The cover image shows Characterization of global gene expression patterns during preimplantation development. Three groups published stage specific gene array analysis of gene expression in mouse preimplantation embryos in 2004 (Hamatani et al., 2004; Wang et al., 2004; Zeng et al., 2004). Two main waves of gene expression were observed corresponding with EGA and a second MGA that contributed to events associated with TE differentiation and blastocyst formation (Hamatani et al., 2004). Hamatani et al. (2004), Wang et al. (2004) and Zeng et al. (2004) are landmark studies in the characterization of gene expression patterns during preimplantation development as they have produced extensive catalogues of global stage specific gene expression patterns. General gene expression patterns are indicated; loss of maternal mRNAs (red); activation of embryonic genome (green); MGA (purple) and continuous expression (orange). Examples of genes expressed in each category are indicated in boxes. (See E. Bell et al., 691-702).
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