LKB1 Regulates Cerebellar Development by Controlling Sonic Hedgehog-mediated Granule Cell Precursor Proliferation and Granule Cell Migration

Abstract

The Liver Kinase B1 (LKB1) gene plays crucial roles in cell differentiation, proliferation and the establishment of cell polarity. We created LKB1 conditional knockout mice (LKB1Atoh1 CKO) to investigate the function of LKB1 in cerebellar development. The LKB1Atoh1 CKO mice displayed motor dysfunction. In the LKB1Atoh1 CKO cerebellum, the overall structure had a larger volume and morelobules. LKB1 inactivationled to an increased proliferation of granule cell precursors (GCPs), aberrant granule cell migration and overproduction of unipolar brush cells. To investigate the mechanism underlying the abnormal foliation, we examined sonic hedgehog signalling (Shh) by testing its transcriptional mediators, the Gli proteins, which regulate the GCPs proliferation and cerebellar foliation during cerebellar development. The expression levels of Gli genes were significantly increased in the mutant cerebellum. In vitro assays showed that the proliferation of cultured GCPs from mutant cerebellum significantly increased, whereas the proliferation of mutant GCPs significantly decreased in the presence of a Shh inhibitor GDC-0049. Thus, LKB1 deficiency in the LKB1Atoh1 CKO mice enhanced Shh signalling, leading to the excessive GCP proliferation and the formation of extra lobules. We proposed that LKB1 regulates cerebellar development by controlling GCPs proliferation through Shh signalling during cerebellar development.

Lkb1 regulates granule cell migration and cortical folding of the cerebellar cortex

“…If Lkb1 were responsible for Hh signaling in GCPs, we would expect Lkb1 cko to be smaller than controls. However, consistent with the findings of others 26 , we noted that Lkb1 cko cerebella were considerably more foliated than littermate controls at adult stages (Figure 2A–B). Given that folia pattern and number were similar among Atoh1-cre; Lkb1 fl/+ , Lkb1 +/− , Lkb1 fl/+ , and Lkb1 fl/− littermates, the term “control” collectively refers to littermates of any of these genotypes.…”

“…We find that GCP-specific loss of Lkb1 resulted in an expanded cerebellar cortex with increased foliation. In contrast to a recently published manuscript 26 , we find that increased foliation occurs without alteration of Hedgehog signaling or GCP proliferation. Neither the orientation of cell division nor mTOR signaling, a known downstream target of Lkb1, are responsible for changes in foliation.…”

“…A recent study has reported that loss of Lkb1 from granule cell precursors increased Hedgehog signaling and GCP proliferation 26 . To test this, we examined expression of the transcription factor Gli1, a transcriptional target of Hh signaling.…”

“…Although Hh signaling is essential for GCP proliferation, it remains possible that cortical expansion and increased foliation in Lkb1 cko could result from Hh-dependent proliferation. Indeed, a recent study 26 demonstrated that loss of Lkb1 from GCPs increased GCP proliferation.…”

Liguisticum wallichii inhibits renal carcinoma progression by downregulating UBE3A and through suppression of NF-κB signaling

“…Consistent with this finding, our results revealed that L. wallichii effectively downregulated UBE3A expression while retarding cell proliferation. Previous studies demonstrated that L. wallichii may change cell polarity (Amini et al, 2012), and this may affect UBE3A expression (Men et al, 2015). Thus, we speculated whether L. wallichii affects UBE3A expression by influencing the cell's polarity.…”