Inside mammalian reproduction

The Jackson Laboratory

Mammalian reproduction—including our own—carries with it an interesting problem. In males, sperm don't mature until puberty. But our immune system is programmed well before puberty to recognize what is our tissue versus what is foreign. As a result, if immune cells encounter mature sperm, they mistakenly attack, leading to infertility.

The solution is the blood-testis barrier, a wall made of specialized cells—known as Sertoli cells—that restricts access to the area in the testes in which sperm mature. The precursor cells—the cells that will develop into sperm—somehow have to pass through the barrier, however. Until now no one knew how it happens.

Benjamin Smith, a doctoral student, teamed with Professor and Vice President for Research Robert Braun, Ph.D., to discover how precursor cells, packaged within cysts containing many cells, manage to cross this barrier. High-resolution microscopy and advanced genetics revealed that the Sertoli cells in the barrier wall form temporary compartments through which the cysts can move. These compartments open ahead of the cysts and close behind them, allowing the cysts and their cargo of precursor cells to move through the barrier, while keeping immune cells out.

The research shows the inner workings of a complex immune barrier, whose function is vital to male fertility.


Smith BE, Braun RE. 2012. Germ Cell Migration across Sertoli Cell Tight Junctions. Science. DOI: 10.1126/science.1219969