Differential expression of the Drosophila Ntan/Öbek controls ploidy in the blood-brain barrier

Abstract

During development tissue growth is mediated by either cell proliferation or cell growth, coupled with polyploidy. Both strategies are employed by the cell types comprising 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 subperineurial glia is controlled by the N-terminal asparagine amidohydrolase homolog Öbek, where high Öbek levels are required to limit replication. In contrast, perineurial glia express moderate levels of Öbek, and increased expression blocks their proliferation. Interestingly, other dividing cells are not affected by alteration of Öbek expression. In glia, Öbek counteracts FGF- and Hippo-signaling to differentially affect cell growth and number. We propose a mechanism where growth signals are integrated differentially in a glia-specific manner through different levels of Öbek protein to adjust cell proliferation versus endoreplication in the blood-brain barrier.