Hes1 and Hes5 as Notch effectors in mammalian neuronal differentiation

Abstract

T.Ohtsuka, M.Ishibashi and G.Gradwohl contributed equally to this workWhile the transmembrane protein Notch plays an important role in various aspects of development, and diseases including tumors and neurological disorders, the intracellular pathway of mammalian Notch remains very elusive. To understand the intracellular pathway of mammalian Notch, the role of the bHLH genes Hes1 and Hes5 (mammalian hairy and Enhancer-of-split homologues) was examined by retrovirally misexpressing the constitutively active form of Notch (caNotch) in neural precursor cells prepared from wild-type, Hes1-null, Hes5-null and Hes1-Hes5 double-null mouse embryos. We found that caNotch, which induced the endogenous Hes1 and Hes5 expression, inhibited neuronal differentiation in the wild-type, Hes1-null and Hes5-null background, but not in the Hes1-Hes5 double-null background. These results demonstrate that Hes1 and Hes5 are essential Notch effectors in regulation of mammalian neuronal differentiation.

The Notch-Hes pathway in mammalian neural development

“…caNotch-AP infection still blocked neuronal differentiation of precursor cells prepared from Hes1 knock-out (Fig 4E-G) or Hes5 knock-out mice (Fig 4H-J) but not from Hes1-Hes5 double knock-out mice (Fig 4K-M) [18]. These results strongly support the conclusion that Hes1 and Hes5 are essential Notch effectors.…”

“…In these mice, Mash1 expression prematurely occurs and is also upregulated, suggesting that this Mash1 upregulation may account for premature neuronal differentiation in the absence of Hes1. Similarly, in Hes5-deficient mice neurons prematurely differentiate although Hes5 deficiency seems to be later compensated [18]. Similar phenotype of premaThe Notch-Hes pathway ture neuronal differentiation is also observed in both Notch1-deficient and RBP-Jdeficient mice [19], indicating that Notch, RBP-J and Hes function in the same pathway to prevent premature differentiation.…”

“…The definitive evidence for Hes1 and Hes5 as essential Notch effectors is presented by the experiments to determine the Notch effects in the absence of Hes genes [18]. When the extracellular domain is deleted, Notch is known to function constitutively.…”

“…This negative regulation by Notch and Hes seems to be essential for Mash1 to function at the proper timing. However, some Hes1-Hes5 double-null cells are still inhibited by caNotch-AP infection from differentiating as mature neurons [18], suggesting that Notch can still partially function independently of Hes1 and Hes5. The molecular nature of Hes1-Hes5-independent Notch pathway is a current hot topic [20,21] and remains to be analyzed.…”

Basic helix–loop–helix gene Hes6 delineates the sensory hair cell lineage in the inner ear

“…In contrast to positive-acting bHLH genes such as Math1, Hes genes are transcriptional repressors (Sasai et al, 1992;Thomas and Rathjen, 1992;Akazawa et al, 1995;Ishibashi et al, 1995;Jarriault et al, 1995;Chen et al, 1997;Ohtsuka et al, 1999;Kageyama et al, 2000). They are capable of repressing directly the transcription of positively acting bHLH genes and inhibiting the positively acting bHLH heterodimers from binding to their DNA targets (Akazawa et al, 1995;Ishibashi et al, 1995;Tomita et al, 1996;Ohtsuka et al, 1999;Cau et al, 2000;Hatakeyama et al, 2004;Hu et al, 2004).…”