EM 320 Spermatids

Spermiogenesis

Transmission electron micrographs (TEM) of spermatids undergoing spermiogenesis.

Spermiogenesis is the differentiation of spermatids (green) into mature sperm cells that occurs in four phases:

• Golgi Phase (not shown) - the Golgi apparatus produces enzymes that become the acrosome
  • Spherical cells
• Cap Phase (left) - Golgi apparatus covers the nucleus forming the acrosome (yellow)
  • Polarity develops with the acrosome at one end (head) and developing mid-piece at the other end
  • DNA becomes tightly packed with histones being replaced by protamines
  • Centriole (yellow) are located at the base of the spermatids
• Tail Phase (middle) - production of the tail of the spermatids
  • One of the centrioles elongates to form the axoneme at the core of the tail
  • Tails point towards the center of the lumen
• Maturation Phase (right) - transformation of spermatids into spermatozoon
  • Early maturation phase before the mitochondria (red) are helically arranged around the axoneme (orange) in the mid-piece
  • Residual organelles and excess cytoplasm are phagocytized by the Sertoli cells (dark green)

Spermiation is the release of mature spermatozoa from the Sertoli cells into the lumen of the seminiferous tubule. The mature spermatozoa are also called sperm cells.

Subcellular Structures

• Nuclei (blue) / Nucleolus (yellow) / Nuclear Envelope (purple)
• Golgi Apparatus (yellow)
• Mitochondria (red)
• Endoplasmic Reticulum (cyan)

Courtesy of Martin Dym, Department of Cell Biology, Georgetown University School of Medicine, Washington, DC