Spermiogenesis in Platichthys flesus.

Early spermatids of Platichthys flesus (flounder) have a central spherical nucleus and cytoplasm with numerous dispersed mitochondria and a pair of peripheral centrioles. One of the centrioles acts as a kinetosome for axoneme formation. After the start of chromatin condensation the centrioles and developing axoneme migrate to adopt a tangential orientation adjacent to a flattened, lateral margin of the nucleus. During migration, pericentriolar material becomes reorganised. The proximal centriole becomes surrounded by nine fibres, and the distal centriole by a complex collar. As the nucleus condenses it undergoes a rotation which shifts it to the anterior of the centrioles and deepens the articular fossa which houses, and is connected to, the two centrioles and their associated structures. This rotation also results in the mitochondria becoming relocated to form a ring around the proximal region of the axoneme to give the cell its mature ultrastructure.