Centrioles are found in animal cells and a few plants. Structures composed of microscopic tubes arranged to rest parallel to each other are positioned around a central hole to form a barrel shape. It’s not always entirely clear what they’re for, but a new study in Nature Communications suggests that a newly discovered second centriole in sperm may be responsible for fertility problems.
Spermatozoa were thought to contain just one centriole, which has been considered to be all-important. Within the trillions of cells that make up the human body, centrioles are vital for constructing cilia – filaments that often provide cellular locomotion – as well as promoting healthy cellular division.
As it happens, there’s much we still have to learn about sperm. This ranges from why lower sperm counts may indicate other health problems to the identification of new structures, and this latest research – led by the University of Toledo – is the latest addition to the latter category.
A longstanding enigma about centrioles in humans is that the father only provides one. At some point, another appears, and both are required for a fertilized egg cell – a zygote – to function properly. The assumption was that this centriole from the father replicated itself, but this latest research took another look at that and found no such evidence for it.
Using a series of extremely powerful microscopy techniques, the team looked at a range of spermatozoa, starting with that of flies, beetles, and cattle before taking a look at that belonging to our very own species. They appear to have relied quite heavily on “super-resolution microscopy”, which circumvents the inability of conventional lenses to resolve extremely tiny details by using multiple visualization techniques at the same time.
Thanks to this cutting-edge tech, the team were able to spot a second centriole within sperm, similar to second centrioles recently discovered in insect sperm. It appears that it functions much like the original, but is structured differently and is comprised of different protein compositions.
Importantly, it’s fairly unclear what it’s for, but the team do speculate a little.
First, it seems that this so-called “atypical” centriole’s core proteins are comparable to those in the original. At the same time, previous work on Drosphila (small fruit flies) found that this atypical centriole is vital for successful fertilization of the egg during reproduction.
The authors infer, then, that “the human atypical [centriole] may be instrumental in fertility.” This, in turn, suggests that forms of male infertility could be solved if we better understand the behavior of these two centrioles. Alternatively, we could design new experimental male contraception techniques around this atypical centriole.
It’s early days, though – right now, this discovery has brought with it more questions than answers.
[H/T: Science Alert]