Transcriptional status of mouse oocytes corresponds with their ability to generate Ca2+ release

Abstract

In fully grown ovarian follicles both transcriptionally active (NSN) and inactive (SN) oocytes are present. NSN oocytes have been shown to display lower developmental potential. It is possible that oocytes that have not completed transcription before meiosis resumption accumulate less RNA and proteins required for their further development, including those responsible for regulation of Ca2+ homeostasis. Oscillations of the cytoplasmic concentration of free Ca2+ ions ([Ca2+]i) are triggered in oocytes by a fertilizing spermatozoon and are crucial for inducing and regulating further embryonic development. We showed that NSN-derived oocytes express less inositol 1,4,5-triphosphate receptor type 1 (IP3R1), store less Ca2+ ions and generate weaker spontaneous [Ca2+]i oscillations during maturation than SN oocytes. Consequently, NSN oocytes display aberrant [Ca2+]i oscillations at fertilization. We speculate that this defective regulation of Ca2+ homeostasis might be one of the factors responsible for the lower developmental potential of NSN oocytes.

A transition phase in late mouse oogenesis impacts DNA methylation of the early embryo

“…NSN-derived embryos arrest at the 2-cell stage 10 , 18 , 20 , 21 , and it was suggested that impaired Ca 2+ oscillation in NSN-GVOs is a reason for this lower competence 55 . Here, we show that the transition of NSN- to SN-GVOs is necessary for the establishment of a specific DNA methylome in early embryonic development (Fig.…”

Reconstitution of chromatin reorganization during mammalian oocyte development

“…During the final stages of oogenesis, condensed chromatin forms a ring around the nucleolus in a surrounded nucleolus (SN) configuration and transcription ceases 1,2 . SN oocytes have a higher developmental competence than NSN oocytes [3][4][5][6][7][8] , and their nucleus primarily accounts for their differences in the success of embryonic development 9 . Therefore, the reorganization of chromatin from NSN to SN configuration is tied to the developmental competence of mammalian oocytes.…”