The process of spermiogenesis is traditionally divided into four stages: the Golgi phase, the cap phase, the acrosomal phase, and the maturation stage.
Spermatid DNA also undergoes packaging, becoming highly condensed. The DNA is packaged firstly with specific nuclear basic proteins, which are subsequently replaced with protamines during spermatid elongation. The resultant tightly packed chromatin is transcriptionally inactive.
During this phase, the developing spermatozoa orient themselves so that their tails point towards the center of the lumen, away from the epithelium.
The resulting spermatozoa are now mature but lack motility, rendering them sterile. The non-motile spermatozoa are transported to the epididymis in testicular fluid secreted by the Sertoli cells with the aid of peristaltic contraction.
Whilst in the epididymis they acquire motility. However, transport of the mature spermatozoa through the remainder of the male reproductive system is achieved via muscle contraction rather than the spermatozoon's recently acquired motility. A glycoprotein coat over the acrosome prevents the sperm from fertilizing the egg prior to traveling through the male and female reproductive tracts. Capacitation of the sperm by the enzymes FPP (fertilization promoting peptide, produced by the male) and heparin (in the female reproductive tract) remove this coat and allow sperm to bind to the egg.