Early Post-fertilization Events in the Rat Model: New Insights on Sperm Decondensation Classification and Chromatin Remodeling Patterning.
Bibliographic record
Abstract
Following fertilization, entry of the spermatozoon triggers the mature oocyte arrested at metaphase II to complete its second meiotic division; oocyte proteins are activated to induce sperm decondensation. Sperm decondensation is divided into four distinct stages: condensed, type a (partially decondensed), type b (totally decondensed) and type c (recondensing) nuclei. Once the spermatozoon has started decondensing, chromatin remodeling is initiated, during which protein exchange occurs and sperm specific proteins are replaced with maternal histones. When this exchange is complete, the paternal chromatin recondenses to form the male pronucleus. Our objective for this in vivo study was to describe sperm decondensation and chromatin remodeling in Sprague-Dawley rats, using both histone H4 acetylated at lysine 12 (H4ack12) and histone H3 phosphorylated at serine 10 (H3S10ph) as markers. H4ack12 is one of the first maternal histones to be incorporated onto the decondensing paternal chromatin and is responsible for decondensing the chromatin structure. In contrast, H3S10ph is involved in sperm chromatin compaction during chromatin remodeling. Males (n = 6-11) were mated overnight to two naturally cycling females; early embryos were collected at 9am the following morning and prepared for analysis by immunofluorescence and confocal microscopy. Interestingly, in the rat model, sperm decondensation occurred first at the base, then the tip and finally in the center of the sperm head. Therefore, in addition to the sperm decondensation stages enumerated above, we further subdivided type a nuclei into three sub classifications; type a1 (sperm base decondensed), type a2 (sperm base and tip decondensed) and type a3 nuclei (sperm base, tip and partial decondensation of the center region). Condensed sperm nuclei showed little to no immunoreactivity for either histone marker, possibly due to the tight packaging of the spermatozoon chromatin. Both histones H4ack12 and H3S10ph stained type a1 nuclei at the base, type a2 nuclei were stained at the base and tip, and type a3 nuclei at the base and tip and to a smaller extent in the central region of the sperm head. In contrast, two distinct patterns of chromatin remodeling were observed for type b and c nuclei; histone H4ack12 showed a homogenous staining, whereas histone H3S10ph displayed a ring-like staining around the sperm head. At pronuclear stages, the staining intensity remained high and homogenous with histone H4ack12 in contrast to a diminished staining intensity and a lost of the ring-like pattern with histone H3S10ph. The early and homogenous staining observed with histone H4ack12 suggests that in the early post-fertilization embryos, the paternal chromatin is decondensed, allowing protein exchange between the female and the male genome through all sperm decondensation stages. In contrast, the transient ring-like staining observed with histone H3S10ph suggests that chromatin condensation around the sperm head may be necessary for the formation of pronuclei. We propose that there are two distinct patterns of chromatin remodeling, one for H4ack12, a marker for opened chromatin structure, and a second for H3S10ph, a marker for condensed chromatin structure. Supported by CIHR.
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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) | 0.001 | 0.000 |
| Meta-epidemiology (broad) | 0.000 | 0.000 |
| Bibliometrics | 0.001 | 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 | 0.001 |
| Insufficient payload (model declined to judge) | 0.002 | 0.001 |
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".