Rab11 is essential for lgl mediated JNK-Dpp signaling in dorsal closure and epithelial morphogenesis in Drosophila

The Enigmas of Tissue Closure: Inspiration from Drosophila

Hollow structures are essential for development and physiological activity. The construction and maintenance of hollow structures never cease throughout the lives of multicellular animals. Epithelial tissue closure is the main strategy used by living organisms to build hollow structures. The high diversity of hollow structures and the simplicity of their development in Drosophila make it an excellent model for the study of hollow structure morphogenesis. In this review, we summarize the tissue closure processes in Drosophila that give rise to or maintain hollow structures and highlight the molecular mechanisms and distinct cell biology involved in these processes.

The molecular characterization of Rab11 and its immune roles in red swamp crayfish (Procambarus clarkii)

The Rab proteins primarily regulate vesicular transport between membrane-bound organelles and are important for innate immune. However, there is currently a lack of studies on crustaceans regarding Rab proteins, particularly core Rabs. We identified a Rab11 gene from Procambarus clarkii (PcRab11) and evaluated its potential involvement in immune response. The results showed PcRab11 was 1789 bp long, with an open reading frame of 645 bp encoding 211 amino acids and an estimated molecular weight of 23.8 kDa. Sequence analysis revealed its remarkable evolutionary conservation. The PcRab11 was widely expressed in various tissues, with highest levels in hepatopancreas, and localized within the cell cytoplasm. Upon infection with white spot syndrome virus (WSSV) or Aeromonas veronii, the expression of PcRab11 in immune organs was significantly induced. Furthermore, silencing PcRab11 reduced phagocytosis-related genes expression and haemocytes' phagocytic activity to FITC-labeled A. veronii, as well as decreased mortality and death time in WSSV or A. veronii infected P. clarkii. Additionally, the potential protein interaction between PcRab11 and 14-3-3ε was identified in haemocytes. Overall, our findings provided evidence for the involvement of Rab11 in P. clarkii's immune response, establishing a foundation to explore the immune role of core Rab proteins in crustaceans' innate immune system.

Vibrio MARTX toxin processing and degradation of cellular Rab GTPases by the cytotoxic effector Makes Caterpillars Floppy

Vibrio vulnificus causes life-threatening wound and gastrointestinal infections, mediated primarily by the production of a Multifunctional-Autoprocessing Repeats-In-Toxin (MARTX) toxin. The most commonly present MARTX effector domain, the Makes Caterpillars Floppy-like (MCF) toxin, is a cysteine protease stimulated by host adenosine diphosphate (ADP) ribosylation factors (ARFs) to autoprocess. Here, we show processed MCF then binds and cleaves host Ras-related proteins in brain (Rab) guanosine triphosphatases within their C-terminal tails resulting in Rab degradation. We demonstrate MCF binds Rabs at the same interface occupied by ARFs. Moreover, we show MCF preferentially binds to ARF1 prior to autoprocessing and is active to cleave Rabs only subsequent to autoprocessing. We then use structure prediction algorithms to demonstrate that structural composition, rather than sequence, determines Rab target specificity. We further determine a crystal structure of aMCF as a swapped dimer, revealing an alternative conformation we suggest represents the open, activated state of MCF with reorganized active site residues. The cleavage of Rabs results in Rab1B dispersal within cells and loss of Rab1B density in the intestinal tissue of infected mice. Collectively, our work describes an extracellular bacterial mechanism whereby MCF is activated by ARFs and subsequently induces the degradation of another small host guanosine triphosphatase (GTPase), Rabs, to drive organelle damage, cell death, and promote pathogenesis of these rapidly fatal infections.

Rab11 maintains the undifferentiated state of adult midgut precursors via DPP pathway

Asymmetric stem cell divisions play instrumental roles in the maintenance, growth and differentiation of organs. Failure of asymmetric stem cell divisions may result in an array of developmental disorders, including cancer. It is well established that the gene, inscuteable, acts as the upstream component of asymmetric cell divisions. In Drosophila larval midgut, a founder adult midgut precursor (AMP) experiences an asymmetric division to instruct its first daughter to become a peripheral cell that serves as a niche where the AMP and its future daughters can remain undifferentiated. The present study demonstrates that inscuteable expressing stem cells require Rab11, a conserved small Ras-like GTPase, for proper proliferation and differentiation. As insc-GAL4 mediated Rab11RNAi in Drosophila larval and adult midguts show the disruption of the niche microenvironment of adult midgut precursors as well as elevated DPP signalling at the larval stage, which is associated with aberrant over-proliferation and early differentiation of larval AMPs and adult intestinal stem cells. The observed connections between Rab11, larval AMP proliferation, niche establishment, and DPP signalling highlight the potential for Rab11 to serve as a key regulatory factor in maintaining tissue homeostasis and balanced cellular growth.

JNK signaling and integrins cooperate to maintain cell adhesion during epithelial fusion in Drosophila

The fusion of epithelial sheets is an essential and conserved morphogenetic event that requires the maintenance of tissue continuity. This is secured by membrane-bound or diffusible signals that instruct the epithelial cells, in a coordinated fashion, to change shapes and adhesive properties and when, how and where to move. Here we show that during Dorsal Closure (DC) in Drosophila, the Jun kinase (JNK) signaling pathway modulates integrins expression and ensures tissue endurance. An excess of JNK activity, as an outcome of a failure in the negative feedback implemented by the dual-specificity phosphatase Puckered (Puc), promotes the loss of integrins [the ß-subunit Myospheroid (Mys)] and amnioserosa detachment. Likewise, integrins signal back to the pathway to regulate the duration and strength of JNK activity. Mys is necessary for the regulation of JNK activity levels and in its absence, puc expression is downregulated and JNK activity increases.

Rab11 negatively regulates wingless preventing JNK-mediated apoptosis in Drosophila epithelium during embryonic dorsal closure

Rab11, a small Ras like GTPase marking the recycling endosomes, plays instrumental roles in Drosophila embryonic epithelial morphogenesis where an array of reports testify its importance in the maintenance of cyto-architectural as well as functional attributes of the concerned cells. Proper Rab11 functions ensure a precise regulation of developmentally active cell signaling pathways which in turn promote the expression of morphogens and other physico-chemical cues which finally forge an embryo out of a single layer of cells. Earlier reports have established that Rab11 functions are vital for fly embryonic development where amorphic mutants such as EP3017 homozygotes show a fair degree of epithelial defects along with incomplete dorsal closure. Here, we present a detailed account of the effects of Rab11 loss of function in the dorso-lateral epithelium which resulted in severe dorsal closure defects along with an elevated JNK-Dpp expression. We further observed that the dorso-lateral epithelial cells undergo epithelial to mesenchymal transition as well as apoptosis in Rab11 mutants with elevated expression levels of MMP1 and Caspase-3, where Caspase-3 contributes to the Rab11 knockout phenotype contrary to the knockdown mutants or hypomorphs. Interestingly, the elevated expressions of the core JNK-Dpp signaling could be rescued with a simultaneous knockdown of wingless in the Rab11 knockout mutants suggesting a genetic interaction of Rab11 with the Wingless pathway during dorsal closure, an ideal model of epithelial wound healing.

The mRNA decapping protein 2 (DCP2) is a major regulator of developmental events in Drosophila-insights from expression paradigms

The Drosophila genome codes for two decapping proteins, DCP1 and DCP2, out of which DCP2 is the active decapping enzyme. The present endeavour explores the endogenous promoter firing, transcript and protein expression of DCP2 in Drosophila wherein, besides a ubiquitous expression across development, we identify an active expression paradigm during dorsal closure and a plausible moonlighting expression in the Corazonin neurons of the larval brain. We also demonstrate that the ablation of DCP2 leads to embryonic lethality and defects in vital morphogenetic processes whereas a knockdown of DCP2 in the Corazonin neurons reduces the sensitivity to ethanol in adults, thereby ascribing novel regulatory roles to DCP2. Our findings unravel novel putative roles for DCP2 and identify it as a candidate for studies on the regulated interplay of essential molecules during early development in Drosophila, nay the living world.