396 Oct-4 EXPRESSION IN CAT INNER CELL MASS-DERIVED CELLS CULTURED IN MEDIUM WITH DIFFERENT PROTEIN SOURCES

Abstract

The domestic cat can be used as a biological model for humans because of similarities in some disease and genetically transmitted conditions. Embryonic stem cells might complete nuclear reprogramming more efficiently than somatic cells and, therefore, are potentially useful for increasing interspecific cloning success. The objective of this study was to establish an effective culture system for inner cell mass (ICM)-derived cells in the domestic cat, testing the ability of the ICM to attach to the culture dish and to form embryonic stem cell colonies in the presence of fetal calf serum (FCS) and Knockout serum (KS). Moreover, knowing that the transcription factor Oct-4 is important for the maintenance of pluripotency in human and murine embryonic stem cells, the expression of this factor was evaluated in in vitro-produced blastocyst and in the attached ICM. Domestic cat oocytes were matured, fertilized, and cultured in vitro until the blastocyst stage. The ICM was mechanically isolated (n = 60) using a scalpel blade and transferred to a monolayer of chemically inactivated cat fibroblasts with 10 μg mL^-1 mitomicin C. The base culture media (BM) was DMEM/F12 supplemented with nonessential amino acids, glutamine, leukemia inhibitory factor, fibroblast growth factor-2, 2-mercaptoethanol, and antibiotics. Three groups were tested: G1 = BM with 20% FCS (20); G2 = BM with 20% KS (20); G3 = BM with 15% FSC and 5% KS (20). Culture was performed in a 5% CO² in air incubator at 38.5°C. No statistical difference was observed among groups in relation to ICM attachment (chi-square, P > 0.05). Ninety percent of the ICM presented good adhesion after 3 days of culture and started to grow in all media tested. However, until now, no good colonies were formed. Fifteen blastocysts and 10 attached ICM were fixed in 3% paraformaldehyde and permeabilized in 0.2% triton X-100 in PBS. Subsequently, to block nonspecific binding of the primary antibody, the preadsorption for 2 h at room temperature with OCT4 blocking peptide (sc-8628P, Santa Cruz Biotechnology, Santa Cruz, CA, USA) was used. Samples were incubated with Oct4 antibody (N-19 : sc 8628, Santa Cruz Biotechnology) and with the appropriate secondary antibody (A21431, Invitrogen) and examined by fluorescence microscopy. Oct4 protein was detected both in the ICM and trophoderm cells, and it was distributed in cytoplasm and nuclei. These embryos were also stained with Hoechst 33342. Although further standardization of the culture media is needed, it seems that the KS can be replaced by FCS in cat embryonic stem cell culture. Furthermore, the immunostain of the trophoderm with Oct-4 indicates a difference in the expression of this factor when compared with its expression on human and murine blastocysts. This could be related to in vitro production, or Oct 4 is not a good pluripotency marker for cat embryos and cat embryonic stem cell, consequently. This fact has been noted in goat, bovine, and porcine embryos.

Acknowledgment is given to FAPESP.