Expression data from bovine oocyte; Identification of molecular markers for oocyte competence in bovine cummulus cells

, 1939) the process by which the most competent oocytes are selected to produce blastocysts remains similar and is still based on morphological aspects of the oocyte cytoplasm and the number of layers and compaction of cumulus cells attached to the oocyte surface (Armstrong, 2001, Coticchio et al. , 2004, Krisher, 2003, Lonergan et al. , 2003). Ovaries from crossbred cows (Bos indicus x Bos taurus) were collected immediately after slaughter and transported to the laboratory in saline solution (0.9% NaCl) supplemented with penicillin G (100 IU/mL) and streptomycin sulfate (100 mg/mL) at 35-37C. The follicles were dissected from the ovarian cortex using scissors, scalpels and tweezers in TCM-199 medium supplemented with Hank’s salts and 10% fetal calf serum (FCS; GIBCO BRL) at 36C. Follicles were measured using a graduated eyepiece (OSM-4; Olympus) and then classified morphologically into two groups according to their diameter: 1.0-3.0 mm or ≥8.0 mm. The criteria used for follicle selection included the presence of extensive and fine vascularization and a shiny and translucent appearance. After follicular rupture, the presence of granulosa cells with a regular and healthy appearance and no free-floating particles in the follicular fluid were also used as selection criteria. Only COCs with a homogeneous granulated cytoplasm and at least three layers of compact of cumulus cells were used in the present study. The selected COCs were transferred to a 50 μL droplet of phosphate-buffered saline (PBS), and the cumulus cells were mechanically removed by repeated pipetting. After cumulus collection, they were transferred to a 0.2-mL tube and centrifuged twice for 2 min at 700 g. The supernatant was removed, and 2μL of RNAlater (Applied Biosystems, Foster City, CA, USA) was added to the pellet, which was then stored at -20C until RNA extraction. For each follicle size group, three replicas of pooled cumulus cells corresponding to 30 oocytes were stored for RNA extraction and subsequent microarray assays, and four independent replicates corresponding to 20 oocytes were stored for RNA extraction for subsequent qPCR assays.