Negative modulation of bone morphogenetic protein signaling by Dullard during wing vein formation in Drosophila

Abstract

Studies in Xenopus have shown that the C-terminal domain phosphatase-like domain (CPD) phosphatase Dullard is essential for proper neural development via inhibition of bone morphogenetic protein (BMP) signaling receptors. In contrast, the orthologous budding yeast Nem1 and human Dullard have been shown to dephosphorylate the phosphatidate phosphatases yeast Smp2 ⁄ Pah1 and human Lipin, and the relationship between phospholipid metabolism and BMP signaling remain unsolved. Here we report evidence that the Dullard-Lipin phosphatase cascade in Drosophila can regulate BMP signaling, most likely by affecting the function of the nuclear envelope. Manipulating expression levels of either the Drosophila Dullard gene, d-dullard (ddd) or the Lipin gene, DmLpin affected wing vein formation in a manner suggesting a negative effect on BMP signaling. Furthermore, both genes exhibit genetic interaction with BMP signaling pathway components, and can affect the levels of phosphorylated-Mothers against dpp (p-Mad). Although changing ddd expression levels did not have an obvious effect on overall nuclear envelope morphology as has been shown for yeast nem1, the nuclear import machinery components Importin-b and RanGAP were mislocalized and membrane lipid staining was altered in cells overexpressing ddd. Considering the known genetic interaction between Nup84 complex nucleoporins and nem1 in yeast, and the recently reported requirement for components from the orthologous nucleoporin complex in the nuclear translocation of Drosophila Mad (Chen & Xu 2010), it is likely that the role of Drosophila Dullard in regulating membrane lipid homeostasis is conserved and is critical for normal BMP signaling.

Drosophila Dullard functions as a Mad phosphatase to terminate BMP signaling

“…From this screen we identified Dullard, a member of the DXDX(T/V) serine/threonine phosphatase family as a potential candidate. In support of further pursuing this lead, Liu and colleagues (2011) had reported a genetic interaction between Dullard and BMP signaling in wing imaginal discs and testes23, thus we set out to build on their informative study by investigating the mechanistic basis for Dullards involvement in BMP signaling. We utilized a combination of biochemical assays and in vivo expression analyses to uncover the role this protein plays in BMP signaling.…”

“…1a,b). This semi lethal fly line was previously described23 and has a P-element inserted into the 5′UTR of the Dullard gene. Allowing these hypomorphic male larvae to mature into adults, revealed adult wings with multiple ectopic crossveins (arrows) and spurs associated with longitudinal veins 2 and 3 when compared to wild type wings (Fig.…”

“…Dullard, a member of the DXDX(T/V) phosphatase family has been previously shown to inhibit BMP signaling in Xenopus embryos by causing the dephosphorylation of type I BMP receptors and the ubiquitin-dependent proteasomal degradation of the BMP type II receptors21. Two more recent reports in mice and Drosophila mutants demonstrate Dullard negatively regulates BMP signaling, however the focus of these studies were to describe genetic interactions between BMP and Dullard, and therefore, insights into the mechanistic interaction of Dullard with BMP remain to be described2223. Our findings add new insights into the role Dullard plays during BMP signaling during Drosophila development.…”

The phosphatase Dullard negatively regulates BMP signalling and is essential for nephron maintenance after birth

“…Studies in Xenopus and Drosophila have suggested that Dullard is a negative regulator of BMP signalling 10,11 . First, we examined the messenger RNA (mRNA) expression levels of BMP2, BMP4…”

“…It was also reported that Drosophila dullard functions via lipin to regulate the production of diacylglycerol from phosphatidic acid and maintains the proper lipid composition of the nuclear membrane at nuclear pore complexes 25 . Thus, impairment of this process could affect the nuclear translocation of phosphorylated Smad proteins 11 .…”