Review papers with raw data transparency

Concise critical verdict

This preprint reports that elevated intracellular Ca2+ supports mESC identity by stabilizing core pluripotency proteins Oct4 and Nanog at the posttranslational level via pCamkIIalpha, and by modulating posttranscriptional processes (p-bodies, NMD and splicing) and mitochondrial state; most claims are supported by microscopy, biochemical assays, CHX/MG132 perturbations and a small phosphoproteomics dataset (MSV000099451), but several conclusions depend on limited sample sizes (phosphoproteomics n=2) and on in vitro pharmacological manipulations that have known off target effects (BAPTA, thapsigargin) so the results are provocative but require additional orthogonal validation Paper Abstract and Key Claims

Detailed critical review of: Calcium: Modulator of Post-transcriptional and post-translational process in mESCs

Paper snapshot

• Preprint DOI: 10.1101/2025.10.16.681898; deposited phosphoproteomics dataset MSV000099451 (MassIVE) MassIVE dataset statement
• Model: mouse embryonic stem cells (E14TG2a, E14) under LIF, Ca2+ manipulated by BAPTA chelation (B2uM etc.) and SERCA or pCamkIIalpha knockdown (shRNA); assays: IF, western, qPCR, polysomes, CHX/MG132, reporters for NMD, confocal microscopy, phosphoproteomics (n=2) Methods summary and dataset

Major claims and supporting data (paper excerpts cited verbatim)

1. High Ca2+ in undifferentiated mESCs; Ca2+ depletion causes G2/M arrest and mesoderm differentiation. Paper excerpt: "We have noted the presence of high Ca2+ in undifferentiated mESCs and showed that its depletion exerts G2/M cell cycle arrest, spontaneous differentiation of mESCs towards mesoderm lineage and mitochondrial biogenesis." High Ca2+ and differentiation claim
2. Ca2+ regulates Oct4 and Nanog stability post-translationally via pCamkIIalpha, independent of transcription, translation and JAK-STAT3. Paper excerpt: "Further, our data demonstrates that Ca2+ regulates the homeostasis and stability of Oct4 and Nanog at the post-translational level through pCamkIIα dependent mechanism independent of polyubiquitin system, JAK-STAT3 pathway, transcriptional and translational control." Oct4 Nanog pCamkIIalpha claim
3. Ca2+ modulates p-bodies/stress granule markers and NMD pathways. Paper excerpt: "Our data also signifies the role of Ca2+ at the post-transcriptional level in regulating p-bodies and stress granule markers (Dcp1a, XRN1, Tudor and EDC4), splicing-dependent and 3’UTR-dependent NMD activity." p-bodies NMD claim
4. Phosphoproteomics link Ca2+ changes to spliceosome and mRNA surveillance pathways. Paper excerpt: "We identified 53 phosphoproteins (PP) that were significantly upregulated and 35 PP downregulated in B2uM samples (n=2)... KEGG/GO enrichment highlighted spliceosome and mRNA surveillance pathways... PPI network: 1385 interactions with expected 689 (p=0)." Phosphoproteomics summary
5. Mitochondrial morphology and biogenesis respond to Ca2+ reduction. Paper excerpt: "Our data also suggest globular mitochondria in undifferentiated mESCs and long tubular mitochondria as well as an increase in the number of mitochondria upon Ca2+ reduction in mESCs which illustrate that low calcium might be needed for mitochondrial biogenesis." Mitochondrial morphology claim

Strengths

• Multi-modal experimental approach: imaging (Fluo4, ER GCamp), reporters (NMD), biochemical (CHX chase, MG132), polysome profiles, genetic perturbation (pCamkIIα and SERCA2 KD) and phosphoproteomics provide convergent evidence for Ca2+ effects on proteostasis and RNA metabolism Multi-assay evidence
• Data deposition (MassIVE) and detailed methods allow re-analysis and follow-up (good for reproducibility) Data deposition

Weaknesses, limitations and potential confounders

1. Phosphoproteomics sample size — n=2 biological samples: the authors state "n=2" for phosphoproteomics which limits confident identification of regulated phosphosites and pathway-level inference (risk of false positives, batch effects) Phosphoproteomics n=2
2. Pharmacological manipulations can be pleiotropic — BAPTA and thapsigargin alter Ca2+ but also have secondary effects (e.g., chelation of other divalent cations, ER stress via thapsigargin). The authors partially address this by SERCA2 KD and pCamkIIα KD, but off-targets remain a concern and require orthogonal rescue experiments (e.g., Ca2+ repletion, Ca2+ channel specific modulation) Pharmacology and KD methods
3. Causality vs correlation for differentiation — Oct4/Nanog protein stability changes may be primary to Ca2+ signalling or downstream of early differentiation signals; authors show transcripts unchanged but more stringent lineage tracking and rescue (restore Ca2+ after BAPTA) would clarify directionality Transcription unchanged claim
4. Proteasome independence claim needs fuller biochemical proof — MG132 partial rescue and decreased pUBQ are consistent with alternative degradation pathways, but distinguishing 20S versus 26S proteasome, lysosomal/autophagy, calpain or caspase pathways requires more selective inhibitors and biochemical fractionation; authors note autophagy marker LC3 is low but that alone is insufficient to exclude noncanonical degradation routes Proteasome and autophagy observations
5. Reporter assays and imaging quantitation — many IF quantifications reported (n=3–5) but image-analysis pipeline details, blinding and statistical tests are in supplement (S1) — these should be explicit for reproducibility and to exclude observer bias Imaging methods and supplement

Key technical and conceptual blindspots

• No in vivo validation or embryo data — mESC culture phenotypes can differ from embryonic development; the paper is limited to cell lines (E14/E14TG2a) and the extrapolation to embryogenesis is speculative without embryonic assays In vitro limitation
• Phosphoproteomics n=2 undermines pathway enrichment p values; more replicates and targeted phosphosite validation (SRM/PRM) recommended Phosphoproteomics n limitation

Suggested follow up experiments (practical, falsifying, and clarifying)

1. Rescue experiments: apply BAPTA then restore cytosolic Ca2+ (ionophore or Ca2+ repletion) and test Oct4/Nanog stability and p-body marker levels; demonstration of reversibility would strengthen causality.
2. Targeted phosphosite validation: validate top regulated phosphosites from MS by phospho-specific antibodies and PRM/SRM in independent biological replicates (n≥4) to confirm pathway links to spliceosome and mRNA surveillance.
3. Selective proteolysis interrogation: use proteasome 20S/26S selective tools, lysosome inhibitors (bafilomycin), and calpain inhibitors to map the degradation route(s) for Oct4/Nanog and brachyury after Ca2+ manipulation.
4. Live-cell Ca2+ reporters with single-cell lineage tracing to resolve whether Ca2+ heterogeneity precedes Oct4/Nanog downregulation during spontaneous differentiation (to resolve cause/effect ambiguity).
5. Test pCamkIIalpha phosphorylation targets: identify whether Oct4/Nanog or p-body proteins are direct pCamkIIα substrates (in vitro kinase assays, mass spec of pulldowns, site mutagenesis to phospho-dead/phospho-mimetic variants).

Overall evaluation and confidence

The study presents a coherent multi-angle dataset supporting a model where intracellular Ca2+ signaling contributes to mESC identity via post-transcriptional and post-translational mechanisms, particularly involving pCamkIIα, p-bodies and proteostasis networks. Experimental breadth is a strength. However, limited phosphoproteomics replicates (n=2), potential off-targets of Ca2+ pharmacology, and lack of deeper mechanistic biochemical proof (direct kinase substrates, pathway-specific degradative routes) temper confidence: the result is plausible and interesting but requires follow-up to upgrade from suggestive to definitive. The authors appropriately deposited MS data and used orthogonal knockdowns which partially address specificity, increasing reproducibility potential if follow-up experiments are performed Overall cautious interpretation

Interactive resources and immediate next-actions

Author Review Shikha Sharma

Caveat and final note

Do not overgeneralize: data are from in vitro mESC lines; conclusions about organismal development or translational applications should be withheld until orthogonal in vivo validation and deeper mechanistic mapping are performed In vitro limitation and author acknowledgement