Role of Imitation Switch (ISWI) Chromatin Remodeling Proteins During Mouse Preimplantation Embryo Development and Embryonic Stem Cell Differentiation.
Bibliographic record
Abstract
Female fertility is dependent on the ability of the oocytes and embryos to follow the developmental program to yield healthy offspring. The preimplantation embryo needs to undergo crucial processes including maternal to zygotic transition and cell differentiation that require profound changes in gene expression dependent on global chromatin remodeling. The ISWI proteins constitute the catalytic subunit of chromatin remodeling complexes capable of altering nucleosome positioning and regulating gene transcription. Two ISWI proteins, Snf2h and Snf2l, have been identified in the mouse and Snf2h was shown to be essential for embryonic development. Interestingly, embryonic stem cells (ESC) could not be derived from Snf2h knockout embryos suggesting a role for Snf2h in the maintenance of pluripotency. However, still very little is known about the roles of Snf2h and Snf2l in mouse oocytes and preimplantation embryos and during stem cell differentiation. Therefore, our aim was to characterize the expression of Snf2h and Snf2l during mouse preimplantation embryo development and embryonic stem cell differentiation. Germinal vesicle (GV) and metaphase II (MII) oocytes and zygotes were recovered from superovulated 25-day old C57BL/6 mice and zygotes were further cultured in KSOM with amino acids to obtain 2-cell embryos, 4-cell embryos, morulae and blastocysts. Total RNA was extracted from groups of 20 oocytes or embryos, reverse transcribed and the levels of expression of Snf2h and Snf2l, normalized to exogenous GFP, were determined by Q-PCR. Groups of oocytes and embryos were also subjected to immunofluorescence for Snf2h localization. ESC were cultured with LIF and induced to differentiate for 0h, 48h or 96h in LIF-free media supplemented with 1 micromole of retinoic acid. Total RNA was extracted, reverse transcribed and the levels of expression of Snf2l, Snf2h, Pou5f1, Nanog and miR-100, normalized to PMSD or miR-191, were determined by Q-PCR. Snf2h and Snf2l protein abundance was quantified by immunoblotting using beta-actin as an endogenous control. All data were analyzed using the general linear model procedure of SAS. Snf2l mRNA could not be reliably detected at any stage of embryo development while Snf2h mRNA behaved as a typical maternal mRNA, decreasing in abundance from GV oocytes to 2-cell embryos and increasing thereafter. Snf2h protein was found to localize to the cytoplasm and nucleus of GV and MII oocytes, zygotes and 2-cell embryos while it was found to localize predominantly to the nucleus of 4-cell embryos, morulae and blastocysts. Interestingly, blastomeres in anaphase or telophase did not positively stain for Snf2h. Immunofluorescence also revealed strong staining at the blastocyst stage, suggesting a role for Snf2h in ESC. ESC differentiation was accompanied by changes in cell morphology and by the reduction in Pou5f1 and Nanog mRNA. Similarly, a decrease in Snf2h protein abundance was observed while its mRNA abundance remained relatively unchanged, suggesting that it might be regulated post-transcriptionally. The increase in miR-100 abundance observed during ESC differentiation strongly supports this concept. In conclusion, our results support the hypothesis that Snf2h is important for the maintenance of the pluripotent state in embryonic stem cells and that its expression is likely under the control of miR-100. F. Paradis is supported by fellowships from CIHR-REDIH and the Lalor Foundation. (poster)
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How this classification was reachedexpand
Full frame distilled prediction
Teacher imitationNot calibrated prevalence, not ground truth. Human validation pending. Learned from the 10,348 direct Codex labels and 10,348 direct Gemma labels. Candidate is the union of thresholded teacher heads; consensus is their intersection. These outputs are machine_predicted_unvalidated and are not human labels or direct frontier model labels.
Codex and Gemma teacher scores by category
| 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) | 0.000 | 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 teacher head, 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".