Monolayers of confluent elongated cells are frequently considered active nematics, featuring topological defects. In extensile systems, where cells extend further along their long axis, they can accumulate at defects and escape from defects. Nevertheless, collective dynamics surrounding integer defects remain insufficiently understood. We induce diverse  + 1 topological defects (asters, spirals, and targets) within neural progenitor cell monolayers using microfabricated patterns. Remarkably, cells migrate toward the cores of all  + 1 defects, challenging existing theories and conventional extensile/contractile dichotomy, which predicts escape from highly bent spirals and targets. By combining experiments and a continuum theory derived from a cell-level model, we identify previously overlooked nonlinear active forces driving this unexpected accumulation toward defect cores, providing a unified framework to explain cell behavior across defect types. Our findings establish  + 1 defects as probes to uncover key nonlinear features of active nematics, offering a methodology to characterize and classify cell monolayers.

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http://dx.doi.org/10.1038/s41467-025-57783-wDOI Listing

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