AAV-mediated gene therapy for sialidosis.

Sialidosis (mucolipidosis I) is a glycoprotein storage disease, clinically characterized by a spectrum of systemic and neurological phenotypes. The primary cause of the disease is deficiency of the lysosomal sialidase NEU1, resulting in accumulation of sialylated glycoproteins/oligosaccharides in tissues and body fluids. Neu1-/- mice recapitulate the severe, early-onset forms of the disease, affecting visceral organs, muscles, and the nervous system, with widespread lysosomal vacuolization evident in most cell types. Sialidosis is considered an orphan disorder with no therapy currently available. Here, we assessed the therapeutic potential of AAV-mediated gene therapy for the treatment of sialidosis. Neu1-/- mice were co-injected with two scAAV2/8 vectors, expressing human NEU1 and its chaperone PPCA. Treated mice were phenotypically indistinguishable from their WT controls. NEU1 activity was restored to different extent in most tissues, including the brain, heart, muscle, and visceral organs. This resulted in diminished/absent lysosomal vacuolization in multiple cell types and reversal of sialyl-oligosacchariduria. Lastly, normalization of lysosomal exocytosis in the cerebrospinal fluids and serum of treated mice, coupled to diminished neuroinflammation, were measures of therapeutic efficacy. These findings point to AAV-mediated gene therapy as a suitable treatment for sialidosis and possibly other diseases, associated with low NEU1 expression.

Distinct functions of dimeric and monomeric scaffold protein Alix in regulating F-actin assembly and loading of exosomal cargo.

Alix is a ubiquitously expressed scaffold protein that participates in numerous cellular processes related to the remodeling/repair of membranes and the actin cytoskeleton. Alix exists in monomeric and dimeric/multimeric configurations, but how dimer formation occurs and what role the dimer has in Alix-mediated processes are still largely elusive. Here, we reveal a mechanism for Alix homodimerization mediated by disulfide bonds under physiological conditions and demonstrate that the Alix dimer is enriched in exosomes and F-actin cytoskeleton subcellular fractions. Proteomic analysis of exosomes derived from Alix-/- primary cells underlined the indispensable role of Alix in loading syntenin into exosomes, thereby regulating the cellular levels of this protein. Using a set of deletion mutants, we define the function of Alix Bro1 domain, which is solely required for its exosomal localization, and that of the V domain, which is needed for recruiting syntenin into exosomes. We reveal an essential role for Cys814 within the disordered proline-rich domain for Alix dimerization. By mutating this residue, we show that Alix remains exclusively monomeric and, in this configuration, is effective in loading syntenin into exosomes. In contrast, loss of dimerization affects the ability of Alix to associate with F-actin, thereby compromising Alix-mediated cytoskeleton remodeling. We propose that dimeric and monomeric forms of Alix selectively execute two of the protein's main functions: exosomal cargo loading and cytoskeleton remodeling.

Intermittent enzyme replacement therapy with recombinant human ß-galactosidase prevents neuraminidase 1 deficiency

Mutations in the galactosidase ß 1 (GLB1) gene cause lysosomal ß-galactosidase (ß-Gal) deficiency and clinical onset of the neurodegenerative lysosomal storage disease, GM1 gangliosidosis. ß-Gal and neuraminidase 1 (NEU1) form a multienzyme complex in lysosomes along with the molecular chaperone, protective protein cathepsin A (PPCA). NEU1 is deficient in the neurodegenerative lysosomal storage disease sialidosis, and its targeting to and stability in lysosomes strictly depend on PPCA. In contrast, ß-Gal only partially depends on PPCA, prompting us to investigate the role that ß-Gal plays in the multienzyme complex. Here, we demonstrate that ß-Gal negatively regulates NEU1 levels in lysosomes by competitively displacing this labile sialidase from PPCA. Chronic cellular uptake of purified recombinant human ß-Gal (rhß-Gal) or chronic lentiviral-mediated GLB1 overexpression in GM1 gangliosidosis patient fibroblasts coincides with profound secondary NEU1 deficiency. A regimen of intermittent enzyme replacement therapy dosing with rhß-Gal, followed by enzyme withdrawal, is sufficient to augment ß-Gal activity levels in GM1 gangliosidosis patient fibroblasts without promoting NEU1 deficiency. In the absence of ß-Gal, NEU1 levels are elevated in the GM1 gangliosidosis mouse brain, which are restored to normal levels following weekly intracerebroventricular dosing with rhß-Gal. Collectively, our results highlight the need to carefully titrate the dose and dosing frequency of ß-Gal augmentation therapy for GM1 gangliosidosis. They further suggest that intermittent intracerebroventricular enzyme replacement therapy dosing with rhß-Gal is a tunable approach that can safely augment ß-Gal levels while maintaining NEU1 at physiological levels in the GM1 gangliosidosis brain.

Intracerebroventricular enzyme replacement therapy with ß-galactosidase reverses brain pathologies due to GM1 gangliosidosis in mice.

Autosomal recessive mutations in the galactosidase ß1 (GLB1) gene cause lysosomal ß-gal deficiency, resulting in accumulation of galactose-containing substrates and onset of the progressive and fatal neurodegenerative lysosomal storage disease, GM1 gangliosidosis. Here, an enzyme replacement therapy (ERT) approach in fibroblasts from GM1 gangliosidosis patients with recombinant human ß-gal (rhß-gal) produced in Chinese hamster ovary cells enabled direct and precise rhß-gal delivery to acidified lysosomes. A single, low dose (3 nm) of rhß-gal was sufficient for normalizing ß-gal activity and mediating substrate clearance for several weeks. We found that rhß-gal uptake by the fibroblasts is dose-dependent and saturable and can be competitively inhibited by mannose 6-phosphate, suggesting cation-independent, mannose 6-phosphate receptor-mediated endocytosis from the cell surface. A single intracerebroventricularly (ICV) administered dose of rhß-gal (100 µg) resulted in broad bilateral biodistribution of rhß-gal to critical regions of pathology in a mouse model of GM1 gangliosidosis. Weekly ICV dosing of rhß-gal for 8 weeks substantially reduced brain levels of ganglioside and oligosaccharide substrates and reversed well-established secondary neuropathology. Of note, unlike with the ERT approach, chronic lentivirus-mediated GLB1 overexpression in the GM1 gangliosidosis patient fibroblasts caused accumulation of a prelysosomal pool of ß-gal, resulting in activation of the unfolded protein response and endoplasmic reticulum stress. This outcome was unsurprising in light of our in vitro biophysical findings for rhß-gal, which include pH-dependent and concentration-dependent stability and dynamic self-association. Collectively, our results highlight that ICV-ERT is an effective therapeutic intervention for managing GM1 gangliosidosis potentially more safely than with gene therapy approaches.

Skeletal muscle cells derived from mouse skin cultures.

We have established a novel, simple, and highly reproducible method to generate skeletal muscle cells from mouse skin. Small pieces of skin from the back of mice were cultured in extracellular material-coated dishes in typical culture medium for about 3 weeks. Myotubes formed after about a week, grew into twitching myotubes, and became twitching myotube clumps after 3 weeks. Skeletal muscle cells are formed spontaneously with no induction. Myotubes were immunologically positive for myosin heavy chains, MyoD, and myogenin. Ultrastructural analysis revealed the presence of the sarcomere structure. Furthermore, PAX7+/MyoD- muscle stem cells proliferated around these myotubes, and MyoD+/myogenin+/MHC-- cells were also observed. Moreover, we investigated the formation of skeletal muscle cells from the sialidosis mouse skin, and showed that it is decreased compared to that of the wild type. Our method to generate skeletal muscle cells from skin is thought to be useful for the investigation of muscle cell development and muscle-related disorders.

Type I sialidosis, a normosomatic lysosomal disease, in the differential diagnosis of late-onset ataxia and myoclonus: An overview.

Lysosomal storage diseases (LSDs) are rare to extremely rare monogenic disorders. Their incidence, however, has probably been underestimated owing to their complex clinical manifestations. Sialidosis is a prototypical LSD inherited as an autosomal recessive trait and caused by mutations in the NEU1 gene that result in a deficiency of alpha-N-acetyl neuraminidase 1 (NEU1). Two basic forms of this disease, type I and type II, are known. The dysmorphic type II form features LSD symptoms including congenital hydrops, dysmorphogenetic traits, hepato-splenomegaly and severe intellectual disability. The diagnosis is more challenging in the normosomatic type I forms, whose clinical findings at onset include ocular defects, ataxia and generalized myoclonus. Here we report the clinical, biochemical and molecular analysis of five patients with sialidosis type I. Two patients presented novel NEU1 mutations. One of these patients was compound heterozygous for two novel NEU1 missense mutations: c.530A>T (p.Asp177Val) and c.1010A>G (p.His337Arg), whereas a second patient was compound heterozygous for a known mutation and a novel c.839G>A (p.Arg280Gln) mutation. We discuss the impact of these new mutations on the structural properties of NEU1. We also review available clinical reports of patients with sialidosis type I, with the aim of identifying the most frequent initial clinical manifestations and achieving more focused diagnoses.

GM1-ganglioside accumulation at the mitochondria-associated ER membranes links ER stress to Ca(2+)-dependent mitochondrial apoptosis.

Mitochondria-associated ER membranes, or MAMs, define the sites of endoplasmic reticulum/mitochondria juxtaposition that control Ca(2+) flux between these organelles. We found that in a mouse model of the human lysosomal storage disease GM1-gangliosidosis, GM1-ganglioside accumulates in the glycosphingolipid-enriched microdomain (GEM) fractions of MAMs, where it interacts with the phosphorylated form of IP3 receptor-1, influencing the activity of this channel. Ca(2+) depleted from the ER is then taken up by the mitochondria, leading to Ca(2+) overload in this organelle. The latter induces mitochondrial membrane permeabilization (MMP), opening of the permeability transition pore, and activation of the mitochondrial apoptotic pathway. This study identifies the GEMs as the sites of Ca(2+) diffusion between the ER and the mitochondria. We propose a new mechanism of Ca(2+)-mediated apoptotic signaling whereby GM1 accumulation at the GEMs alters Ca(2+) dynamics and acts as a molecular effector of both ER stress-induced and mitochondria-mediated apoptosis of neuronal cells.

Neuraminidase-1 mediates skeletal muscle regeneration.

Neuraminidase-1 (NEU1) is the sialidase responsible for the catabolism of sialoglycoconjugates in lysosomes. Congenital NEU1 deficiency causes sialidosis, a severe lysosomal storage disease associated with a broad spectrum of clinical manifestations, which also include skeletal deformities, skeletal muscle hypotonia and weakness. Neu1(-/-) mice, a model of sialidosis, develop an atypical form of muscle degeneration caused by progressive expansion of the connective tissue that infiltrates the muscle bed, leading to fiber degeneration and atrophy. Here we investigated the role of Neu1 in the myogenic process that ensues during muscle regeneration after cardiotoxin-induced injury of limb muscles. A comparative analysis of cardiotoxin-treated muscles from Neu1(-/-) mice and Neu1(+/+) mice showed increased inflammatory and proliferative responses in the absence of Neu1 during the early stages of muscle regeneration. This was accompanied by significant and sequential upregulation of Pax7, MyoD, and myogenin mRNAs. The levels of both MyoD and myogenin proteins decreased during the late stages of regeneration, which most likely reflected an increased rate of degradation of the myogenic factors in the Neu1(-/-) muscle. We also observed a delay in muscle cell differentiation, which was characterized by prolonged expression of embryonic myosin heavy chain, as well as reduced myofiber cross-sectional area. At the end of the regenerative process, collagen type III deposition was increased compared to wild-type muscles and internal controls, indicating the initiation of fibrosis. Overall, these results point to a role of Neu1 throughout muscle regeneration.

Sialylation of prion protein controls the rate of prion amplification, the cross-species barrier, the ratio of PrPSc glycoform and prion infectivity.

The central event underlying prion diseases involves conformational change of the cellular form of the prion protein (PrP(C)) into the disease-associated, transmissible form (PrP(Sc)). Pr(PC) is a sialoglycoprotein that contains two conserved N-glycosylation sites. Among the key parameters that control prion replication identified over the years are amino acid sequence of host PrP(C) and the strain-specific structure of PrPSc. The current work highlights the previously unappreciated role of sialylation of PrP(C) glycans in prion pathogenesis, including its role in controlling prion replication rate, infectivity, cross-species barrier and PrP(Sc) glycoform ratio. The current study demonstrates that undersialylated PrP(C) is selected during prion amplification in Protein Misfolding Cyclic Amplification (PMCAb) at the expense of oversialylated PrP(C). As a result, PMCAb-derived PrP(Sc) was less sialylated than brain-derived PrP(Sc). A decrease in PrPSc sialylation correlated with a drop in infectivity of PMCAb-derived material. Nevertheless, enzymatic de-sialylation of PrP(C) using sialidase was found to increase the rate of PrP(Sc) amplification in PMCAb from 10- to 10,000-fold in a strain-dependent manner. Moreover, de-sialylation of PrP(C) reduced or eliminated a species barrier of for prion amplification in PMCAb. These results suggest that the negative charge of sialic acid controls the energy barrier of homologous and heterologous prion replication. Surprisingly, the sialylation status of PrP(C) was also found to control PrP(Sc) glycoform ratio. A decrease in Pr(PC) sialylation levels resulted in a higher percentage of the diglycosylated glycoform in PrP(Sc). 2D analysis of charge distribution revealed that the sialylation status of brain-derived PrP(C) differed from that of spleen-derived PrP(C). Knocking out lysosomal sialidase Neu1 did not change the sialylation status of brain-derived PrP(C), suggesting that Neu1 is not responsible for desialylation of PrP(C). The current work highlights previously unappreciated role of PrP(C) sialylation in prion diseases and opens multiple new research directions, including development of new therapeutic approaches.

The GM1 and GM2 Gangliosidoses: Natural History and Progress toward Therapy.

The gangliosidoses are lysosomal storage disorders caused by accumulation of GM1 or GM2 gangliosides. GM1 gangliosidosis has both central nervous system and systemic findings; while, GM2 gangliosidosis is restricted primarily to the central nervous system. Both disorders have autosomal recessive modes of inheritance and a continuum of clinical presentations from a severe infantile form to a milder, chronic adult form. Both are devastating diseases without cure or specific treatment however, with the use of supportive aggressive medical management, the lifespan and quality of life has been extended for both diseases. Naturally occurring and engineered animal models that mimic the human diseases have enhanced our understanding of the pathogenesis of disease progression. Some models have shown significant improvement in symptoms and lifespan with enzyme replacement, substrate reduction, and anti-inflammatory treatments alone or in combination. More recently gene therapy has shown impressive results in large and small animal models. Treatment with FDA-approved glucose analogs to reduce the amount of ganglioside substrate is used as off-label treatments for some patients. Therapies also under clinical development include small molecule chaperones and gene therapy.

Bis(monoacylglycero)phosphate: a secondary storage lipid in the gangliosidoses.

Bis(monoacylglycero)phosphate (BMP) is a negatively charged glycerophospholipid with an unusual sn-1;sn-1' structural configuration. BMP is primarily enriched in endosomal/lysosomal membranes. BMP is thought to play a role in glycosphingolipid degradation and cholesterol transport. Elevated BMP levels have been found in many lysosomal storage diseases (LSDs), suggesting an association with lysosomal storage material. The gangliosidoses are a group of neurodegenerative LSDs involving the accumulation of either GM1 or GM2 gangliosides resulting from inherited deficiencies in ß-galactosidase or ß-hexosaminidase, respectively. Little information is available on BMP levels in gangliosidosis brain tissue. Our results showed that the content of BMP in brain was significantly greater in humans and in animals (mice, cats, American black bears) with either GM1 or GM2 ganglioside storage diseases, than in brains of normal subjects. The storage of BMP and ganglioside GM2 in brain were reduced similarly following adeno-associated viral-mediated gene therapy in Sandhoff disease mice. We also found that C22:6, C18:0, and C18:1 were the predominant BMP fatty acid species in gangliosidosis brains. The results show that BMP accumulates as a secondary storage material in the brain of a broad range of mammals with gangliosidoses.

Lysosomal multienzyme complex: pros and cons of working together.

The ubiquitous distribution of lysosomes and their heterogeneous protein composition reflects the versatility of these organelles in maintaining cell homeostasis and their importance in tissue differentiation and remodeling. In lysosomes, the degradation of complex, macromolecular substrates requires the synergistic action of multiple hydrolases that usually work in a stepwise fashion. This catalytic machinery explains the existence of lysosomal enzyme complexes that can be dynamically assembled and disassembled to efficiently and quickly adapt to the pool of substrates to be processed or degraded, adding extra tiers to the regulation of the individual protein components. An example of such a complex is the one composed of three hydrolases that are ubiquitously but differentially expressed: the serine carboxypeptidase, protective protein/cathepsin A (PPCA), the sialidase, neuraminidase-1 (NEU1), and the glycosidase ß-galactosidase (ß-GAL). Next to this 'core' complex, the existence of sub-complexes, which may contain additional components, and function at the cell surface or extracellularly, suggests as yet unexplored functions of these enzymes. Here we review how studies of basic biological processes in the mouse models of three lysosomal storage disorders, galactosialidosis, sialidosis, and GM1-gangliosidosis, revealed new and unexpected roles for the three respective affected enzymes, Ppca, Neu1, and ß-Gal, that go beyond their canonical degradative activities. These findings have broadened our perspective on their functions and may pave the way for the development of new therapies for these lysosomal storage disorders.

Chaperone-mediated gene therapy with recombinant AAV-PPCA in a new mouse model of type I sialidosis.

The lysosomal storage disease sialidosis is caused by a primary deficiency of the sialidase N-acetyl-α-neuraminidase-1 (NEU1). Patients with type I sialidosis develop an attenuated, non-neuropathic form of the disease also named cherry red spot myoclonus syndrome, with symptoms arising during juvenile/ adult age. NEU1 requires binding to its chaperone, protective protein/cathepsin A (PPCA), for lysosomal compartmentalization, stability and catalytic activation. We have generated a new mouse model of type I sialidosis that ubiquitously expresses a NEU1 variant carrying a V54M amino acid substitution identified in an adult patient with type I sialidosis. Mutant mice developed signs of lysosomal disease after 1year of age, predominantly in the kidney, albeit low residual NEU1 activity was detected in most organs and cell types. We demonstrate that the activity of the mutant enzyme could be effectively increased in all systemic tissues by chaperone-mediated gene therapy with a liver-tropic recombinant AAV2/8 vector expressing PPCA. This resulted in clear amelioration of the disease phenotype. These results suggest that at least some of the NEU1 mutations associated with type I sialidosis may respond to PPCA-chaperone-mediated gene therapy.

Protocol for the isolation and purification of endoplasmic reticulum-plasma membrane junctions from the mouse brain.

Dynamic communication between intracellular organelles often takes place at specialized membrane contact sites that form between their membranes. Here we detail a procedure for the purification of endoplasmic reticulum-plasma membrane (ER-PM) junctions from the mouse brain. We describe steps for homogenizing isolated brain hemispheres and sequential centrifugation to remove the nuclear fraction from the other membrane fractions. We then detail procedures for separating the resulting crude membrane fractions by sucrose density gradients and purifying into their respective pellets. For complete details on the use and execution of this protocol, please refer to Weesner et al.1.

Neuraminidase 1 regulates the cellular state of microglia by modulating the sialylation of Trem2.

Neuraminidase 1 (Neu1) cleaves terminal sialic acids from sialoglycoproteins in endolysosomes and at the plasma membrane. As such, Neu1 regulates immune cells, primarily those of the monocytic lineage. Here we examined how Neu1 influences microglia by modulating the sialylation of full-length Trem2 (Trem2-FL), a multifunctional receptor that regulates microglial survival, phagocytosis, and cytokine production. When Neu1 was deficient/downregulated, Trem2-FL remained sialylated, accumulated intracellularly, and was excessively cleaved into a C-terminal fragment (Trem2-CTF) and an extracellular soluble domain (sTrem2), enhancing their signaling capacities. Sialylated Trem2-FL (Sia-Trem2-FL) did not hinder Trem2-FL-DAP12-Syk complex assembly but impaired signal transduction through Syk, ultimately abolishing Trem2-dependent phagocytosis. Concurrently, Trem2-CTF-DAP12 complexes dampened NFκB signaling, while sTrem2 propagated Akt-dependent cell survival and NFAT1-mediated production of TNFα and CCL3. Because Neu1 and Trem2 are implicated in neurodegenerative/neuroinflammatory diseases, including Alzheimer disease (AD) and sialidosis, modulating Neu1 activity represents a therapeutic approach to broadly regulate microglia-mediated neuroinflammation.

Notch receptor-ligand binding facilitates extracellular vesicle-mediated neuron-to-neuron communication.

Extracellular vesicles (EVs) facilitate intercellular communication by transferring cargo between cells in a variety of tissues. However, how EVs achieve cell-type-specific intercellular communication is still largely unknown. We found that Notch1 and Notch2 proteins are expressed on the surface of neuronal EVs that have been generated in response to neuronal excitatory synaptic activity. Notch ligands bind these EVs on the neuronal plasma membrane, trigger their internalization, activate the Notch signaling pathway, and drive the expression of Notch target genes. The generation of these neuronal EVs requires the endosomal sorting complex required for transport-associated protein Alix. Adult Alix conditional knockout mice have reduced hippocampal Notch signaling activation and glutamatergic synaptic protein expression. Thus, EVs facilitate neuron-to-neuron communication via the Notch receptor-ligand system in the brain.

Altered GM1 catabolism affects NMDAR-mediated Ca2+ signaling at ER-PM junctions and increases synaptic spine formation in a GM1-gangliosidosis model.

Endoplasmic reticulum-plasma membrane (ER-PM) junctions mediate Ca2+ flux across neuronal membranes. The properties of these membrane contact sites are defined by their lipid content, but little attention has been given to glycosphingolipids (GSLs). Here, we show that GM1-ganglioside, an abundant GSL in neuronal membranes, is integral to ER-PM junctions; it interacts with synaptic proteins/receptors and regulates Ca2+ signaling. In a model of the neurodegenerative lysosomal storage disease, GM1-gangliosidosis, pathogenic accumulation of GM1 at ER-PM junctions due to ß-galactosidase deficiency drastically alters neuronal Ca2+ homeostasis. Mechanistically, we show that GM1 interacts with the phosphorylated N-methyl D-aspartate receptor (NMDAR) Ca2+ channel, thereby increasing Ca2+ flux, activating extracellular signal-regulated kinase (ERK) signaling, and increasing the number of synaptic spines without increasing synaptic connectivity. Thus, GM1 clustering at ER-PM junctions alters synaptic plasticity and worsens the generalized neuronal cell death characteristic of GM1-gangliosidosis.

Alix protein is substrate of Ozz-E3 ligase and modulates actin remodeling in skeletal muscle.

Alix/AIP1 is a multifunctional adaptor protein that participates in basic cellular processes, including membrane trafficking and actin cytoskeleton assembly, by binding selectively to a variety of partner proteins. However, the mechanisms regulating Alix turnover, subcellular distribution, and function in muscle cells are unknown. We now report that Alix is expressed in skeletal muscle throughout myogenic differentiation. In myotubes, a specific pool of Alix colocalizes with Ozz, the substrate-binding component of the muscle-specific ubiquitin ligase complex Ozz-E3. We found that interaction of the two endogenous proteins in the differentiated muscle fibers changes Alix conformation and promotes its ubiquitination. This in turn regulates the levels of the protein in specific subcompartments, in particular the one containing the actin polymerization factor cortactin. In Ozz(-/-) myotubes, the levels of filamentous (F)-actin is perturbed, and Alix accumulates in large puncta positive for cortactin. In line with this observation, we show that the knockdown of Alix expression in C2C12 muscle cells affects the amount and distribution of F-actin, which consequently leads to changes in cell morphology, impaired formation of sarcolemmal protrusions, and defective cell motility. These findings suggest that the Ozz-E3 ligase regulates Alix at sites where the actin cytoskeleton undergoes remodeling.

Identification and characterization of PlAlix, the Alix homologue from the Mediterranean sea urchin Paracentrotus lividus.

The sea urchin provides a relatively simple and tractable system for analyzing the early stages of embryo development. Here, we use the sea urchin species, Paracentrotus lividus, to investigate the role of Alix in key stages of embryogenesis, namely the egg fertilization and the first cleavage division. Alix is a multifunctional protein involved in different cellular processes including endocytic membrane trafficking, filamentous (F)-actin remodeling, and cytokinesis. Alix homologues have been identified in different metazoans; in these organisms, Alix is involved in oogenesis and in determination/differentiation events during embryo development. Herein, we describe the identification of the sea urchin homologue of Alix, PlAlix. The deduced amino acid sequence shows that Alix is highly conserved in sea urchins. Accordingly, we detect the PlAlix protein cross-reacting with monoclonal Alix antibodies in extracts from P. lividus, at different developmental stages. Focusing on the role of PlAlix during early embryogenesis we found that PlAlix is a maternal protein that is expressed at increasingly higher levels from fertilization to the 2-cell stage embryo. In sea urchin eggs, PlAlix localizes throughout the cytoplasm with a punctuated pattern and, soon after fertilization, accumulates in larger puncta in the cytosol, and in microvilli-like protrusions. Together our data show that PlAlix is structurally conserved from sea urchin to mammals and may open new lines of inquiry into the role of Alix during the early stages of embryo development.