New structure found in sperm may help understand infertility

Cutting-edge microscopy has unveiled a structure inside sperm that may play a key role in infertility and birth defects.

The structure, which is newly identified in mammalian and human sperm, is a second centriole – a barrel-shaped structure found in cells which acts as a kind of scaffolding during cell division. It was thought that that mammalian sperm cells have only one centriole. The newly discovered second centriole is similar in function but has a slightly different shape, so the researchers have dubbed it as the 'atypical' centriole.

'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 Dr Tomer Avidor-Reiss at the University of Toledo in Toledo, Ohio, and senior study author.

He added: 'It also may have a role in early pregnancy loss and embryo development defects.' The research was published in Nature Communications.

Centrioles act in pairs during cell division and have a crucial role in the development of an embryo. Since oocytes lack centrioles, it was always thought that the sperm's centriole was duplicated within the zygote to give the two centrioles needed for it to divide.

The new study suggests this to be incorrect – the sperm already carries two centrioles. The atypical centriole contains a set of proteins that helps the other centriole to function after fertilisation.

Key to this discovery was super-resolution microscopy, which allowed the researchers to see proteins at the highest resolution. '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,' said Dr Avidor-Reiss.

Understanding more about the sperm's centrioles will help to determine whether these structures are involved in male infertility or defects in embryo development. The researchers are now planning to work with urology colleagues to understand the clinical implications of the atypical centriole.