EZH2 is essential for fate determination in the mammalian Isthmic area

Abstract

The polycomb group proteins (PcGs) are a group of epigenetic factors associated with gene silencing. They are found in several families of multiprotein complexes, including Polycomb Repressive Complex (PRC) 2. EZH2, EED and SUZ12 form the core components of the PRC2 complex, which is responsible for the mono, di-and trimethylation of lysine 27 of histone 3 (H3K27Me3), the chromatin mark associated with gene silencing. Loss-of-function studies of Ezh2, the catalytic subunit of PRC2, have shown that PRC2 plays a role in regulating developmental transitions of neuronal progenitor cells; from self-renewal to differentiation and the neurogenic-to-gliogenic fate switch. To further address the function of EZH2 and H3K27me3 during neuronal development we generated a conditional mutant in which Ezh2 was removed in the mammalian isthmic (mid-hindbrain) region from E10.5 onward. Loss of Ezh2 changed the molecular coding of the anterior ventral hindbrain leading to a fate switch and the appearance of ectopic dopaminergic neurons. The correct specification of the isthmic region is dependent on the signaling factors produced by the Isthmic organizer (IsO), located at the border of the mid-and hindbrain. We propose that the change of cellular fate is a result of the presence of Otx2 in the hindbrain of Ezh2 conditional knock-outs and a dysfunctional IsO, as represented by the loss of Fgf8 and Wnt1. Our work implies that next to controlling developmental transitions, EZH2 mediated gene silencing is important for specification of the isthmic region by influencing IsO functioning and repressing Otx2 in the hindbrain. Kouwenhoven et al., 2016;Martinez et al., 1999). In this study we show that the En1Cre driven deletion of Ezh2 and a consequential loss of H3K27me3 leads to a disorganized IsO and ectopic expression of the transcription factor Otx2 in the hindbrain. In accordance with other studies in which Otx2 expression is expanded caudally, DA cells are formed in rhombomere (R) 1 at the expense of R1 born neuronal subtypes, including 5-HT neurons (Brodski et al., 2003;Kouwenhoven et al., 2016;Sherf et al., 2015). Together, our data suggest that next to transcription factors, gene repression via EZH2 and H3K27me3 are required for the repression of Otx2 in the hindbrain, maintenance of the IsO and the correct fate-determination of the isthmic area.

The role and mechanisms of polycomb repressive complex 2 on the regulation of osteogenic and neurogenic differentiation of stem cells

“…Knockdown of EZH2 effectively promotes mdDA neuronal differentiation during midbrain development 96 . Conditional knockout of EZH2 produces ectopic mdDA neurons in the isthmic organizer (IsO) of mice hindbrain 86 . These suggest that PRC2‐EZH2 participates in the progress of neural differentiation of stem cells and functional neural structure formation by supporting the generation, maturation and maintenance of differential neural lineage.…”

“…NPCs/NSCs seems to differentiate into neurons firstly and later astrocytes during the neocortical development; this neurogenic‐to‐astrogenic fate switch determines the final repaired neuron generation. Researchers find that EZH2 maintains NPCs self‐renewal and the neurogenic‐to‐gliogenic fate switch of NPCs 86 . In addition, EZH2 represses the neurogenic and promotes the astrogenic fate transition of NPCs 87 .…”