Early developmental research on human embryos is impossible due to ethical considerations, and is technically difficult to perform in other mammals, making resources for this type of research extremely rare. For example, the Functional Annotation of Mammalian Genome (FANTOM) 5 project based in Japan, established in 2000, is a worldwide collaborative project with the goal of identifying all functional elements in mammalian genomes, but it has no Cap Analysis of Gene Expression (CAGE)-based transcription start site (TSS) data for human embryos or for murine embryos representing early developmental stages.