Failure of human rhombic lip differentiation underlies medulloblastoma formation

Medulloblastoma (MB) comprises a group of heterogeneous paediatric embryonal neoplasms of the hindbrain with strong links to early development of the hindbrain^1-4. Mutations that activate Sonic hedgehog signalling lead to Sonic hedgehog MB in the upper rhombic lip (RL) granule cell lineage^5-8. By contrast, mutations that activate WNT signalling lead to WNT MB in the lower RL^9,10. However, little is known about the more commonly occurring group 4 (G4) MB, which is thought to arise in the unipolar brush cell lineage^3,4. Here we demonstrate that somatic mutations that cause G4 MB converge on the core binding factor alpha (CBFA) complex and mutually exclusive alterations that affect CBFA2T2, CBFA2T3, PRDM6, UTX and OTX2. CBFA2T2 is expressed early in the progenitor cells of the cerebellar RL subventricular zone in Homo sapiens, and G4 MB transcriptionally resembles these progenitors but are stalled in developmental time. Knockdown of OTX2 in model systems relieves this differentiation blockade, which allows MB cells to spontaneously proceed along normal developmental differentiation trajectories. The specific nature of the split human RL, which is destined to generate most of the neurons in the human brain, and its high level of susceptible EOMES⁺KI67⁺ unipolar brush cell progenitor cells probably predisposes our species to the development of G4 MB.

Risk and protective factors associated with youth violence among secondary school students in a nationally representative sample in Puerto Rico

During the past decade, youth violence has received increasing attention as a major public health issue in Puerto Rico as well as in the United States. This study sought to identify risk and protective factors of youth violence in a representative sample of school adolescents in Puerto Rico. Risk and protective factors were grouped into five domains: individual, family, peer group, school and community. From a total of 2,385 participants, 10.7% reported at least one violent behavior and 3.4% reported two or more violent behaviors. In multiple regression analysis the risk factors identified were male gender, junior grade students, having a favorable attitude towards antisocial behavior, use of ecstasy, involvement with antisocial peers and reporting antisocial parents. Participation in family decisions was the only protective factor associated with violence. Findings from this study could have important implications for the development of preventive programs for the adolescent population in Puerto Rico.