Model for NuMA’s role in nuclear formation and mechanics, and its structural role over the cell cycle. NuMA (blue) plays a spindle-independent role in nuclear formation (“Mitotic exit,” center) and mechanics (“Interphase,” right). It keeps the chromosome (pink) mass compact at nuclear formation, and is essential to building a single, round and mechanically robust nucleus (“+NuMA”, top). Without NuMA (“-NuMA”, bottom), micronucleation and nuclear shape defects occur. We propose two models for how NuMA, whose C terminus binds interphase chromosomes (pink arrow), performs its nuclear function. To promote nuclear formation and mechanics, NuMA could cross-link chromosomes (Model A, blue filaments) or regulate nuclear envelope (green) assembly and maturation (Model B, black arrow), either directly or indirectly. At “Mitosis” (left), NuMA plays a critical role in spindle formation and mechanics, and its coiled-coil prevents it from binding chromosomes (blue inhibitory arrow), when these must but segregated instead of kept together. At mitotic exit and interphase, the coiled-coil drives NuMA’s nuclear dynamics and function (blue arrow). As such, we propose that NuMA’s coiled-coil acts as a central regulatory and structural element to control its function in space and time. Altogether, NuMA is essential to the formation and stability of two of the cell’s largest structures, the spindle and the nucleus. Figure created with Biorender.com.