Reproduction Abstracts

Each egg, when ovulated from a follicle, is surrounded by cumulus cells. Prior to ovulation, these cumulus cells secrete cumulus extracellular matrix (cECM) molecules, resulting in cumulus expansion. Cumulus expansion has been linked to the developmental quality of the oocyte. Hyaluronan (HA), the major constituent of the cECM, is stabilised by molecules such as heavy chains (HCs), pentraxin 3 (PTX3) and tumour necrosis factor-stimulated gene 6 (TSG6) during expansion. All of these molecules, except HCs, are secreted by the cumulus cells and are dependent on oocyte-secreted factors, such as bone morphogenetic protein 15 (BMP15) and growth and differentiation factor 9 (GDF9), both of which signal via SMAD pathways. The Double Mutant mouse model (DM), with oocyte-specific deletion of C1galt1 and Mgat1, has altered cumulus expansion without affecting fertilisation. We investigated whether the absence of oocyte-specific complex N- and O-glycans in DM affected levels of HA, HCs, PTX3, TSG6, pSMAD1/5/8 and pSMAD2 using immunohistochemistry in cumulus-oocyte complexes (COCs) at 48h post PMSG and 9 h later, post hCG stimulation. DM COCs did not differ in cumulus size or cell density at either 48 h post PMSG or 9 h post hCG stimulation compared to Controls. However, HA, HC and pSMAD1/5/8 levels were reduced in DM COCs compared to Controls. No significant correlations were found linking the matrix molecules with pSMADs, or with cumulus area. We propose that although oocyte-specific ablation of C1galt1 and Mgat1 reduces cECM levels of HA, HC and pSMAD1/5/8 expression, the levels are sufficient for cumulus expansion.