Epigenetic regulation of germ cell differentiation

Abstract

Germ cells and somatic cells have the identical genome. However, unlike the mortal fate of somatic cells, germ cells have the unique ability to differentiate into gametes that retain totipotency and produce an entire organism upon fertilization. The processes by which germ cells differentiate into gametes, and those by which gametes become embryos, involve dramatic cellular differentiation accompanied by drastic changes in gene expression, which are tightly regulated by genetic circuitries as well as epigenetic mechanisms. Epigenetic regulation refers to heritable changes in gene expression that are not due to changes in primary DNA sequence. The past decade has witnessed an ever-increasing understanding of epigenetic regulation in many different cell types/tissues during embryonic development and adult homeostasis. In this review, we focus on recent discoveries of epigenetic regulation of germ cell differentiation in various metazoan model organisms, including worms, flies, and mammals.

Figure 1. Summary of different epigenetic mechanisms in regulating germ cell differentiation during metazoan life cycle

Male (blue circles) and female (pink circles) germ cells at equivalent differentiation stages are aligned vertically. Chromatin regulators, histone modifying enzymes and histone modifications regulated by them are placed according to the stages they are functional. Solid lines represent direct enzymatic reaction and dotted lines represent potential indirect regulation. Sperm and early embryonic cells in mammals share similar epigenomic signatures, indicated by the dotted circle. Different metazoan model organisms discussed in this review are labeled as C. elegans (C), Drosophila (D), and mouse (M). Refer to the text for detailed illustration and discussion of these data.