Paternal Exposure to Cyclophosphamide Leads to a Dampened DNA Repair Response and Enhanced DNA Damage in 8-Cell Embryos.
Bibliographic record
Abstract
The treatment of male rats with cyclophosphamide (CPA), a commonly used anticancer alkylating agent, results in adverse progeny outcomes that range from increased pre- and post-implantation loss to growth retardation and congenital malformations. The DNA damage introduced by CPA in male germ cells is recognized by maternally stored repair proteins in the early zygote. Phosphorylated H2AX (gammaH2AX) foci, a mark of DNA double strand breaks, are increased biphasically in the male pronuclei of zygotes sired by CPA treated males. Poly(ADP-ribose) polymerase-1(PARP-1), activated by both single and double strand DNA breaks, is substantially elevated in both parental genomes in the zygote. We hypothesize that the ability of subsequent cleavage stages embryos to activate a repair response will determine their fate. We used two markers to assess DNA repair capacity. The first, 53BP1, is a component of the non-homologous end joining repair pathway. The second, poly(ADP-ribose) polymer (PAR), is the product of PARP activity and recruits the DNA repair proteins involved in homologous recombination and base excision repair pathways to sites of damage. The formation of micronuclei was used as a measure of DNA damage accumulation and outcome of the repair process. Male Sprague-Dawley rats were gavaged daily with saline or 6mg/kg/day of CPA for 4 weeks prior to mating to two naturally cycling pro-estrous females. Eight cell embryos were collected on gestation day 3 and prepared for the detection of 53BP1 and PAR by immunofluorescence; DNA was counterstained with propidium iodide. Images were acquired using confocal microscopy and analyzed with Imaris software. The numbers of embryos evaluated for each endpoint ranged from 33 to 83. 53BP1 immunoreactivity was found homogenously distributed in nuclei and in the endoplasmic reticulum. The mean intensity of nuclear 53BP1 was lower by almost 50% in the embryos sired by CPA treated males compared to control 8 cell embryos. PAR was also homogenously distributed in nuclei and in the endoplasmic reticulum. Embryos sired by CPA-treated males displayed a decrease in PAR nuclear mean intensity, attaining only 50% of the control. This apparent decrease in DNA repair response was accompanied by a dramatic increase in DNA damage or genetic instability. While micronuclei were found in only 4% of control 8 cell embryos, the incidence of micronuclei in embryos sired by CPA exposed males was elevated to 83%. This inability of the embryo to adequately repair the paternal genome is likely to contribute to the elevated pre- and post-implantation death observed as a consequence of paternal CPA exposure. Decreases in 53BP1 immunoreactivity and PARP activity may reflect a decrease in the transcription of DNA repair proteins in the early embryo. Supported by CIHR. (poster)
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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 | 0.001 |
| Insufficient payload (model declined to judge) | 0.002 | 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".