Role of DNA topoisomerase IIβ in neurite outgrowth

Failure to establish neuromuscular junctions is a major phenotype of top2β knockout mice. However, the precise mechanism for this defect is not known. In the current study, we have investigated the role of TopIIβ in cultured neurons. We showed that the TopII inhibitor ICRF-193 significantly blocked neurite outgrowth and growth cone formation in cultured cerebellar granule neurons (CGNs), dorsal root ganglions (DRGs) and cortical neurons (CNs). In addition, ICRF-193 also blocked neurite outgrowth and growth cone formation of PC12 cells undergoing NGF-induced differentiation. Isolated cortical neurons from top2β knockout embryos elaborated shorter neurites than did those from their wild type counterparts, confirming the role of TopIIβ in neurite outgrowth. Together, these results demonstrate a critical role of TopIIβ in neurite outgrowth in cultured neurons. Furthermore, we demonstrated that neurons derived from top2β knockout mice failed to form contacts with muscle cells in co-cultures. These results suggest that the defect in establishing neuromuscular junctions in top2β knockout mice could be due to the lack of TopIIβ-mediated neurite outgrowth.