Characterization of the O-GlcNAc protein modification in Xenopus laevis oocyte during oogenesis and progesterone-stimulated maturation

Little information exists about single N-acetylglucosamine modifications on proteins in growth and developmental model systems. To explore these phenomena, Xenopus laevis oocytes from stages I-VI of oogenesis were isolated and proteins analyzed on SDS-PAGE. The proteins were probed with antibodies specific for O-GlcNAc. Levels of the O-GlcNAc protein modification were highest in stages I and II, while decreasing in stages III-VI. The reduction in amount of O-GlcNAc-modified proteins was correlated to increases in apparent O-GlcNAcase (streptozotocin-inhibitable neutral hexosaminidase), activity involved in removing protein monoglycosylations. The O-GlcNAc modification was also characterized during progesterone-stimulated oocyte maturation. Although O-GlcNAcase activity appeared relatively constant between quiescent and matured stage VI oocytes, a small decrease in the levels of both total and specific O-GlcNAc-modified proteins was observed. Investigating the function of O-GlcNAc during maturation, oocytes were incubated with compounds known to modulate the levels of the O-GlcNAc protein modification and then stimulated to mature. Oocytes treated with compounds known to increase O-glycosylation consistently matured slower than non-treated controls, while oocytes treated with compounds that decrease O-glycosylation matured slightly faster than controls. The O-GlcNAc modification may play important roles in both the developmental and cell division processes of X. laevis oocytes.