Cyclin D1 controls development of cerebellar granule cell progenitors through phosphorylation and stabilization of ATOH1

Abstract

During development, neural progenitors are in proliferative and immature states; however, the molecular machinery that cooperatively controls both states remains elusive. Here, we report that cyclin D1 (CCND1) directly regulates both proliferative and immature states of cerebellar granule cell progenitors (GCPs). CCND1 not only accelerates cell cycle but also upregulates ATOH1 protein, an essential transcription factor that maintains GCPs in an immature state. In cooperation with CDK4, CCND1 directly phosphorylates S309 of ATOH1, which inhibits additional phosphorylation at S328 and consequently prevents S328 phosphorylation-dependent ATOH1 degradation. Additionally, PROX1 downregulates Ccnd1 expression by histone deacetylation of Ccnd1 promoter in GCPs, leading to cell cycle exit and differentiation. Moreover, WNT signaling upregulates PROX1 expression in GCPs. These findings suggest that WNT-PROX1-CCND1-ATOH1 signaling cascade cooperatively controls proliferative and immature states of GCPs. We revealed that the expression and phosphorylation levels of these molecules dynamically change during cerebellar development, which are suggested to determine appropriate differentiation rates from GCPs to GCs at distinct developmental stages. This study contributes to understanding the regulatory mechanism of GCPs as well as neural progenitors.

Transit Amplifying Progenitors in the Cerebellum: Similarities to and Differences from Transit Amplifying Cells in Other Brain Regions and between Species

“…However, our group and another have confirmed that there are ATOH1-negative populations located just beneath the ATOH1-positive cells in the EGL that, surprisingly, remain mitotic [ 59 , 60 ]. In a previous report, we also noted that the protein expression of NEUROD1, a transcription factor, was expressed in ATOH1-negative GCPs [ 9 ]. A recent study also confirmed these expression patterns in the mouse cerebellum [ 61 ].…”

“…In addition, a small number of GCPs located at the border between AT + GCPs and ND + GCPs express both ATOH1 and NEUROD1. These findings suggested that AT + GCPs give rise to ND + GCPs (called “AT-ND transition” [ 9 ]), which differentiate into GCs ( Figure 3 D), as well as the presence of a two-step amplification system of GCPs in the EGL.…”

“… Novel developmental machinery of mammalian granule cells in the EGL. Schematic illustrations of the previous model ( A ) and our model ( B , referencing our recent studies [ 9 , 62 ]) of GC development in the EGL. Notch-signaling activity and the regulation of the NEUROD1 protein in the AT + GCPs ( C ).…”

“…In the chick cerebellum, in situ hybridization and Neurod1 -promoter activity indicates that all GCPs in the EGL express Atoh1 , while Neurod1 is expressed only in postmitotic GCs [ 69 , 71 ]. However, in the mouse cerebellum, some GCPs express NEUROD1 protein instead of the ATOH1 protein, as revealed by tissue staining and scRNAseq [ 9 ]. An early study also supported this notion [ 73 ].…”

“…In this review, we first summarize the known transit amplification systems in the CNS. Thereafter, we will summarize the transit amplification system in the cerebellum [ 8 , 9 ]. Moreover, we will show that these transit amplifying cells are only present in mammals and contribute to the expansion of the mammalian cerebellum.…”