Differential expression of Obek controls ploidy in the Drosophila blood-brain barrier

During development, tissue growth is mediated by either cell proliferation or cell growth, coupled with polyploidy. Both strategies are employed by the cell types that make up the Drosophila blood-brain barrier. During larval growth, the perineurial glia proliferate, whereas the subperineurial glia expand enormously and become polyploid. Here, we show that the level of ploidy in the subperineurial glia is controlled by the N-terminal asparagine amidohydrolase homolog Obek, and high Obek levels are required to limit replication. In contrast, perineurial glia express moderate levels of Obek, and increased Obek expression blocks their proliferation. Interestingly, other dividing cells are not affected by alteration of Obek expression. In glia, Obek counteracts fibroblast growth factor and Hippo signaling to differentially affect cell growth and number. We propose a mechanism by which growth signals are integrated differentially in a glia-specific manner through different levels of Obek protein to adjust cell proliferation versus endoreplication in the blood-brain barrier.