93 THE INVOLVEMENT OF E-CADHERIN IN THERMOPROTECTIVE FUNCTION OF INSULIN-LIKE GROWTH FACTOR-1 IN 4-CELL HAMSTER EMBRYOS

Abstract

Studies have demonstrated that the early pre-implantation embryo is very sensitive to effects of heat stress in vitro. Heat stress reduces the total cell number in blastocysts and increases apoptosis in blastomeres. Insulin-like growth factor-1 (IGF-1) has been widely studied as a thermoprotective agent for its anti-apoptotic actions. Addition of IGF-1 to the culture medium decreases the effects of heat stress on blastocysts but has no effects on 2-cell embryos. Molecular mechanisms by which IGF-1 decreases apoptosis involve activation of the PI3K/Akt pathway. It is also known that adherens junctions contribute to PI3K/AKT activation mediated by the transmembrane glycoprotein E-cadherin, which is involved in Ca²⁺-dependent cell-cell adhesion. Within 2- to 8-cell embryos, E-cadherin is mainly inactive and has cytoplasmic localization. 6-Dimethylaminopurine (6-DMAP) induces premature cell flattening and E-cadherin redistribution to adhesion sites in 4-cell embryos. The aim of this study was to induce E-cadherin redistribution in 4-cell hamster embryos and evaluate the thermoprotective function of IGF-1 in these embryos. Four-cell embryos were incubated in the presence of 6-DMAP to induce E-cadherin redistribution to adhesion sites and cultured for 24 h under conditions of heat stress and compared with controls without 6-DMAP. Culture medium was supplemented with IGF-1. At the end of culture, developmental stage and rate of apoptosis were determined and analysed by ANOVA using the General Linear Model (GLM) of SAS (SAS Institute Inc., Cary, NC, USA) procedure with statistical significance at P < 0.05. E-Cadherin redistribution induced by 6-DMAP increased development to the 6-cell stage after 24 h (63.57% v. 38.81%, respectively; P < 0.05) and reduced apoptosis (25% v. 33%, respectively; P < 0.05) under heat-stress conditions. In conclusion, we hypothesise a role for E-cadherin-mediated cell flattening in promoting IGF-1-mediated thermoprotection in pre-compact 4-cell hamster embryos. Further studies are required to confirm this link.