130 ANTI-APOPTOTIC pTEGT SHOWS A DIFFERENTIAL mRNA TRANSCRIPT LEVEL DURING IN VITRO MATURATION AND EARLY DEVELOPMENT OF PORCINE IVP EMBRYO

Abstract

It is well known that very early development of the mammalian pre-implantation embryo is regulated by gene transcripts and proteins stored in the oocyte and that the embryonic genome gains control of development following 1 to 3 cleavage divisions. An active transcription and translation is required for chromatin condensation and germinal vesicle breakdown in pig oocyte. The transition from maternal to embryonic control of development is a gradual event, and following this transition, the maternally derived transcripts and proteins are gradually degraded. Successful embryonic development is dependent on the temporal and stage-specific expression of proper genes, but information on specific gene expression during early stages before zygotic gene activation (ZGA) is limited. Before activation of the embryonic genome, mRNA and proteins synthesized during oocyte growth and maturation contribute to early development. In this study, we compared the mRNA transcripts level among porcine immature, in vitro-matured and cleaved 2- to 4-cell stage embryos after in vitro fertilization to identify genes that show differential mRNA transcript levels during maturation and very early embryonic development. For the first strand cDNA synthesis, oligo (dT) primers were added to the total RNA isolated from each sample. Using annealing control primer (ACP)-based GeneFishing PCR, we detected tens of different genes showing differential mRNA transcript level (DRTL) and nine DRTL genes were identified to be KCRF, CAMSAP1, SMP1, FLJ20647, LOC132321, NADH1, NADH6, HERC3, and TEGT. Of 9 DRTL genes, TEGT showed higher mRNA transcript level at the immaturation stage, and mRNA transcript levels of the other 8 genes were increased after in vitro maturation. Therefore, we focused on TEGT (testis enhanced gene transcript), which is highly expressed in testis and also in oocytes before in vitro maturation. Differential mRNA transcripts pattern of CAMSAP1 and TEGT were confirmed using RT-PCR and real-time RT-PCR. Porcine TEGT (pTEGT) was cloned and sequenced to have an ORF of 714 bp nucleotides and to encode an integral membrane protein. When overexpressed in HEK293 cells, pTEGT suppressed apoptosis induced by etoposide. We found that pTEGT, but not TEGT-C (C-terminal deletion mutant), inhibited etoposide- and staurosporine-induced cell death. Next, we found that introduction of TEGT siRNA suppressed the anti-apoptotic effect of TEGT. Interestingly, expression of TEGT suppressed etoposide-induced ERK activation, suggesting that ERK phosphorylation is involved in the anti-apoptotic function of the gene. Several reports showed that apoptosis and MAP kinase signaling pathways play important roles in oocyte maturation and early embryo development. Therefore, the anti-apoptotic effect of TEGT was suggested to play a key role in the normal ooctye maturation and early embryo development.

This work was supported by the Research Project on the Production of Bio-organs, Ministry of Agriculture and Forestry, Republic of Korea.