A core challenge in biology is understanding how processes in the body, such as cellular development and regeneration, unfold over long stretches of time, making them notoriously difficult to view at the molecular level. Now, a team led by researchers at Caltech has shown that a single snapshot of a mouse testis is enough to reconstruct the entire weeks-long cycle of sperm production, along with the cell-to-cell coordination that organizes it. The key lies in using the spatial organization of the tissue. Each testis is essentially a tightly packed bundle of long tubes called seminiferous tubules, and sperm production unfolds inside them as a slow periodic cycle, known as the seminiferous epithelial cycle. "Because each tubule cycles independently, a snapshot of the tissue catches different tubules at different stages, like frames from a movie scattered around a room," says Arun Chakravorty (PhD '25), a student in the MD-PhD joint program between Caltech and the David Geffen School of Medicine at UCLA.…