Flagellar centriole

The connecting piece of spermatozoa contains two centrioles. The proximal centriole is of typical barrel shape and templates the axoneme as well attaches to the connecting piece to rigidly connect head and tail of the sperm cell. Both centrioles are subjected to remodeling during spermatogenesis, but the atypical distal centriole is further altered so that the doublet microtubules are disconnected from each other and additional rod-like structures appear between them. The distal centriole has an essential role in formation of the flagellar axoneme. Both centrioles are transferred to the oocyte upon fertilization and have a role in orchestrating the cytoskeleton in the early zygote.

The centrioles of spermatozoa can be seen as a dot in the neck region of the sperm. The proximal centriole is close to the nucleus, while the distal centriole is further away from the nucleus and closer to the plasma membrane of the connecting piece.

Read more about the flagellar centrioles as substructures of sperm.