BMPs regulate msx gene expression in the dorsal neuroectoderm of Drosophila and vertebrates by distinct mechanisms.

In a broad variety of bilaterian species the trunk central nervous system (CNS) derives from three primary rows of neuroblasts. The fates of these neural progenitor cells are determined in part by three conserved transcription factors: vnd/nkx2.2, ind/gsh and msh/msx in Drosophila melanogaster/vertebrates, which are expressed in corresponding non-overlapping patterns along the dorsal-ventral axis. While this conserved suite of "neural identity" gene expression strongly suggests a common ancestral origin for the patterning systems, it is unclear whether the original regulatory mechanisms establishing these patterns have been similarly conserved during evolution. In Drosophila, genetic evidence suggests that Bone Morphogenetic Proteins (BMPs) act in a dosage-dependent fashion to repress expression of neural identity genes. BMPs also play a dose-dependent role in patterning the dorsal and lateral regions of the vertebrate CNS, however, the mechanism by which they achieve such patterning has not yet been clearly established. In this report, we examine the mechanisms by which BMPs act on cis-regulatory modules (CRMs) that control localized expression of the Drosophila msh and zebrafish (Danio rerio) msxB in the dorsal central nervous system (CNS). Our analysis suggests that BMPs act differently in these organisms to regulate similar patterns of gene expression in the neuroectoderm: repressing msh expression in Drosophila, while activating msxB expression in the zebrafish. These findings suggest that the mechanisms by which the BMP gradient patterns the dorsal neuroectoderm have reversed since the divergence of these two ancient lineages.

The Drosophila BMPRII, wishful thinking, is required for eggshell patterning.

The Drosophila eggshell is an elaborate structure that is derived from a monolayer of follicular epithelium surrounding the developing oocyte within the female ovary. The bone morphogenetic protein (BMP) signaling pathway is essential for controlling the patterning and morphogenesis of the eggshell. During oogenesis, the roles of patterning and morphogenesis by the BMP type I receptor thickveins (tkv) have been studied extensively. However, signaling through this pathway requires both type I and II receptors, and the latter has yet to be established in oogenesis. We focus on wishful thinking (wit), the Drosophila homolog to the mammalian BMP type II receptor, BMPRII. We found that wit is expressed dynamically in the FCs of D. melanogaster in an evolutionary conserved pattern. The expression patterns are highly correlated with the dynamics of the BMP signaling, which is consistent with our finding that wit is a target of BMP signaling. Furthermore, we established that WIT is necessary for BMP signaling, and loss of WIT is associated with cell autonomous loss of BMP responses. Of importance, we demonstrated that perturbations in WIT led to changes in eggshell morphologies in domains that are patterned by BMP signaling. Previous studies have shown a role for WIT in BMP signaling during neurogenesis; however, our results reveal a role for WIT in epithelial cells' development.

Author Correction: Olfaction regulates organismal proteostasis and longevity via microRNA-dependent signalling.

An amendment to this paper has been published and can be accessed via a link at the top of the paper.

Western blot analysis of the autophagosomal membrane protein LGG-1/LC3 in Caenorhabditis elegans.

Autophagy is being studied intensively in Caenorhabditis elegans in the context of protein homeostasis and aging. However, in contrast to the yeast and mammalian autophagosomal membrane proteins Atg8 and LC3, lipidation of the C. elegans ortholog LGG-1 with phosphatidylethanolamine has rarely been investigated by western blotting. We attribute this shortcoming to technical problems with separating the nonlipidated from the lipidated LGG-1 protein by gel electrophoresis. Our new protocol for Western blot analysis is applicable for both the detection of transgenic and endogenous LGG-1 proteins and provides a quantifiable method to assess autophagic flux. As a proof of principle, we use this assay to analyze the role of the transcriptional master regulator HLH-30/TFEB in starvation-induced autophagy.

Olfaction regulates organismal proteostasis and longevity via microRNA-dependent signaling.

The maintenance of proteostasis is crucial for any organism to survive and reproduce in an ever-changing environment, but its efficiency declines with age1. Posttranscriptional regulators such as microRNAs control protein translation of target mRNAs with major consequences for development, physiology, and longevity2,3. Here we show that food odor stimulates organismal proteostasis and promotes longevity in Caenorhabditis elegans through mir-71-mediated inhibition of tir-1 mRNA stability in olfactory AWC neurons. Screening a collection of microRNAs that control aging3 we find that miRNA mir-71 regulates lifespan and promotes ubiquitin-dependent protein turnover, particularly in the intestine. We show that mir-71 directly inhibits the toll receptor domain protein TIR-1 in AWC olfactory neurons and that disruption of mir-71/tir-1 or loss of AWC olfactory neurons eliminates the influence of food source on proteostasis. mir-71-mediated regulation of TIR-1 controls chemotactic behavior and is regulated by odor. Thus, odor perception influences cell-type specific miRNA-target interaction to regulate organismal proteostasis and longevity. We anticipate that the proposed mechanism of food perception will stimulate further research on neuroendocrine brain-to-gut communication and may open the possibility for therapeutic interventions to improve proteostasis and organismal health via the sense of smell, with potential implication for obesity, diabetes and aging.

The autophagy receptor p62/SQST-1 promotes proteostasis and longevity in C. elegans by inducing autophagy.

Autophagy can degrade cargos with the help of selective autophagy receptors such as p62/SQSTM1, which facilitates the degradation of ubiquitinated cargo. While the process of autophagy has been linked to aging, the impact of selective autophagy in lifespan regulation remains unclear. We have recently shown in Caenorhabditis elegans that transcript levels of sqst-1/p62 increase upon a hormetic heat shock, suggesting a role of SQST-1/p62 in stress response and aging. Here, we find that sqst-1/p62 is required for hormetic benefits of heat shock, including longevity, improved neuronal proteostasis, and autophagy induction. Furthermore, overexpression of SQST-1/p62 is sufficient to induce autophagy in distinct tissues, extend lifespan, and improve the fitness of mutants with defects in proteostasis in an autophagy-dependent manner. Collectively, these findings illustrate that increased expression of a selective autophagy receptor is sufficient to induce autophagy, enhance proteostasis and extend longevity, and demonstrate an important role for sqst-1/p62 in proteotoxic stress responses.

Pentagone internalises glypicans to fine-tune multiple signalling pathways.

Tight regulation of signalling activity is crucial for proper tissue patterning and growth. Here we investigate the function of Pentagone (Pent), a secreted protein that acts in a regulatory feedback during establishment and maintenance of BMP/Dpp morphogen signalling during Drosophila wing development. We show that Pent internalises the Dpp co-receptors, the glypicans Dally and Dally-like protein (Dlp), and propose that this internalisation is important in the establishment of a long range Dpp gradient. Pent-induced endocytosis and degradation of glypicans requires dynamin- and Rab5, but not clathrin or active BMP signalling. Thus, Pent modifies the ability of cells to trap and transduce BMP by fine-tuning the levels of the BMP reception system at the plasma membrane. In addition, and in accordance with the role of glypicans in multiple signalling pathways, we establish a requirement of Pent for Wg signalling. Our data propose a novel mechanism by which morphogen signalling is regulated.

The Dpp/TGFß-dependent corepressor Schnurri protects epithelial cells from JNK-induced apoptosis in drosophila embryos.

Jun N-terminal kinase (JNK) often mediates apoptosis in response to cellular stress. However, during normal development, JNK signaling controls a variety of live cell behaviors, such as during dorsal closure in Drosophila embryos. During this process, the latent proapoptotic activity of JNK becomes apparent following Dpp signaling suppression, which leads to JNK-dependent transcriptional activation of the proapoptotic gene reaper. Dpp signaling also protects cells from JNK-dependent apoptosis caused by epithelial disruption. We find that repression of reaper transcription by Dpp is mediated by Schnurri. Moreover, reporter gene analysis shows that a transcriptional regulatory module comprising AP-1 and Schnurri binding sites located upstream of reaper integrate the activities of JNK and Dpp. This arrangement allows JNK to control a migratory behavior without triggering apoptosis. Dpp plays a dual role during dorsal closure. It cooperates with JNK in stimulating cell migration and also prevents JNK from inducing apoptosis.

Control of Dpp morphogen signalling by a secreted feedback regulator.

In many instances during development, morphogens specify cell fates by forming concentration gradients. In the Drosophila melanogaster wing imaginal disc, Decapentaplegic (Dpp), a bone morphogenetic protein (BMP), functions as a long-range morphogen to control patterning and growth. Dpp is secreted from a stripe of cells at the anterior-posterior compartment boundary and spreads into both compartments to generate a characteristic BMP activity gradient. Ever since the identification of the morphogen activity of Dpp in the developing wing, the system has served as a paradigm to understand how long-range gradients are established and how cells respond to such gradients. Here we reveal the tight and direct connection of these two processes with the identification and characterization of pentagone (pent), a transcriptional target of BMP signalling encoding a secreted regulator of the pathway. Absence of pent in the wing disc causes a severe contraction of the BMP activity gradient resulting in patterning and growth defects. We show that Pent interacts with the glypican Dally to control Dpp distribution and provide evidence that proper establishment of the BMP morphogen gradient requires the inbuilt feedback loop embodied by Pent.