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Saccharomyces cerevisiae protein She9 is localized to the inner mitochondrial membrane and is required for normal mitochondrial morphology. While deletion mutants of SHE9 ( she9Δ ) are viable and display large ring-like mitochondrial structures, the molecular function of SHE9 is still unknown. We report a decreased growth of she9Δ cells during a diauxic shift, where mitochondria are primarily employing oxidative phosphorylation to generate ATP versus the alternative mechanism of glycolysis in high glucose conditions. Further bioinformatics analysis reveal putative functional protein associations, and proposes a model to aid in the understanding of the molecular function of She9., Competing Interests: The authors declare that there are no conflicts of interest present., (Copyright: © 2023 by the authors.)

Biochemical methods can reveal stable protein-protein interactions occurring within cells, but the ability to observe transient events and to visualize the subcellular localization of protein-protein interactions in cells and tissues in situ provides important additional information. The Proximity Ligation Assay ® (PLA) offers the opportunity to visualize the subcellular location of such interactions at endogenous protein levels, provided that the probes that recognize the target proteins are within 40 nm. This sensitive technique not only elucidates protein-protein interactions, but also can reveal post-translational protein modifications. The technique is useful even in cases where material is limited, such as when paraffin-embedded clinical specimens are the only available material, as well as after experimental intervention in 2D and 3D model systems. Here we describe the basic protocol for using the commercially available Proximity Ligation Assay™ materials (Sigma-Aldrich, St. Louis, MO), and incorporate details to aid the researcher in successfully performing the experiments. © 2020 Wiley Periodicals LLC. Basic Protocol 1: Proximity ligation assay Support Protocol 1: Antigen retrieval method for formalin-fixed, paraffin-embedded tissues Support Protocol 2: Creation of custom PLA probes using the Duolink™ In Situ Probemaker Kit when commercially available probes are not suitable Basic Protocol 2: Imaging, quantification, and analysis of PLA signals., (© 2020 Wiley Periodicals LLC.)

Tissue integrity is crucial for maintaining the homeostasis of living organisms. Abnormalities that affect sites of cell-cell contact can cause a variety of debilitating disorders. The desmosome is an essential cell-cell junctional protein complex in tissues that undergo stress, and it orchestrates intracellular signal transduction. Desmosome assembly and junctional integrity are required to maintain the overall homeostasis of a tissue, organ, and organism. This review discusses the desmosome and the human diseases associated with its disruption.

Cell junctions are scaffolds that integrate mechanical and chemical signaling. We previously showed that a desmosomal cadherin promotes keratinocyte differentiation in an adhesion-independent manner by dampening Epidermal Growth Factor Receptor (EGFR) activity. Here we identify a potential mechanism by which desmosomes assist the de-neddylating COP9 signalosome (CSN) in attenuating EGFR through an association between the Cops3 subunit of the CSN and desmosomal components, Desmoglein1 (Dsg1) and Desmoplakin (Dp), to promote epidermal differentiation. Silencing CSN or desmosome components shifts the balance of EGFR modifications from ubiquitination to neddylation, inhibiting EGFR dynamics in response to an acute ligand stimulus. A reciprocal relationship between loss of Dsg1 and neddylated EGFR was observed in a carcinoma model, consistent with a role in sustaining EGFR activity during tumor progression. Identification of this previously unrecognized function of the CSN in regulating EGFR neddylation has broad-reaching implications for understanding how homeostasis is achieved in regenerating epithelia.

SVEP1 is a recently identified multidomain cell adhesion protein, homologous to the mouse polydom protein, which has been shown to mediate cell-cell adhesion in an integrin-dependent manner in osteogenic cells. In this study, we characterized SVEP1 function in the epidermis. SVEP1 was found by qRT-PCR to be ubiquitously expressed in human tissues, including the skin. Confocal microscopy revealed that SVEP1 is normally mostly expressed in the cytoplasm of basal and suprabasal epidermal cells. Downregulation of SVEP1 expression in primary keratinocytes resulted in decreased expression of major epidermal differentiation markers. Similarly, SVEP1 downregulation was associated with disturbed differentiation and marked epidermal acanthosis in three-dimensional skin equivalents. In contrast, the dispase assay failed to demonstrate significant differences in adhesion between keratinocytes expressing normal vs low levels of SVEP1. Homozygous Svep1 knockout mice were embryonic lethal. Thus, to assess the importance of SVEP1 for normal skin homoeostasis in vivo, we downregulated SVEP1 in zebrafish embryos with a Svep1-specific splice morpholino. Scanning electron microscopy revealed a rugged epidermis with perturbed microridge formation in the centre of the keratinocytes of morphant larvae. Transmission electron microscopy analysis demonstrated abnormal epidermal cell-cell adhesion with disadhesion between cells in Svep1-deficient morphant larvae compared to controls. In summary, our results indicate that SVEP1 plays a critical role during epidermal differentiation., (© 2016 John Wiley & Sons A/S. Published by John Wiley & Sons Ltd.)

In the budding yeast Saccharomyces cerevisiae, unnatural stabilization of the cyclin-dependent kinase inhibitor Sic1 during meiosis can trigger extra rounds of DNA replication. When programmed DNA double-strand breaks (DSBs) are generated but not repaired due to absence of DMC1, a pathway involving the checkpoint gene RAD17 prevents this DNA rereplication. Further genetic analysis has now revealed that prevention of DNA rereplication also requires MEC1, which encodes a protein kinase that serves as a central checkpoint regulator in several pathways including the meiotic recombination checkpoint response. Downstream of MEC1, MEK1 is required through its function to inhibit repair between sister chromatids. By contrast, meiotic recombination checkpoint effectors that regulate gene expression and cyclin-dependent kinase activity are not necessary. Phosphorylation of histone H2A, which is catalyzed by Mec1 and the related Tel1 protein kinase in response to DSBs, and can help coordinate activation of the Rad53 checkpoint protein kinase in the mitotic cell cycle, is required for the full checkpoint response. Phosphorylation sites that are targeted by Rad53 in a mitotic S phase checkpoint response are also involved, based on the behavior of cells containing mutations in the DBF4 and SLD3 DNA replication genes. However, RAD53 does not appear to be required, nor does RAD9, which encodes a mediator of Rad53, consistent with their lack of function in the recombination checkpoint pathway that prevents meiotic progression. While this response is similar to a checkpoint mechanism that inhibits initiation of DNA replication in the mitotic cell cycle, the evidence points to a new variation on DNA replication control., (Copyright © 2016 Najor et al.)