Domain: Natural Science — Cell & Developmental Biology
Target concept: Time-lapse imaging of eukaryotic cell mitosis demonstrates the breakdown and reformation of the nuclear envelope.

Video generation prompt: Time-lapse fluorescence microscopy of cultured eukaryotic cells with DNA labeled by a fluorescent dye, imaging the same cells continuously throughout mitotic division.

Evaluation guide:
(i) Target concept: Open mitosis in eukaryotic somatic cells requires reversible disassembly and reassembly of the nuclear envelope to permit spindle access to chromosomes.
Minimum mechanism: Nuclear lamina depolymerization triggers envelope vesiculation; post-mitotic membrane fusion and lamin reassembly restore compartmentalization; because only DNA is fluorescently labeled (not the envelope itself), the fluorescent DNA signal stays confined with a sharp edge only while the envelope is intact, so envelope status must be inferred from that edge rather than from a separately labeled rim.
(ii)Storyline: Frame 1-3: Interphase - the DNA fluorescence forms a compact mass with a smooth, sharply bounded edge, reflecting an intact envelope confining it. Frame 4-6: Prophase - that sharp edge grows uneven and develops gaps as the DNA begins condensing into discrete threads. Frame 7-8: Metaphase/Anaphase - the sharp DNA-signal boundary is fully lost as chromosomes align and then split into two separated groups. Frame 9-10: Telophase - a smooth, sharp edge reappears around each of the two separated DNA masses as they begin to decondense. Perspective: Fixed focal plane, single-cell view, no z-stack blending; the DNA signal and its boundary must be visible in the same optical section at all times.

Manual:
Experimental Procedure
1. Culture eukaryotic cells (e.g., HeLa) on glass-bottom dish.
2. Label DNA with fluorescent dye (e.g., Hoechst).
3. Acquire time-lapse fluorescence images at 30-sec intervals using confocal or widefield microscope.
Observation of Experimental Phenomena
- Because DNA is retained inside the nucleus only while the envelope is intact, the fluorescent DNA signal itself shows a smooth, sharply bounded edge in interphase - an indirect proxy for an intact nuclear envelope, not a separately labeled envelope structure.
- During mitosis, this sharp boundary breaks down and the DNA signal spreads or fragments as chromosomes condense and separate, consistent with loss of envelope confinement.
- After chromosome segregation, a sharp boundary re-forms around each daughter DNA mass as the envelope reassembles.
Summary of Experimental Principles
Time-lapse imaging of eukaryotic cell mitosis demonstrates the breakdown and reformation of the nuclear envelope - a hallmark of open mitosis in eukaryotes; because only DNA is labeled here, envelope integrity is inferred from the sharpness of the DNA signal's boundary rather than directly visualized.

Prompt Grounding rubric:
level_1: No cultured eukaryotic cells are visible; no fluorescently labeled DNA signal is present; no nuclear boundary or envelope-like structure is depicted; no time-lapse progression through mitosis is shown.
level_2: Cultured eukaryotic cells are present but are not clearly adherent or of typical interphase shape (e.g., rounded or phase-bright throughout); a fluorescent signal is present but is not confined to the nucleus; no boundary around the DNA signal is ever visible; no sequence from interphase into mitosis is discernible.
level_3: Cultured eukaryotic cells are visible and adherent; fluorescently labeled DNA signal is present inside the nucleus; the edge of that DNA signal forms a visible boundary around the DNA in at least one frame; at least two sequential frames show DNA condensation followed by the two DNA masses moving apart, consistent with mitotic progression, even if the boundary's breakdown is not clearly resolved.
level_4: Everything required for a 3-level score is present, and in early frames the fluorescent DNA signal is also confined within a continuous, smooth, ring-like edge indicating an intact nuclear envelope; in later frames that edge becomes patchy, broken into fragments, or disappears entirely while the DNA remains fluorescent and condenses; the loss and reappearance of this boundary is shown across the sequence; no extraneous objects or mislabeled signals appear.
level_5: Everything required for a 4-level score is present, and the DNA signal is exclusively nuclear during interphase with a smooth, closed, bright edge fully bounding it; in mid-sequence that edge visibly breaks into discrete puncta or disappears entirely while the condensed chromosomes separate; in late frames a new continuous edge reappears around each of the two segregated DNA masses; all of this happens within the same cell, in the same focal plane, from a fixed viewpoint, with no non-cellular artifacts.

Scientific and Causal Correctness rubric:
level_1: The fluorescent signal is mislocalized (e.g., present throughout the cytoplasm rather than the nucleus); the DNA signal stays diffuse throughout with no confinement at any point; no chromosome segregation is observed; the stages occur in a physically impossible order (e.g., the DNA boundary re-forms before chromosome segregation has completed).
level_2: The fluorescent signal is nuclear but stays static, with no visible condensation or separation; the DNA boundary stays intact throughout with no breakdown; or the boundary disappears before DNA condensation begins; or chromosomes separate while the boundary is still fully intact; or two daughter DNA masses form with no boundary ever reappearing around them.
level_3: The fluorescent DNA signal condenses and separates into two groups; the DNA boundary is intact through the first half of the sequence and broken or absent in the second half; the loss of the boundary coincides in time with chromosome separation; no frame shows the boundary intact while segregation is already underway; the boundary breakdown visibly precedes chromosome condensation and separation, consistent with envelope loss enabling spindle access.
level_4: The DNA boundary is continuous and intact around the signal in interphase; it fragments or disappears only after DNA begins condensing; chromosomes fully separate only while that boundary is absent or fragmented; the boundary reappears only after segregation is complete and the DNA begins to decondense; no frame shows the boundary reformed before segregation finishes, or the boundary absent after reformation has begun.
level_5: Boundary integrity is unambiguous at every stage: a fully continuous edge in interphase, progressive gaps and puncta during prophase, complete absence during metaphase/anaphase, reappearance as partial arcs during telophase, and full closure around each daughter DNA mass; the DNA fluorescence signal's intensity stays roughly constant and confined throughout; no frame mixes a partial boundary with completed segregation or otherwise breaks the canonical mitotic order.

Spatiotemporal Consistency rubric:
level_1: Cells teleport between frames; a cell or the DNA signal suddenly appears or disappears; the background lighting flips abruptly, e.g., from bright to black between consecutive frames; the DNA boundary jumps discontinuously in position or shape; a DNA mass vanishes and reappears elsewhere with no visible path connecting the two positions.
level_2: Cell boundaries flicker or warp unnaturally; the DNA-signal boundary pulses in and out of visibility without cause; the fluorescent signal blinks on and off rather than persisting continuously; motion freezes or skips for more than two consecutive frames; the background changes texture or contrast abruptly between adjacent frames.
level_3: Cell position stays stable across frames; the fluorescent DNA signal persists continuously; the DNA boundary changes gradually, e.g., smoothly thinning, then gapping, then disappearing, rather than jumping; there is no teleportation, blinking, or sudden structural break; chromosome movement is directional and continuous with no reversal or jump; the implied lighting and focus stay consistent throughout.
level_4: All cellular structures keep consistent spatial relationships: the cell shape changes only through the natural rounding of mitosis; the DNA boundary deforms smoothly with no tearing or warping; DNA condensation proceeds without sudden fragmentation or duplication; chromosome movement follows a straight or gently curved path toward the poles; no frame shows an implausible event such as the boundary re-forming across chromosomes that are still in the middle of separating.
level_5: Everything required for a 4-level score is present, and spatial continuity is complete: the cell outline, the nuclear region, and the fluorescent DNA boundary all change gradually frame to frame with no visible jump in position or shape; the boundary's breakdown looks like local fading and gap formation rather than vanishing all at once; boundary reformation in telophase starts at multiple points around each daughter mass and closes up continuously; no frame shows ghosting or a halo around the DNA signal inconsistent with ordinary microscope optics.