The evaluati̇on of expressi̇ons of FOXO1, FOXO3,and FOXO4 duri̇ng prei̇mplantati̇on embryo development i̇n mi̇ce

After fertilization, while passing through the fallopian tubes to enter the uterus, embryo gets prepared for implantation. The period between fertilization and implantation is defined as preimplantation embryo development. Fertilized zygote starts to cleave and develops into 2 cell, 4 cell, 8 cell embryo, morula, and blastocyst. Preimplantation embryo developmental period is affected by various cellular events that depend on signals generated by growth factors present in the maternal environment. The PI3K/Akt pathway is one of these pathways that support growth and development. FoxO transcription factors are members of a subgroup of Forkhead family which are characterized by a conserved DNA-binding domain and function in the nucleus. Their activities are regulated by PI3K/Akt signalling pathway. In mammals, there are four FoxO genes, FoxO1, 3, 4, and 6. FoxO transcription factors are at the interface of crucial cellular processes, orchestrating programs of gene expression that regulate apoptosis, cell-cycle arrest, and oxidative stress resistance, DNA repair, glucose metabolism, energy homeostasis and differentiation. In the presence of growth factors, FoxO transcription factors are localized in the cytoplasm. Under stress conditions such as oxidative stress and genotoxic stress, FoxO transcription factors move to the nucleus and trigger transcriptional activities of their target genes. Studies have shown that FoxO molecules play important roles and protect fertility in male and female reproduction. Additionally, it has been shown that the PI3K/Akt signaling pathway, the main regulator of FoxOs', is present both in the oocyte and in the preimplantation embryo. Thus, the aim of the present study is to investigate whether FoxO transcription factors are present during oocyte maturation and preimplantation embryo development. Female Balb/C mice were superovulated with PMSG and hCG and then prophase I, metaphase I, metaphase II oocytes, 1 cell embryo, 2 cell embryo, 4 cell embryo, 8 cell embryo, morula and blastocyst were collected from their fallopian tubes and uterus. Presence and localizations of FoxO1, FoxO3 and FoxO4 proteins have been determined with immunofluorescence staining. Our results have confirmed that FoxO1, FoxO3 and FoxO4 proteins are differentially expressed in prophase I, metaphase I, metaphase II oocytes and in 1 cell embryo, 2 cell embryo, 4 cell embryo, 8 cell embryo, morula and blastocyst. Our findings are the first results in the literature showing that FoxO transcription factors are present during both oocyte and embryo in vivo maturation. These findings may provide basic information for planning future studies which investigate whether these factors are affected or not when the embryo faces stress conditions (such as pH, oxygen level or temperature changes) during in vitro maturation, especially in the IVF laboratories. Based on the findings of the present study, new studies are in progress in our laboratory.