Germ cells: ENCODE's forgotten cell type

More than a decade ago, the ENCODE and NIH Epigenomics Roadmap consortia organized large multilaboratory efforts to profile the epigenomes of >110 different mammalian somatic cell types. This generated valuable publicly accessible datasets that are being mined to reveal genome-wide patterns of a variety of different epigenetic parameters. This consortia approach facilitated the powerful and comprehensive multiparametric integrative analysis of the epigenomes in each cell type. However, no germ cell types were included among the cell types characterized by either of these consortia. Thus, comprehensive epigenetic profiling data are not generally available for the most evolutionarily important cells, male and female germ cells. We discuss the need for reproductive biologists to generate similar multiparametric epigenomic profiling datasets for both male and female germ cells at different developmental stages and summarize our recent effort to derive such data for mammalian spermatogonial stem cells and progenitor spermatogonia.