New Key to Sperm Development

Researchers at the University of Illinois-Urbana recently discovered a gene and related mechanism that are fundamental to the embryonic development of the epididymis. The epididymis is the tightly coiled tube that readies sperm cells for their most important task – fertilization. Human sperm cells travel quickly from the testes to the penis mostly via the epididymis.

In findings published in the July 2007 issue of Proceedings of the National Academy of Sciences, the researchers noted that sperm cells in mice without sufficient amounts of the growth factor inhibin beta A do not experience normal epididymis development. Instead of creating a coiling effect, the structure remains a stunted, straight tube. Due to this fact, the sperm cannot travel through the epididymis. According to lead researcher Humphrey Hung-Chang Yao, professor of veterinary biosciences at the University of Chicago, when the sperm travels through the epididymis it changes its biochemical properties and helps develop the energy mechanism that allows it to swim. “So without this structure, under normal circumstances a male cannot be fertile,” he says.

Although a lack of testosterone in embryonic sperm development has been documented for decades as the reason for normal sperm growth and maintenance, this new study sheds new light on that view. All the normal indicators of sufficient testosterone levels were present in the mutant embryos. According to Yao, this new research shows that testosterone does not work alone in developing sperm. Previous studies have linked testosterone with other “regionally specific” factors to boost the development of structures such as the seminal vesicles or prostate gland. Inhibitin A is the first such factor shown to help produce epididymal coiling.

Before being formed in the embryo, the epididymis is part of a structure called the Wolffian duct. When testosterone levels in males begin to increase, the structure begins to grow and separate into the plumbing system connecting the testes and vas deferens, which brings the sperm to the penis.

The researchers hope that their discovery will help develop new treatments for male infertility.