MOS

MOS encodes the oocyte-enriched serine/threonine kinase c-Mos, a cytostatic factor that maintains metaphase II arrest through ERK pathway activation^[1]. Mechanistically, MOS activates MAP kinase in mouse oocytes, and MAPK-p90^RSK^ signaling down-regulates Myt1 to promote p34^cdc2^/cyclin B activation during oocyte maturation^[2][3]. In mouse models, c-mos disruption causes parthenogenetic development or activation of unfertilized eggs, establishing MOS as a functional regulator of meiotic arrest and oocyte-to-embryo transition control^[4][5]. In human infertility models, biallelic MOS mutations impair MEK1/2-ERK1/2 activation and associate with recurrent early embryonic arrest, fragmentation, large polar body phenotypes, and female infertility^[6][7]. Compared with downstream ERK, MAPK, and p90^RSK^ components, MOS functions upstream as the oocyte-specific trigger that links meiotic signaling to cytoskeletal organization, maternal-effect gene stability, and early embryo competence^[2][3][6]. For experimental research, MOS mRNA microinjection, MOS-deficient oocytes, and MEK/ERK pathway perturbation provide practical systems to test meiotic maturation, spindle integrity, polar body formation, and early embryo arrest mechanisms^[2][6][7].