Nicotinamide salvage is required for proliferation and sustaining self-renewal in undifferentiated embryonic stem cells
Bibliographic record
Abstract
Stem cells use oxidized nicotinamide adenine dinucleotide (NAD+) in distinct subcellular compartments to support self-renewal and to regulate chromatin. There is limited information, however, about the biosynthetic pathways that replenish intracellular NAD+, which is continuously turned over in undifferentiated mouse embryonic stem cells. Establishing specific metabolic inputs for maintaining self-renewal can help direct reprogramming efforts. We used single fluorescent protein biosensors for in situ NAD+ measurements in J1 mouse embryonic stem cells. Sensors and controls were localized to the nucleus, cytoplasm, and mitochondrial compartments. Using a specific inhibitor for nicotinamide salvage, we found that loss of this pathway depleted NAD+ concentrations in all three subcellular compartments in undifferentiated culture conditions. We determined that loss of nicotinamide salvage reduced colony size, extended cell cycle, and resulted in diminished expression of self-renewal markers. Supplementation with precursors in the nicotinamide salvage pathway bypassed the pharmacological block, replenished cytosolic NAD+ levels, and reversed the effects on colony size. Notably, supplementation with deaminated precursors did not replenish intracellular NAD+ levels, suggesting minimal contribution from this pathway at this stage. In support, expression data from multiple mouse and human lines showed that nicotinamide salvage pathway enzyme NAMPT was predominantly expressed at the embryonic stem cell stage compared to the enzymes in other NAD+ biosynthesis pathways. Collectively, the data showed that undifferentiated embryonic stem cells heavily rely on nicotinamide salvage, indicating that this dependency is conserved.
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How this classification was reachedexpand
Full frame machine prediction
Teacher imitationNot calibrated prevalence, not ground truth. Human validation pending. The Gemma side is a direct model label for every work in the frame, read from the title-only record. The Codex side is a classifier learned from the 10,348 direct Codex labels and calibrated to design-weighted sample rates; fields without enough sample support carry no Codex call. Candidate is the union of the two sides; consensus is their intersection. These outputs are machine_predicted_unvalidated and are not human labels.
Distilled classifier scores by category (both heads)
| Category | Codex | Gemma |
|---|---|---|
| Metaresearch | 0.000 | 0.000 |
| Meta-epidemiology (narrow) | 0.000 | 0.000 |
| Meta-epidemiology (broad) | 0.000 | 0.000 |
| Bibliometrics | 0.000 | 0.000 |
| Science and technology studies | 0.000 | 0.000 |
| Scholarly communication | 0.000 | 0.000 |
| Open science | 0.000 | 0.000 |
| Research integrity | 0.000 | 0.000 |
| Insufficient payload (model declined to judge) | 0.001 | 0.000 |
Machine scores (provisional)
The two teacher heads of the student model, read on this work. A score orders the frame for review; it never asserts a category, and the validation status ships verbatim with every row.
Baseline scores from an immature model (maturity gate not passed, 7 training rounds). Scores rank; they never assert a category.
score_only:v0-immature-baseline · verbatim from the scoring run: score_only means the number may rank works, and no category label ships from itClassification
machine, unvalidatedMachine predicted; a candidate call from one source (direct Gemma or distilled Codex), not a consensus.
How this classification was reached, model by model and score by score, is at the end of the page under "How this classification was reached".