When Does the Cleavage Furrow Form? Mitosis Timeline Explained
The cleavage furrow is the indentation that appears around the equator of a dividing animal cell, pinching it inward until it splits into two daughter cells during cytokinesis. If you’re asking when the cleavage furrow forms, the precise answer is: the contractile ring that drives it begins assembling in early anaphase, and the physical furrow becomes obvious as anaphase gives way to telophase, completing during cytokinesis.
Cleavage Furrow Timing
The furrow does not appear out of nowhere at the end of division. Its machinery is built earlier, but the visible indentation belongs to the tail end of mitosis. Assembly of the contractile ring begins in early anaphase, while the chromosomes are still being pulled apart toward opposite poles Wikipedia — Cleavage furrow.
By late anaphase, that ring starts to tighten, and the cell’s surface visibly puckers at the equator. The indentation then deepens through telophase, where the furrow compresses the cell into a narrow intercellular bridge containing bundled spindle microtubules. That bridge is the last physical connection between the two halves, and it eventually breaks and reseals, producing two separate, membrane-complete daughter cells during cytokinesis.
In short: ring assembly starts in anaphase, the furrow becomes visible in late anaphase, deepens in telophase, and finishes the split in cytokinesis.
Mechanism of Furrow Formation
The engine behind the furrow is the contractile ring, a band of actin filaments and myosin motor proteins that assembles just inside the plasma membrane at the cell’s equator. Actin and myosin are the same proteins that drive muscle contraction, and here they work in a similar way. Myosin motors pull on overlapping actin filaments, shortening the ring’s circumference. The actin pool is a mix of pre-existing filaments and newly assembled ones.
As the ring shortens, it drags the attached plasma membrane inward with it, creating the characteristic groove. The ring is not acting alone: additional cytoskeletal proteins and actin-binding proteins help anchor and organize the structure National Center for Biotechnology Information. Positioning matters as much as contraction. The ring forms specifically at the equatorial region, guided by signals from the mitotic spindle, so the cell divides evenly rather than off-center.
During telophase, the deepening furrow leaves behind an intercellular bridge built around spindle fibers. The lipid phosphatidylethanolamine is present at this stage, suggesting it helps shuttle membrane material as the surface rearranges Molecular Biology of the Cell (Garland Science). The bridge then breaks, and calcium-dependent exocytosis using Golgi vesicles reseals each new cell with an intact membrane.
Furrow in Mitosis Timeline
Here is where furrow formation fits across the phases of mitosis, using the standard four-phase framework Nature Education (Scitable):
| Phase | Main event | Furrow status |
|---|---|---|
| Prophase | Spindle fibers appear; chromosomes condense | No furrow |
| Metaphase | Chromosomes align along the equatorial plate | No furrow; ring components begin to gather |
| Anaphase | Chromosomes move to opposite poles | Ring assembles early; furrow appears late |
| Telophase | Nuclear division completes | Furrow deepens, forms bridge, then splits the cell |
A short worked example makes the sequence concrete. Imagine watching a single animal cell divide under a microscope. During metaphase, the chromosomes sit neatly in the middle, and the surface looks smooth. Early in anaphase, the chromosomes start moving apart and molecular machinery quietly collects at the equator. Late in anaphase, a small dimple appears. Through telophase, that dimple cinches tighter, like pulling a drawstring on a pouch, until the cell is pinched into two.
Note that mitosis (nuclear division) and cytokinesis (cytoplasmic division) overlap at the boundary. The furrow is the visible handoff between them. Because the furrow can begin before the nuclear envelope has fully rebuilt, it is best described as spanning the anaphase-telophase boundary rather than belonging to any single phase.
Animal vs Plant Cells
The cleavage furrow is animal-specific. Animal cells divide by physically pinching the membrane inward, which works because they have a flexible outer membrane and no rigid cell wall.
Plant cells face a structural problem: a stiff cell wall prevents them from being squeezed in half. Instead, Golgi vesicle secretions gather along the equatorial plane and fuse to build a cell plate that grows outward and eventually becomes a new cell wall. This process is directed by microtubules of the phragmoplast. The two strategies are not totally unrelated. Both rely on microtubules and microfilaments for movement, and both use Golgi-derived vesicular secretions to build new membrane and reseal the dividing cells. So the furrow and the cell plate are different structures solving the same problem: separating one cell into two.
Key Takeaways
- The cleavage furrow first appears in late anaphase and deepens through telophase into cytokinesis.
- The contractile ring of actin and myosin begins assembling in early anaphase at the cell equator.
- Myosin motors pull actin filaments together, shrinking the ring and pulling the membrane inward to form the indentation.
- During telophase, the furrow creates an intercellular bridge that breaks and reseals to yield two daughter cells.
- Cleavage furrows occur in animal cells; plant cells instead build a cell plate via Golgi vesicles and the phragmoplast.
