During the transition from maternal to embryonic control of development, maternal transcripts (common to both the unfertilised oocyte and preimplantation embryo) are depleted and embryo-specific transcripts involved in orchestrating early embryogenesis are generated in a process known as ZGA (zygotic genome activation). Protein synthesis is required for ZGA (zygotic genome activation), which occurs at the 2-cell stage in mice and between the 4 to 8-cell stage in human and 8 to16 cell stage in bovine. This is consistent with a need to synthesize essential transcription factors and other regulatory proteins lacking in the oocyte. An illustration of preimplantation development is depicted in the figure below.

Despite the fundamental importance of ZGA and the observed morphological changes in the developmental program, progress in understanding how preimplantation embryonic cells establish regulation of transcription and their own pattern of gene expression from a completely inactive genome has been hampered by the lack of molecules known to regulate these processes.

To date, the most detailed whole genome expression studies related to preimplantation development have been carried out in the mouse and have served to provide us with much of our knowledge of early mammalian development. However, there are differences in the developmental timing between mammals and it is not always possible to extrapolate from other mammals to the human to establish molecular correlates of early human development.

Due to an increasing interest in the application of ART in human (Assisted Reproduction Techniques), there is a direct need to increase our understanding of human preimplantation development. However, the scarcity and ethical constrains associated with the use of human embryos for research purposes, would mean that a model species is needed. With this in mind we previously demonstrated the feasibility and reproducibility of cross-species transcriptional analysis employing a human cDNA microarray as probe (Adjaye et al, 2004). As an extension to this study, we now report the first comparative transcriptome profiles of bovine oocytes and, human and bovine blastocysts using a human 15, 500 cDNA array (The Ensemble chip) as an initial step to gain insight into evolutionarily conserved gene regulation during preimplantation development. The full dataset comprising all results is presented in this database to enable the interrogation of the expression levels of orthologous genes and their related Gene Ontologies.