Maternal Factors Involved in Nuclear Reprogramming by Eggs and Oocytes

Abstract

When a somatic cell nucleus is transplanted into an egg or an oocyte, the transplanted nucleus can be reprogrammed to support early embryonic develop- ment so that the reconstructed embryo gives rise to a cloned animal. Nuclear reprogramming of somatic nuclei is induced by maternal components stored in eggs and oocytes. These endogenous reprogramming factors and mechanisms have been explored for decades in mam- mals and amphibia. There are several ways of investi- gating reprogramming mechanisms, including nuclear transfer to eggs/oocytes and incubation in egg/oocyte extracts. In this review I describe the type of reprogram- ming events induced in each system and what factors in eggs and oocytes are responsible for these. Based on our current knowledge, I propose a model for the early phase of nuclear reprogramming in eggs and oocytes.