Convergent insulin and TGF-ß signalling drives cancer cachexia by promoting aberrant fat body ECM accumulation in a Drosophila tumour model.

In this study, we found that in the adipose tissue of wildtype animals, insulin and TGF-ß signalling converge via a BMP antagonist short gastrulation (sog) to regulate ECM remodelling. In tumour bearing animals, Sog also modulates TGF-ß signalling to regulate ECM accumulation in the fat body. TGF-ß signalling causes ECM retention in the fat body and subsequently depletes muscles of fat body-derived ECM proteins. Activation of insulin signalling, inhibition of TGF-ß signalling, or modulation of ECM levels via SPARC, Rab10 or Collagen IV in the fat body, is able to rescue tissue wasting in the presence of tumour. Together, our study highlights the importance of adipose ECM remodelling in the context of cancer cachexia.

Macrophage self-renewal is regulated by transient expression of PDGF- and VEGF-related factor 2.

Macrophages are an ancient blood cell lineage critical for homeostasis and defence against pathogens. Although their numbers were long thought to be sustained solely by haematopoietic organs, it has recently become clear that their proliferation, or self-renewal, also plays a major role. In the Drosophila larva, macrophages undergo a phase of rapid self-renewal, making this an attractive model for elucidating the signals and regulatory mechanisms involved. However, a central self-renewal pathway has not been identified in this system. Here, we show that the PDGF- and VEGF-receptor related (Pvr) pathway fulfils this role. Our data show that two of the three known Pvr ligands, PDGF- and VEGF-related factor 2 (Pvf2) and Pvf3, are major determinants of overall macrophage numbers, yet they each act in a temporally independent manner and via distinct mechanisms. While Pvf3 is needed prior to the self-renewal period, we find that Pvf2 is critical specifically for expanding the larval macrophage population. We further show that Pvf2 is a potent macrophage mitogen that is kept at limiting quantities by its transient expression in a remarkably small number of blood cells. Together, these data support a novel mechanism for the regulation of macrophage self-renewal rates by the dynamic transcriptional control of Pvf2. Given the strong parallels that exist between Drosophila and vertebrate macrophage systems, it is likely that a similar self-renewal control mechanism is at play across animal phyla.

A cis-regulatory-directed pipeline for the identification of genes involved in cardiac development and disease.

BACKGROUND: Congenital heart diseases are the major cause of death in newborns, but the genetic etiology of this developmental disorder is not fully known. The conventional approach to identify the disease-causing genes focuses on screening genes that display heart-specific expression during development. However, this approach would have discounted genes that are expressed widely in other tissues but may play critical roles in heart development. RESULTS: We report an efficient pipeline of genome-wide gene discovery based on the identification of a cardiac-specific cis-regulatory element signature that points to candidate genes involved in heart development and congenital heart disease. With this pipeline, we retrieve 76% of the known cardiac developmental genes and predict 35 novel genes that previously had no known connectivity to heart development. Functional validation of these novel cardiac genes by RNAi-mediated knockdown of the conserved orthologs in Drosophila cardiac tissue reveals that disrupting the activity of 71% of these genes leads to adult mortality. Among these genes, RpL14, RpS24, and Rpn8 are associated with heart phenotypes. CONCLUSIONS: Our pipeline has enabled the discovery of novel genes with roles in heart development. This workflow, which relies on screening for non-coding cis-regulatory signatures, is amenable for identifying developmental and disease genes for an organ without constraining to genes that are expressed exclusively in the organ of interest.

Tumor-derived MMPs regulate cachexia in a Drosophila cancer model.

Cachexia, the wasting syndrome commonly observed in advanced cancer patients, accounts for up to one-third of cancer-related mortalities. We have established a Drosophila larval model of organ wasting whereby epithelial overgrowth in eye-antennal discs leads to wasting of the adipose tissue and muscles. The wasting is associated with fat-body remodeling and muscle detachment and is dependent on tumor-secreted matrix metalloproteinase 1 (Mmp1). Mmp1 can both modulate TGFß signaling in the fat body and disrupt basement membrane (BM)/extracellular matrix (ECM) protein localization in both the fat body and the muscle. Inhibition of TGFß signaling or Mmps in the fat body/muscle using a QF2-QUAS binary expression system rescues muscle wasting in the presence of tumor. Altogether, our study proposes that tumor-derived Mmps are central mediators of organ wasting in cancer cachexia.

Insulin-Like Signalling Influences the Coordination of Larval Hemocyte Number with Body Size in Drosophila melanogaster.

Blood cells, known as hemocytes in invertebrates, play important and conserved roles in immunity, wound healing and tissue remodelling. The control of hemocyte number is therefore critical to ensure these functions are not compromised, and studies using Drosophila melanogaster are proving useful for understanding how this occurs. Recently, the embryonic patterning gene, torso-like (tsl), was identified as being required both for normal hemocyte development and for providing immunity against certain pathogens. Here, we report that Tsl is required specifically during the larval phase of hematopoiesis, and that tsl mutant larvae likely have reduced hemocyte numbers due to a reduced larval growth rate and compromised insulin signaling. Consistent with this, we find that impairing insulin-mediated growth, either by nutrient deprivation or genetically, results in fewer hemocytes. This is likely the result of impaired insulin-like signaling in the hemocytes themselves, since modulation of Insulin-like Receptor (InR) activity specifically in hemocytes causes concomitant changes to their population size in developing larvae. Taken together, our work reveals the strong relationship that exists between body size and hemocyte number, and suggests that insulin-like signaling contributes to, but is not solely responsible for, keeping these tightly aligned during larval development.

The torso-like gene functions to maintain the structure of the vitelline membrane in Nasonia vitripennis, implying its co-option into Drosophila axis formation.

Axis specification is a fundamental developmental process. Despite this, the mechanisms by which it is controlled across insect taxa are strikingly different. An excellent example of this is terminal patterning, which in Diptera such as Drosophila melanogaster occurs via the localized activation of the receptor tyrosine kinase Torso. In Hymenoptera, however, the same process appears to be achieved via localized mRNA. How these mechanisms evolved and what they evolved from remains largely unexplored. Here, we show that torso-like, known for its role in Drosophila terminal patterning, is instead required for the integrity of the vitelline membrane in the hymenopteran wasp Nasonia vitripennis We find that other genes known to be involved in Drosophila terminal patterning, such as torso and Ptth, also do not function in Nasonia embryonic development. These findings extended to orthologues of Drosophila vitelline membrane proteins known to play a role in localizing Torso-like in Drosophila; in Nasonia these are instead required for dorso-ventral patterning, gastrulation and potentially terminal patterning. Our data underscore the importance of the vitelline membrane in insect development, and implies phenotypes caused by knockdown of torso-like must be interpreted in light of its function in the vitelline membrane. In addition, our data imply that the signalling components of the Drosophila terminal patterning systems were co-opted from roles in regulating moulting, and co-option into terminal patterning involved the evolution of a novel interaction with the vitelline membrane protein Torso-like.This article has an associated First Person interview with the first author of the paper.

Control of growth factor signalling by MACPF proteins.

Members of the membrane attack complex/perforin-like (MACPF) protein superfamily have long captured interest because of their unique ability to assemble into large oligomeric pores on the surfaces of cells. The best characterised of these act in vertebrate immunity where they function to deliver pro-apoptotic factors or induce the cytolysis and death of targeted cells. Less appreciated, however, is that rather than causing cell death, MACPF proteins have also evolved to control cellular signalling pathways and influence developmental programmes such as pattern formation and neurogenesis. Torso-like (Tsl) from the fruit fly Drosophila, for example, functions to localise the activity of a growth factor for patterning its embryonic termini. It remains unclear whether these developmental proteins employ an attenuated form of the classical MACPF lytic pore, or if they have evolved to function via alternative mechanisms of action. In this minireview, we examine the evidence that links pore-forming MACPF proteins to the control of growth factor and cytokine signalling. We will then attempt to reconcile how the MACPF domain may have been repurposed during evolution for developmental events rather than cell killing.