The explosion of life: lessons from live imaging of ovulation.

In brief: Ovulation converts endocrine signals into coordinated cellular, extracellular-matrix, and tissue remodelling to release an egg ready for fertilization. This review highlights how historical and emerging live-imaging approaches have transformed ovulation from a process inferred through static snapshots into a directly observable, staged programme whose multiscale regulation can now be studied quantitatively. Abstract: Ovulation is the process by which an egg is released from an ovarian follicle, ready for fertilization. It is a multiscale transformation that converts endocrine cues into coordinated tissue and extracellular matrix remodelling, culminating in physical rupture of the follicle wall. Live imaging has reshaped understanding by replacing static snapshots with direct observation of sequence and timing. Here, we outline the architecture of the preovulatory follicle and the LH-driven signalling programmes that coordinate cumulus expansion, oocyte maturation, tissue remodelling, and rupture. We then chart key imaging milestones-from early time-lapse of exteriorized ovaries, to clinical endoscopy in humans, perfused ovary preparations, intravital multiphoton microscopy, and ex vivo live imaging of isolated follicles. Finally, we summarize emerging approaches to probe physical regulation, including intrafollicular pressure measurements and complementary methods to quantify tissue and matrix mechanics. Together, these advances show that ovulation is a staged programme that demands quantitative, time-resolved measurements.