bluuebunny/crossref_metadata_2025 huggingface dataset:
ATP depletion: a novel method to study junctional properties in epithelial tissues: II. Internalization of Na+, K+-ATPase E-cadherin
Authors: Mandel Lazaro J. , Doctor R. Brian , Bacallao Robert
Published: April 2021

MDCK and JTC cells were subjected to ATP depletion by treating the cells with 10 μM antimycin A and 10 mM 2-deoxyglucose. As visualized by confocal fluorescence microscopy, E-cadherin and Na+,K+-ATPase were rapidly internalized following depletion of the intracellular ATP stores. The time course of internalization was similar to the depolymerization of the cortical actin network and dissolution of the actin ring (see companion paper, this volume, pp. 3301-3313). Cell surface biotinylation was used to assay the amount of surface-accessible E-cadherin and Na+,K+-ATPase during ATP depletion. At 30 minutes of ATP depletion, 74% and 69% of E-cadherin and Na+,K+-ATPase were internalized, respectively, in MDCK cells. By 60 minutes of ATP depletion, internalization increased to 95% and 89%, respectively. The redistribution of both plasma membrane proteins was not microtubule dependent. Similar results were observed in JTC cells. Total biotinylated protein decreased by 67% and 82%, after 30 minutes and 60 minutes of ATP depletion, respectively. The E-cadherin internalization strongly suggests that disruption of adherens junctions occurred following ATP depletion. These results, along with the previously described loss of tight junction integrity, suggest that ATP depletion may be a useful method to study the assembly and disassembly of junctional complexes in epithelial cells.
A group of integral membrane proteins of the rat liver Golgi contains a conserved protein of 100 kDa
Authors: Pryde James G.
Published: April 2021

Rat liver Golgi membranes were washed with KCl and urea, and a polyclonal antiserum that stained the Golgi complex by immunofluorescence microscopy was raised. A group of proteins of apparent molecular mass 500 kDa, 200 kDa and 100 kDa were identified by immunoblotting with the antiserum, and were enriched in the Golgi membrane fraction. These proteins were also localised to the Golgi by immunofluorescence microscopy with affinity-purified antibodies. They are integral membrane proteins, and protease digestion experiments suggested that they are not exposed on the cytoplasmic face of the Golgi membrane.

Immunofluorescence microscopy showed that staining of the Golgi complex by antibodies to the 100 kDa Golgi protein can be demonstrated among a wide range of mammalian species. This conservation may point to an important structural or functional role for the molecule. When the 100 kDa protein was reduced with dithiothreitol it was no longer recognised by the anti-Golgi antiserum. During phase separation in Triton X-114 the 100 kDa protein partitioned into the aqueous phase, rather than into the detergent phase, suggesting that it has a large luminal domain of hydrophilic amino acids.
The protein phosphatase inhibitor okadaic acid induces defects in cytokinesis and organellar genome segregation in Trypanosoma brucei
Authors: Das Arpita , Gale Michael , Carter Victoria , Parsons Marilyn
Published: April 2021

Mitosis and cytokinesis are events that are highly coordinated in most eukaryotic cell cycles. African trypanosomes possess a single mitochondrion and must additionally coordinate the organellar division cycle. Here we report that okadaic acid, a potent and specific inhibitor of protein phosphatases PP1and PP2A, uncouples these cycles in living trypanosomes. Cell cycle analysis of treated cells revealed elevated DNA content. Microscopic examination indicated that okadaic acid treatment yielded multinucleate cells with a single mitochondrial network indicating these cells have undergone mitosis but failed to complete cytokinesis. Immunofluorescence analysis of 5-bromo-2deoxyuridine incorporation demonstrated that the mitochondrial DNA was replicated but did not segregate. The dose response curve for inhibition of the normal cell cycle paralleled that for the in vitro inhibition of protein phosphatase activities with IC50s of approximately 20 nM okadaic acid. These results suggest the involvement of a PP1/PP2A-like activity in coordinating mitosis, mitochondrial DNA division and cytokinesis in trypanosomes.
Heterogeneity and microtubule interaction of the CHO1 antigen, a mitosisspecific kinesin-like protein: Analysis of subdomains expressed in insect sf9 cells
Authors: Kuriyama Ryoko , Dragas-Granoic Sasa , Maekawa Takami , Vassilev Alexei , Khodjakov Alexey , Kobayashi Hitoshi
Published: April 2021

The CHO1 antigen is a mitosis-specific kinesin-like motor located at the interzonal region of the spindle. The human cDNA coding for the antigen contains a domain with sequence similarity to the motor domain of kinesin-like protein (Nislow et al., Nature 359, 543, 1992). Here we cloned cDNAs encoding the CHO1 antigen by immunoscreening of a CHO Uni-Zap expression library, the same species in which the original monoclonal antibody was raised. cDNAs of CHO cells encode a 953 amino acid polypeptide with a calculated molecular mass of 109 kDa. The N-terminal 73% of the antigen was 87% identical to the human clone, whereas the remaining 27% of the coding region showed only 48% homology. Insect Sf9 cells infected with baculovirus containing the full-length insert produced 105 and 95 kDa polypeptides, the same doublet identified as the original antigen in CHO cells. Truncated polypeptides corresponding to the N-terminal motor and Cterminal tail produced a 56 and 54 kDa polypeptide in Sf9 cells, respectively. Full and N-terminal proteins co-sedimented with, and caused bundling of, brain microtubules in vitro, whereas the C-terminal polypeptide did not. Cells expressing the N terminus formed one or more cytoplasmic processes. Immunofluorescence as well as electron microscopic observations revealed the presence of thick bundles of microtubules, which were closely packed, forming a marginal ring just beneath the cell membrane and a core in the processes. The diffusion coefficient and sedimentation coefficient were determined for the native CHO1 antigen by gel filtration and sucrose density gradient centrifugation, respectively. The native molecular mass of overinduced protein in Sf9 cells was calculated as 219 kDa, suggesting that the antigen exists as a dimer. Intrinsic CHO1 antigen in cultured mammalian cells forms a larger native complex (native molecular mass, 362 kDa), which may suggest the presence of additional molecule(s) associating with the CHO1 motor molecule.
A maternal product of the Punch locus of Drosophila melanogaster is required for precellular blastoderm nuclear divisions
Authors: Chen Xiongying , Reynolds Elaine R. , Ranganayakulu Gogineni , O’Donnell Janis M.
Published: April 2021

The Punch locus of Drosophila melanogaster encodes the pteridine biosynthesis enzyme guanosine triphosphate cyclohydrolase. One class of Punch mutants is defective for a maternal function that results in embryonic death. We demonstrate here that the embryos exhibit nuclear division defects during the precellular blastoderm stage of development. These defects include abnormal nuclear distribution, mitotic asynchrony, and persisting chromatin bridges. Daughter nuclei that do not complete chromosome separation nevertheless initiate new interphase and mitotic cycles. As a result, interconnected mitotic figures are observed. Mitotic spindles and nuclear envelopes appear essentially normal. A mutant phenocopy was induced in wild-type embryos by treatment with the guanosine triphosphate cyclohydrolase inhibitor, 2,4-diamino-6-hydroxypyrimidine, at a very early cleavage stage. Furthermore, an inhibitor of a terminal step in pteridine biosynthesis produced an identical phenotype. Immunolocalization experiments define expression of Punch protein in nurse cells during oogenesis. The protein is packaged into granules as it is transported into the oocyte cytoplasm. As syncytial blastoderm nuclear divisions proceed, Punch protein levels decrease and disappear by cellularization. Defects in the expression of the protein in Punch maternal effect mutants correlate well with the early phenotypes. These results show that a Punch product is directly involved in early nuclear divisions and suggest a possible role in chromosome separation.
Periodic expression of nuclear and mitochondrial DNA replication genes during the trypanosomatid cell cycle
Authors: Pasion Sally G. , Brown Grant W. , Brown Lisa M. , Ray Dan S.
Published: April 2021

In trypanosomatids, DNA replication in the nucleus and in the single mitochondrion (or kinetoplast) initiates nearly simultaneously, suggesting that the DNA synthesis (S) phases of the nucleus and the mitochondrion are coordinately regulated. To investigate the basis for the temporal link between nuclear and mitochondrial DNA synthesis phases the expression of the genes encoding DNA ligase I, the 51 and 28 kDa subunits of replication protein A, dihydrofolate reductase and the mitochondrial type II topoisomerase were analyzed during the cell cycle progression of synchronous cultures of Crithidia fasciculata. These DNA replication genes were all expressed periodically, with peak mRNA levels occurring just prior to or at the peak of DNA synthesis in the synchronized cultures. A plasmid clone (pdN-1) in which TOP2, the gene encoding the mitochondrial topoisomerase, was disrupted by the insertion of a NEO drug-resistance cassette was found to express both a truncated TOP2 mRNA and a truncated topoisomerase polypeptide. The truncated mRNA was also expressed periodically coordinate with the expression of the endogenous TOP2 mRNA indicating that cis elements necessary for periodic expression are contained within cloned sequences. The expression of both TOP2 and nuclear DNA replication genes at the G1/S boundary suggests that regulated expression of these genes may play a role in coordinating nuclear and mitochondrial S phases in trypanosomatids.
Multiple unconventional myosin domains of the intestinal brush border cytoskeleton
Authors: Heintzelman Matthew B. , Hasson Tama , Mooseker Mark S.
Published: April 2021

Representatives of class V and class VI unconventional myosins are identified as components of the intestinal brush border cytoskeleton. With brush border myosin-I and myosin-II, this brings to four the number of myosin classes associated with this one subcellular domain and represents the first characterization of four classes of myosins expressed in a single metazoan cell type. The distribution and cytoskeletal association of each myosin is distinct as assessed by both biochemical fractionation and immunofluorescence localization. Myosin-VI exists in both the microvillus and terminal web although the terminal web is the predominant site of concentration. Myosin-V is present in the terminal web and, most notably, at the distal ends of the microvilli, thus becoming the first actin-binding protein to be localized to this domain as assessed by both immunohistochemical and biochemical methods. In the undifferentiated enterocytes of the intestinal crypts, myosin-VI is expressed but not yet localized to the brush border, in contrast to myosin-V, which does demonstrate an apical distribution in these cells. An assessment of myosin abundance indicates that while myosin-II is the most abundant in the cell and in the brush border, brush border myosin-I is only slightly less abundant in contrast to myosins-V and -VI, both of which are two orders of magnitude less abundant than the others. Extraction studies indicate that of these four myosins, myosin-V is the most tightly associated with the brush border membrane, as detergent, in addition to ATP, is required for efficient solubilization.
Branching morphogenesis of human mammary epithelial cells in collagen gels
Authors: Berdichevsky Feodor , Alford Deborah , D’Souza Brendan , Taylor-Papadimitriou Joyce
Published: April 2021

To study the morphogenesis of human epithelial cells in vitro we have used a three-dimensional collagen matrix and a newly developed mammary epithelial cell line, 1-7 HB2. In standard medium 1-7 HB2 cells formed compact balls/spheres inside collagen type I gels, while cocultivation with various fibroblast cell lines or growth in fibroblastconditioned media resulted in the appearance of branching structures. At least two different soluble factors secreted by fibroblasts were found to be implicated in the branching morphogenesis. Firstly, hepatocyte growth factor/scatter factor could induce branching in a concentrationdependent manner. Moreover, a polyclonal serum against hepatocyte growth factor/scatter factor completely inhibited the branching morphogenesis induced by medium conditioned by MRC-5 fibroblast cells. In contrast, a morphogenetic activity secreted by human foreskin fibroblasts was identified that appears to be different from hepatocyte growth factor/scatter factor and from a number of other well-characterized growth factors or cytokines. This model system has been used to examine the role of integrins in mammary morphogenesis. The expression of the α2β1, α3β1 and α6β4 integrins was decreased when cells were plated on collagen gels. The addition of specific blocking monoclonal antibodies directed to the α2and β1-integrin subunits to growth media impaired cell-cell interactions and interfered with the formation of compact structures inside collagen gels, suggesting that the α2β1 integrin can control intercellular adhesion in mammary morphogenesis. In contrast one of the blocking monoclonal antibodies against the α3-integrin subunit (P1B5) mimicked the effect of soluble ‘morphogens’. Our results suggest that the modulation of α3β1 activity may represent an important event in the induction of branching morphogenesis of human mammary epithelial cells.
E-cadherin mediates adherens junction organization through protein kinase C
Authors: Lewis Jani E. , Jensen Pamela J. , Johnson Keith R. , Wheelock Margaret J.
Published: April 2021

Cultured human keratinocytes maintained in 30 μM Ca2+ do not form adherens junctions; however, when the extracellular Ca2+ concentration is raised to 1 mM, adherens junctions form very rapidly. The formation of a junction involves the coordinate organization of intracellular and extracellular components. Cadherins have been shown to mediate this coordinate organization. In this report we show that E-cadherin organizes the various junctional components by signalling through protein kinase C.
C/A dynein isolated from sea urchin sperm flagellar axonemes: Enzymatic properties and interaction with microtubules
Authors: Yokota Etsuo , Mabuchi Issei
Published: April 2021

C/A dynein is a novel dynein isolated from sea urchin sperm flagellar axonemes. It is composed of C and A heavy chains and some additional lower molecular mass polypeptide chains. The characterization of ATPase activity and the interaction of this dynein with microtubules polymerized from calf brain tubulin were investigated in this study. The ATPase activity of C/A dynein (0.3-0.4 μmol Pi/min per mg) was about one half that of outer arm 21 S dynein (0.6-0.8 μmol Pi/min per mg) at 25°C. Vanadate inhibited the ATPase activity with a half-maximal inhibition at 1 μM. C/A dynein adsorbed to the glass surface was able to translocate the microtubules towards its plus end. The velocity of the microtubule movement in the presence of 1 mM ATP was 4.0 to 4.5 μm/s at 22°C. C/A dynein binds to and bundles the microtubules even in the presence of ATP. Cross-bridges were found between adjacent microtubules in the bundle with an axial periodicity of about 24 nm. The ATPase activity of C/A dynein was enhanced up to several-fold by the microtubules at concentration as low as 1 mg/ml. On the other hand, 21 S dynein bound to the micro-tubules with 24 nm axial periodicity only in the absence of ATP. Its ATPase activity was not activated by the micro-tubules. From these results, it is concluded that the manner of interaction with microtubules of C/A dynein is different from that of the outer arm dynein.
Developmental expression of mucin genes MUC1 and MUC2
Authors: Chambers Julie A. , Hollingsworth Michael A. , Trezise Ann E. O. , Harris Ann
Published: April 2021

The mucin gene MUC1, is expressed in a number of human ductal epithelia in vivo including those within the pancreas, mammary gland, kidney and genital ducts. Further it is expressed at a high level in certain tumours and tumour-derived cell lines. MUC2 was initially isolated from a human jejunum cDNA library and is thought to be one of the major intestinal mucin genes, though it is also expressed in the trachea. We have examined the develop-mental expression of these two mucin genes in human tissues. High level expression of MUC1 has been seen by 12.5 weeks of gestation in the epithelia of the distal respiratory tract and the collecting ducts in the kidney. By 18 weeks MUC1 mRNA is detectable in the colon but pancreatic expression of MUC1 is not seen until late in gestation. MUC2 mRNA is seen by 12 weeks of gestation in the jejunum, ileum and colon, and in large bronchioles of the lung by 18 weeks. The pattern of expression of MUC1 suggests that this mucin may not be involved in early ductal obstruction in the CF pancreas, but both MUC1 and MUC2 may play a role in the development of intestinal disease and MUC1 in early respiratory disease associated with CF.
Analysis of HPV16 e6 and mutant p53-transfected keratinocytes in reconstituted epidermis suggests that wild-type p53 inhibits cytokeratin 19 expression
Authors: Molès Jean-Pierre , Schiller John T. , Tesniere Anne , Leigh Irene M. , Guilhou Jean-Jacques , Basset-Séguin Nicole
Published: April 2021

Using a reconstituted skin culture model we have analysed the effects of oncogenic human papillomavirus (HPV) and mutant TP53 genes on the proliferation and differentiation of human keratinocytes. Immortal cell lines generated by transfection of early passage normal human keratinocytes with HPV16 E7 plus mutant human TP53 (KN #1), HPV16 E7/E6 (KN #2), or HPV16 E7 plus murine p53 (KN #3) were examined. KN #1 and KN #2 behaved identically, reconstructing a tumor-like epidermis characterized by the lack of differentiation and the presence of an aberrant epidermal architecture. In contrast, KN #3 reconstructed an epidermis that was more similar to that obtained with normal keratinocytes. KN #1 and KN #2 were further characterized by the inversion of the proliferative compartment and the abnormal expression of cytokeratin 19 (CK19). Because p53 function is reduced in these cells, either by heterocomplex formation between endogenous wild-type p53 and transfected mutant p53 or by E6-induced degradation of wild-type p53, we hypothesized that CK19 expression may be normally repressed by wild-type p53. This hypothesis was supported by the strict correlation observed between TP53 mutation and CK19 expression in a set of human skin tumors. CK19 was detected in all eight carcinomas containing a mutated TP53 gene but in none of the 16 carcinomas containing only wild-type TP53. These results illustrate the utility of the in vitro reconstituted skin model for investigating the consequences of genetic alterations in human keratinocytes.
Constitutive expression of mhc and adhesion molecules by alveolar epithelial cells (type ii pneumocytes) isolated from human lung and comparison with immunocytochemical findings
Authors: Cunningham Anne C. , Milne Debra S. , Wilkes Julie , Dark John H. , Tetley Teresa D. , Kirby John A.
Published: April 2021

Highly purified populations of alveolar epithelial cells (type II pneumocytes) were isolated from human lung specimens. These cells were characterised histochemically, by demonstrating the presence of intracellular alkaline phosphatase, and morphologically, by electron microscopic demonstration of lamellar bodies and microvilli. Expression of the epithelial glycoprotein HEA-125, of MHC class I and class II (HLA-DR, -DP and -DQ) antigens and of the intercellular adhesion molecules ICAM-1, VCAM-1, LFA-3 and B7 was quantified by flow cytometry. Comparison was made between the expression of these molecules by isolated type II cells and by alveolar epithelium in normal human lung tissue after immunocytochemical staining of frozen sections of donor lung.

Isolated type II pneumocytes expressed HEA-125 and class I MHC molecules and the class II MHC molecules HLA-DR and -DP; HLA-DQ was not detected. The inter-cellular adhesion molecule ICAM-1 was expressed constitutively at low levels but there was minimal expression of VCAM-1, LFA-3 and B7.

It was not possible to differentiate type II cells from the predominant type I pneumocytes on frozen sections. Alveolar epithelium expressed HEA-125, class I MHC antigens, the class II molecules HLA-DR, and -DP and the intercellular adhesion molecule LFA-3. Expression of the adhesion molecules ICAM-1, VCAM-1 and B7 was variable. As with the isolates, HLA-DQ was not observed on alveolar epithelium.

In conclusion, a reproducible method for the isolation of pure populations of human type II pneumocytes has been developed. These cells were not damaged by the isolation procedure. It is not known whether alveolar epithelium can present antigens to T lymphocytes. However, the expression of potentially immunogenic class II MHC antigens and of intercellular adhesion molecules may facilitate pulmonary inflammation.
Cell cycle redistribution of U3 snRNA and fibrillarin: presence in the cytoplasmic nucleolus remnant and in the prenucleolar bodies at telophase
Authors: Azum-Gélade Marie-Claude , Noaillac-Depeyre Jacqueline , Caizergues-Ferrer Michèle , Gas Nicole
Published: April 2021

The distribution of the U3 small nuclear RNA during the cell cycle of the CHO cell line was studied by in situ hybridization using digoxigenin-labelled oligonucleotide probes. The location of the hybrids by immunofluorescence microscopy and at the ultrastructural level was correlated with the distribution of two nucleolar proteins, nucleolin and fibrillarin. The U3 snRNA molecules persist through-out mitosis in close association with the nucleolar remnant. U3 snRNA is present in the prenucleolar bodies (PNBs) and could participate in nucleologenesis in association with several nucleolar proteins such as nucleolin and fibrillarin. The interaction of U3 snRNP with the 5′ external spacer of pre-RNA newly synthesized by active NORs is proposed to be the promoting event of nucleologenesis.
Induction of fibroblast 92 kDa gelatinase/type iv collagenase expression by direct contact with metastatic tumor cells
Authors: Himelstein Bruce P. , Canete-Soler Rafaela , Bernhard Eric J. , Muschel Ruth J.
Published: April 2021

Previous studies have correlated release of the 92 kDa type IV collagenase/gelatinase by tumor cells in culture with metastatic potential. We have now demonstrated that the ability of tumor cells that do not express the 92 kDa gelatinase to induce release of this metalloproteinase from normal fibroblasts may also be associated with the metastatic phenotype.

A transformed rat embryo cell line, 2.8, failed to release the 92 kDa gelatinase alone in culture, but gave rise to metastatic tumors whose explants contained the 92 kDa gelatinase. In contrast, a non-metastatic transformed cell line, RA3, did not express the 92 kDa gelatinase alone in culture or in tumor explants. To explore the mechanisms that might govern host-tumor cell interactions in this system, we have studied the effects of co-culture of these transformed cell lines with rat embryo fibroblasts (REF) in culture. 92 kDa gelatinase expression was induced by coculture of 2.8 with REF, but co-culture of the non-metastatic line RA3 with REF did not result in induction of the 92 kDa gelatinase. The 92 kDa gelatinase in these co-cultures was released by the fibroblasts; methanol-fixed 2.8 cells induced 92 kDa gelatinase expression in REF, but fixed REF cells did not induce enzyme expression in 2.8 cells. This suggested that cell contact was required for induction, which was confirmed by showing that 92 kDa gelatinase induction in co-culture was abolished by separating REF from 2.8 by solute-permissive membranes. In addition, REF could not be stimulated to produce the 92 kDa gelatinase by 2.8-derived conditioned medium, by 2.8-derived extracellular matrix, or by isolated matrix components. These data indicate that metastatic tumor cells can induce 92 kDa gelatinase expression in fibroblasts through a mechanism dependent upon cell contact.

In situ hybridization of nude mouse tumors derived from these transformed cell lines revealed 92 kDa gelatinase expression in the stroma of tumors from 2.8, but not in tumors from RA3. Therefore, the experiments based on in vitro co-culture of tumor cells and fibroblasts, together with the in situ localization of mRNA to host cells, suggest that host production of the 92 kDa gelatinase may occur in response to direct contact with metastatic tumor cells.
Integrin expression and localization in normal MDCK cells and transformed MDCK cells lacking apical polarity
Authors: Schoenenberger Cora-Ann , Zuk Anna , Zinkl Gregory M. , Kendall Donna , Matlin Karl S.
Published: April 2021

Epithelial cells polarize in response to contacts with the extracellular matrix and with neighboring cells. Interac-tions of cells with the extracellular matrix are mediated mainly by the integrin family of receptors. To begin to understand the role of integrins in polarization, we have investigated the expression and localization of three integrin families in the polarized Madin-Darby canine kidney (MDCK) epithelial cell line and in transformed MDCK cells lacking apical polarity. We find that MDCK cells express several β1 integrins, including α2β1, α3β1, and an unidentified integrin designated αxβ1. The β1 integrins are the major receptors for collagens I and IV and laminin in MDCK cells, since a blocking anti-β1 antibody almost totally abolishes adhesion to these proteins. They also express a vitronectin receptor tentatively identified as αvβ3, and the epithelial-specific integrin α6β4. The latter is not a laminin receptor in MDCK cells because a function blocking anti-α6 antibody has no effect on cell adhesion to laminin. All three integrin families are expressed exclu-sively on both the basal and lateral surfaces, as determined by immunofluorescence microscopy and surface biotinyla-tion. Transformed MDCK cells express β1 integrins as well as αvβ3 and α6β4, but show alterations in the β1 family. Expression of αx is lacking, and the relative amount of the β1 subunit is diminished, resulting in the accumulation of Endo-H-sensitive α3. In addition, surface biotinylation and immunofluorescence indicate that significant amounts of both α2β1 and α3β1 appear on not only the basolateral but also the apical plasma membrane. These results indicate that integrins are the major receptors for the extracellular matrix in MDCK cells, and that they may affect epithelial cell polarization by mediating not only cell-substratum but also cell-cell contacts.
Expression of the integrin α6β4 in peripheral nerves: localization in schwann and perineural cells and different variants of the β4 subunit
Authors: Niessen C. M. , Cremona O. , Daams H. , Ferraresi S. , Sonnenberg A. , Marchisio P. C.
Published: April 2021

Integrin α6β4 is expressed in human peripheral nerves, but not in the central nervous system. This integrin het-erodimer has previously been found in perineural fibrob-last-like cells and in Schwann cells (SCs), which both assemble a basement membrane but do not form hemidesmosomes. We show here that in SCs, which had formed a myelin sheath, α6β4 was enriched in the proximity of the nucleus, at Ranvier paranodal areas and at Schmitt-Lanterman clefts; α6β4 was also found at the grooved interface between small axons and non-myelinating SCs. Immunoprecipitation of human peripheral nerves, in com-bination with Western blotting showed that β4 is associated with the α6A subunit. Northern blot analysis of human peripheral nerves showed a single β4 transcript of 6 kb. Using the reverse transcriptase polymerase chain reaction, we detected two mRNA species, one for the most common (−70, −53) form of β4 and the other encoding the (+53) variant of β4. Cultured SCs were devoid of α6β4 but expressed α6β1, indicating that SCs lose β4 expression when contact with neurons is lost. Thus, resting SCs in contact with axons express α6A in combination with β4, irrespec-tive of myelin formation. We suggest that α6β4 expressed in SCs plays a role in peripheral neurogenesis.
Compartmentalization, processing and redistribution of the plasma membrane protein CE9 on rodent spermatozoa: Relationship of the annulus to domain boundaries in the plasma membrane of the tail
Authors: Cesario Mario M. , Bartles James R.
Published: April 2021

Western blotting, immunofluorescence and immunogold electron microscopy were used to examine the compartmentalization, processing and redistribution of the integral plasma membrane protein CE9 on the spermatozoa of rats, mice and hamsters. In each species examined, spermatozoal CE9 was found to undergo endoproteolytic processing followed by a net redistribution from the posterior-tail domain into the anterior-tail domain of the plasma membrane during epididymal maturation. Compared to spermatozoa of the rat and mouse, those of the hamster were found to express a greater proportion of their CE9 within the anterior-tail plasma membrane domain at all stages of maturation. As a consequence, CE9 was judged to be a suitable marker for two different spermatozoal plasma membrane domains: the posterior-tail plasma membrane domain (spermatozoa from the testis and caput epididymidis of the rat and mouse) and the anterior-tail domain (spermatozoa from the cauda epididymidis of the hamster). Immunogold electron microscopy was used to pinpoint the positions of the boundaries of these CE9-con-taining plasma membrane domains at a high level of resolution. In each case, the position of the CE9 domain boundary was found to be strongly correlated with that of the subplasmalemmal electron-dense ring known as the annulus. The precise spatial relationship between the CE9 domain boundary and the annulus was, however, found to differ significantly among species and/or as a function of maturation.
The expression of proliferation-dependent antigens during the lifespan of normal and progeroid human fibroblasts in culture
Authors: Kill Ian R. , Faragher Richard G. A. , Lawrence Kay , Shall Sydney
Published: April 2021

Normal human fibroblasts display a limited lifespan in culture, which is due to a steadily decreasing fraction of cells that are able to proliferate. Using antibodies that react with antigens present in proliferating cells only, in an indirect immunofluorescence assay, we have estimated the fraction of proliferating cells in cultures of normal human fibroblasts. Furthermore, we have estimated the rate of decline in the fraction of proliferating cells during the process of cellular ageing by application of the assay to normal human fibroblasts throughout their lifespan in culture. Werner’s Syndrome is an autosomal recessive disease in which individuals display symptoms of ageing prematurely. Werner’s Syndrome fibroblasts display a reduced lifespan in culture compared with normal human fibroblasts. Like normal human fibroblasts, the growth of Werner’s Syndrome fibroblasts is characterised by a decreasing fraction of cells reacting with the proliferation-associated antibodies throughout their lifespan in culture. However, the rate of loss of proliferating cells in Werner’s Syndrome fibroblasts during the process of cellular ageing is accelerated 5-to 6-fold compared with the rate deter-mined for normal human fibroblasts.
The photosynthetic endosymbiont in cryptomonad cells produces both chloroplast and cytoplasmic-type ribosomes
Authors: McFadden G.I. , Gilson P.R. , Douglas S.E.
Published: April 2021

Cryptomonad algae contain a photosynthetic, eukaryotic endosymbiont. The endosymbiont is much reduced but retains a small nucleus. DNA from this endosymbiont nucleus encodes rRNAs, and it is presumed that these rRNAs are incorporated into ribosomes. Surrounding the endosymbiont nucleus is a small volume of cytoplasm proposed to be the vestigial cytoplasm of the endosymbiont. If this compartment is indeed the endosymbiont's cytoplasm, it would be expected to contain ribosomes with components encoded by the endosymbiont nucleus. In this paper, we used in situ hybridization to localize rRNAs encoded by the endosymbiont nucleus of the cryptomonad alga, Cryptomonas phi. Transcripts of the endosymbiont rRNA gene were observed within the endosymbiont nucleus, and in the compartment thought to represent the endosymbiont's cytoplasm. These results indicate that the endosymbiont produces its own set of cytoplasmic translation machinery. We also localized transcripts of the host nucleus rRNA gene. These transcripts were found in the nucleolus of the host nucleus, and throughout the host cytoplasm, but never in the endosymbiont compartment. Our rRNA localizations indicate that the cryptomonad cell produces two different of sets of cytoplasmic-type ribosomes in two separate subcellular compartments. The results suggest that there is no exchange of rRNAs between these compartments. We also used the probe specific for the endosymbiont rRNA gene to identify chromosomes from the endosymbiont nucleus in pulsed field gel electrophoresis. Like other cryptomonads, the endosymbiont nucleus of Cryptomonas phi contains three small chromosomes.
The regulation of chemotaxis and chemokinesis in Dictyostelium amoebae by temporal signals and spatial gradients of cyclic AMP
Authors: Vicker Michael G.
Published: April 2021

The tactic and kinetic locomotion of Dictyostelium dis- coideum amoebae were examined in cyclic AMP (cAMP) spatial gradient and temporal signal fields. The distribu- tions of migrating cells were examined within 150 µm-thick micropore filters after incubation with different cAMP concentrations, [cAMP], applied in three ways across the fields: as positively or negatively developing gradients, generated either by increasing or decreasing the [cAMP] on one side of the filter, respectively, or as static, linear gradients after negative development. Chemotaxis was only induced by oriented, temporally increasing [cAMP]. Pulses propagated by molecular diffusion or mechanical flow were equally effective. Negatively developing cAMP gradients had no initial effect on cell accumulation. However, if the subsequent static spatial gradient was maintained by an infusion system, some gradients also induced cell accumu- lation, whose degree and direction depended on the gradient [cAMP]. The basis of this new effect was examined by tracking individual cells by computer-assisted videomi- croscopy during locomotion in different [cAMP]. Cells produced a triphasic [cAMP]-dependent response, with optimal cell motility induced by 10-30 nM. The results demonstrate that cell accumulation either up-field or down-field in spatial gradients is governed by the field locations of the attractant concentrations that induce the relative locomotory maxima and minima in the gradient field. Cells perceive the ambient [cAMP], but cannot read the spatial gradient orientation in static or yet steeper regions of developing gradients. Accumulation in static spatial gradients is a function of klino- and orthokinesis, but chemotaxis requires an oriented cAMP pulse or impulse. A mechanism of tactic signal perception is proposed in terms of the recently discovered intracellular oscillator, which determines cell shape and movement.
Characterisation of the paxillin-binding site and the C-terminal focal adhesion targeting sequence in vinculin
Authors: Wood C. K. , Turner C. E. , Jackson P. , Critchley D. R.
Published: April 2021

Paxillin and vinculin are cytoskeletal proteins that co- localise to focal adhesions, specialised regions of the cell involved in attachment to the extracellular matrix. These two molecules form part of a complex of proteins that link the actin network to the plasma membrane. Paxillin has been shown to bind directly in vitro to the C-terminal region of vinculin (Turner et al. (1990). J. Cell Biol. 111, 1059-1068), which also contains a focal adhesion targeting sequence (Bendori et al. (1989). J. Cell Biol. 108, 2383- 2393). In the present study, we have used a series of vinculin deletion mutants to map more precisely the sites in vinculin responsible for paxillin binding and focal adhesion localisation. A glutathione-S-transferase fusion protein spanning vinculin residues 881-1000 was sufficient to support 125I-paxillin binding in a gel-blot assay while no detectable binding was observed to a fusion protein spanning residues 881-978. Transfection experiments using cDNAs encoding chick vinculin residues 398-1066 and 398- 1028 demonstrated that amino acids C-terminal to residue 1028 were not necessary for targeting to focal adhesions. In contrast, a vinculin polypeptide expressed from a cDNA encoding residues 398-1000 failed to localise to focal adhesions in stably transfected NIH3T3 cells. We have therefore identified a region of 50 amino acids (residues 979-1028) within the C-terminal region of vinculin that contains both the paxillin-binding site and the focal adhesion targeting sequence. This region is highly conserved in human and chicken vinculin and is likely to be important in regulation of the assembly of focal adhesions.
Rearrangement of mRNAs for costamere proteins during costamere development in cultured skeletal muscle from chicken
Authors: Morris E. J. , Fulton A. B.
Published: April 2021

Mature skeletal myofibrils are surrounded by costameres, ribs of metavinculin, vinculin, intermediate filaments, and other proteins that connect the myofibril to the extracellular matrix. Costameres have recently been shown to be the sites at which the forces generated by the myofibril are transduced laterally into the extracellular matrix. We observed costameres developing in cultured skeletal muscles, grown in micromass culture from cells taken from embryonic chicken leg. We detected proteins by immunofluorescence and mRNA by in situ hybridization. Antibody and probe signals were imaged by laser scanning confocal microscopy. Antibody to vimentin protein is first detected in stripes in register with the Z line of the myofibril, at ∼day 12 after fusion; soon thereafter probe to vimentin mRNA is also detected in the same stripes. Optical sections indicate that vimentin mRNA and protein are very close, no more than 0.1 mm apart and possibly in immediate contact. Antibody to vimentin is detected in stripes only in cells that twitch spontaneously. Antibodies and probes to desmin and vinculin protein and mRNA are next detected in stripes of the same periodicity, at ∼day 17 after fusion. Vinculin protein (but not mRNA) is detected at focal contacts much earlier in development. Controls for bleed through of fluorescence, RNase H sensitivity, hybridization without probe, and binding to the myofibril all gave appropriate results. Probes to glyceraldehyde-3-phosphate dehydrogenase, a glycolytic enzyme, stained diffusely and did not associate with the myofibril. These results show that components of the costamere arrive at the structure in a defined sequence, and that mRNA organization is a conspicuous, precise and temporally controlled aspect of costamere development.

These results may have wider implications. In these cells, some mRNAs are positioned with submicrometer precision in space and differentially over time. Particular mRNAs differ in the time and place of such positioning. This implies both that cellular structures provide physical cues for such positioning and that mRNA contains information that interacts with such cues in a message-specific manner. If such precision in mRNA location is found in other somatic cells, it could have significant implications for the ways in which cells generate and maintain cellular structures.
Dictyostelium prespore-specific gene Dp87 encodes a sorus matrix protein
Authors: Nakao Hajime , Yamamoto Akitugu , Takeuchi Ikuo , Tasaka Masao
Published: April 2021

In this paper we report on the characteristics of the product of a prespore-specific gene (Dp87) of Dictyostelium discoideum. Polyclonal antibody was made against a bacterially synthesized Dp87-encoded protein fragment. Using this antibody, the product was characterized by immunochemical and immunocytological methods. It was shown that the Dp87-encoded protein is a prespore-specific protein with a molecular mass of 83 kDa, which first appears at the standing slug stage and persists in mature fruiting bodies. Western blot studies revealed the presence of an additional 81 kDa protein prior to the appearance of the 83 kDa protein from the tipped aggregate to the standing slug stage, thus indicating the former to be a precursor protein. Immunocytochemical and immunoelectron microscopic studies showed that the protein is bound to ER at the early stages of development when only the 81 kDa protein is present. At the later stages when the 83 kDa protein predominates, however, it becomes localized in prespore-specific vacuoles (PSVs) and is associated with the inner fibrous material of PSVs, but not with the peripheral membranous material. This is in contrast to spore coat proteins, which are localized in PSVs from the beginning of their appearance and associated with both structures of PSVs. In mature fruiting bodies, most Dp87 protein is localized to the interspore space (matrix) of the sori, with some left on the surface of the stalk tube. Disruptants of the Dp87 gene were also produced. Although they contained neither 81 kDa nor 83 kDa protein, they showed no phenotypic defects as compared to the parental strain.
A 50 kDa protein present in conditioned medium of COLO-16 cells stimulates cell spreading and motility, and activates tyrosine phosphorylation of Neu/HER-2, in human SK-BR-3 mammary cancer cells
Authors: Corte Veerle De , Potter Christian De , Vandenberghe Dirk , Laerebeke Nicolas Van , Azam Mohamad , Roels Hendrik , Mareel Marc , Vandekerckhove Joël
Published: April 2021

A factor present in conditioned medium of COLO-16 human cancer cells causes fast spreading, fast plasma membrane ruffling, cell shape change, net translocation, stimulation of chemotaxis and growth arrest in human SK-BR-3 mammary cancer cells. Based on the spreading effect, the factor was purified to homogeneity and migrated as a 50 kDa protein in SDS-polyacrylamide gel electrophoresis. Addition of the purified 50 kDa factor to the target cells in culture results in tyrosine phosphorylation of the p185erbB2 receptor concomitant with a fast redistribution and clustering of the receptor. The 50 kDa factor is also specifically retained by affinity chromatog-raphy on the immobilized extracellular domain of p185erbB2. Antibodies directed against this domain also inhibit the induction of motility. These data suggest that the 50 kDa factor is a putative ligand of p185erbB2 in SK-BR-3 cells. Biochemical and immunological evidence further indicate that this factor differs from p185erbB2 ligands described so far. Its activity could play a role in the pathogenesis of breast cancer.
The spatial localization of 18 S rRNA genes, in relation to the descent of the cells, in the root cortex of Petunia hybrida
Authors: Montijn M. B. , Houtsmuller A. B. , Nanninga J. L. Oud and N.
Published: April 2021

The 3-D localization of transcription inactive 18 S rRNA genes was studied in interphase nuclei of Petunia hybrida root tip cells. To enable a cell type (i.e. cortex)-specific study in which also the orientation and descent of the cells could be taken into account, a method was developed to preserve the spatial organization of the root meristem. The ribosomal genes were detected by fluorescence in situ hybridization using a biotinylated cDNA probe. 3-D images of 81 nuclei, obtained by confocal scanning laser microscopy, were processed with newly developed computer software. 3-D nucleolar and nuclear dimensions, and the localization of the FISH-spots, were recorded interactively. We compared the absolute and relative position of the genes within and between files of cells of the cortex region of several roots, taking into account the genealogical relationship of the cells. Statistical analysis showed that both the relative and absolute positions of the inactive genes were random, also in more closely related cells within a file of cells. A ‘relict telophase orientation’ of the genes (i.e. the position of the genes in the daughter cells are mirror images of each other) could only be observed in the G0/1 phase of ‘true’ daughter cells; the orientation was not preserved throughout the next cell cycle.
Targeting of chimeric Gαi proteins to specific membrane domains
Authors: Almeida J. Bruno de , Holtzman Eliezer J. , Peters Philip , Ercolani Louis , Ausiello Dennis A. , Stow Jennifer L.
Published: April 2021

Heterotrimeric guanine nucleotide-regulatory (G) proteins are associated with a variety of intracellular membranes and specific plasma membrane domains. In polarized epithelial LLC-PK1 cells we have shown previously that endogenous Gαi-2 is localized on the basolateral plasma membrane, whereas Gαi-3 is localized on Golgi membranes. The targeting of these highly homologous Gαi proteins to distinct membrane domains was studied by the transfection and expression of chimeric Gαi proteins in LLC-PK1 cells. Chimeric cDNAs were constructed from the cDNAs for Gαi-3 and Gαi-2 and introduced into a pMXX eukaryotic expression vector containing a mouse metallothionein-I promotor. Stably transfected cell lines were produced that expressed either Gαi-2/3 or Gαi-3/2 chimeric proteins. Chimeric and endogenous Gαi proteins were detected in cells using specific carboxy-terminal peptide antibodies. Immunofluorescence staining was used to localize en-dogenous and chimeric Gαi proteins in LLC-PK1 cells. The staining of chimeric proteins was detected as an increased intensity of staining on membranes containing endogenous Gαi proteins. Using confocal microscopy and image analysis we localized Gαi-2 to a specific sub-domain of the lateral membrane of polarized cells, the chimeric Gαi-3/2 protein was then shown to colocalize with endognenous Gαi-2 in the same lateral plasma membrane domain. The chimeric Gαi-2/3 protein colocalized with endogenous Gαi-3 on Golgi membranes in LLC-PK1 cells. These results show that chimeric Gαi proteins were targeted to the same membrane domains as endogenous Gαi proteins and the specificity of their membrane targeting was conferred by the carboxy-terminal end of the proteins. These data provide the first evidence for specific targeting information contained in the carboxy termini of Gαi proteins, which appears to be independent of amino-terminal membrane attachment sites in these proteins.