetic furrow is strongly neurogenic, driving most cells posterior to the morphogenetic furrow into photoreceptor fate. H. Dl overexpression within and anterior to the morphogenetic furrow leads to a disorganized pattern of ommatidia (associated with the acceleration of the morphogenetic furrow) and is also weakly neurogenic. I,J Expression of the N target E(spl)mδ. I. wild type. J. Expression of E(spl)mδ, an important N target for lateral inhibition of R8, is lost when Ser is overexpressed in and anterior to the morphogenetic furrow. K-N. Eye discs labelled for ELAV expression reveals the extent of neural photoreceptor differentiation. All these discs were exposed to a 1 hour heat shock 22 hours before dissection. K. wild type. L. hs-Nintra. Photoreceptor differentiation is absent from a band of cells sensitive to N signaling at the time of the heat shock (arrow). M. Ser overexpression in and anterior to the morphogenetic furrow drives most cells posterior to the furrow into neural photoreceptor fates. N. Nintra expression is epistatic to ectopic Ser, preventing neural differentiation by a band of cells. O-R. Dl and N proteins on apical cell surfaces in the morphogenetic furrow region. Detergent-free antibody incubations only access protein on the cell surface. O. Wild type. Dl protein first appears on cell surfaces at the anterior of the morphogenetic furrow (arrow). P. Surface Dl protein is elevated and clearly detected both anterior and posterior to the furrow when expression is driven by the hH10transgene. Q. wild type. N protein outlines most eye disc cells. R. Similar levels of N protein reach the cell surface when Ser is overexpressed in and anterior to the furrow, even though these eye discs are strongly neurogenic due to reduced N function. S, T. Eye discs labelled for total Dl protein using detergent (bright fluorescent signal). S. wild type. An evolving pattern of Dl expression includes R8 precursors within groups of Dl-expressing cells just posterior to the morphogenetic furrow (arrowhead). T. hH10>SESI (same magnification; image recorded and processed identically to panel S). Dl protein reaches high levels in most eye disc cells. Note that Dl protein levels around the morphogenetic furrow (arrowhead) are higher than in any wild type cells.