TrxT and dhd are dispensable for Drosophila brain development but essential for l(3)mbt brain tumour growth.

Expression of the Drosophila cancer-germline (CG), X-linked, head-to-head gene pair TrxT and dhd is normally germline-specific but becomes upregulated in brain tumours caused by mutation in l(3)mbt. Here, we show that TrxT and dhd play a major synergistic role in the emergence of l(3)mbt tumour-linked transcriptomic signatures and tumour development, which is remarkable, taking into account that these two genes are never expressed together under normal conditions. We also show that TrxT, but not dhd, is crucial for the growth of l(3)mbt allografts, hence suggesting that the initial stages of tumour development and long-term tumour growth may depend on different molecular pathways. In humans, head-to-head inverted gene pairs are abundant among CG genes that map to the X chromosome. Our results identify a first example of an X-linked, head-to-head CG gene pair in Drosophila, underpinning the potential of such CG genes, dispensable for normal development and homoeostasis of somatic tissue, as targets to curtail malignant growth with minimal impact on overall health.

The Drosophila L1CAM homolog Neuroglian signals through distinct pathways to control different aspects of mushroom body axon development.

The spatiotemporal integration of adhesion and signaling during neuritogenesis is an important prerequisite for the establishment of neuronal networks in the developing brain. In this study, we describe the role of the L1-type CAM Neuroglian protein (NRG) in different steps of Drosophila mushroom body (MB) neuron axonogenesis. Selective axon bundling in the peduncle requires both the extracellular and the intracellular domain of NRG. We uncover a novel role for the ZO-1 homolog Polychaetoid (PYD) in axon branching and in sister branch outgrowth and guidance downstream of the neuron-specific isoform NRG-180. Furthermore, genetic analyses show that the role of NRG in different aspects of MB axonal development not only involves PYD, but also TRIO, SEMA-1A and RAC1.

Centrosome localization determines neuronal polarity.

Neuronal polarization occurs shortly after mitosis. In neurons differentiating in vitro, axon formation follows the segregation of growth-promoting activities to only one of the multiple neurites that form after mitosis. It is unresolved whether such spatial restriction makes use of an intrinsic program, like during C. elegans embryo polarization, or is extrinsic and cue-mediated, as in migratory cells. Here we show that in hippocampal neurons in vitro, the axon consistently arises from the neurite that develops first after mitosis. Centrosomes, the Golgi apparatus and endosomes cluster together close to the area where the first neurite will form, which is in turn opposite from the plane of the last mitotic division. We show that the polarized activities of these organelles are necessary and sufficient for neuronal polarization: (1) polarized microtubule polymerization and membrane transport precedes first neurite formation, (2) neurons with more than one centrosome sprout more than one axon and (3) suppression of centrosome-mediated functions precludes polarization. We conclude that asymmetric centrosome-mediated dynamics in the early post-mitotic stage instruct neuronal polarity, implying that pre-mitotic mechanisms with a role in division orientation may in turn participate in this event.

The histone code reader PHD finger protein 7 controls sex-linked disparities in gene expression and malignancy in Drosophila.

The notable male predominance across many human cancer types remains unexplained. Here, we show that Drosophila l(3)mbt brain tumors are more invasive and develop as malignant neoplasms more often in males than in females. By quantitative proteomics, we have identified a signature of proteins that are differentially expressed between male and female tumor samples. Prominent among them is the conserved chromatin reader PHD finger protein 7 (Phf7). We show that Phf7 depletion reduces sex-dependent differences in gene expression and suppresses the enhanced malignant traits of male tumors. Our results identify potential regulators of sex-linked tumor dimorphism and show that these genes may serve as targets to suppress sex-linked malignant traits.

An in vivo genetic screen in Drosophila identifies the orthologue of human cancer/testis gene SPO11 among a network of targets to inhibit lethal(3)malignant brain tumour growth.

Using transgenic RNAi technology, we have screened over 4000 genes to identify targets to inhibit malignant growth caused by the loss of function of lethal(3)malignant brain tumour in Drosophila in vivo We have identified 131 targets, which belong to a wide range of gene ontologies. Most of these target genes are not significantly overexpressed in mbt tumours hence showing that, rather counterintuitively, tumour-linked overexpression is not a good predictor of functional requirement. Moreover, we have found that most of the genes upregulated in mbt tumours remain overexpressed in tumour-suppressed double-mutant conditions, hence revealing that most of the tumour transcriptome signature is not necessarily correlated with malignant growth. One of the identified target genes is meiotic W68 (mei-W68), the Drosophila orthologue of the human cancer/testis gene Sporulation-specific protein 11 (SPO11), the enzyme that catalyses the formation of meiotic double-strand breaks. We show that Drosophila mei-W68/SPO11 drives oncogenesis by causing DNA damage in a somatic tissue, hence providing the first instance in which a SPO11 orthologue is unequivocally shown to have a pro-tumoural role. Altogether, the results from this screen point to the possibility of investigating the function of human cancer relevant genes in a tractable experimental model organism like Drosophila.

Loss of Centrobin Enables Daughter Centrioles to Form Sensory Cilia in Drosophila.

Sensory cilia are organelles that convey information to the cell from the extracellular environment. In vertebrates, ciliary dysfunction results in ciliopathies that in humans comprise a wide spectrum of developmental disorders. In Drosophila, sensory cilia are found only in the neurons of type I sensory organs, but ciliary dysfunction also has dramatic consequences in this organism because it impairs the mechanosensory properties of bristles and chaetae and leads to uncoordination, a crippling condition that causes lethality shortly after eclosion. The cilium is defined by the ciliary membrane, a protrusion of the cell membrane that envelops the core structure known as the axoneme, a microtubule array that extends along the cilium from the basal body. In vertebrates, basal body function requires centriolar distal and subdistal appendages and satellites. Because these structures are acquired through centriole maturation, only mother centrioles can serve as basal bodies. Here, we show that although centriole maturity traits are lacking in Drosophila, basal body fate is reserved to mother centrioles in Drosophila type I neurons. Moreover, we show that depletion of the daughter-centriole-specific protein Centrobin (CNB) enables daughter centrioles to dock on the cell membrane and to template an ectopic axoneme that, although structurally defective, protrudes out of the cell and is enveloped by a ciliary membrane. Conversely, basal body capability is inhibited in mother centrioles modified to carry CNB. These results reveal the crucial role of CNB in regulating basal body function in Drosophila ciliated sensory organs.

Quantitative differences, qualitative outcomes.

Fruit fly neuroblasts can either self-renew, rest or take on a specialized form, depending on the levels of a protein called Prospero.

Cytokinesis remnants define first neuronal asymmetry in vivo.

Polarization of a neuron begins with the appearance of the first neurite, thus defining the ultimate growth axis. Unlike late occurring polarity events (such as axonal growth), very little is known about this fundamental process. We show here that, in Drosophila melanogaster neurons in vivo, the first membrane deformation occurred 3.6 min after precursor division. Clustering of adhesion complex components (Bazooka (Par-3), cadherin-catenin) marked this place by 2.8 min after division; the upstream phosphatidylinositol 4,5-bisphosphate, by 0.7 min after division; and the furrow components RhoA and Aurora kinase, from the time of cytokinesis. Local DE-cadherin inactivation prevented sprout formation, whereas perturbation of division orientation did not alter polarization from the cytokinesis pole. This is, to our knowledge, the first molecular study of initial neuronal polarization in vivo. The mechanisms of polarization seem to be defined at the precursor stage.