The Eya1 Phosphatase Mediates Shh-Driven Symmetric Cell Division of Cerebellar Granule Cell Precursors

Abstract

During neural development, stem and precursor cells can divide either symmetrically or asymmetrically. The transition between symmetric and asymmetric cell divisions is a major determinant of precursor cell expansion and neural differentiation, but the underlying mechanisms that regulate this transition are not well understood. Here, we identify the Sonic hedgehog (Shh) pathway as a critical determinant regulating the mode of division of cerebellar granule cell precursors (GCPs). Using partial gain and loss of function mutations within the Shh pathway, we show that pathway activation determines spindle orientation of GCPs, and that mitotic spindle orientation correlates with the mode of division. Mechanistically, we show that the phosphatase Eya1 is essential for implementing Shh-dependent GCP spindle orientation. We identify atypical protein kinase C (aPKC) as a direct target of Eya1 activity and show that Eya1 dephosphorylates a critical threonine (T410) in the activation loop. Thus, Eya1 inactivates aPKC, resulting in reduced phosphorylation of Numb and other components that regulate the mode of division. This Eya1-dependent cascade is critical in linking spindle orientation, cell cycle exit and terminal differentiation. Together these findings demonstrate that a Shh-Eya1 regulatory axis selectively promotes symmetric cell divisions during cerebellar development by coordinating spindle orientation and cell fate determinants.

The Eyes Absent Proteins: Unusual HAD Family Tyrosine Phosphatases

“…This has all been called into question by a study suggesting that interaction between EYA3 and PP2A is responsible for the threonine phosphatase activity previously attributed to the EYA3 N-terminal domain [16]. However, a more recent report failed to detect any PP2A during the EYA1-mediated dephosphorylation of Thr410 of aPKCζ [38]. This could possibly be ascribed to differences between EYA3 and EYA1.…”

The Eyes Absent proteins in development and in developmental disorders

“…The N-terminal domain of the EYA proteins has an independent transactivation function localized to a Pro/Ser/Thr-rich ∼210 amino-acid segment in Drosophila Eya [16]. In addition, a threonine phosphatase activity (either intrinsic or via interaction with protein phosphatase 2A (PP2A)) is associated with the N-terminal domain [17][18][19][20][21][22].…”

“…A Shh-Eya1 axis is also involved in promoting symmetric cell divisions during cerebellar development [22]. This is believed to occur through dephosphorylation of Thr410 and thus inactivation of the atypical protein kinase aPKCζ [22], once again implicating an EYA-linked threonine phosphatase activity in development.…”

Otic Neurogenesis in Xenopus laevis: Proliferation, Differentiation, and the Role of Eya1

“…Its function as transcriptional coactivator may be modulated by its tyrosine phosphatase activity in some contexts ( Li et al, 2003 ). In addition, Eya protein also binds directly to other proteins and serves as a phosphatase in either the nucleus or the cytoplasm, but these functions are still poorly characterized ( Fan et al, 2000 ; Li et al, 2003 ; Embry et al, 2004 ; Cook et al, 2009 ; Krishnan et al, 2009 ; Xiong et al, 2009 ; Ahmed et al, 2012a , b ; Merk et al, 2020 ).…”

“…Furthermore, recent evidence suggests that Eya1 may also affect the balance between proliferating progenitors and differentiating neurons in Six1-independent ways and possibly by acting in the cytoplasm. In the cerebellum, Eya1 has been shown to directly dephosphorylate cell polarity proteins such as atypical protein kinase C (aPKC), thereby affecting apicobasal cell polarity and changing the balance between proliferating and differentiating cells by controlling the proportion between symmetric and asymmetric cell divisions ( Merk et al, 2020 ). Another study ( El Hashash et al, 2011 ) reported a similar role of Eya1 in the lung epithelium but was subsequently retracted ( El Hashash et al, 2017 ).…”