The spatial relationship between heterochromatin protein 1 alpha and histone modifications during mouse oocyte meiosis.

Heterochromatin protein 1 (HP1) is closely associated with diverse chromatin organization and function in mitosis. However, we almost know nothing about HP1 in mammalian oocyte. Here, we investigated the subcellular distribution of HP1alpha and its spatial relationship to histone modifications during mouse oocyte maturation. Dynamic migration of HP1alpha was observed in germinal vesicle with non-surrounded nucleolus (NSN) to surrounded nucleolus (SN) oocytes, which may be essential for the transition of chromatin conformation during the development of antral oocytes. In meiosis, HP1alpha was clearly detectable at the periphery of chromosomes from pre-metaphase I stage to anaphase-telophase I stage. Spatial correlation between HP1alpha and histone modifications is highly variable around the time of meiotic resumption. In germinal vesicle oocytes, HP1alpha almost colocalized with all histone modifications examined in this study except for phosphorylation of serine 28 on histone H3. However, with the breakdown of germinal vesicle, HP1alpha was detected mostly in the chromosomal domains with strong phosphorylation of serine 10 and 28 on histone H3, and they also partially associated with methylated histones. These results presented the functional implication of histone modifications in the regulation of HP1alpha during oocyte maturation. In addition, we also showed that blocking the function of HP1alpha by microinjecting anti-HP1alpha antibody caused the delay of GVBD, however, this effect may not be achieved through modifying histones.