Histone acetylation as a barrier to cell fate reprogramming via nuclear transfer

Janeva, Ana (2025): Histone acetylation as a barrier to cell fate reprogramming via nuclear transfer. Dissertation, LMU München: Fakultät für Biologie

Abstract

Cell fates are established during embryonic development and differentiation. Under physiological conditions in healthy organisms, cell fates rarely change, and any changes are often considered abnormal. Specific experimental manipulations, initially performed by John Gurdon in 1958, demonstrated that cell fates can be reversed to totipotency by injecting somatic nuclei into an enucleated Xenopus laevis egg and give rise to fertile adults in a process known as somatic cell nuclear transfer (SCNT). This process has low efficiency, as the cloned embryos often do not survive or demonstrate developmental abnormalities. The failure of cloned embryos to develop and survive has partly been attributed to a phenomenon known as epigenetic memory, referring to the aberrant expression of genes indicative of the transcriptional profile of the donor cell, or the failure of genes to accurately re-activate in the newly generated cell types, which is thought to be dependent on the propagation of chromatin marks. The failure of genes to activate their expression in reprogrammed cells has widely been attributed to ‘repressive’ chromatin features in the starting cell type, yet the phenomenon in which genes maintain an active chromatin and transcription state from the donor cell to the reprogrammed cell, has not been fully addressed yet. This phenomenon has in part been attributed to the persistence of trimethylation at histone H3 lysine K4 (H3K4me3) around the transcription start site (TSS) of genes that fail to downregulate their expression in reprogramming, so-called ON-memory genes. Currently, however, it is unknown which factors, and which ‘active’ chromatin marks contribute to ON-memory, acting alongside or together with H3K4me3, to form an “epigenetic barcode” that stabilizes cell fate specific gene expression and prevents cell fate reprogramming. To address this question, our group has previously developed Digital Reprogramming, a computational model capable of predicting reprogramming resistance and identifying epigenetic barriers from chromatin and transcriptome data in donor nuclei and wild-type target cells. With this approach, acetylation on Histone H3 lysine 27 (H3K27ac) was identified as a potential novel barrier to reprogramming and was thus chosen as the focus of this project. Reducing H3K27ac levels using p300/CBP inhibitors in donor cells before reprogramming correlated with an improved downregulation of genes linked to H3K27ac-modified enhancers during reprogramming. Importantly, these effects were accompanied by an improvement in the embryonic development of the resulting NT embryos. Taken together, these findings implicate H3K27ac as a protective mechanism maintaining cell fates and acting as a barrier to cell fate changes during reprogramming.

• Dokumententyp: Dissertationen (Dissertation, LMU München)
• Keywords: reprogramming, epigenetics, chromatin, development, Xenopus
• Themengebiete: 500 Naturwissenschaften und Mathematik ; 500 Naturwissenschaften und Mathematik > 570 Biowissenschaften, Biologie
• Fakultäten: Fakultät für Biologie
• Sprache der Hochschulschrift: Englisch
• Datum der mündlichen Prüfung: 9. Dezember 2025
• 1. Bericht­erstatter:in: Torres-Padilla, Maria Elena