A fluorescent ubiquitination-based cell-cycle indicator using phase-dependent stability of reporter fusions. The original Cdt1 and geminin reporters distinguish much of G1 phase from S phase/G2 phase/M phase, rather than reporting all phase boundaries independently.^[ref]

A replication-control protein whose regulated degradation motif is used in the original Fucci reporters.

Its normal role includes restricting replication licensing through interaction with Cdt1. In a Fucci construct, a selected degradation region is used to report regulated turnover; the reporter signal should not be equated with the full native protein’s activity. ^[ref]

An SKP1–cullin–F-box ubiquitin ligase complex directing substrate-selective ubiquitination. Recognition of degradation signals couples substrate destruction to cellular state.

Division with a preferred spindle or daughter-placement direction relative to tissue axes. An association with organ elongation requires causal tests before division orientation can be assigned the shaping role.

A budding-yeast cyclin-dependent-kinase inhibitor. Phosphorylation-dependent recognition by an SCF ubiquitin ligase couples its destruction to S-phase entry.

A pause or block in progression through the cell cycle. It can permit repair or become durable; arrest is not itself proof that molecular damage has been repaired.

The retinoblastoma tumour-suppressor protein, which restrains E2F-dependent proliferation when appropriately active. Regulation by cyclin-dependent kinases couples this restraint to cell-cycle signals.

A regulatory coactivator of the anaphase-promoting complex. Its activity helps maintain low mitotic-cyclin abundance during late mitosis and G1, before the next cell-cycle programme.

A cell-division-cycle mutant identified by a defect in cycle progression. A conditional growth defect alone does not establish a stage-specific cycle function.

A surveillance mechanism that restrains mitotic exit when the budding-yeast spindle is mispositioned. It is distinct from kinetochore-attachment surveillance by the spindle checkpoint.

A mechanism delaying mitotic entry when interphase centrosomes are misoriented relative to the niche in fly male germline stem cells. It couples geometry to the timing of an oriented division.

The budding-yeast signalling network promoting sustained Cdc14 activity and completion of mitosis. Its upstream Tem1 activity is restrained during an active spindle position checkpoint.

Quiescence is a reversible nonproliferating cellular state, often designated $G_0$, from which suitable signals can permit re-entry into the cell cycle. A biological cell in quiescence can retain active metabolism, maintain its specialized functions and respond to its environment. This distinguishes quiescence from cell death and from irreversible loss of proliferative capacity. For example, some resting lymphocytes resume cell proliferation after activation. ^[ref]

A 3D cell culture grows biological cells in a spatial arrangement extending through three dimensions, for example as aggregates or within an extracellular matrix. This changes contact geometry, mechanical constraints and access to nutrients relative to a flat monolayer. An epithelial cyst can reveal an enclosed lumen and directional organization that a two-dimensional image misses. Three-dimensional geometry alone does not establish that the culture reproduces every property of its source tissue. ^[ref]

A focal adhesion is a multiprotein connection between integrins and the actin cytoskeleton. It can transmit traction and change its assembly in response to loading.

A cell-cell junction coupling adhesion to the cytoskeleton. It can transmit mechanical load while being remodelled during epithelial movements.

A positively charged species with a formally trivalent oxygen center.