Jiawei Xu

Histone modifications regulate gene expression and development. To address how they are reprogrammed in human early development, we investigated key histone marks in human oocytes and early embryos. Unlike that in mouse oocytes, the permissive mark trimethylated histone H3 lysine 4 (H3K4me3) largely exhibits canonical patterns at promoters in human oocytes. After fertilization, prezygotic genome activation (pre-ZGA) embryos acquire permissive chromatin and widespread H3K4me3 in CpG-rich regulatory regions. By contrast, the repressive mark H3K27me3 undergoes global depletion. CpG-rich regulatory regions then resolve to either active or repressed states upon ZGA, followed by subsequent restoration of H3K27me3 at developmental genes. Finally, by combining chromatin and transcriptome maps, we revealed transcription circuitry and asymmetric H3K27me3 patterning during early lineage specification. Collectively, our data unveil a priming phase connecting human parental-to-zygotic epigenetic transition.

<i>Background</i>: Parity is widely recognized as protective for breast cancer, but breast cancer risk may be increased shortly after childbirth. Whether this risk varies with breastfeeding, family history of breast cancer, or specific tumor subtype has rarely been evaluated.<p>\n \n<p><i>Objective</i>: To characterize breast cancer risk in relation to recent childbirth.<p>\n \n<p>Design</i> : Pooled analysis of individual-level data from 15 prospective cohort studies.<p>\n \n<p><i>Setting</i>: The international Premenopausal Breast Cancer Collaborative Group.<p>\n \n<p><i>Participants</i>: Women younger than 55 years.<p>\n \n<p><i>Measurements</i>: During 9.6 million person-years of follow-up, 18 826 incident cases of breast cancer were diagnosed. Hazard ratios (HRs) and 95% CIs for breast cancer were calculated using Cox proportional hazards regression.<p>\n \n<p><i>Results</i>: Compared with nulliparous women, parous women had an HR for breast cancer that peaked about 5 years after birth (HR, 1.80 [95% CI, 1.63 to 1.99]) before decreasing to 0.77 (CI, 0.67 to 0.88) after 34 years. The association crossed over from positive to negative about 24 years after birth. The overall pattern was driven by estrogen receptor (ER)–positive breast cancer; no crossover was seen for ER-negative cancer. Increases in breast cancer risk after childbirth were pronounced when combined with a family history of breast cancer and were greater for women who were older at first birth or who had more births. Breastfeeding did not modify overall risk patterns.<p>\n \n<p><i>Limitations</i>: Breast cancer diagnoses during pregnancy were not uniformly distinguishable from early postpartum diagnoses. Data on human epidermal growth factor receptor 2 (HER2) oncogene overexpression were limited.<p>\n \n<p><i>Conclusion</i>: Compared with nulliparous women, parous women have an increased risk for breast cancer for more than 20 years after childbirth. Health care providers should consider recent childbirth a risk factor for breast cancer in young women.<p>\n \n<p><i>Primary Funding Source</i>: The Avon Foundation, the National Institute of Environmental Health Sciences, Breast Cancer Now and the UK National Health Service, and the Institute of Cancer Research.

Background: Parity is widely recognized as protective for breast cancer, but breast cancer risk may be increased shortly after childbirth. Whether this risk varies with breastfeeding, family history of breast cancer, or specific tumor subtype has rarely been evaluated. Objective: To characterize breast cancer risk in relation to recent childbirth. Design: Pooled analysis of individual-level data from 15 prospective cohort studies. Setting: The international Premenopausal Breast Cancer Collaborative Group. Participants: Women younger than 55 years. Measurements: During 9.6 million person-years of follow-up, 18 826 incident cases of breast cancer were diagnosed. Hazard ratios (HRs) and 95% CIs for breast cancer were calculated using Cox proportional hazards regression. Results: Compared with nulliparous women, parous women had an HR for breast cancer that peaked about 5 years after birth (HR, 1.80 [95% CI, 1.63 to 1.99]) before decreasing to 0.77 (CI, 0.67 to 0.88) after 34 years. The association crossed over from positive to negative about 24 years after birth. The overall pattern was driven by estrogen receptor (ER)-positive breast cancer; no crossover was seen for ER-negative cancer. Increases in breast cancer risk after childbirth were pronounced when combined with a family history of breast cancer and were greater for women who were older at first birth or who had more births. Breastfeeding did not modify overall risk patterns. Limitations: Breast cancer diagnoses during pregnancy were not uniformly distinguishable from early postpartum diagnoses. Data on human epidermal growth factor receptor 2 (HER2) oncogene overexpression were limited. Conclusion: Compared with nulliparous women, parous women have an increased risk for breast cancer for more than 20 years after childbirth. Health care providers should consider recent childbirth a risk factor for breast cancer in young women. Primary Funding Source: The Avon Foundation, the National Institute of Environmental Health Sciences, Breast Cancer Now and the UK National Health Service, and the Institute of Cancer Research.