In this new study, published in Science Advances and carried out in collaboration with the teams of Marie-Hélène Verlhac (Collège de France) and Elvan Böke (CRG Barcelona), we describe and characterise the Zollo body, a newly identified organelle-rich structure that forms transiently in growing oocytes.

Named after PhD student Noemi Zollo, who first observed the structure and drove the project, the Zollo body assembles next to the nucleus as the oocyte rapidly increases in size. It contains RNA, proteins, mitochondria, Golgi and endoplasmic reticulum organised around a central acentriolar microtubule-organising centre. Unlike the Balbiani body, a related structure associated with quiescence in very early oocytes, the Zollo body is an active site of protein synthesis. We further show that the helicase DDX5 is required to maintain the structure: its inhibition rapidly dissolves the Zollo body and arrests both oocyte and follicle growth.

Together, these findings reveal a new mechanism by which growing oocytes organise the cellular machinery required for their remarkable increase in size.