Cycling cells

Cycling cells are cells actively progressing through the cell cycle (G1, S, G2, and M phases), typically identified by expression of proliferation markers such as MKI67 and TOP2A. In single-cell atlases they represent a transient proliferative state rather than a fixed lineage and can arise from multiple progenitor or stem cell populations within a tissue. Their abundance reflects the turnover and regenerative activity of the tissue sampled.