G1early

G1early is a term used in cellular biology to describe an early substage of the G1 phase of the eukaryotic cell cycle. In this framing, G1 is divided into an initial phase, G1early, followed by later G1 when cells commit to DNA synthesis (S phase). The concept emerges in studies of how cells exit mitosis and re-enter the cycle, and how transcriptional and metabolic programs are re-initiated after cytokinesis. In G1early, cells typically display initial chromatin remodeling, accumulation of G1 cyclins, and partial phosphorylation of the retinoblastoma (Rb) protein, which primes E2F targets for later activation, but does not yet commit the cell to S phase.

Measurement and interpretation: G1early is inferred from time-resolved measurements such as single-cell RNA-seq, live-cell imaging of cyclin levels, and markers like Cyclin D and early S-phase entry indicators. It is used in computational models of the cell cycle to capture the tempo and heterogeneity of early re-entry after division. It is not universally adopted; some researchers view G1 as a continuous phase with no distinct sub-stages, while others use G1early to describe rapid early re-entry features.

Relation to G0, G1, S: G1early is distinct from G0 (quiescent) and from late G1; it marks the return from mitosis and the initial pass through G1 before restriction point. The exact timing varies between cell types and conditions. Potential applications include cancer research, developmental biology, and tissue regeneration, where the timing of early G1 decisions can influence proliferation and cell fate.

See also: G1 phase, cell cycle, Cyclin D, CDK4/6, Rb.