Fig. 1. Early germ cells accumulate in stet mutant testes. (A,C,E,G,I) Wild-type and (B,D,F,H,J) stet mutant testes, apical tips towards the left. Scale bars: 0.1 mm. (A,B) Phase-contrast images of adult (A) wild-type and (B) stet ⁸⁷¹ mutant testes; small early germ cells (arrowheads) at the apical tip of wild-type testes and throughout stet mutant testes. Larger spermatocytes (black arrow) displaced away from the tip, differentiating round spermatids (white arrow) along the coil of the testis, bundles of elongated spermatids (ST), in wild type as indicated. (C,D) Third instar larval testes showing cells expressing the S3-46 marker (C) at the tip of wild-type testis (arrowhead) and (D) filling almost the entire stet mutant testis. (E,F) Third instar larval testes from (E) wild-type and (F) stet stained with anti-FasIII (red) and anti-phosphorylated Histone-H3 (green). Single anti-phosphorylated H3-positive cells are indicated by arrowheads. Dividing spermatogonia (arrow) are seen as clusters of eight anti-phosphorylated Histone-H3-positive cells in wild type. (G,H) Third instar larval testes stained with anti-FasIII (green) and anti--spectrin (red) of (G) wild-type and (H) stet with -spectrin staining in spectrosomes (arrowheads) and in branched fusomes (arrows). Note slightly enlarged apical hub (green) in stet mutant testis compared with wild type. (I,J) In situ hybridization with esg mRNA in adult (G) wild-type and (H) stet mutant testes. Arrows indicate esg-positive cells at tip in wild type.