Medulloblastoma (MB) is an embryonal tumour that arises in the posterior fossa, being the most common malignant paediatric brain tumour. Currently there are four subgroups of medulloblastoma described, which arise from the alteration of specific neuronal stem or progenitor cell populations in exact spatio-temporal patterns(1). Group 4 MB (G4MB) is the most common subgroup of MB and has recently been described to arise from the failure of developmental processes in the differentiation of the rhombic lip (RL), implicating glutamatergic progenitors as putative cells of origin (2). Such cells originate from a population of Math1+ progenitors during embryonic days 13-14 in mice(3). Currently neither in vitro nor in vivo models of G4MB have been described, mainly due to the limited knowledge regarding the cell of origin and mechanisms of tumour progression, up until recently. Therefore, the overall aim of this project is to develop and establish new models of G4MB through the activation of the oncogenic hit using lentiviral delivery in glutamatergic progenitors (Math1+) in vitro. Such cellular models were then characterised using RT-qPCR, growth tracking analysis and immunohistochemistry.We have been able to generate RL-derived neurospheres that upon oncogenic hit activation led to the formation of tumourspheres that show increase proliferation abilities and expression of markers specific of G4MB (EOMES, BARHL1, LHX2). Next, we will assess if grafting of those tumourspheres leads to the formation of a tumoural mass in vivo resembling the features of G4MB. References: 1.Northcott et al,Nature, 2019; 2.Hendrickse et al,Nature, 2022; 3.Englung et al,J Neuroscience, 2006