Here we dissected the role of RNA helicase Belle (DDX3) in somatic cyst cells of the testes and showed that Belle function in cyst cells is required non-autonomously for proper differentiation of early germ cells; RNAi bel knockdown (belKD) in cyst cells led to the segregation of early germ cells and cyst cells from each other and the accumulation of over-proliferating tumor-like clusters of early germ cells. This evidence concerns the gene DDX3X and cyst.