Disruption of CK2β in Embryonic Neural Stem Cells Compromises Proliferation and Oligodendrogenesis in the Mouse Telencephalon

Abstract

Genetic programs that govern neural stem/progenitor cell (NSC) proliferation and differentiation are dependent on extracellular cues and a network of transcription factors, which can be regulated posttranslationally by phosphorylation. However, little is known about the kinase-dependent pathways regulating NSC maintenance and oligodendrocyte development. We used a conditional knockout approach to target the murine regulatory subunit (beta) of protein kinase casein kinase 2 (CK2␤) in embryonic neural progenitors. Loss of CK2␤ leads to defects in proliferation and differentiation of embryonic NSCs. We establish CK2␤ as a key positive regulator for the development of oligodendrocyte precursor cells (OPCs), both in vivo and in vitro. We show that CK2␤ directly interacts with the basic helix-loop-helix (bHLH) transcription factor Olig2, a critical modulator of OPC development, and activates the CK2-dependent phosphorylation of its serine-threonine-rich (STR) domain. Finally, we reveal that the CK2-targeted STR domain is required for the oligodendroglial function of Olig2. These findings suggest that CK2 may control oligodendrogenesis, in part, by regulating the activity of the lineage-specific transcription factor Olig2. Thus, CK2␤ appears to play an essential and uncompensated role in central nervous system development.Casein kinase 2 (CK2) is a conserved serine/threonine kinase with more than 300 substrates, mostly proteins related to transcription-directed signaling (27). CK2 is a heterotetrameric holoenzyme formed by two catalytic subunits, ␣ and ␣Ј, that associate with a dimeric building block of regulatory ␤ subunits (␣ 2 ␤ 2 ). CK2␤ modulates the substrate specificity of the CK2 enzymatic activity, and its architecture is consistent with its role as a docking partner for other interacting proteins (4). We previously demonstrated that disruption of CK2␤ function in mice results in postimplantation lethality. Moreover, many attempts to generate CK2␤ Ϫ/Ϫ embryonic stem (ES) cells failed, suggesting an essential role of mammalian CK2␤ for ES cell viability (2).The function of CK2␤ for cell cycle progression has been investigated, but its precise role is largely unknown. The cell proliferation function of CK2␤ was first characterized in human fibroblasts, by use of antisense oligodeoxynucleotides and microinjection of specific antibodies (19,26). Recently, a genome-wide survey of protein kinases required for cell progression into cultured Drosophila melanogaster S2 cells by doublestranded RNA demonstrated that CK2␤ is required for centrosomal normality (1). In the same vein, downregulation of CK2␤ by small interfering RNA (siRNA) results in delayed cell cycle progression in cultured mammalian cells (42). Finally, in a genetic screen for mutations affecting the central brain of Drosophila, a hypomorphic allele of D. melanogaster CK2␤ has been isolated, and that study suggested a

A Sequentially Priming Phosphorylation Cascade Activates the Gliomagenic Transcription Factor Olig2

“…However, targeted disruption of the CK2 regulatory subunit CK2β in embryonic stem cells does recapitulate some features of the Olig2-null mouse including compromised neural progenitor cell proliferation and oligodendrogenesis (Huillard et al, 2010). …”

Separated at birth? The functional and molecular divergence of OLIG1 and OLIG2

“…Huillard et al showed that a murine OLIG2 protein fragment containing the ST box, fused to glutathione S-transferase, was a substrate for the serine–threonine protein kinase CK2 104 . Tryptic peptide digests revealed phosphorylation of the OLIG2 fragment at residues Ser85 and Ser87 within the ST box.…”

Protein Kinase CK2 and Angiogenesis

“…There is some indication that CK2 plays a role in spermatogenesis [8,7,23] as well as during certain stages of embryogenesis [24,25]. Furthermore, it was shown by several groups that CK2 seems to be an important protein kinase for a variety of different cellular processes in developing organs and organogenesis [5,6,26,27]. In the differentiation of pre-adipocytes into adipocytes, CK2 was found to be accompanied by a decrease in the protein level and in the kinase activity [28,29].…”