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Biomedical subjects

H Maisel

Publications and source records attributed to H Maisel.

At least 19 recordsLinked to original sources
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↗
PubMed1979

Age changes in the skeleton of the human lens.

The cytoskeleton of the human lens (newborn, 24 year-old and 80 year-old) was studied by morphological methods. Actin and intermediate (10 nm) filaments were identified in the epithelial cells of all the lenses. In the newborn lens intermediate filaments and chains of protein were found in cortical and nuclear fiber cells. Many intermediate filaments and protein chains in the elongated form were observed in the superficial cortical fiber cells of the 24 year-old lens. However, in the deep cortical cells the number of intermediate filaments decreased and the protein chains became more coiled and aggregated. In the nuclear region the protein chains were markedly aggregated and intermediate filaments were absent. The 80 year-old fiber cells contained only protein aggregates in the fiber cells. While the size of the chain backbone corresponds to actin, the conclusive demonstration that it is actin remains to be shown.

Actins↗
PubMed1979

The plasma membrane of the rabbit lens cortical fiber. I. Isolation, characterization, and biosynthesis of two membrane intrinsic polypeptides.

Rabbit lens cortical fiber plasma membrane polypeptides were isolated and two membrane intrinsic proteins were characterized by SDS-PAGE. A polypeptide with a molecular weight of 26 kilodaltons is the major constituent of the plasma membrane. The molecular weight and antigenic properties of the other polypeptide studied are similar to polypeptides of cortical water-soluble alpha-crystalline. Biosynthesis of these two polypeptides was studied. After initially high rates, synthesis of both of these polypeptides decreased considerably and maintained a steady rate for the rest of the culture time.

Animals↗
PubMed1978

Chain-proteins of the vertebrate lens.

Some lens proteins exist in a chain-like form in the vertebrate lens fibre cells. They consist of globular proteins arranged on a filamentous backbone.

Animals↗