EM 319 Spermatogonium

Spermatogenesis

Transmission electron microscopy (TEM) of a spermatogonium in the seminiferous tubules of the testis.

Spermatogenesis is the process of sperm cell production. Histologically, the least mature cells are closest to the basal lamina, and the most mature cells are closest to the lumen of the seminiferous tubule

• Spermatogonia - diploid stem cells that undergo mitosis to produce more spermatogonia or differentiate into primary spermatocytes
• Primary Spermatocytes - undergo the first meiotic division to produce two haploid secondary spermatocytes
• Secondary Spermatocytes - undergo the second meiotic division to produce four haploid spermatids
• Spermiogenesis - complex differentiation that transforms spermatids into mature sperm cells (spermatozoa)

This image shows a spermatogonium (green) in the basal compartment of a seminiferous tubule. These cells have round nuclei surrounded by a narrow rim of cytoplasm.

Subcellular Structures:

• Nuclei (blue) / Nucleolus (yellow) / Nuclear Envelope (purple)
• Mitochondria (red)

Courtesy of Martin Dym, Department of Cell Biology, Georgetown University Medical Center, Washington, DC

Blood-Testis Barrier

Transmission electron microscopy (TEM) of a spermatogonium in the seminiferous tubules of the testis.

The blood-testis barrier is a complex structure formed by Sertoli cells within the seminiferous tubule of the testes. It creates a specific compartment for developing and maturing germ cells (spermatocytes and spermatids) by isolating them from the bloodstream.

This specimen was perfused with the electron-dense tracer lanthanum nitrate (dark blue) to demonstrate the blood-testis barrier. It diffused through the underlying connective tissue (orange) and intensely stained the thick basal lamina.

The seminiferous epithelium is divided into two compartments:

• Basal Compartment - open to the circulation
  • Tracer (dark blue) penetrated between Sertoli cells (tan) near the basal lamina
  • Plasma membrane (dark blue) of the spermatogonium is also stained
• Luminal Compartment - isolated from the circulation
  • Tracer could not pass the Sertoli-to-Sertoli junctional complexes (yellow) above the spermatogonium (dark brown)

Disruption of the blood-testis barrier can lead to male infertility.

Subcellular Structures:

• Nuclei (blue) / Nucleolus (yellow) / Nuclear Envelope (purple)
• Mitochondria (red)