Besides affecting uterine environment, a direct effect of n-3 poly-unsaturated fatty acids (PU-FA) on the oocyte could enhance fertility. We previously showed that docosahexaenoic acid (DHA, C22:6 n-3, Sigma), when provided during in vitro maturation (IVM), improved oocyte developmental competence through possible effects on cytoplasm but not nuclear maturation and without affecting lipid metabolism gene expression in cumulus cells (CC) (Oseikria et al Theriogenology 85:1625-1634. 2016). DHA could act through several mechanisms of action: i.e. via surface fatty acid receptors (free fatty acid receptor 1 or 4, FFAR1 and 4) or sensors involving PPAR or NFkB pathways; via changes in composition of cell membrane phospholi-pids; via production of eicosanoids… The aim of the present work was to investigate whether the FFAR4 was involved in the DHA effects previously reported on oocyte quality. We there-fore investigated the effect of a specific agonist of the FFAR4, TUG-891, on embryo deve-lopment after IVF. The response of surrounding CC to DHA or TUG treatment was also stu-died by gene expression analyses. Oocyte cumulus complexes were collected from slaughtered cows. The protein FFAR4 was first localized by immunohistochemistry, by using a cus-tomized antibody produced specifically against the bovine protein. FFAR4 is expressed in CC and localized close to the cellular membrane, as expected. After 22h IVM with or without DHA 1 µM or TUG 1 and 5 µM oocytes were subjected to in vitro fertilization (IVF) and in vitro development in modified synthetic oviduct fluid supplemented with 10% fetal calf serum for 7 days. At day 7, both blastocyst and expanded blastocyst rates were significantly increased with either DHA 1µM or TUG 1 or 5 µM (logistic regression, P < 0.05). In order to decipher the DHA mechanisms linked to oocyte developmental competence, we then investi-gated the common pathways of DHA and TUG actions. Microarray hybridization of CC after 4h IVM in the presence or absence of 1µM DHA was performed (n = 4 samples per condi-tion). A customized 60K bovine microarray (Agilent technology) including 97.4% of Ensembl Bos taurus transcripts was used (GEO accession: GPL21724). Only 14 differentially expres-sed genes varied more than two-fold and were enriched in gene ontologies related to regula-tion of translation, RNA splicing and spliceosome formation, oxidation/reduction, actin cy-toskeleton organization and vesicle-mediated transport. The kinetic of expression of these genes is currently characterized by qRT-PCR analysis on CC samples at 0, 4, 10 and 24h IVM with or without DHA 1 µM, TUG 1 or 5 µM. Altogether the IVF data suggest that DHA exert its effect partly through FFAR4 on oocyte developmental competence. Also, we are studying the common transcriptomic modulation between DHA and TUG to provide insights on its detailed mechanism of action.