Smurf Downregulates Echinoid in the Amnioserosa To Regulate Drosophila Dorsal Closure

Commissureless acts as a substrate adapter in a conserved Nedd4 E3 ubiquitin ligase pathway to promote axon growth across the midline

In both vertebrates and invertebrates, commissural neurons prevent premature responsiveness to the midline repellant Slit by downregulating surface levels of its receptor Roundabout1 (Robo1). In Drosophila, Commissureless (Comm) plays a critical role in this process; however, there is conflicting data on the underlying molecular mechanism. Here, we demonstrate that the conserved PY motifs in the cytoplasmic domain of Comm are required allow the ubiquitination and lysosomal degradation of Robo1. Disruption of these motifs prevents Comm from localizing to Lamp1 positive late endosomes and to promote axon growth across the midline in vivo. In addition, we conclusively demonstrate a role for Nedd4 in midline crossing. Genetic analysis shows that nedd4 mutations result in midline crossing defects in the Drosophila embryonic nerve cord, which can be rescued by introduction of exogenous Nedd4. Biochemical evidence shows that Nedd4 incorporates into a three-member complex with Comm and Robo in a PY motif-dependent manner. Finally, we present genetic evidence that Nedd4 acts with Comm in the embryonic nerve cord to downregulate Robo1 levels. Taken together, these findings demonstrate that Comm promotes midline crossing in the nerve cord by facilitating Robo ubiquitination by Nedd4, ultimately leading to its degradation.

The α-Catenin mechanosensing M region is required for cell adhesion during tissue morphogenesis

α-Catenin couples the cadherin-catenin complex to the actin cytoskeleton. The mechanosensitive α-Catenin M region undergoes conformational changes upon application of force to recruit interaction partners. Here, we took advantage of the tension landscape in the Drosophila embryo to define three different states of α-Catenin mechanosensing in support of cell adhesion. Low-, medium-, and high-tension contacts showed a corresponding recruitment of Vinculin and Ajuba, which was dependent on the α-Catenin M region. In contrast, the Afadin homolog Canoe acts in parallel to α-Catenin at bicellular low- and medium-tension junctions but requires an interaction with α-Catenin for its tension-sensitive enrichment at high-tension tricellular junctions. Individual M region domains make complex contributions to cell adhesion through their impact on interaction partner recruitment, and redundancies with the function of Canoe. Our data argue that α-Catenin and its interaction partners are part of a cooperative and partially redundant mechanoresponsive network that supports AJs remodeling during morphogenesis.

Orchestrating morphogenesis: building the body plan by cell shape changes and movements

During embryonic development, a simple ball of cells re-shapes itself into the elaborate body plan of an animal. This requires dramatic cell shape changes and cell movements, powered by the contractile force generated by actin and myosin linked to the plasma membrane at cell-cell and cell-matrix junctions. Here, we review three morphogenetic events common to most animals: apical constriction, convergent extension and collective cell migration. Using the fruit fly Drosophila as an example, we discuss recent work that has revealed exciting new insights into the molecular mechanisms that allow cells to change shape and move without tearing tissues apart. We also point out parallel events at work in other animals, which suggest that the mechanisms underlying these morphogenetic processes are conserved.

Single Nucleotide Polymorphisms of Ubiquitin-Related Genes were Associated with Allograft Fibrosis of Renal Transplant Fibrosis

BACKGROUND Interstitial fibrosis and tubular atrophy (IF/TA) have been recognized as crucial factors contributing to graft loss resulting from chronic renal allograft injuries. Recent studies have indicated a significant association between the progression of organ fibrosis and single nucleotide polymorphisms (SNPs) found on certain genes. Our research sought to understand these potential associations and detect the potential impact of SNPs on ubiquitin-related genes related to allograft fibrosis in kidney transplant recipients. MATERIAL AND METHODS There were 200 patients enrolled in this study, from which samples were extracted for total DNA. Targeted next-generation sequencing was used to detect SNPs on 9 genes (FBXL21, PIAS1/2, SUMO1/2/3/4, UBE2D1, and UBE2I). Minor allele frequency (MAF) and Hardy-Weinberg equilibrium (HWE) tests were used and followed by linkage disequilibrium analysis. General linear models (GLM) were used to identify significant confounding factors. Finally, multiple inheritance models and haplotype analyses were conducted to explore associations between SNPs and the degree of the severity of renal allograft fibrosis. RESULTS In total, 144 SNPs were identified in targeted sequencing. After filtering based on results from MAF and HWE tests, 15 tagger SNPs were selected for further analyses of associations. GLMs indicated that the administration of sirolimus significantly contributed to the degree of severity of allograft fibrosis (P=0.011). After adjusting for confounding factors and applying a Bonferroni correction, multiple inheritance model analyses indicated that the recessive model of rs644731 of the PIAS2 gene was significantly correlated with the occurrence of IF/TA (P=0.01). Furthermore, single-locus based analysis of rs644731 did not indicate that it had a positive influence on IF/TA in a degree-dependent manner. Finally, linkage disequilibrium analysis revealed 3 haplotypes all lacking significant correlation with respect to the IF/TA experimental cohort. CONCLUSIONS We are the first to reveal that mutations of rs644731 in the PIAS2 gene were significantly correlated with the progression of IF/TA in kidney transplant recipients.