Abstract
Cerebellar granule cell progenitors (GCPs) undergo proliferation in the post-natal cerebellum that is dependent on sonic hedgehog (SHH) signalling. Deregulated SHH signalling leads to type 2 medulloblastoma (MB). In this work, a novel cell culture protocol is described, which is suitable for the establishment and long-term maintenance of GCP-derived cells. This method is first applied to SHH pathway active MB cells from Atoh1-cre; Ptch1FL/FL tumours, which leads to the generation of neurosphere-like cell lines expressing GCP markers and an active SHH signalling pathway. These cells also show high sensitivity to the Smoothened inhibitor vismodegib, therefore recapitulating the SHH pathway requirement for survival shown by type 2 MB. Analysis of culture supplements reveals that bFGF and fetal bovine serum act as inhibitors of the SHH pathway and therefore preclude generation of cell lines that are relevant to the study of the SHH pathway. Consequently, these insights are transferred from the context of MB to non-transformed, post-natal day 7 cerebellum-derived cellular explants. In contrast to other, previously used methods, these GCP cultures proliferate indefinitely and depend on SHH pathway activation, either by means of the small molecule SAG or through genetic ablation of Ptch1. This culture method therefore leads to the generation of immortal neurosphere-like cell lines, that are named murine SAG-dependent spheres (mSS). Despite long-term culture, mSS cells remain dependent on continuous stimulation of the SHH pathway. Further, mSS cells maintain their lineage after extensive periods in vitro, as demonstrated by their differentiation towards the neural lineage. Herein a simple method for the generation of immortal cell lines from murine cerebella is defined. These lines can be maintained indefinitely through hedgehog pathway activation and maintain the GCP lineage.