PubMed Health⌕ Search

Biomedical subjects

J Alcala

Publications and source records attributed to J Alcala.

17 recordsLinked to original sources
PubMed1996

Developmental changes in glycoconjugate composition during chick lens morphogenesis.

The following lectins: Con A, WGA, sWGA, PNA, RCA and UEA were used to study developmental changes in the expression of glycoconjugates during chicken lens morphogenesis. Con A, WGA, sWGA binding epitopes were observed in the lens placode and vesicle. Once the fiber mass was formed, the glycoconjugates were mainly found at the epithelial-fiber-cell junction, on epithelial cell membranes but only weakly on fiber-cell membranes. The PNA reaction was restricted to the apical surface of cells of the lens placode and vesicle and to the epithelial-fiber junction throughout the rest of lens development. The RCA reaction was mainly localized to the apical plasma membrane and moderately at the lateral plasma membrane of cells of the lens placode and vesicle and maintained this staining pattern in the lens epithelial cell during the progressive development of lens. UEA binding was initially localized along the posterior elongating cells of the lens vesicle, and then expressed in both epithelial and fiber cells. Subsequently UEA binding was restricted to the epithelium and central fiber mass. The extensive distribution of glycoconjugates on the surface of the invaginating placode cells suggests a role during invagination and subsequent detachment of the placode from the surface ectoderm. The capsule was labelled by Con A, WGA, sWGA, RCA and PNA but not by UEA. The posterior capsule was more intensely reactive with Con A, RCA and PNA than the anterior capsule.

Animals↗
PubMed1995

Pyoderma gangrenosum associated with acne conglobata.

We report a 16-year-old male in whom pyoderma gangrenosum appeared in conjunction with acne conglobata. The patient also developed a seronegative spondyloarthropathy that was the main presenting complaint. There was no evidence of inflammatory bowel disease. Treatment with isotretinoin was successful. Both acne and pyoderma lesions healed and the articular symptoms improved. The present case, together with other reports in the literature show that acne conglobata must be included in the list of possible associations of pyoderma gangrenosum. We also comment on acne arthritis, a relatively frequent phenomenon, although still not generally known, in acne conglobata.

Acne Vulgaris↗
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↗
PubMed1990

Reversal of the limited proteolysis of MP26 during the reversal and prevention of the galactose cataract in rat lenses.

The reversal and prevention of the galactose-induced cataract in rats were employed to study their effects on the acceleration of the limited proteolysis of MP26 into MP23-24 previously observed in cataractous lenses of galactose-fed animals. Lenses of rats on a cataract reversal-diet demonstrated the reversal of MP23-24 and MP26 levels to control levels in the clearing cortical areas but not in remaining cataractous nuclear areas. Acceleration of the limited proteolysis of MP26 was observed in the nucleus but not the cortex in the clear lenses of animals on a cataract prevention-diet. The results demonstrated that the limited proteolysis of MP26 may form part of a gradual aging process that although not directly (causally) related to cataractogenesis may at least be accelerated by cataractogenic agents or conditions.

Aging↗
PubMed1989

Validation of a role-play measure of children's social skills.

A videotape-administered role-play test of children's social skills was developed and its psychometric properties tested. Performance criteria for the test were derived from popular children's ratings of the effectiveness of different role-play responses. The test was administered to 157 fourth- and fifth-grade boys and girls who had been classified as popular, average, neglected, or rejected, on the basis of sociometric testing. The test evidenced good interrater, test-retest, and internal consistency reliabilities. Children's role-play performance correlated significantly with teacher ratings of social competence and with peer-liking ratings. Neglected children performed more poorly on the role-play test than popular children. When differences in intelligence among social status groups were statistically controlled, social status groups did not differ on the role-play test. Results of the discriminant analyses support the conclusion that teacher ratings are better than role-play tests for identifying rejected children, whereas role-play tests and measures of intelligence appear more accurate than teacher ratings for identifying neglected children.

Child↗
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

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↗
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↗
PubMed1986

Limited proteolysis of MP26 in lens fiber plasma membranes of the galactose-induced cataract in the rat.

Lenses of rats maintained on a 50% galactose diet displayed the development of a progressive cataract which was cortical at 3-11 days, and progressively internalized (nuclear as well) and mature at 16-20 days of feeding. Lens fiber plasma membranes were isolated from female rats subjected to the galactose diet and from controls at 11, 19, and 31 days of feeding, and analyzed by SDS-PAGE. Examination of the fiber plasma membranes from whole lenses of galactose-fed rats demonstrated the limited proteolysis of MP26 into MP23-24, in both the cortical and mature stages of the resultant cataracts. The limited proteolysis of MP26 was first evident in the lens cortex at 11 days of galactose feeding, and was evident as well, and more severe in proportion, in the lens nucleus at 19 days of feeding. The greatest proportion in MP26 limited proteolysis was observed in whole lenses at 31 days of galactose feeding. The regional progression of MP26 limited proteolysis closely paralleled the morphological progression of the galactose-induced cataract in the rat. The proportion of lens MP26 which underwent limited proteolysis into MP23-24 increased the longer the animals were kept on the galactose diet.

Animals↗
PubMed1985

Limited proteolysis of MP26 in lens fiber plasma membranes of the U18666A-induced cataract in rats.

Most of the animals treated with U18666A every other day beginning at one-day of age developed permanent nuclear cataracts by 3-4 weeks of age. Lens fiber plasma membranes were isolated from cortical and nuclear areas of untreated controls, treated but clear, and treated cataractous lenses, and analyzed by SDS-PAGE. MP26 was the major intrinsic polypeptide in the plasma membranes of both cortical and nuclear fibers of control lenses. MP26 was largely replaced by MP23-24 in the plasma membranes of nuclear fibers of treated but clear lenses, and in the membranes of both cortical and nuclear fibers of cataractous lenses.

Androstenes↗
PubMed1982

Calmodulin binds to chick lens gap junction protein in a calcium-independent manner.

A biochemically active conjugate of calmodulin and tetramethylrhodamine isothiocyanate (CaM-RITC) was synthesized. When incubated with sections of chick lens, this conjugate bound to the surface membranes of lens fiber cells in the presence of absence of calcium. Incubation of lens sections with antibodies to gap junction protein of lens completely blocked the binding of the conjugate to cell membranes, whereas serum from nonimmunized animals or antibodies to others lens proteins reduced the binding only slightly. By means of a gel overlay procedure, 125I-labeled calmodulin was found to bind to the gap junction protein of lens, also in a calcium-independent manner. These results support the concept that calmodulin may interact with and regulate gap junctions in living cells.

Animals↗
PubMed1980

The surface morphology of embryonic and adult chick lens-fiber cells.

The surface morphology of lens fibers in embryonic and adult chicken lenses has been studied by scanning electron microscopy. As the elongating epithelial cells enter into a state of terminal differentiation they elaborate a number of cellular processes interconnecting neighboring fibers. The interlocking devices take the shapes of balls on a short stalk, tonguelike flaps, and fingerlike processes that fit into complementarily shaped sockets, imprints, and fingerprints, respectively, of adjoining fibers. Gap junctions comprising more than 50% of the fiber-cell membrane may serve as ultrastructural interlocking devices. The interlocking devices and gap junctions are probably necessary to maintain fiber order--a critical requirement for lens transparency. With increase maturation, the uniform morphology of the fibers and their interlocking devices is lost. The highly repetitive ordered alignment of young uniformly shaped fiber cells acts to minimize large-particle scatter. The results of this study show a progressive loss of uniform shape and order in chicken fibers of advanced maturity. This phenomenon of lens development may be the basis for the increase in light scattering seen in aged lenses of other species such as man.

Animals↗
PubMedDate not supplied

Lipid composition of chick lens fiber cell gap junctions.

Chick lens fiber cell gap junctions were isolated to homogeneity by the urea-deoxycholate method, characterized ultrastructurally and biochemically, and their lipid composition determined by quantitative thin layer chromatography (TLC). The junctions were estimated to comprise about 52% of the lens fiber plasma membrane. Unlike the junctions of other organs, the lens gap junctions were found to contain sphingomyelin. The cholesterol/phospholipid molar ratio was 2.1 for total fiber membranes but 3.1 for the fiber gap junctions. The levels of major phospholipids in decreasing order were SPH, PC, PE, PI for fiber junctions and PE, SPH, PC, PI for total fiber membranes. The gap junctions were found to contain about 57% of the total fiber cholesterol and 53% of the total fiber sphingomyelin. The high cholesterol and sphingomyelin content suggests that lens fiber gap junctions constitute highly rigid membrane regions conferring significant constraints to the movement of their intramembrane particles (connexons) in the plane of the membrane. The findings help to explain the resistance to the crystallization of their connexons, observed so far only in lens gap junctions.

Animals↗