Fig. 4. Kr is necessary and sufficient to specify the second temporal identity. (A) In Kr mutant Drosophila embryos, RP3 is missing in the majority of hemisegments examined (both rows) and RP5 is occasionally missing (second row), whereas RP1/RP4 are normal (Table 1). Wild type has RP1, RP4, RP3 and RP5 neurons (see Fig. 2). (B) Kr misexpression (insc-gal4 UAS-Kr) generates ectopic RP3 neurons, RP5 is usually absent, and RP1/RP4 are normal (Table 1). For all panels, a single representative hemisegment of a stage-16 CNS is shown as a maximum intensity projection. Midline, left; anterior, up. A phenotype summary is shown to the right. Scale bar: 3 µm.