Int. J. Dev. Biol. 56: 889 - 899 (2012)
doi: 10.1387/ijdb.120246rd
© UPV/EHU Press

Histone hyperacetylation during meiosis interferes with large-scale chromatin remodeling, axial chromatid condensation and sister chromatid separation in the mammalian oocyte

Feikun Yang1, Claudia Baumann, Maria M. Viveiros and Rabindranath De La Fuente*

Department of Physiology and Pharmacology, College of Veterinary Medicine, University of Georgia, Athens, GA, USA

ABSTRACT Histone acetylation regulates higher-order chromatin structure and function and is critical for the control of gene expression. Histone deacetylase inhibitors (HDACi) are currently un¬der investigation as novel cancer therapeutic drugs. Here, we show that female germ cells are extremely suscep¬tible to chromatin changes induced by HDACi. Our results indicate that exposure to trichostatin A (TSA) at nanomolar levels interferes with major chromatin remodeling events in the mammalian oocyte leading to chromosome instability. High resolution analysis of chromatin structure and live-cell imaging revealed a striking euchromatin decondensation associated with histone H4 hyperacetylation following exposure to 15 nM TSA in >90% of pre-ovulatory oocytes. Dynamic changes in large-scale chromatin structure were detected after 2 h of exposure and result in the formation of misaligned chromosomes in >75% (P<0.05) of in vitro matured oocytes showing chromosome lagging as well as abnormal sister chromatid separation at anaphase I. Abnormal axial chromatid condensation during meiosis results in the formation of elongated chromosomes exhibiting hyperacetylation of histone H4 at lysine 5 and lysine 16 at interstitial chromosome segments, but not pericentric heterochro¬matin, while highly decondensed bivalents exhibit prominent histone H3 phosphorylation at centromeric domains. Notably, no changes were observed in the chromosomal localization of the condensin protein SMC4. These results indicate that HDAC activity is required for proper chromosome condensation in the mammalian oocyte and that HDACi may induce abnormal chromosome segregation by interfering with both chromosome-microtubule interactions, as well as sister chromatid separation. Thus, HDACi, proposed for cancer therapy, may disrupt the epigenetic status of female germ cells, predisposing oocytes to an¬euploidy at previously unrecognized low doses.

Keywords:

centromere, heterochromatin, chromatin remodeling, histone deacetylase, TSA epigenetic modifications, meiosis

*Corresponding author e-mail: rfuente@uga.edu