Fig. 3.

Small RNA functions in stem cells derived from the mouse blastocyst. By the time of implantation, the mammalian blastocyst has developed three different cell lineages: trophectoderm, primitive endoderm and epiblast (shown on left). Three distinct self-renewing cell lines can be derived from these lineages: trophoblast stem (TS) cells, extra-embryonic endoderm (XEN) cells and embryonic stem (ES) cells. Studies of stem cell lines lacking either Dgcr8 or Dicer provide insights into small RNA-mediated regulation of stem cell maintenance, proliferation and differentiation (right).