Presence of an excess of tubules containing step 8–9 spermatids in 4-week-old RARα−/− testes. A–H: Histological sections of 4-week-old testes from RARα+/+ (A,C,G) and RARα−/−mice (B,D–F,H). Arrows in B point to vacuolated regions. Arrows in D–F point to step 8–9 spermatids. G,H: γ-H2AX was used to confirm the presence of preleptotene/leptotene spermatocytes in both RARα+/+ (G) and RARα−/− testes (H). A,B: Original magnification, ×20. C–H: Original magnification, ×40. P, pachytene spermatocytes; PL/L, preleptotene or leptotene spermatocytes; B, type B spermatogonia; Z, zygotene spermatocytes; DSG, degenerating spermatogonia; ES, elongated spermatids. Arabic numerals indicate the step of spermatid differentiation. Roman numerals in C and G indicate the stage of the seminiferous tubules.