Biomedical subjects

H Maisel

Publications and source records attributed to H Maisel.

At least 37 records · Page 2Linked to original sources

PubMed1995

The predicted structure of chick lens CP49 and a variant thereof, CP49ins, the first vertebrate cytoplasmic intermediate filament protein with a lamin-like insertion in helix 1B.

The full length cDNA sequence for the lens-specific intermediate filament protein, CP49, from chicken is presented. The sequence contains features typical of the other intermediate filament proteins, including two major alpha-helical regions, helix I and II and appropriate linker regions. CP49 lacks a C-terminal non-alpha-helical domain and is only the second intermediate filament protein to be described missing this feature. Comparison to the bovine CP49 shows significant homology in all domains except the N-terminal non-alpha-helical domain. Besides bovine CP49, the other protein most homologous to chicken CP49 in the database was keratin 18, a type I keratin. A variant of CP49 is also described, called CP49ins. Of the 61 positive clones identified in the library, two encoded CP49ins, one of these being a full-length clone. The sequence differed to CP49 by the insertion of 49 amino acids in helix IB. This is the first chordate cytoplasmic intermediate filament protein sequence to be identified with an archetypal lamin-like insertion in this helical subdomain and represents a key discovery in tracing the evolutionary pathway of intermediate filament protein family.

Amino Acid Sequence↗

PubMed1993

NCAM of the mammalian lens.

NCAM is present in the plasma membranes of human and rat lens epithelial cells and superficial fiber cells. The predominant isoform in epithelial cells is NCAM 140, while NCAM 120 appears only in the superficial fiber cells. The immunofluorescence patterns are consistent with a decreasing concentration of NCAM associated with fiber cell differentiation.

Animals↗

PubMed1993

Evidence that the chick lens cytoskeletal protein CP 49 belongs to the family of intermediate filament proteins.

A partial cDNA sequence for chick lens beaded-filament protein CP 49 showed the greatest similarity to the sequence of acidic cytokeratins, especially human cytokeratin 18. The predicted amino acid sequence of chick CP 49 corresponded to the entire coil 1a region of the rod domain of human cytokeratin 18, spacer 1, coil 1b, spacer 2 and about half of coil 2. For this sequence of 242 amino acids, there was an overall 38% identity and 76.8% similarity between the chick CP 49 and human cytokeratin 18. This is further evidence that CP 49 belongs to the family of intermediate filament proteins.

Amino Acid Sequence↗

PubMed1992

Adhesion and junction molecules in embryonic and adult lens cell differentiation.

The expression of the neural cell adhesion molecule NCAM and its polysialic acid (PSA) moiety was documented during embryonic development and adult differentiation of chicken lens cells. In both the embryo and adult, NCAM is predominantly found in the epithelium and the zone of young elongating cells of the annular pad. NCAM abundance drops markedly in the cortical fibers and is further reduced in the lens nucleus. Epithelial cell NCAM is more highly poly-sialylated in the adult than in the embryonic lens. Three isoforms of NCAM at 180, 140, and 120 kDa were detected in the lens and predominantly associated with the unit membrane-enriched plasma membranes of fiber cells. The distribution of NCAM relative to MP26 and the adherence junction-associated glycoprotein N-cadherin suggests that NCAM could influence the formation of fiber cell gap junctions and adherence junctions.

Animals↗

PubMed1992

Functional characterization of insulin and IGF-I receptors in chicken lens epithelial and fiber cells.

Insulin and insulin-like growth factor I (IGF-I) play a role in lens cell growth and development. The binding of these hormones to their respective receptors with its concomitant signal transduction is an important step in these cellular processes. Hormone binding to adult chicken lens insulin and IGF-I receptors, partially purified from epithelial and fiber cells, was studied to examine this activity in lens. The associated stimulation of receptor-mediated tyrosine kinase by the hormones was also studied. At an insulin concentration of 0.02 nM, specific binding was similar for epithelial and fiber receptor preparations (Epi = 0.23 +/- 0.03 fmol, Fib = 0.19 +/- 0.02 fmol). Displacement studies revealed that there was also no difference between epithelial and fiber receptor preparations in the concentration of insulin necessary for half maximal displacement of specific [125I]-insulin binding (IC50: Epi = 0.32 nM +/- 0.07 nM, Fib = 0.31 nM +/- 0.05 nM). Comparison of IGF-I (0.02 nM) binding to receptor preparations from epithelial and fiber cells demonstrated that specific binding was similar in the two preparations (Epi = 0.50 +/- 0.05 fmol, Fib = 0.42 +/- 0.05 fmol). Also, there was no difference in the concentration of IGF-I necessary for half maximal displacement of specific [125I]-IGF-I binding (IC50 = Epi: 0.27 +/- 0.05 nM, Fib: 0.28 +/- 0.04 nM). The ability of IGF-I to displace bound [125I]-insulin was also examined. The IC50 for IGF-I binding to the insulin receptors isolated from epithelial and fiber cells was 37.4 +/- 2.4 nM, and 35.4 +/- 2.8 nM, respectively.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗

PubMed1991

Reconstitution of the filamentous backbone of lens beaded-chain filaments from a purified 49kD polypeptide.

The beaded-chain filaments unique to the fiber cells of the crystalline lens are composed of a linear array of spheroidal particles which appear to be connected by a filamentous backbone. In order to determine the existence of the putative backbone and to characterize its constituents, one of the major proteins associated with beaded-chains in the chicken lens was investigated. 49kD was isolated in an enriched fraction derived from the 8M urea extract of the lens cell water-insoluble residue. The polypeptide (which exists in several charge isoforms, the major at pI 5.2) was purified sequentially by gel filtration on Sephacryl S-200, hydrophobic interaction chromatography on phenyl-Sepharose, and anionic exchange chromatography on Mono Q, all under denaturing conditions. Immunoblot analyses established that 49kD was immunologically distinct from vimentin, actin, and tubulin/MAPs (representing the three classes of cytoplasmic filaments), as well as from the crystallins. Amino acid analyses demonstrated compositional differences for 49kD compared with lens actin and vimentin, and one- and two-dimensional peptide mapping of 49kD and vimentin revealed no homology. Electron microscopy demonstrated that short, contorted filaments were produced upon removal of purified 49kD from urea to low-salt buffers. In the presence of physiological salt concentrations 49kD assembled into extensive 4-6nm diameter, straight filaments similar to the backbone seen in native beaded-chain filaments, but morphologically distinct from the other cytoplasmic filament classes.

Amino Acids↗

PubMed1990

N-cadherin detected in the membrane fraction of lens fiber cells.

N-cadherin was identified as a glycoprotein present in the fiber cell membranes of frog, chick, bovine, rabbit and human lenses. The molecular size of N-cadherin varies with the species. Homogenization of the chick lens in the presence of Ca2+ resulted in a decrease in the concentration of N-cadherin. This suggests that the lens contains a Ca2(+)-activated protease which can act on N-cadherin.

Animals↗

PubMed1990

Ankyrin of the ocular lens.

Ankyrin was identified in the human, bovine and chicken lens as a protein of molecular weight 216 kilodaltons. It is specifically extracted from association with the fiber cell plasma membranes by high-ionic-strength salt solution and is predominantly found in young fiber cells. A protein which is unrelated to plakoglobin, protein 4.1 or ankyrin is also specifically extracted by high-salt solution.

Animals↗

PubMed1990

Enolase in the avian and turtle lens.

Enolase is a dimeric enzyme of molecular weight of 100,000 daltons, which plays an important role in the glycolytic cycle. The aim of this study was to characterize the enzyme of the chicken lens epithelium and to compare its distribution in different regions of the chicken, duck and turtle lens. Enolase of the chicken lens epithelium was found to be an enzymatically active dimeric protein of molecular weight 100,000 daltons and representing alpha-enolase. It is a major component of the epithelium comprising 4%, 12% and 46% of the water-soluble protein of chicken, duck and turtle epithelium respectively. Enolase is found in trace amount in the fiber cells of the chicken and duck, but is retained in much greater concentration in the turtle fiber mass as a predominantly inactive enzyme.

Animals↗

PubMed1989

In vitro translation of cytoskeletal beaded-chain filament proteins from chicken lens mRNA.

The beaded-chain filament is a unique cytoskeletal structure that appears in the elongating fiber cells during the differentiation of lens epithelial cells to form the mature fiber cells. This beaded-chain structure is made up of two proteins of molecular weight 95 kDa and 49 kDa. As a prerequisite for cloning the cDNAs of these proteins, newborn chicken lens total poly(A+) mRNA was translated in vitro, using a rabbit reticulocyte lysate system and [35S]-L-methionine. The labelled translation products were analyzed by one-and two dimensional gel electrophoresis followed by autoradiography. Immunoprobing of the translation products on Western blots using specific polyclonal antibodies identified the above proteins, and demonstrated the presence and expression of specific mRNAs in the neonatal chick lens, that code for the in vitro synthesis of these two cytoskeletal proteins. These mRNAs are low abundant mRNAs as compared to the crystallin mRNAs.

Amino Acid Sequence↗

PubMed1989

NCAM in the differentiation of embryonic lens tissue.

The role of the neural cell adhesion molecule (NCAM)2 in ocular lens differentiation was investigated in chicken embryos. Changes in expression of NCAM were documented by immunohistology of frozen sections. This analysis revealed that NCAM diminished during lens fiber differentiation, in contrast to the gap junction-associated protein MP26 which became more abundant. The form of NCAM expressed was determined by Western blot analysis of proteins extracted from the different regions of the Embryonic Day 6 lenses. All regions expressed NCAM with an apparent molecular weight of 140 kDa and relatively low levels of polysialylation. The function of NCAM in lens differentiation was investigated using antibodies that inhibit NCAM-mediated adhesion. Two parameters that change during maturation of the lens epithelial cells were monitored: the thickness of the tissue, indicating the length of lens cells, and the particle arrangement of gap junctions, reflecting the state of junctional differentiation. When epithelial cell explants of Embryonic Day 6 lenses were cultured for 5 days, the cells elongated and displayed an increase in the loose, random intramembranous particle arrangements characteristic of maturing lens fiber gap junctions. When the explants were cultured in the presence of anti-NCAM Fabs, the epithelia were thinner than in matched controls and had particle arrangements characteristic of a less mature state. The expression of NCAM during lens differentiation and the effects of attenuating NCAM function suggest that adhesion mediated by NCAM is an essential event in lens cell differentiation.

Animals↗

PubMed1989

A family of lens fiber cell specific proteins.

A family of related polypeptides of molecular weights 97 kd, 93 kd, 64 kd, 62 kd, 51 kd and 49 kd is unique to chick lens fiber cells, and is not found in the epithelial cells. Cross-reacting proteins were also detected in bovine and human lenses. This family of membrane-associated proteins is cytoskeletal in nature and localized to the beaded-chain filaments.

Animals↗

PubMed1989

N-cadherin of the human lens.

N-cadherin was identified in the human lens by its immunological specificity, and concanavalin-A (Con-A) binding. The 135 kd glycoprotein was partially purified from human lens plasma membranes by Con-A affinity column chromatography. In the newborn lens, N-cadherin is distributed equally in amount between cortical and nuclear membranes. It is markedly decreased in the nuclear membranes of the 2 year-old lens and was no longer detectable in the nucleus of 15 yr-old and older lenses (15 yrs - 86 yrs). Such nuclear loss of N-cadherin is consistent with similar findings in the chicken and bovine lens. At all ages, N-cadherin was readily detected in cortical fiber-cells. When expressed as a ratio to MP26 content, the amount of N-cadherin of the total fiber mass declines at least 4-fold from newborn to 15 years of age, and remains stable thereafter. Homogenization of bovine lenses in the presence of Ca++ resulted in a marked loss of the protein, suggestive of degradation by a calcium-activated protease. The loss of N-cadherin with aging in fiber cells suggests either an alteration in the mode of membrane adhesion of these cells, or a decline in adhesiveness of nuclear as compared to cortical fiber-cells.

Adolescent↗

PubMed1988

Human beta crystallins: regional and age related changes.

The composition of human beta-crystallins displayed specific changes with age and region of the lens. 27 kD and 29 kD human beta-crystallin subunits were singled out for study. The 29 kD beta-crystallin subunit constituted approximately 10% of the total lens crystallins at 8 months of fetal life. Its accumulation decreased steadily to 3.3% during postnatal year 1, to 0.5% by year 5 and to 0.3% thereafter. At all postnatal ages, however, it persisted mainly in the superficial fibers. Thus in a 17-years old lens it made up 1.3% of the superficial fiber soluble protein but was already absent from deep cortical and nuclear fibers. The 27 kD subunit increased steadily from 3.5% at 8 months fetal to 7% at year 5; it then decreased steadily to 1.2% in the 86-year old lens. It persisted in all regions of the lens but decreased markedly in the deep cortical and nuclear fibers with increasing age beginning at 5-17 years of age. Studies on the oligomeric structure of human beta-crystallin must take into account age-related changing quantitative patterns in the subunit polypeptide composition of this lens protein.

Adolescent↗

PubMed1988

Isoproterenol treatment causes cytoskeletal reorganization in chicken lens fiber cells.

Cytoskeletal organization in organ cultured embryonic chicken lens was affected by isoproterenol treatment. Immunofluorescent localization of a 49 kD fiber cell-specific cytoskeletal protein showed a cytoplasmic and membrane localization in control lenses. Following isoproterenol treatment, fluorescence was predominantly membrane-associated. Changes in 49 kD distribution as determined by immunofluorescence occurred within minutes of isoproterenol application and were completely blocked by propranolol pretreatment. These results suggest that beta-adrenergic stimulation influences the apparent localization of a fiber cell-specific cytoskeletal protein.

Animals↗

PubMed1987

Band 3 and ankyrin homologues are present in eye lens: evidence for all major erythrocyte membrane components in same non-erythroid cell.

Although immunological homologues of erythrocyte membrane proteins have been individually discovered in a wide variety of tissues and cultured cells, the major structural components of the membrane have not yet been demonstrated simultaneously in the same cell type. Thus, considerable uncertainty continues to exist concerning whether the red cell homologues form elements of a structure which is similar to or unique from the framework which supports the erythrocyte membrane. Because the red cell cytoskeletal proteins, spectrin, actin and band 4.1, have been previously found in the superficial cortex of the lens, we decided to determine whether the corresponding membrane anchoring components of band 3 and ankyrin also occur in this cell type. Using antiserum specific for band 3 and ankyrin, we report the existence of immunologically cross-reactive proteins of similar molecular weight. Because these anchoring proteins appear and disappear coordinately with the aforementioned cytoskeletal proteins during the intermediate stages of lens cell maturation, it is conceivable that an erythrocyte-like membrane structural organization may occur transiently in the eye lens.

Anion Exchange Protein 1, Erythrocyte↗

PubMed1987

Structural studies of lens fiber junction protein MP26 by cyanogen bromide cleavage.

The lens fiber-cell plasma membrane MP26 from chick, bovine, and human lenses yielded identical cyanogen bromide peptide maps, confirming the essential conservation of structure in the junction protein of vertebrate lens fiber cells. Immunoblot analyses of the cyanogen bromide peptide maps of human lens MP26 and of its age-dependent proteolytic product MP22 confirmed that MP22 is a derivative of MP26. The findings in this study are the first consistent with the positioning of the methionine residues in lens MP26 as predicted by its cDNA-derived sequence.

Animals↗

PubMed1987

Limited proteolysis of gap junction protein is intrinsic in mammalian lens fiber-cell plasma membranes.

We demonstrate that the limited proteolysis of the lens fiber-cell gap junction protein, MP26, is intrinsic in mammalian lens fiber plasma membranes. Incubations of isolated intact bovine lens fiber plasma membranes in buffer alone did not elicit proteolysis of MP26. Incubations in the buffer with detergent, however, resulted in the limited proteolysis of MP26 which was totally inhibited by calcium chelators, thiol-alkylating agents, and protease inhibitors. As the limited proteolysis required the presence of detergent, it must depend on an enzymatic activity intrinsic in the lens fiber plasma membranes or in MP26 itself.

Animals↗