249 PROFILE OF MEMBERS OF IGF SYSTEM GENE EXPRESSION IN BOVINE IMMATURE OOCYTES: COMPARISON BETWEEN NELLORE (BOS INDICUS) AND HOLSTEIN (BOS TAURUS)

There is evidence that IGF system can be involved in the oocyte competence and, consequently, in the embryo development. To better understand possible differences between Bos taurus and Bos indicus in in vitro embryo development, the current work aimed to assess the expression of IGF ligands (IGF-1 and 2), types 1 and 2 IGF receptors (IGFR1 and 2), IGF-binding proteins 2 and 4 (IGFBP-2 and 4), and type A pregnancy-associated plasmatic protein (PAPP-A) mRNA in bovine immature oocytes fromBos Taurus and Bos indicus. Nellore and Holstein cows were submitted to ovum pickup, and the oocytes with grade 1, 2, and 3 were selected. To remove cumulus cells and pellucida zone, respectively, the oocytes were submitted to vortex (900 × g for 3 min) and protease treatment (Protease® from Streptomyces griseus, Sigma-Aldrich Corporation, St. Louis, MO, USA). Pools of 20 oocytes obtained from Nellore (n = 8) and Holstein (n = 4) cows were submitted to total RNA extraction (RNeasy, Qiagen, Valencia, CA, USA). The gene expression of target genes was measured by real-time RT-PCR with oligo-dT in the RT and bovine-specific primers in the PCR. Expression of cyclophlin A (CYC-A) was used as internal control. The means of mRNA levels of target genes between the breeds were compared using t-test and Mann-Whitney test when the data had normal or not normal distribution, respectively. The means values of mRNA expression of IGF-1, IGF-2, IGF receptors (1 and 2), and IGFBP 2 and 4 were greater in Holstein (0.96 ± 0.21, 0.74 ± 0.27, 1.08 ± 0.04, 1.19 ± 0.5, 1.21 ± 0.23, 0.53 ± 0.15, respectively) compared with Nellore (0.48 ± 0.10, 0.07 ± 0.02, 0.04 ± 0.03, 0.06 ± 0.02, 0.05 ± 0.01, 0.03 ± 0.15, respectively; P < 0.01). Never- theless, mRNA expression of PAPP-A was much greater in Nellore (28.10 ± 18.96) than in Holstein (1.32 ± 0.17; P < 0.05). These results suggest that high expression of PAPP-A and low expression of IGFBP-2 and 4 could allow more efficiency on the degradation of IGFBP and increase the IGF bioavailability in the oocytes from Nellore as compared with Holstein cows. Satrapa, Simoes, and Castilho received a fellowship and funding from FAPESP (Sao Paulo, Brazil).