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It was observed in a recent study that sperm gets switched on as they move closer to the egg, thereby penetrating and fertilizing the egg, according to a study published in the journal Science.

When the sperm moves closer to the egg, female sex hormone progesterone is released from the egg. The hormone thus released triggers the sperm to enter the egg in order for fertilization, reported Medical Daily.

The findings give a deep insight on male infertility as well as serve as a key for the development of unisex contraceptives. 

Progesterone released from the egg activates the protein receptor, enzyme alpha/beta hydrolase domain containing protein 2 (ABHD2) present on the surface of the tail region of the sperm. Once after the activation cascade of reactions take place that kick start the sperm to move rapidly and enter the egg.

"This is an important advance in explaining how sperm become hypermotile in the female reproductive tract," said Dr Stuart Moss, director of the male reproductive health program at NIH's Eunice Kennedy Shriver National Institute of Child Health and Human Development, which funded the study, according to NIH.

"Developing new compounds that block ABHD2 ultimately may yield new contraceptive methods to prevent sperm from reaching the egg," Moss added.

For the sperm to attain the hyper-active phase, calcium must enter through the outer-membrane of the sperm and reach the flagella. The flagella is the tail-like structure that helps the sperm in mobility. CatSper, a sperm protein alongside few other similar proteins assist the entry of calcium into the flagella.

The researchers studied whether progesterone is directly involved in the activation of CatSper, in series of experiments. The sperms were subjected to chemical inactivation of certain enzymes and were also exposed to progesterone directly and so on. It was found that with inactivated ABHD2, the progesterone were unable to trigger the CatSper, noted MNT.