The spatiotemporal distribution of LIN-5/NuMA regulates spindle orientation and tissue organization in the C. elegans germ line

Mitotic spindle orientation sets the cell division plane and is thus critical for maintaining tissue organization. The C. elegans gonad is tube-shaped, with germ cells forming a circumferential monolayer around a shared inner core of cytoplasm called the rachis. Each germ cell is connected to the rachis via a stable cytoplasmic bridge, polarizing germ cells along their rachis-basal axis. How this tissue organization is maintained during development is unclear, as germ cells lack the canonical cell-cell junctions that, in other tissue types, ensure proper spindle orientation. Here we use live-cell imaging of C. elegans germ cells, both in situ and in gonad explants, to show that the microtubule force generator dynein and its conserved regulator LIN-5/NuMA regulate spindle orientation in C. elegans germ cells and are required for germline tissue organization. We uncover a cyclic, polarized pattern of LIN-5/NuMA cortical localization that predicts centriole/centrosome positioning throughout the cell cycle, providing a means to align spindle orientation with the tissue plane. This work reveals a new mechanism by which oriented cell division can be achieved to maintain tissue organization during animal development.