Overexpression of the lamina proteins Lamin and Kugelkern induces specific ultrastructural alterations in the morphology of the nuclear envelope of intestinal stem cells and enterocytes

A nuclear architecture screen in Drosophila identifies Stonewall as a link between chromatin position at the nuclear periphery and germline stem cell fate

The association of genomic loci to the nuclear periphery is proposed to facilitate cell-type specific gene repression and influence cell fate decisions. However, the interplay between gene position and expression remains incompletely understood, in part because the proteins that position genomic loci at the nuclear periphery remain unidentified. Here, we used an Oligopaint-based HiDRO screen targeting ~1000 genes to discover novel regulators of nuclear architecture in Drosophila cells. We identified the heterochromatin-associated protein, Stonewall (Stwl), as a factor promoting perinuclear chromatin positioning. In female germline stem cells (GSCs), Stwl binds and positions chromatin loci, including GSC differentiation genes, at the nuclear periphery. Strikingly, Stwl-dependent perinuclear positioning is associated with transcriptional repression, highlighting a likely mechanism for Stwl's known role in GSC maintenance and ovary homeostasis. Thus, our study identifies perinuclear anchors in Drosophila and demonstrates the importance of gene repression at the nuclear periphery for cell fate.

Use of Farnesyl Transferase Inhibitors in an Ageing Model in Drosophila

The presence of farnesylated proteins at the inner nuclear membrane (INM), such as the Lamins or Kugelkern in Drosophila, leads to specific changes in the nuclear morphology and accelerated ageing on the organismal level reminiscent of the Hutchinson-Gilford progeria syndrome (HGPS). Farnesyl transferase inhibitors (FTIs) can suppress the phenotypes of the nuclear morphology in cultured fibroblasts from HGPS patients and cultured cells overexpressing farnesylated INM proteins. Similarly, FTIs have been reported to suppress the shortened lifespan in model organisms. Here, we report an experimental system combining cell culture and Drosophila flies for testing the activity of substances on the HGPS-like nuclear morphology and lifespan, with FTIs as an experimental example. Consistent with previous reports, we show that FTIs were able to ameliorate the nuclear phenotypes induced by the farnesylated nuclear proteins Progerin, Kugelkern, or truncated Lamin B in cultured cells. The subsequent validation in Drosophila lifespan assays demonstrated the applicability of the experimental system: treating adult Drosophila with the FTI ABT-100 reversed the nuclear phenotypes and extended the lifespan of experimentally induced short-lived flies. Since kugelkern-expressing flies have a significantly shorter average lifespan, half the time is needed for testing substances in the lifespan assay.

Autophagy-mediated plasma membrane removal promotes the formation of epithelial syncytia

Epithelial wound healing in Drosophila involves the formation of multinucleate cells surrounding the wound. We show that autophagy, a cellular degradation process often deployed in stress responses, is required for the formation of a multinucleated syncytium during wound healing, and that autophagosomes that appear near the wound edge acquire plasma membrane markers. In addition, uncontrolled autophagy in the unwounded epidermis leads to the degradation of endo‐membranes and the lateral plasma membrane, while apical and basal membranes and epithelial barrier function remain intact. Proper functioning of TORC1 is needed to prevent destruction of the larval epidermis by autophagy, in a process that depends on phagophore initiation and expansion but does not require autophagosomes fusion with lysosomes. Autophagy induction can also affect other sub‐cellular membranes, as shown by its suppression of experimentally induced laminopathy‐like nuclear defects. Our findings reveal a function for TORC1‐mediated regulation of autophagy in maintaining membrane integrity and homeostasis in the epidermis and during wound healing.

Nuclear Morphological Remodeling in Human Granulocytes Is Linked to Prenylation Independently from Cytoskeleton

Nuclear shape modulates cell behavior and function, while aberrant nuclear morphologies correlate with pathological phenotype severity. Nevertheless, functions of specific nuclear morphological features and underlying molecular mechanisms remain poorly understood. Here, we investigate a nucleus-intrinsic mechanism driving nuclear lobulation and segmentation concurrent with granulocyte specification, independently from extracellular forces and cytosolic cytoskeleton contributions. Transcriptomic regulation of cholesterol biosynthesis is equally concurrent with nuclear remodeling. Its putative role as a regulatory element is supported by morphological aberrations observed upon pharmacological impairment of several enzymatic steps of the pathway, most prominently the sterol ∆14-reductase activity of laminB-receptor and protein prenylation. Thus, we support the hypothesis of a nuclear-intrinsic mechanism for nuclear shape control with the putative involvement of the recently discovered GGTase III complex. Such process could be independent from or complementary to the better studied cytoskeleton-based nuclear remodeling essential for cell migration in both physiological and pathological contexts such as immune system function and cancer metastasis.

Organelle aging: Lessons from model organisms

Most cellular processes descend into failure during aging. While a large collection of longevity pathways has been identified in the past decades, the mechanism for age-related decline of cellular homeostasis and organelle function remains largely unsolved. It is known that many organelles undergo structural and functional changes during normal aging, which significantly contributes to the decline of tissue function at old ages. Since recent studies have revealed an emerging role of organelles as regulatory hubs in maintaining cellular homeostasis, understanding of organelle aging will provide important insights into the cellular basis of organismal aging. Here we review current progress on the characterization of age-dependent structural and functional alterations in the more well-studied organelles, as well as the known mechanisms governing organelle aging in model organisms, with a special focus on the fruit fly Drosophila melanogaster.