Fig. 5. Birth and death of En-positive and En-negative neurons. (A,B) Birth of neurons. The embryo was injected with BrdU at 35% and dissected after a further 48 hours (45% embryogenesis). Labeling was by anti-HRP (green), anti-BrdU (blue) and anti-En (red). The MNB, GMCs, GCs and the neurons born during the injection period are BrdU positive. In A, a T3 neuromere, examples of BrdU-positive neurons that have downregulated En (En-negative) are marked by single stars; those that have some level of En are marked by double stars. Two neurons born prior to BrdU injection are also marked: one En negative (En-) and the other En positive (En+). The horizontal arrow indicates a dividing GMC. In B, an A1 neuromere, sibling BrdU-positive neurons are marked: one is En negative (single arrow, left); the other is En positive (double arrow, right). (C,D) Death of neurons. Pyknotic profiles shown in DIC images, with superimposed labeling from anti-HRP (green) and anti-En (red). (C) Pyknotic profiles at 70% in T3 (En positive, black arrows; En negative, white arrow); (D) pyknotic profiles at 55% in A1 (En negative, white arrows). Scale bar: 20 µm.