336. EXPRESSION AND REGULATION OF TWO PROTO-ONCOGENES BCL2 AND FOS IN THE PREIMPLANTATION MOUSE EMBRYO

Abstract

Development of the preimplantation embryo requires survival signalling by autocrine embryotrophins. Paf is the first defined embryotrophin and acts via a receptor- and phosphatidylinositol-3-kinase -dependent induction of intracellular calcium transients.1,2 These calcium transients induce a calmodulin-dependent nuclear accumulation and phosphorylation of the Creb transcription factor at the time that definitive transcription from the embryonic gene is initiated in the 2-cell embryo.3 A round 4084 loci possess CRE elements including Bcl2 and Fos.4 In this study we examined the role of Paf in the transcription of the key proto-oncogenes, Bcl2 and Fos in the early mouse embryo. Quantitative RT-PCR detected Bcl2 and Fos in oocytes and some cohorts of zygotes , but not in 2-cell, 8-cell and blastocysts. Immunolocalization of Bcl2 and Fos showed little staining in oocytes and zygotes but increased staining in the 2-cell to blastocyst stages. Paf treatment of 2-cell embryos caused an α-amanitin-sensitive expression of Bcl2 and Fos for 20 min that subsided by 40 min. This transcription was blocked by inhibition of calcium (BAPTA-AM) or phosphatidylinositol-3-kinase signa l ling (LY 294002). Analysis of individual embryos showed most zygotes , but only ~12 % of 2-cell embryos had detectable Bcl2 and Fos. A significantly smaller proportion of Ptafr–/– (Paf-receptor null) 2-cell embryos had detectable Bcl2 transcript and embryo culture (which diminishes Paf signalling) decreased transcription of Bcl2. This dichotomous pattern of transcript expression is consistent with the known periodic actions of Paf (with a periodicity of 90–120 min)2 and the relatively short-half life of the resulting transcripts. Bcl2 antagonist (HA14-1) caused a dose-dependent inhibition of cultured zygotes to develop to morphological blastocysts , which was partially reversed by exogenous Paf. The results show for the first time the autocrine embryotrophi n Paf induces periodic transient expression of key proto-oncogenes and provides evidence for a role of embryotrophins in the onset of gene expression in preimplantation embryo. (1) O’Neill C. Hum Reprod Update 2005; 11: 215–228.(2) Emerson M, et al J Biol Chem 2000; 275: 21 905–21 913.(3) Jin XL, O’Neill C. Biology of Reproduction 2010; 82: 459–468.(4) Zhang X, et al. Proc Natl Acad Sci USA 2005; 102: 4459–4464.