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At least 955 records · Page 53Linked to original sources
PubMed1999

Directionality of wingless protein transport influences epidermal patterning in the Drosophila embryo.

Active endocytotic processes are required for the normal distribution of Wingless (Wg) protein across the epidermal cells of each embryonic segment. To assess the functional consequences of this broad Wg distribution, we have devised a means of perturbing endocytosis in spatially restricted domains within the embryo. We have constructed a transgene expressing a dominant negative form of shibire (shi), the fly dynamin homologue. When this transgene is expressed using the GAL4-UAS system, we find that Wg protein distribution within the domain of transgene expression is limited and that Wg-dependent epidermal patterning events surrounding the domain of expression are disrupted in a directional fashion. Our results indicate that Wg transport in an anterior direction generates the normal expanse of naked cuticle within the segment and that movement of Wg in a posterior direction specifies diverse denticle cell fates in the anterior portion of the adjacent segment. Furthermore, we have discovered that interfering with posterior movement of Wg rescues the excessive naked cuticle specification observed in naked (nkd) mutant embryos. We propose that the nkd segment polarity phenotype results from unregulated posterior transport of Wg protein and therefore that wild-type Nkd function may contribute to the control of Wg movement within the epidermal cells of the segment.

Alleles↗
PubMed2000

Synaptic development is controlled in the periactive zones of Drosophila synapses.

A cell-adhesion molecule fasciclin 2 (FAS2), which is required for synaptic growth and still life (SIF), an activator of RAC, were found to localize in the surrounding region of the active zone, defining the periactive zone in Drosophila neuromuscular synapses. BetaPS integrin and discs large (DLG), both involved in synaptic development, also decorated the zone. However, shibire (SHI), the Drosophila dynamin that regulates endocytosis, was found in the distinct region. Mutant analyses showed that sif genetically interacted with Fas2 in synaptic growth and that the proper localization of SIF required FAS2, suggesting that they are components in related signaling pathways that locally function in the periactive zones. We propose that neurotransmission and synaptic growth are primarily regulated in segregated subcellular spaces, active zones and periactive zones, respectively.

Animals↗
PubMed2003

A novel endocytic pathway induced by clustering endothelial ICAM-1 or PECAM-1.

Antibody conjugates directed against intercellular adhesion molecule (ICAM-1) or platelet-endothelial cell adhesion molecule (PECAM-1) have formed the basis for drug delivery vehicles that are specifically recognized and internalized by endothelial cells. There is increasing evidence that ICAM-1 and PECAM-1 may also play a role in cell scavenger functions and pathogen entry. To define the mechanisms that regulate ICAM-1 and PECAM-1 internalization, we examined the uptake of anti-PECAM-1 and anti-ICAM-1 conjugates by endothelial cells. We found that the conjugates must be multimeric, because monomeric anti-ICAM-1 and anti-PECAM-1 are not internalized. Newly internalized anti-ICAM-1 and anti-PECAM-1 conjugates did not colocalize with either clathrin or caveolin, and immunoconjugate internalization was not reduced by inhibitors of clathrin-mediated or caveolar endocytosis, suggesting that this is a novel endocytic pathway. Amiloride and protein kinase C (PKC) inhibitors, agents known to inhibit macropinocytosis, reduced the internalization of clustered ICAM-1 and PECAM-1. However, expression of dominant-negative dynamin-2 constructs inhibited uptake of clustered ICAM-1. Binding of anti-ICAM-1 conjugates stimulated the formation of actin stress fibers by human umbilical vein endothelial cells (HUVEC). Latrunculin, radicicol and Y27632 also inhibited internalization of clustered ICAM-1, suggesting that actin rearrangements requiring Src kinase and Rho kinase (ROCK) were required for internalization. Interestingly, these kinases are part of the signal transduction pathways that are activated when circulating leukocytes engage endothelial cell adhesion molecules, suggesting the possibility that CAM-mediated endocytosis is regulated using comparable signaling pathways.

Amides↗
PubMed2003

Sorting nexin 4 and amphiphysin 2, a new partnership between endocytosis and intracellular trafficking.

Endocytosis is a regulated physiological process by which membrane receptors and their extracellular ligands are internalized. After internalization, they enter the endosomal trafficking pathway for sorting and processing. Amphiphysins consist of a family of proteins conserved throughout evolution that are crucial elements of the endocytosis machinery in mammalian cells. They act as adaptors for a series of proteins important for the endocytic process, such as dynamin. In order to improve our knowledge of amphiphysin function, we performed a two-hybrid screen with the N-terminal part of murine amphiphysin 2 (residues 1-304). One of the interacting clones corresponded to sorting nexin 4 (SNX4), a member of the SNX family of proteins which are suspected to regulate vesicular trafficking. This interaction was confirmed in vivo by co-immunoprecipitation. Immunofluorescence analysis revealed that amphiphysin 2 might bind reticulo-vesicular structures present throughout the cell body and be associated with SNX4 on these structures. In an endocytosis assay, overexpressed C-terminal or full-length SNX4 was able to inhibit transferrin receptor endocytosis as efficiently as the SH3 domain of amphiphysin 2. At lower levels of expression, SNX4 colocalized with transferrin-containing vesicles, some of which were also positive for amphiphysin 2. These results indicate that SNX4 may be part of the endocytic machinery or, alternatively, that SNX4 may associate with key elements of endocytosis such as amphiphysin 2 and sequester them when overexpressed. The presence of amphiphysin 2 on intracellular vesicles and its interplay with SNX4, which is likely to take part in intracellular trafficking, suggest that amphiphysin 2 is not only a regulator of the early steps of endocytosis. It could also play a role at the surface of the endocytic vesicle that has just been formed and of the future endosomes, in order to regulate intracellular trafficking.

3T3 Cells↗
PubMed2003

Activity, phosphorylation state and subcellular distribution of GLUT4-targeted Akt2 in rat adipose cells.

In this study, fusion of the kinase domain of Akt2 to the cytosolic C terminus of exofacially-HA-tagged GLUT4 is used to investigate the activity, phosphorylation state and subcellular localization of Akt2 specifically targeted to the GLUT4-trafficking pathway in rat adipose cells. Fusion of wild-type (wt) Akt2, but not a kinase-dead (KD) mutant results in constitutive targeting of the HA-GLUT4 fusion protein to the cell surface to a level similar to that of HA-GLUT4 itself in the insulin-stimulated state. Insulin does not further enhance the cell-surface level of HA-GLUT4-Akt2-wt, but does stimulate the translocation of HA-GLUT4-Akt2-KD. Cell-surface HA-GLUT4-Akt2-wt is found to be phosphorylated on Ser474 in both the absence and presence of insulin, and mutation of Ser474 to Ala reduces the increased basal cell-surface localization of the fusion protein. While Ser474 phosphorylation of HA-GLUT4-Akt2-KD is detected only in the insulin-stimulated state, trapping this fusion protein on the cell surface by coexpression of a dominant negative mutant dynamin does not induce Ser474 phosphorylation. Phosphorylation on Thr309 is not detectable in either HA-GLUT4-Akt2-wt or HA-GLUT4-Akt2-KD, in either the basal or insulin-stimulated state, and mutation of Thr309 to Ala does not influence the insulin-independent increases in cell-surface localization and Ser474 phosphorylation. Expression of HA-GLUT4-Akt2-wt stimulates the translocation of cotransfected myc-GLUT4 to a level similar to that in the insulin-stimulated state; this increase is moderately reduced by mutation of Ser474 to Ala and absent with the kinase-dead mutant. These results demonstrate that targeting Akt2 to the GLUT4-trafficking pathway induces Akt2 activation and GLUT4 translocation. Ser474 phosphorylation is an autocatalytic reaction requiring an active kinase, and kinase activity is associated with a plasma membrane localization. Fusion of Akt2 to the C terminus of GLUT4 appears to substitute for Thr309 phosphorylation in activating the autocatalytic process.

Adipocytes↗
PubMed2003

Caveosomes and endocytosis of lipid rafts.

Endocytosis of various endogenous plasma membrane molecules, including signalling receptors, glycosphingolipids and glycosylphosphatidylinositol (GPI)-linked proteins, occurs in the absence of functional clathrin-coated pits. Most of these molecules are found in biochemically defined lipid rafts, which suggests that at least some clathrin-independent endocytosis may be raft specific or raft mediated. However, recent studies of the uptake of raft markers have revealed a diversity of internalization methods. Although lipid rafts may somehow be recognized by endocytic machinery, at this stage the data do not readily fit with the idea of a single raft-specific or raft-dependent endocytic pathway. Many studies report uptake of raft molecules by caveolar endocytosis (defined by sensitivity to cholesterol depletion and to overexpression of a specific mutant of dynamin 2). It is now apparent that this is a highly regulated process, and caveolin 1, one of the characteristic protein components of caveolae, might in fact act to slow or inhibit endocytosis. The molecular details of caveolar endocytosis have yet to be elucidated. Several sources indicate that clathrin-independent uptake to a distinct class of caveolin-1-containing endosome, termed the caveosome, allows different types of endocytic mechanisms to have different functional consequences for the cell. It is likely that there are mechanisms that allow recruitment and targeting of specific molecules to caveosomes.

Animals↗
PubMed2004

The C-terminal domain of Drosophila (beta) heavy-spectrin exhibits autonomous membrane association and modulates membrane area.

Current models of cell polarity invoke asymmetric cues that reorganize the secretory apparatus to induce polarized protein delivery. An important step in this process is the stabilization of the protein composition in each polarized membrane domain. The spectrin-based membrane skeleton is thought to contribute to such stabilization by increasing the half-life of many proteins at the cell surface. Genetic evidence is consistent with a negative role for Drosophila beta(Heavy)-spectrin in endocytosis, but the inhibitory mechanism has not been elucidated. Here, we investigated the membrane binding properties of the C-terminal nonrepetitive domain of beta(Heavy)-spectrin through its in vivo expression in transgenic flies. We found that this region is a membrane-association domain that requires a pleckstrin homology domain for full activity, and we showed for the first time that robust membrane binding by such a C-terminal domain requires additional contributions outside the pleckstrin homology. In addition, we showed that expression of the beta(Heavy)-spectrin C-terminal domain has a potent effect on epithelial morphogenesis. This effect is associated with its ability to induce an expansion in plasma membrane surface area. The membrane expansions adopt a very specific bi-membrane structure that sequesters both the C-terminal domain and the endocytic protein dynamin. Our data provide supporting evidence for the inhibition of endocytosis by beta(Heavy)-spectrin, and suggest that the C-terminal domain mediates this effect through interaction with the endocytic machinery. Spectrin may be an active partner in the stabilization of polarized membrane domains.

Animals↗
PubMed2005

Regulation of mitochondrial fission and apoptosis by the mitochondrial outer membrane protein hFis1.

Mitochondrial fission is a highly regulated process mediated by a defined set of protein factors and is involved in the early stage of apoptosis. In mammals, at least two proteins, the dynamin-like protein DLP1/Drp1 and the mitochondrial outer membrane protein hFis1, participate in mitochondrial fission. The cytosolic domain of hFis1 contains six alpha-helices that form two tetratricopeptide repeat (TPR) motifs. Overexpression of hFis1 induces DLP1-mediated fragmentation of mitochondria, suggesting that hFis1 is a limiting factor in mitochondrial fission by recruiting cytosolic DLP1. In the present study, we identified two regions of hFis1 that are necessary for correct fission of mitochondria. We found that the TPR region of hFis1 participates in the interaction with DLP1 or DLP1-containing complex and that the first helix (alpha1) of hFis1 is required for mitochondrial fission presumably by regulating DLP1-hFis1 interaction. Misregulated interaction between DLP1 and hFis1 by alpha1 deletion induced mitochondrial swelling, in part by the mitochondrial permeability transition, but significantly delayed cell death. Our data suggest that hFis1 is a main regulator of mitochondrial fission, controlling the recruitment and assembly of DLP1 during both normal and apoptotic fission processes.

Amino Acid Motifs↗
PubMed2006

Fis1p and Caf4p, but not Mdv1p, determine the polar localization of Dnm1p clusters on the mitochondrial surface.

The mitochondrial division machinery consists of the large dynamin-related protein Dnm1p (Drp1/Dlp1 in humans), and Fis1p, Mdv1p and Caf4p. Proper assembly of Dnm1p complexes on the mitochondrial surface is crucial for balanced fission and fusion events. Using quantitative confocal microscopy, we show that Caf4p is important for the recruitment of Dnm1p to the mitochondria. The mitochondrial Dnm1p assemblies can be divided into at least two morphologically distinguishable fractions. A small subset of these assemblies appear to be present as Dnm1p-spirals (or rings) that encircle tubule constrictions, with seldom more than seven turns. A larger fraction of the Dnm1p assemblies is primarily present at one side of the mitochondrial tubules. We show that a majority of these mitochondria-associated Dnm1p clusters point towards the cell cortex. This polarized orientation is abolished in fis1Delta and caf4Delta yeast cells, but is maintained in mdv1Delta cells and after disruption of the actin cytoskeleton. This study suggests that Caf4p plays a key role in determining the polarized localization of those Dnm1p clusters that are not immediately involved in the mitochondrial fission process.

Actins↗
PubMed2001

c-Cbl ubiquitinates the EGF receptor at the plasma membrane and remains receptor associated throughout the endocytic route.

Cbl family members have an evolutionarily conserved role in attenuating receptor tyrosine kinase function. Their negative regulatory capacity depends on a Ring finger domain that interacts with ubiquitin conjugating enzymes. Cbl molecules constitute a novel type of E3 or ubiquitin ligase family that is recruited to phosphotyrosine motifs. Ubiquitination of the receptor system is coupled to its downregulation, but it is unclear at which point in the endocytic pathway Cbl molecules come into play. Using low temperature and a dynamin mutant, we find that c-Cbl associates with and ubiquitinates the activated epidermal growth factor (EGF) receptor at the plasma membrane in the absence of endocytosis. With the aid of confocal microscopy and immunogold electron microscopy, we could demonstrate that c-Cbl associates with the EGF receptor at the plasma membrane prior to receptor recruitment into clathrin-coated pits and remains associated throughout the clathrin-mediated endocytic pathway. c-Cbl and the EGF receptor also colocalize in internal vesicles of multivesicular endosomes. Our data are consistent with a role for c-Cbl in clathrin-mediated endocytosis of tyrosine kinase receptors, as well as their intracellular sorting.

Animals↗
PubMed2002

Roles of the N- and C-termini of GLUT4 in endocytosis.

In insulin target cells, the predominantly expressed glucose transporter isoform GLUT4 recycles between distinct intracellular compartments and the plasma membrane. To characterize putative targeting signals within GLUT4 in a physiologically relevant cell type, we have analyzed the trafficking of hemagglutinin (HA)-epitope-tagged GLUT4 mutants in transiently transfected primary rat adipose cells. Mutation of the C-terminal dileucine motif (LL489/90) did not affect the cell-surface expression of HA-GLUT4. However, mutation of the N-terminal phenylalanine-based targeting sequence (F5) resulted in substantial increases, whereas deletion of 37 or 28 of the 44 C-terminal residues led to substantial decreases in cell-surface HA-GLUT4 in both the basal and insulin-stimulated states. Studies with wortmannin and coexpression of a dominant-negative dynamin GTPase mutant indicate that these effects appear to be primarily due to decreases and increases, respectively, in the rate of endocytosis. Yeast two-hybrid analyses revealed that the N-terminal phenylalanine-based targeting signal in GLUT4 constitutes a binding site for medium chain adaptins mu1, mu2, and mu3A, implicating a role of this motif in the targeting of GLUT4 to clathrin-coated vesicles.

Adipocytes↗
PubMed2005

Molecular dissection of internalization of Porphyromonas gingivalis by cells using fluorescent beads coated with bacterial membrane vesicle.

Porphyromonas gingivalis is one of the causative agents of adult periodontitis, and has been reported to be internalized by nonphagocytic epithelial cells. However, the mechanism for the internalization remains unclear. In the present study, we addressed this issue using fluorescent beads coated with bacterial membrane vesicles (MVs) that retain surface components of P. gingivalis. We established an assay system in which we could easily quantify the bead internalization to cells. MVs-coated beads were internalized by HeLa cells in kinetics similar to that of living bacteria. The internalization depended on dynamin but not clathrin. The beads were internalized through the actin-mediated pathway that is controlled by phosphatidylinositol (PI) 3-kinase. The dynamics of microtubule assembly and disassembly was also required. Further, the treatment of cells with cholesterol-binding reagents significantly inhibited bead internalization, and the internalized beads were apparently colocalized with ganglioside GM1 and caveolin-1, which suggest the involvement of the lipid raft in the process. These results suggest that P. gingivalis accomplishes its internalization utilizing membrane lipid raft and cytoskeletal functions of the target cells.

Actin Cytoskeleton↗
PubMed2006

Activation of NK cells by an endocytosed receptor for soluble HLA-G.

Signaling from endosomes is emerging as a mechanism by which selected receptors provide sustained signals distinct from those generated at the plasma membrane. The activity of natural killer (NK) cells, which are important effectors of innate immunity and regulators of adaptive immunity, is controlled primarily by receptors that are at the cell surface. Here we show that cytokine secretion by resting human NK cells is induced by soluble, but not solid-phase, antibodies to the killer cell immunoglobulin-like receptor (KIR) 2DL4, a receptor for human leukocyte antigen (HLA)-G. KIR2DL4 was constitutively internalized into Rab5-positive compartments via a dynamin-dependent process. Soluble HLA-G was endocytosed into KIR2DL4-containing compartments in NK cells and in 293T cells transfected with KIR2DL4. Chemokine secretion induced by KIR2DL4 transfection into 293T cells occurred only with recombinant forms of KIR2DL4 that trafficked to endosomes. The profile of genes up-regulated by KIR2DL4 engagement on resting NK cells revealed a proinflammatory/proangiogenic response. Soluble HLA-G induced secretion of a similar set of cytokines and chemokines. This unique stimulation of resting NK cells by soluble HLA-G, which is endocytosed by KIR2DL4, implies that NK cells may provide useful functions at sites of HLA-G expression, such as promotion of vascularization in maternal decidua during early pregnancy.

Chemokines↗
PubMed2006

Pathomechanisms of mutant proteins in Charcot-Marie-Tooth disease.

We review the putative functions and malfunctions of proteins encoded by genes mutated in Charcot-Marie-Tooth disease (CMT; inherited motor and sensory neuropathies) in normal and affected peripheral nerves. Some proteins implicated in demyelinating CMT, peripheral myelin protein 22, protein zero (P0), and connexin32 (Cx32/GJB1) are crucial components of myelin. Periaxin is involved in connecting myelin to the surrounding basal lamina. Early growth response 2 (EGR2) and Sox10 are transcriptional regulators of myelin genes. Mutations in the small integral membrane protein of lysosome/late endosome, the myotubularin-related protein 2 (MTMR2), and MTMR13/set-binding factor 2 are involved in vesicle and membrane transport and the regulation of protein degradation. Pathomechanisms related to alterations of these processes are a widespread phenomenon in demyelinating neuropathies because mutations of myelin components may also affect protein biosynthesis, transport, and/or degradation. Related disease mechanisms are also involved in axonal neuropathies although there is considerably more functional heterogeneity. Some mutations, most notably in P0, GJB1, ganglioside-induced differentiation-associated protein 1 (GDAP1), neurofilament light chain (NF-L), and dynamin 2 (DNM2), can result in demyelinating or axonal neuropathies introducing additional complexity in the pathogenesis. Often, this relates to the intimate connection between Schwann cells and neurons/axons leading to axonal damage even if the mutation-caused defect is Schwann-cell-autonomous. This mechanism is likely for P0 and Cx32 mutations and provides the basis for the unifying hypothesis that also demyelinating neuropathies develop into functional axonopathies. In GDAP1 and DNM2 mutants, both Schwann cells and axons/neurons might be directly affected. NF-L mutants have a primary neuronal defect but also cause demyelination. The major challenge ahead lies in determining the individual contributions by neurons and Schwann cells to the pathology over time and to delineate the detailed molecular functions of the proteins associated with CMT in health and disease.

Cell Cycle Proteins↗
PubMed2006

WNK1 affects surface expression of the ROMK potassium channel independent of WNK4.

The WNK (with no lysine kinase) kinases are a novel class of serine/threonine kinases that lack a characteristic lysine residue for ATP docking. Both WNK1 and WNK4 are expressed in the mammalian kidney, and mutations in either can cause the rare familial syndrome of hypertension and hyperkalemia (Gordon syndrome, or pseudohypoaldosteronism type 2). The molecular basis for the action of WNK4 is through alteration in the membrane expression of the NaCl co-transporter (NCCT) and the renal outer-medullary K channel KCNJ1 (ROMK). The actions of WNK1 are less well defined, and evidence to date suggests that it can affect NCCT expression but only in the presence of WNK4. The results of co-expressing WNK1 with ROMK in Xenopus oocytes are reported for the first time. These studies show that WNK1 is able to suppress total current directly through ROMK by causing a marked reduction in its surface expression. The effect is mimicked by a kinase-dead mutant of WNK1 (368D > A), suggesting that it is not dependent on its catalytic activity. Study of the time course of ROMK expression further suggests that WNK1 accelerates trafficking of ROMK from the membrane, and this effect seems to be dynamin dependent. Using fragments of full-length WNK1, it also is shown that the effect depends on residues in the middle section of the protein (502 to 1100 WNK1) that contains the acidic motif. Together, these findings emphasize that the molecular mechanisms that underpin WNK1 regulation of ROMK expression are distinct from those that affect NCCT expression.

Animals↗
PubMed2005

[Caveolar endocytosis and virus entry].

The endocytic function of caveolae has been controversial for a long time. However, a real-time-imaging analysis of Simian virus 40 (SV40) 's entry in cells has indicated the existence of caveolar endocytosis during virus entry. The caveolae engulfed SV40 virions begin budding from plasma membrane depending on dynamin. SV40 enclosed in caveolae vesicles move to the caveosome, then to the endoplasmic reticulum. In addition, it was demonstrated that human coronavirus-229E enters the cell through caveolae. This review examines the involvement of caveolae in endocytosis used by the viral entry system.

Caveolae↗
PubMed2026

High-fat diet-responsive DNM1 promotes hepatocellular carcinoma progression and predicts poor prognosis in viral-associated patients.

Hepatocellular carcinoma (HCC) arises from diverse etiologies, among which metabolic dysfunction-associated liver disease and chronic viral hepatitis are the two major drivers worldwide. However, the molecular mechanisms linking metabolic stress to HCC progression remain incompletely understood. Dynamin-1 (DNM1), primarily known for its role in vesicular trafficking, has emerged as a potential oncogene, yet its prognostic and functional significance in HCC remains largely unexplored. Here, we investigated the role of DNM1 in high-fat diet (HFD)-associated hepatocarcinogenesis. Transcriptomic profiling was conducted to identify differentially expressed genes between normal and high-fat diet murine models, with human orthologs mapped. Clinical relevance was validated using The Cancer Genome Atlas (TCGA-LIHC) dataset. Survival analysis, GSEA (Gene Set Enrichment Analysis), and subgroup stratifications based on viral hepatitis status were performed. In vitro, loss-of-function assays (shRNA knockdown) were executed in HepG2 and SK-Hep1 cell lines to assess cell viability and migration. DNM1 was significantly upregulated in high-fat diet models. In the TCGA-LIHC cohort, high DNM1 expression was an independent risk factor for poor overall survival (HR=1.44, P=0.039) and correlated with advanced tumor stages (Stage III+IV, P=0.010). In vitro knockdown of DNM1 profoundly impaired cell proliferation and migration in HCC cell lines. Strikingly, DNM1 expression was further elevated in patients with concurrent viral hepatitis (P=0.009). GSEA revealed that high DNM1 expression was positively associated with viral infection pathways and negatively correlated with critical immune responses, including interferon-alpha/gamma responses and host immune cytolysis. Survival analysis stratified by four subgroups demonstrated that patients with both viral infection and high DNM1 expression exhibited the worst prognosis (Overall Log-rank P < 0.001). Our findings identify DNM1 as a high-fat diet-responsive regulator that links metabolic stress to hepatocellular carcinoma progression. Elevated DNM1 expression promotes malignant phenotypes in HCC and identifies a subgroup of viral-associated patients with particularly poor prognosis, highlighting DNM1 as a potential prognostic biomarker and therapeutic target.

Hepatocellular carcinoma (HCC)↗
PubMed1999

Crustacean frequenins: molecular cloning and differential localization at neuromuscular junctions.

Crustacean muscles are innervated by phasic and tonic motor neurons that display differential physiology and have morphologically distinct synaptic terminals. Phasic motor neurons release much more transmitter per impulse and have filiform terminals, whereas tonic motor neurons release less transmitter and have larger terminals with prominent varicosities. Using an antibody raised against Drosophila frequenin (frq), a calcium-binding protein that enhances transmitter release in Drosophila synaptic terminals, we found that frq-like immunoreactivity is prominent in many of the phasic, but not tonic nerve endings of crayfish motor neurons. In contrast, synapsin- and dynamin-like immunoreactivities are strongly expressed in both types of terminal. The immunocytochemical findings strongly suggested the presence of an frq-like molecule in crayfish, and its differential expression indicated a possible modulatory role in transmitter release. Therefore, we cloned the cDNA sequences for the crayfish and lobster homologues of Drosophila frq. Crustacean frequenins are very similar in sequence to their Drosophila counterpart, and calcium-binding regions (EF hands) are conserved. The widespread occurrence of frq-like molecules and their differential localization in crayfish motor neurons indicate a significant role in physiology or development of these neurons.

Animals↗