Temporal and anteriorly positioned mitotic zones drive asymmetric microtubule patterns needed for Left-Right Organizer development

Cellular proliferation plays a crucial role in tissue development, particularly in the Left-Right Organizer (LRO) essential for vertebrate LR body plans. We hypothesize that LRO precursor cells coordinate specific, temporally, and spatially modulated division events. Utilizing zebrafish, we mapped all LRO (Kupffer’s Vesicle, KV) mitotic events, revealing an FGF-dependent, anteriorly enriched mitotic pattern. We engineered a KV-specific fluorescent microtubule (MT) line, where we found that mitotic events align their spindle along the KV’s longest axis until the rosette developmental stage, where "spinning" spindles followed by KV exclusion occur. The daughter cells that remain are linked by cytokinetic bridges, shaping anteriorly focused KV MT patterns. Targeted loss of temporal zonal mitotic populations unveils an early mitotic population crucial for asymmetric MT pattern formation and LRO development, while later events are dispensable. Our findings underscore the importance of spatially regulated mitotic events in establishing MT pattern formation essential for LRO development.