Fig. 2. Growth of the retina is accompanied by changes in the patterning of progenitor cells. (A,B,E) Between stages 18 and 26, the ATH5 domain expands in register with the threefold increase in retina diameter. (C) HES1 transcripts are abundant at the periphery and sparse in the central region. Scattered cells expressing HES1 at a high level are detected in the central retina (arrowheads in L). The HES1 and ATH5 expression domains are complementary (B,C), but the anterior margin of the ATH5 domain overlaps the posterior HES1 region, where HES1 transcript levels are decreasing (brackets in H,I). ATH5 and NGN2 transcripts accumulate in the posterior retina (B,D). The NGN2 domain extends beyond that of ATH5 (brackets in J,K). At stage 26, ASH1- and ATH5-expressing cells are interspersed in the posterior retina. ASH1 extends beyond ATH5 (arrowheads in E,F). At stage 30, ATH5 transcripts are distributed throughout the whole retina (G), except at the ciliary margin (arrows). ATH5 transcripts are not evenly distributed across the retina. They are abundant on the ventricular side of the proliferative zone (pz) (inset in G). At stage 30, HES1 expression is downregulated both in the peripheral and in the central retina (M). Sections in L and M were counterstained with Toluidine Blue. Scale bar: 380 µm in A-G; 40 µm in L; 60 µm in M; 240 µm in H,I; 150 µm in J,K.