Identification and functional analysis of healing regulators in Drosophila

Regulation of Epithelial and Endothelial Barriers by Molecular Chaperones

The integrity and permeability of epithelial and endothelial barriers depend on the formation of tight junctions, adherens junctions, and a junction-associated cytoskeleton. The establishment of this junction-cytoskeletal module relies on the correct folding and oligomerization of its protein components. Molecular chaperones are known regulators of protein folding and complex formation in different cellular compartments. Mammalian cells possess an elaborate chaperone network consisting of several hundred chaperones and co-chaperones. Only a small part of this network has been linked, however, to the regulation of intercellular adhesions, and the systematic analysis of chaperone functions at epithelial and endothelial barriers is lacking. This review describes the functions and mechanisms of the chaperone-assisted regulation of intercellular junctions. The major focus of this review is on heat shock protein chaperones, their co-chaperones, and chaperonins since these molecules are the focus of the majority of the articles published on the chaperone-mediated control of tissue barriers. This review discusses the roles of chaperones in the regulation of the steady-state integrity of epithelial and vascular barriers as well as the disruption of these barriers by pathogenic factors and extracellular stressors. Since cytoskeletal coupling is essential for junctional integrity and remodeling, chaperone-assisted assembly of the actomyosin cytoskeleton is also discussed.

Imaginal Disc Regeneration: Something Old, Something New

Imaginal discs are simple epithelial sacs found in Drosophila larvae, which generate adult structures including wings and legs. The first studies of imaginal disc regeneration involved technically challenging transplantation experiments. Yet despite the difficulty, many aspects of regeneration including wound healing, blastema formation, and the repatterning of regenerated tissue were characterized. An important discovery was the phenomenon of transdetermination, where a small group of cells in regenerating tissue collectively switch fate ("collective cell reprogramming"). The development of genetic tissue-ablation systems over the last 12 years has energized this field, by making experiments less technically challenging, more reproducible, and by incorporating additional genetic analysis. Recent progress includes defining mechanistic links between early responses to wounding and the signaling pathways that drive proliferation, uncovering a role for localized silencing of damage-responsive enhancers to limit regenerative capacity as tissues mature, and identifying genes that maintain cellular plasticity within acceptable limits during regeneration.

Proteomics of purified lamellocytes from Drosophila melanogaster HopTum-l identifies new membrane proteins and networks involved in their functions

In healthy Drosophila melanogaster larvae, plasmatocytes and crystal cells account for 95% and 5% of the hemocytes, respectively. A third type of hemocytes, lamellocytes, are rare, but their number increases after oviposition by parasitoid wasps. The lamellocytes form successive layers around the parasitoid egg, leading to its encapsulation and melanization, and finally the death of this intruder. However, the total number of lamellocytes per larva remains quite low even after parasitoid infestation, making direct biochemical studies difficult. Here, we used the Hop^Tum-l mutant strain that constitutively produces large numbers of lamellocytes to set up a purification method and analyzed their major proteins by 2D gel electrophoresis and their plasma membrane surface proteins by 1D SDS-PAGE after affinity purification. Mass spectrometry identified 430 proteins from 2D spots and 344 affinity-purified proteins from 1D bands, for a total of 639 unique proteins. Known lamellocyte markers such as PPO3 and the myospheroid integrin were among the components identified with specific chaperone proteins. Affinity purification detected other integrins, as well as a wide range of integrin-associated proteins involved in the formation and function of cell-cell junctions. Overall, the newly identified proteins indicate that these cells are highly adapted to the encapsulation process (recognition, motility, adhesion, signaling), but may also have several other physiological functions (such as secretion and internalization of vesicles) under different signaling pathways. These results provide the basis for further in vivo and in vitro studies of lamellocytes, including the development of new markers to identify coexisting populations and their respective origins and functions in Drosophila immunity.

Requirement for and polarized localization of integrin proteins during Drosophila wound closure

Wound reepithelialization is an evolutionarily conserved process in which skin cells migrate as sheets to heal the breach and is critical to prevent infection but impaired in chronic wounds. Integrin heterodimers mediate attachment between epithelia and underlying extracellular matrix and also act in large signaling complexes. The complexity of the mammalian wound environment and evident redundancy among integrins has impeded determination of their specific contributions to reepithelialization. Taking advantage of the genetic tools and smaller number of integrins in Drosophila, we undertook a systematic in vivo analysis of integrin requirements in the reepithelialization of skin wounds in the larva. We identify αPS2-βPS and αPS3-βPS as the crucial integrin dimers and talin as the only integrin adhesion component required for reepithelialization. The integrins rapidly accumulate in a JNK-dependent manner in a few rows of cells surrounding a wound. Intriguingly, the integrins localize to the distal margin in these cells, instead of the frontal or lamellipodial distribution expected for proteins providing traction and recruit nonmuscle myosin II to the same location. These findings indicate that signaling roles of integrins may be important for epithelial polarization around wounds and lay the groundwork for using Drosophila to better understand integrin contributions to reepithelialization.

Phenolic compounds responding to zinc and/or cadmium treatments in Gynura pseudochina (L.) DC. extracts and biomass

Gynura pseudochina (L.) DC. is a Zn/Cd hyperaccumulative plant. In an in vivo system under controlled plant age, this research reveals that phenolic compounds and lignification play beneficial roles in protecting G. pseudochina from exposure to an excess of Zn and/or Cd, and Zn reduces Cd toxicity under the dual treatments. The total phenolic content (TPC), total flavonoid content (TFC), and half-maximal inhibitory concentration (IC₅₀) values correspond to the metal dose-response curves. Liquid chromatography-electrospray ionization-quadrupole time of flight-tandem mass spectrometry (LC-ESI-QTOF-MS/MS) is used to characterize phenolic compounds and their glycosides, which could play roles in antioxidant activities and in the esterification of the cell wall, especially derivatives of p-coumaric and caffeic acid. Confocal laser scanning microscopy (CLSM) and micro X-ray fluorescence (μ-XRF) imaging revealed that the accumulation of Zn and Cd in the cell wall involves flavonoid compounds. Low extractable pools of Cd and Zn in the leaf extracts indicate that these elements are tightly bound to the plant biomass structures. The bulk X-ray absorption near edge structure (XANES) spectra indicate that Zn²⁺ and Cd²⁺ dominate with O and S ligands, which could be provided by cell walls, phenolic compounds, and sulphur protein. Consequently, the benefit of these results is to support the growth of G. pseudochina for phytoremediation in a Zn- and/or Cd-contaminated site.

ROS-Induced JNK and p38 Signaling Is Required for Unpaired Cytokine Activation during Drosophila Regeneration

Upon apoptotic stimuli, epithelial cells compensate the gaps left by dead cells by activating proliferation. This has led to the proposal that dying cells signal to surrounding living cells to maintain homeostasis. Although the nature of these signals is not clear, reactive oxygen species (ROS) could act as a signaling mechanism as they can trigger pro-inflammatory responses to protect epithelia from environmental insults. Whether ROS emerge from dead cells and what is the genetic response triggered by ROS is pivotal to understand regeneration of Drosophila imaginal discs. We genetically induced cell death in wing imaginal discs, monitored the production of ROS and analyzed the signals required for repair. We found that cell death generates a burst of ROS that propagate to the nearby surviving cells. Propagated ROS activate p38 and induce tolerable levels of JNK. The activation of JNK and p38 results in the expression of the cytokines Unpaired (Upd), which triggers the JAK/STAT signaling pathway required for regeneration. Our findings demonstrate that this ROS/JNK/p38/Upd stress responsive module restores tissue homeostasis. This module is not only activated after cell death induction but also after physical damage and reveals one of the earliest responses for imaginal disc regeneration.

Regenerative biology pursues to unveil the genetic networks triggered by tissue damage. Regeneration can occur after damage by cell death or by injury. We used the imaginal disc of Drosophila in which we genetically activated apoptosis or physically removed some parts and monitored the capacity to repair the damage. We found that dying cells generate a burst of reactive oxygen species (ROS) necessary to activate JNK and p38 signaling pathways in the surrounding living cells. The action of these pathways is necessary for the activation of the cytokines Unpaired (Upd). Eventually, Upd will turn on the JAK/STAT signaling pathway to induce regenerative growth. Thus, we present here a module of signals that depends on oxidative stress and that, through the p38-JNK interplay, will activate cytokine-dependent regeneration.