Figure 6.

Ultrastructural analysis of the control and Merlin mutant cysts during the elongation and individualization stages. (A-C) Sections of the cysts from the control FM6 (A), Mer³ (B), or Mer⁴ (C) testis at the elongation stage. (A) A dark paracrystalline body was seen within the major mitochondrial derivative in the control spermatid. Bar = 2 μm. (B) Some of the spermatids in the Mer³ cyst contained two paracrystalline bodies (filled arrowhead points to one example). Also, some spermatids had two axonemes (open arrowhead). Bar = 0.5 μm. (C) Two paracrystalline bodies within the major mitochondrial derivative were frequently seen in the elongating spermatids of the Mer⁴ cyst. Bar = 0.5 μm. (D-F) Cysts from the control FM6 (D), Mer³ (E), or Mer⁴ (F) testis at the individualization stage. (D) The association of axoneme with the mitochondrial derivatives was seen in the spermatids of the control cyst. Bar = 2 μm. (E) Spermatids in the Mer³ cyst might contain two abnormally-shaped (filled arrowhead) or three (arrow) paracrystalline bodies together with one axoneme, or have two paracrystalline-filled Nebenkerns but without the axoneme (open arrowhead). Bar = 0.5 μm. (F) Spermatids with multiple Nebenkerns with (open arrowhead) or without (filled arrowhead) axonemes together with cytoplasmic fragmentation were seen in the Mer⁴ cyst. Bar = 0.5 μm. (G-I) Cysts from the control FM6 (G), Mer³ (H), or Mer⁴ (I) testis at the late stage of individualization. (G) Individualized spermatids in the control cyst displayed a highly-ordered axoneme-Nebenkern pair. Bar = 0.5 μm. (H) The spermatids in the Mer³ cyst were poorly arranged and some of them appeared to be fused together. Bar = 0.5 μm. (I) The Mer⁴ cyst showed a complete destruction of spermatid individualization, resulting in empty spermatids with or without axoneme or Nebenkern. Insert illustrates the structure of axoneme appeared to be intact. Bar = 1 μm. Bar in the insert = 0.2 μm.