Tscherner Allison K, Baltz Jay M
Ottawa Hospital Research Institute, Ottawa, Ontario, Canada.
Department of Obstetrics and Gynecology, University of Ottawa Faculty of Medicine, Ottawa, Ontario, Canada.
Biol Reprod. 2025 Jul 13;113(1):97-108. doi: 10.1093/biolre/ioaf080.
Glycine is a key regulator of cell volume in early preimplantation mouse embryos and supports embryo viability. Its accumulation is initiated when the GLYT1 glycine transporter (SLC6A9) is activated in oocytes at about the same time the oocyte is released from meiotic arrest at the germinal vesicle (GV) stage. The mechanism by which GLYT1 is maintained in an inactive state before ovulation is triggered is unknown. Here, we have shown that GLYT1 activity can remain suppressed in isolated cumulus-oocyte complexes (COCs) under defined culture conditions that include keeping COCs physically separated and using the physiological mediator of GV arrest, natriuretic peptide precursor C. When GV arrest is instead maintained in oocytes within COCs by inhibiting phosphodiesterase 3A or cyclin-dependent kinase 1, GLYT1 similarly remains inactive. However, GLYT1 becomes activated in isolated GV oocytes similarly maintained in GV arrest, indicating that cumulus cells are required for suppressing GLYT1 activity. This implies that meiotic arrest is necessary but not sufficient for preventing GLYT1 activation and that an inhibitory factor likely arising from the cumulus is also required. Finally, we have found that pyrrophenone, a selective inhibitor of arachidonic acid production by cytoplasmic phospholipase A alpha, causes GLYT1 to become activated in oocytes within COCs despite maintenance of meiotic arrest of the oocyte. Since arachidonic acid levels decrease in oocytes after release from GV arrest, we propose that arachidonic acid may be a candidate for the inhibitory factor in COCs that regulates GLYT1 activity.
甘氨酸是小鼠植入前早期胚胎细胞体积的关键调节因子，并支持胚胎的存活能力。当卵母细胞在生发泡（GV）期从减数分裂阻滞中释放出来时，大约在同一时间，卵母细胞中的GLYT1甘氨酸转运体（SLC6A9）被激活，甘氨酸开始积累。在排卵触发之前，GLYT1保持无活性状态的机制尚不清楚。在这里，我们已经表明，在特定的培养条件下，包括使卵丘-卵母细胞复合体（COC）保持物理分离，并使用GV阻滞的生理介质利钠肽前体C，分离的COC中的GLYT1活性可以保持被抑制。相反，当通过抑制磷酸二酯酶3A或细胞周期蛋白依赖性激酶1在COC内的卵母细胞中维持GV阻滞时，GLYT1同样保持无活性。然而，在同样维持GV阻滞的分离的GV卵母细胞中，GLYT1会被激活，这表明卵丘细胞是抑制GLYT1活性所必需的。这意味着减数分裂阻滞对于防止GLYT1激活是必要的，但不是充分的，可能还需要一种可能来自卵丘的抑制因子。最后，我们发现，吡洛芬酮，一种细胞质磷脂酶Aα产生花生四烯酸的选择性抑制剂，尽管卵母细胞的减数分裂阻滞得以维持，但它会导致COC内的卵母细胞中的GLYT1被激活。由于卵母细胞从GV阻滞中释放后花生四烯酸水平会降低，我们提出花生四烯酸可能是COC中调节GLYT1活性的抑制因子的候选物。
