Live imaging captures the events immediately following fertilization.

High-resolution live imaging reveals two distinct phases of sperm remodeling and movement during mammalian fertilization, including in human oocytes.

• Why it matters: Understanding the dynamic processes immediately after fertilization is crucial for insights into reproductive biology and potential fertility interventions, as most studies have relied on static samples.
• What they did: The study employed high-resolution live imaging to observe fertilization in zona-intact mouse oocytes and human oocytes, identifying static and mobile phases of sperm behavior and the cellular mechanisms driving movement.
• The result: Findings establish a detailed spatiotemporal framework of fertilization, highlighting the roles of cytoplasmic streaming, chromatin decondensation, and cortical flows, which could inform fertility research and assisted reproductive technologies.