Cargo sorting to intraluminal vesicles (ILVs) of multivesicular endosomes is required for lysosome-related organelle (LRO) biogenesis. PMEL—a component of melanocyte LROs (melanosomes)—is sorted to ...ILVs in an ESCRT-independent manner, where it is proteolytically processed and assembled into functional amyloid fibrils during melanosome maturation. Here we show that the tetraspanin CD63 directly participates in ESCRT-independent sorting of the PMEL luminal domain, but not of traditional ESCRT-dependent cargoes, to ILVs. Inactivating CD63 in cell culture or in mice impairs amyloidogenesis and downstream melanosome morphogenesis. Whereas CD63 is required for normal PMEL luminal domain sorting, the disposal of the remaining PMEL transmembrane fragment requires functional ESCRTs but not CD63. In the absence of CD63, the PMEL luminal domain follows this fragment and is targeted for ESCRT-dependent degradation. Our data thus reveal a tight interplay regulated by CD63 between two distinct endosomal ILV sorting processes for a single cargo during LRO biogenesis.
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► ESCRT-independent sorting of PMEL to intraluminal vesicles depends on CD63 ► CD63 depletion inhibits formation of PMEL-derived amyloid fibers in vitro and in vivo ► PMEL C-terminal fragment is degraded in an ESCRT-dependent manner ► PMEL becomes sensitive to ESCRT-dependent degradation in CD63-depleted cells
Lysosome‐related organelles (LROs) comprise a diverse group of cell type‐specific, membrane‐bound subcellular organelles that derive at least in part from the endolysosomal system but that have ...unique contents, morphologies and functions to support specific physiological roles. They include: melanosomes that provide pigment to our eyes and skin; alpha and dense granules in platelets, and lytic granules in cytotoxic T cells and natural killer cells, which release effectors to regulate hemostasis and immunity; and distinct classes of lamellar bodies in lung epithelial cells and keratinocytes that support lung plasticity and skin lubrication. The formation, maturation and/or secretion of subsets of LROs are dysfunctional or entirely absent in a number of hereditary syndromic disorders, including in particular the Hermansky‐Pudlak syndromes. This review provides a comprehensive overview of LROs in humans and model organisms and presents our current understanding of how the products of genes that are defective in heritable diseases impact their formation, motility and ultimate secretion.
Lysosome‐related organelles (LROs) are cell type‐specific subcellular structures that derive from both the secretory and endolysosomal pathways and that play key roles in numerous physiological systems, in most cases following stimulus‐dependent secretion of their contents. The biogenesis and/or secretion of LRO subsets are disrupted in hereditary syndromic disorders such as the Hermansky‐Pudlak syndromes and familial hemophagocytic lymphohistiocytosis. We comprehensively review LROs in humans and model organisms and the mechanisms by which products of disease genes regulate their formation, motility and ultimate secretion.
Synopsis
Melanins, the main pigments of the skin and hair in mammals, are synthesized within membrane-bound organelles of melanocytes called melanosomes. Melanosome structure and function are ...determined by a cohort of resident transmembrane proteins, many of which are expressed only in pigment cells and localize specifically to melanosomes. Defects in the genes that encode melanosome-specific proteins or components of the machinery required for their transport in and out of melanosomes underlie various forms of ocular or oculocutaneous albinism, characterized by hypopigmentation of the hair, skin, and eyes and by visual impairment. We review major components of melanosomes, including the enzymes that catalyze steps in melanin synthesis from tyrosine precursors, solute transporters that allow these enzymes to function, and structural proteins that underlie melanosome shape and melanin deposition. We then review the molecular mechanisms by which these components are biosynthetically delivered to newly forming melanosomes—many of which are shared by other cell types that generate cell type-specific lysosome-related organelles. We also highlight unanswered questions that need to be addressed by future investigation.
Abstract Background We report a prospective randomized study comparing early clinical results between the direct anterior (DAA) and posterior approaches (PA) in primary hip arthroplasty. Methods ...Surgeries were performed by two senior hip arthroplasty surgeons. 72 patients with complete data were assessed pre-operatively, 2, 6 and 12 weeks post-operatively. The primary outcomes were the WOMAC and Oxford Hip Scores. Secondary outcome measures included the EuroQoL, 10 meter walk test, clinical and radiographic parameters. Results Data analyses showed no difference between DAA (n=35) and PA (n=37) groups when comparing total scores for primary outcomes. No significant differences were observed for 10 meter walk test, EuroQoL and radiographic analyses. Subgroup analysis for surgeon 1 identified that the DAA group had shorter acute hospital stay, less post-operative opiate requirements and smaller wounds. However, this was offset by increased operative time, higher intra-operative blood loss and weaker hip flexion at 2 and 6 weeks. Subgroup analysis of items on the WOMAC and OHS identified that hip flexion activity favoured the DAA group up to 6 weeks post-operatively. There was an 83% incidence of lateral cutaneous nerve of thigh neuropraxia at the 12 week mark in the DAA group. No neuropraxias occurred in the PA group. One dislocation occurred in each group. A single patient from the DAA group required reoperation for leg length discrepancy. Conclusion DAA THA has comparable results with PA THA. Choice of surgical approach for THA should be based on patient factors, surgeon preference and experience.
It is fundamentally important for many animal ecologists to quantify the costs of animal activities, although it is not straightforward to do so. The recording of triaxial acceleration by ...animal‐attached devices has been proposed as a way forward for this, with the specific suggestion that dynamic body acceleration (DBA) be used as a proxy for movement‐based power.
Dynamic body acceleration has now been validated frequently, both in the laboratory and in the field, although the literature still shows that some aspects of DBA theory and practice are misunderstood. Here, we examine the theory behind DBA and employ modelling approaches to assess factors that affect the link between DBA and energy expenditure, from the deployment of the tag, through to the calibration of DBA with energy use in laboratory and field settings.
Using data from a range of species and movement modes, we illustrate that vectorial and additive DBA metrics are proportional to each other. Either can be used as a proxy for energy and summed to estimate total energy expended over a given period, or divided by time to give a proxy for movement‐related metabolic power. Nonetheless, we highlight how the ability of DBA to predict metabolic rate declines as the contribution of non‐movement‐related factors, such as heat production, increases.
Overall, DBA seems to be a substantive proxy for movement‐based power but consideration of other movement‐related metrics, such as the static body acceleration and the rate of change of body pitch and roll, may enable researchers to refine movement‐based metabolic costs, particularly in animals where movement is not characterized by marked changes in body acceleration.
Quantifying the costs of animal activities is important yet difficult to achieve. Dynamic body acceleration, derived from triaxial acceleration sensors, is a powerful method with which to examine the energetic implications of animal decision‐making in a wide range of systems, including with respect to the effects of individual experience, state and the abiotic/ biotic environment.
Vertebrate pigment cells in the eye and skin are useful models for cell types that use specialized endosomal trafficking pathways to partition cargo proteins to unique lysosome-related organelles ...such as melanosomes. This review describes current models of protein trafficking required for melanosome biogenesis in mammalian melanocytes.
Recycling endosomes consist of a tubular network that emerges from vacuolar sorting endosomes and diverts cargoes toward the cell surface, the Golgi, or lysosome-related organelles. How recycling ...tubules are formed remains unknown. We show that recycling endosome biogenesis requires the protein complex BLOC-1. Mutations in BLOC-1 subunits underlie an inherited disorder characterized by albinism, the Hermansky-Pudlak Syndrome, and are associated with schizophrenia risk. We show here that BLOC-1 coordinates the kinesin KIF13A-dependent pulling of endosomal tubules along microtubules to the Annexin A2/actin-dependent stabilization and detachment of recycling tubules. These components cooperate to extend, stabilize and form tubular endosomal carriers that function in cargo recycling and in the biogenesis of pigment granules in melanocytic cells. By shaping recycling endosomal tubules, our data reveal that dysfunction of the BLOC-1-KIF13A-Annexin A2 molecular network underlies the pathophysiology of neurological and pigmentary disorders.
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•BLOC-1 controls the formation of recycling endosomal tubules from sorting endosomes•BLOC-1 cooperates with microtubule- and actin-associated machineries•KIF13A and Annexin A2 are both required for the formation of recycling tubules•Defects in recycling endosome biogenesis contribute to heritable disorders
Delevoye et al. define the function of BLOC-1, mutated in neurological and pigmentary disorders. BLOC-1 forms recycling endosomes by orchestrating elongation and scission of tubules from sorting endosomes. By cooperating with microtubule (KIF13A) and actin (Annexin A2) components, BLOC-1 functions in cargo recycling and melanosome biogenesis.
Summary
PMEL is a pigment cell‐specific protein responsible for the formation of fibrillar sheets within the pigment organelle, the melanosome. The fibrillar sheets serve as a template upon which ...melanins polymerize as they are synthesized. The PMEL fibrils are required for optimal pigment cell function, as animals that either lack PMEL expression or express mutant PMEL variants show varying degrees of hypopigmentation and pigment cell inviability. The PMEL fibrils have biophysical properties of amyloid, a protein fold that is frequently associated with neurodegenerative and other diseases. However, PMEL is one of a growing number of non‐pathogenic amyloid proteins that contribute to the function of the cell and/or organism that produces them. Understanding how PMEL generates amyloid in a non‐pathogenic manner might provide insights into how to avoid toxicity due to pathological amyloid formation. In this review, we summarize and reconcile data concerning the fate of PMEL from its site of synthesis in the endoplasmic reticulum to newly formed melanosomes and the role of distinct PMEL subdomains in trafficking and amyloid fibril formation. We then discuss how its progression through the secretory pathway into the endosomal system might allow for the regulated and non‐toxic conversion of PMEL into an ordered amyloid polymer.
Early endosomes consist of vacuolar sorting and tubular recycling domains that segregate components fated for degradation in lysosomes or reuse by recycling to the plasma membrane or Golgi. The ...tubular transport intermediates that constitute recycling endosomes function in cell polarity, migration, and cytokinesis. Endosomal tubulation and fission require both actin and intact microtubules, but although factors that stabilize recycling endosomal tubules have been identified, those required for tubule generation from vacuolar sorting endosomes (SEs) remain unknown. We show that the microtubule motor KIF13A associates with recycling endosome tubules and controls their morphogenesis. Interfering with KIF13A function impairs the formation of endosomal tubules from SEs with consequent defects in endosome homeostasis and cargo recycling. Moreover, KIF13A interacts and cooperates with RAB11 to generate endosomal tubules. Our data illustrate how a microtubule motor couples early endosome morphogenesis to its motility and function.
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•The kinesin-3 KIF13A associates with endosomal tubules•KIF13A controls the morphogenesis of recycling tubules from sorting endosomes•KIF13A interacts with the GTP-bound form of RAB11•KIF13A and RAB11 cooperate for generation of endosomal tubules
Recycling endosomes are tubules that originate from vacuolar early endosomes. In this study, Delevoye and colleagues identify the kinesin-3 KIF13A as a key component for endocytic tubule morphogenesis. Impairing KIF13A function affects endosomal tubule formation and cargo recycling back to the plasma membrane. Moreover, KIF13A interacts and cooperates with the small GTPase RAB11 in order to generate tubular recycling intermediates. These data highlight how a microtubule-based motor coordinates early endosome biogenesis, motility, and function.
Phagocytosis provides innate immune cells with a mechanism to take up and destroy pathogenic bacteria, apoptotic cells and other large particles. In some cases, however, peptide antigens from these ...particles are preserved for presentation in association with major histocompatibility complex (MHC) class I or class II molecules in order to stimulate antigen‐specific T cells. Processing and presentation of antigens from phagosomes presents a number of distinct challenges relative to antigens internalized by other means; while bacterial antigens were among the first discovered to be presented to T cells, analyses of the cellular mechanisms by which peptides from phagocytosed antigens assemble with MHC molecules and by which these complexes are then expressed at the plasma membrane have lagged behind those of conventional model soluble antigens. In this review, we cover recent advances in our understanding of these processes, including the unique cross‐presentation of phagocytosed antigens by MHC class I molecules, and in their control by signaling modalities in phagocytic cells.
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