It had been believed for decades that spermatozoa are translationally silent. However, Dr. Yael Gur and Haim Breitbart (Bar-Ilan University, Israel) now show that, in fact, protein translation does take place in mammalian sperm prior to fertilization.

Their paper has been released online ahead of print at www.genesdev.

After ejaculation, sperm reside in the female reproductive tract for several hours. During this time, a number of biochemical changes take place within sperm, collectively known as "capacitation," that render the sperm competent to penetrate and fertilize the female oocyte.

In their new report, Drs. Gur and Breitbart demonstrate that human, rat, bovine and mouse sperm all incorporate labeled amino acids into polypeptides during the capacitation phase. They identify that mitochondrial translation machinery (as opposed to cytoplasmic) directs translation of nuclear-encoded genes in sperm, and that its inhibition leads to a marked decrease in sperm motility, actin polymerization, the acrosome reaction and in vitro fertilization rates.

Thus, protein translation in sperm is essential for sperm functions that directly contribute to fertilization. Dr. Breitbart is confident that "The new findings would give us better understanding for treatment of male infertility and developing new male or female contraceptives."

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The researchers found that long-term use of antidepressants, such as fluoxetine (Prozac) and imipramine (Trofanil), were successful in reversing the social withdrawal in these mice. But the successful use of the gene therapy approach to block the expression of the BDNF gene in a highly localized area of the brain suggests the potential for the development of new drug therapies with fewer side effects.

"We have made great progress in our understanding of how antidepressants work, but despite years of research, our knowledge of the changes that these drugs induce in the brain is rudimentary," Bolanos said. "Though available treatments for depression are generally safe and effective, they are still not ideal. It takes long-term treatment before seeing clinical benefit, and potential side effects are a serious problem. The findings of this study provide exciting new leads and point to potential strategies, such as developing drugs capable of targeting specific proteins in restricted brain areas."

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