Life doesn't begin the way we thought it did. A new study shows that a father donates not one, but two centrioles through the sperm during fertilization, and the newly discovered sperm structure may contribute to infertility, miscarriages and birth defects.
The newly discovered centriole functions similarly and along with the known centriole. However, it is structured differently.
"This research is significant because abnormalities in the formation and function of the atypical centriole may be the root of infertility of unknown cause in couples who have no treatment options available to them," said the senior author. "It also may have a role in early pregnancy loss and embryo development defects."
The centriole is the only essential cellular structure contributed solely by the father. It is the origin of all of the centrioles in the trillions of cells that make up the adult human body. Centrioles are essential for building the cell's antennae, known as cilia, and cytoskeleton, as well as completing accurate cell division.
A zygote, or fertilized egg cell, needs two centrioles to start life. It was previously thought that sperm provides a single centriole to the egg and then duplicates itself.
"Since the mother's egg does not provide centrioles, and the father's sperm possesses only one recognizable centriole, we wanted to know where the second centriole in zygotes comes from," senior author said. "We found the previously elusive centriole using cutting-edge techniques and microscopes. It was overlooked in the past because it's completely different from the known centriole in terms of structure and protein composition."
Authors show that the sperm centrosome contains, in addition to the known typical barrel-shaped centriole (the proximal centriole, PC), a surrounding matrix (pericentriolar material, PCM), and an atypical centriole (distal centriole, DC) composed of splayed microtubules surrounding previously undescribed rods of centriole luminal proteins. The sperm centrosome is remodeled by both reduction and enrichment of specific proteins and the formation of these rods during spermatogenesis.
In vivo and in vitro investigations show that the flagellumattached, atypical DC is capable of recruiting PCM, forming a daughter centriole, and localizing to the spindle pole during mitosis. Thus, the authors show that the DC is compositionally and structurally remodeled into an atypical centriole, which functions as the zygote’s second centriole.
Sperm provides both centrioles during fertilization!
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