The distribution of the fiber cell intrinsic membrane proteins MP20 and connexin46 in the bovine lens

1992 ◽  
Vol 103 (1) ◽  
pp. 245-257 ◽  
Author(s):  
E. Tenbroek ◽  
M. Arneson ◽  
L. Jarvis ◽  
C. Louis
Keyword(s):  
Monoclonal Antibody ◽  
Fiber Cell ◽  
Immunogold Electron Microscopy ◽  
Lens Fiber ◽  
Lens Fiber Cell ◽  
Western Blots ◽  
Fiber Cells ◽  
Bovine Lens ◽  
Narrow Side ◽  
Lens Membranes

MP20 is an intrinsic membrane protein previously identified in mammalian lens fiber cells. To identify a possible role for this protein in the lens, the distribution of MP20 and connexin46 has now been examined. Western immunoblotting with an anti-peptide antibody generated to the C-terminal 8 amino acids of MP20 confirmed the presence of this protein in the lens of several different mammalian species. A monoclonal antibody 5H1 was prepared that, in Western blots of bovine lesn membranes, recognized the same component as an antibody to rat connexin46 (Cx46). The apparent molecular mass of this component decreased from 59 kDa to 55 kDa following treatment of lens membranes with alkaline phosphatase. A monoclonal antibody to connexin-related MP70 recognized a 70 kDa component in bovine lens membranes confirming the presence of these two different connexin proteins in bovine lens membranes. To localize MP20 and Cx46 in the bovine lens membrane, lens fiber cell bundles were immunofluorescently labeled with both the MP20 antibody, and the monoclonal antibody to Cx46. Cx46 was identified in large plaques on the broad faces of the lens fiber cells throughout the outer 1 mm of the lens cortex. MP20 colocalized with Cx46 only in a restricted area 0.5 mm to 1.0 mm into the lens. In other regions of the lens, MP20 appeared more diffusely distributed over the fiber cell surface, although apparently concentrated in the ball-and-socket regions at the corners of the narrow side of the inner cortical lens fiber cells. These inner cortical regions were devoid of Cx46. A difference in distribution of these two proteins was confirmed in studies of immunofluorescently labeled lens cryosections. Furthermore, immunogold electron microscopy of purified lens membranes identified MP20 in both junctional regions (with Cx46) and in single membranes. These results provide evidence for a role for MP20 in mammalian lens fiber cell junctional formation or organization.

Chicken filensin: a lens fiber cell protein that exhibits sequence similarity to intermediate filament proteins

1993 ◽  
Vol 105 (4) ◽  
pp. 1057-1068 ◽  
Author(s):  
S.G. Remington
Keyword(s):  
Amino Acid ◽  
Intermediate Filament ◽  
Fiber Cell ◽  
Heptad Repeat ◽  
Lens Fiber ◽  
Lens Fiber Cell ◽  
Intermediate Filament Proteins ◽  
Fiber Cells ◽  
Amino Terminal ◽  
Sequence Identity

Filensin, a 100 kDa, membrane-associated, cytoskeletal protein, is uniquely expressed in the lens fiber cell (Merdes, A., Brunkener, M., Horstmann, H., and Georgatos, S. D. (1991) J. Cell Biol. 115, 397–410). I cloned and sequenced a full-length chicken lens cDNA encoding filensin, also known as CP95 (Ireland, M. and Maisel, H. (1989) Lens and Eye Toxicity Research 6, 623–638). The deduced amino acid sequence of 657 residues contained an internal 280 residue heptad repeat domain with sequence similarities to the rod domain of intermediate filament proteins. The putative filensin rod domain could be divided into three alpha-helical segments (1A, 1B and 2) separated by short, non-helical linkers. The sequence of the amino-terminal end of the filensin rod domain contained the highly conserved intermediate filament segment 1A motif (Conway, J. F. and Parry, D. A. D. (1988) Int. J. Biol. Macromol. 10, 79–98). Allowing conservative amino acid substitutions, the sequence of the carboxy-terminal end of the filensin rod domain was similar to that of the highly conserved intermediate filament rod carboxy terminus. The alpha-helical segments of the shorter filensin rod domain aligned with the corresponding segments of intermediate filament proteins by allowing a gap of four heptad repeats in the amino-terminal half of filensin segment 2. Filensin rod segment 2 contained the characteristic stutter in heptad repeat phasing, nine heptads from the end of the intermediate filament rod. The overall sequence identity between the rod domains of filensin and individual intermediate filament proteins was 20 to 25%, approximately the level of sequence identity observed between intermediate filament proteins of different types. The open reading frame of chicken filensin predicted a 657 amino acid protein with molecular mass of 76 kDa. Embryonic chicken filensin migrated in SDS-PAGE as a triplet of 102, 105 and 109 kDa, while rooster filensin migrated as a 105 and 109 kDa doublet. Antibodies to filensin labeled lens fiber cells but not lens epithelial cells. By immunofluorescence methods filensin was localized to the fiber cell plasma membranes, including the ends of elongated fiber cells.

scholarly journals Ankyrin-B directs membrane tethering of periaxin and is required for maintenance of lens fiber cell hexagonal shape and mechanics

2016 ◽  
Vol 310 (2) ◽  
pp. C115-C126 ◽  
Author(s):  
Rupalatha Maddala ◽  
Mark Walters ◽  
Peter J. Brophy ◽  
Vann Bennett ◽  
Ponugoti V. Rao
Keyword(s):  
Pdz Domain ◽  
Adaptor Protein ◽  
Membrane Skeleton ◽  
Fiber Cell ◽  
Null Mouse ◽  
Lens Fiber ◽  
Lens Fiber Cell ◽  
Fiber Cells ◽  
Lens Fibers ◽  
Ankyrin B

Periaxin (Prx), a PDZ domain protein expressed preferentially in myelinating Schwann cells and lens fibers, plays a key role in membrane scaffolding and cytoarchitecture. Little is known, however, about how Prx is anchored to the plasma membrane. Here we report that ankyrin-B (AnkB), a well-characterized adaptor protein involved in linking the spectrin-actin cytoskeleton to integral membrane proteins, is required for membrane association of Prx in lens fibers and colocalizes with Prx in hexagonal fiber cells. Under AnkB haploinsufficiency, Prx accumulates in the soluble fraction with a concomitant loss from the membrane-enriched fraction of mouse lenses. Moreover, AnkB haploinsufficiency induced age-dependent disruptions in fiber cell hexagonal geometry and radial alignment and decreased compressive stiffness in mouse lenses parallel to the changes observed in Prx null mouse lens. Both AnkB- and Prx-deficient mice exhibit disruptions in membrane organization of the spectrin-actin network and the dystrophin-glycoprotein complex in lens fiber cells. Taken together, these observations reveal that AnkB is required for Prx membrane anchoring and for maintenance of lens fiber cell hexagonal geometry, membrane skeleton organization, and biomechanics.

scholarly journals Lens Fiber Cell Differentiation and Denucleation Are Disrupted through Expression of the N-Terminal Nuclear Receptor Box ofNcoa6and Result in p53-dependent and p53-independent Apoptosis

2010 ◽  
Vol 21 (14) ◽  
pp. 2453-2468 ◽  
Author(s):  
Wei-Lin Wang ◽  
Qingtian Li ◽  
Jianming Xu ◽  
Aleš Cvekl
Keyword(s):  
Cell Differentiation ◽  
Nuclear Receptor ◽  
Wide Spectrum ◽  
Dominant Negative ◽  
Fiber Cell ◽  
Terminal Deoxynucleotidyl Transferase ◽  
Lens Fiber ◽  
Lens Fiber Cell ◽  
Multifunctional Protein ◽  
Fiber Cells

Nuclear receptor coactivator 6 (NCOA6) is a multifunctional protein implicated in embryonic development, cell survival, and homeostasis. An 81-amino acid fragment, dnNCOA6, containing the N-terminal nuclear receptor box (LXXLL motif) of NCOA6, acts as a dominant-negative (dn) inhibitor of NCOA6. Here, we expressed dnNCOA6 in postmitotic transgenic mouse lens fiber cells. The transgenic lenses showed reduced growth; a wide spectrum of lens fiber cell differentiation defects, including reduced expression of γ-crystallins; and cataract formation. Those lens fiber cells entered an alternate proapoptotic pathway, and the denucleation (karyolysis) process was stalled. Activation of caspase-3 at embryonic day (E)13.5 was followed by double-strand breaks (DSBs) formation monitored via a biomarker, γ-H2AX. Intense terminal deoxynucleotidyl transferase dUTP nick-end labeling (TUNEL) signals were found at E16.5. Thus, a window of ∼72 h between these events suggested prolonged though incomplete apoptosis in the lens fiber cell compartment that preserved nuclei in its cells. Genetic experiments showed that the apoptotic-like processes in the transgenic lens were both p53-dependent and p53-independent. Lens-specific deletion of Ncoa6 also resulted in disrupted lens fiber cell differentiation. Our data demonstrate a cell-autonomous role of Ncoa6 in lens fiber cell differentiation and suggest novel insights into the process of lens fiber cell denucleation and apoptosis.

scholarly journals Novel mitochondrial derived Nuclear Excisosome degrades nuclei during differentiation of prosimian Galago (bush baby) monkey lenses

PLoS ONE ◽  
2020 ◽  
Vol 15 (11) ◽  
pp. e0241631
Author(s):  
M. Joseph Costello ◽  
Kurt O. Gilliland ◽  
Ashik Mohamed ◽  
Kevin L. Schey ◽  
Sönke Johnsen ◽  
...  
Keyword(s):  
Chick Embryo ◽  
Nuclear Envelope ◽  
Mitochondrial Membrane ◽  
Fiber Cell ◽  
Outer Mitochondrial Membrane ◽  
Lens Fiber ◽  
Linear Structures ◽  
Lens Fiber Cell ◽  
Fiber Cells ◽  
Bush Baby

The unique cellular organization and transparent function of the ocular lens depend on the continuous differentiation of immature epithelial cells on the lens anterior surface into mature elongated fiber cells within the lens core. A ubiquitous event during lens differentiation is the complete elimination of organelles required for mature lens fiber cell structure and transparency. Distinct pathways have been identified to mediate the elimination of non-nuclear organelles and nuclei. Recently, we reported the discovery of a unique structure in developing fiber cells of the chick embryo lens, called the Nuclear Excisosome, that is intractably associated with degrading nuclei during lens fiber cell differentiation. In the chick lens, the Nuclear Excisosome is derived from projections of adjacent cells contacting the nuclear envelope during nuclear elimination. Here, we demonstrate that, in contrast to the avian model, Nuclear Excisosomes in a primate model, Galago (bush baby) monkeys, are derived through the recruitment of mitochondria to form unique linear assemblies that define a novel primate Nuclear Excisosome. Four lenses from three monkeys aged 2–5 years were fixed in formalin, followed by paraformaldehyde, then processed for Airyscan confocal microscopy or transmission electron microscopy. For confocal imaging, fluorescent dyes labelled membranes, carbohydrate in the extracellular space, filamentous actin and nuclei. Fiber cells from Galago lenses typically displayed prominent linear structures within the cytoplasm with a distinctive cross-section of four membranes and lengths up to 30 μm. The outer membranes of these linear structures were observed to attach to the outer nuclear envelope membrane to initiate degradation near the organelle-free zone. The origin of these unique structures was mitochondria in the equatorial epithelium (not from plasma membranes of adjacent cells as in the chick embryo model). Early changes in mitochondria appeared to be the collapse of the cristae and modification of one side of the mitochondrial outer membrane to promote accumulation of protein in a dense cluster. As a mitochondrion surrounded the dense protein cluster, an outer mitochondrial membrane enclosed the protein to form a core and another outer mitochondrial membrane formed the outermost layer. The paired membranes of irregular texture between the inner core membrane and the outer limiting membrane appeared to be derived from modified mitochondrial cristae. Several mitochondria were involved in the formation and maturation of these unique complexes that apparently migrated around the fulcrum into the cytoplasm of nascent fiber cells where they were stabilized until the nuclear degradation was initiated. Thus, unlike in the chick embryo, the Galago lenses degraded nuclear envelopes with a Nuclear Excisosome derived from multiple mitochondria in the epithelium that formed novel linear assemblies in developing fiber cells. These findings suggest that recruitment of distinct structures is required for Nuclear Excisosome formation in different species.

scholarly journals Filensin: a new vimentin-binding, polymerization-competent, and membrane-associated protein of the lens fiber cell.

1991 ◽  
Vol 115 (2) ◽  
pp. 397-410 ◽  
Author(s):  
A Merdes ◽  
M Brunkener ◽  
H Horstmann ◽  
S D Georgatos
Keyword(s):  
Limited Proteolysis ◽  
Intermediate Filament Protein ◽  
Lens Fiber ◽  
Lens Fiber Cell ◽  
Fiber Cells ◽  
Nonionic Detergent ◽  
High Concentrations ◽  
Lens Membranes ◽  
Filament Protein

We have studied the molecular properties of a 100-kD protein, termed filensin, which we have isolated from porcine lens membranes. Filensin represents a membrane-associated element, resistant to salt and nonionic detergent treatment, and extractable only by alkali or high concentrations of urea. By indirect immunofluorescence and immunoelectron microscopy, this protein can be localized at the periphery of the lens fiber cells. Immunochemical analysis suggests that filensin originates from a larger 110-kD component which is abundantly expressed in lens but not in other tissues. Purified filensin polymerizes in a salt-dependent fashion and forms irregular fibrils (integral of 10 nm in diameter) when reconstituted into buffers of physiological ionic strength and neutral pH. Radiolabeled filensin binds specifically to lens vimentin under isotonic conditions, as demonstrated by affinity chromatography and ligand-blotting assays. By the latter approach, filensin also reacts with a 47-kD peripheral membrane protein of the lens cells. Purified filensin binds to PI, a synthetic peptide modelled after a segment of the COOH-terminal domain of peripherin (a type III intermediate filament protein highly homologous to vimentin), but not to various other peptides including the NH2-terminal headpiece of vimentin and derivatives of its middle (rod) domain. The filensin-PI binding is inhibited by purified lamin B, which is known to interact in vitro with PI (Djabali, K., M.-M. Portier, F. Gros, G. Blobel, and S. D. Georgatos. 1991. Cell. 64:109-121). Finally, limited proteolysis indicates that the filensin-vimentin interaction involves a 30-kD segment of the filensin molecule. Based on these observations, we postulate that the lens fiber cells express a polymerization-competent protein which is tightly associated with the plasma membrane and has the potential to serve as an anchorage site for vimentin intermediate filaments.

Bmp signaling is required for development of primary lens fiber cells

Development ◽  
2002 ◽  
Vol 129 (15) ◽  
pp. 3727-3737 ◽  
Author(s):  
Sonya C. Faber ◽  
Michael L. Robinson ◽  
Helen P. Makarenkova ◽  
Richard A. Lang
Keyword(s):  
Cell Differentiation ◽  
Mouse Genome Informatics ◽  
Bmp Signaling ◽  
Dominant Negative ◽  
Fiber Cell ◽  
Pax6 Gene ◽  
Lens Fiber ◽  
Lens Fiber Cell ◽  
Fiber Cells ◽  
Lens Vesicle

We have investigated the role of Bmp signaling in development of the mouse lens using three experimental strategies. First, we have shown that the Bmp ligand inhibitor noggin can suppress the differentiation of primary lens fiber cells in explant culture. Second, we have expressed a dominant-negative form of the type 1 Bmp family receptor Alk6 (Bmpr1b – Mouse Genome Informatics) in the lens in transgenic mice and shown that an inhibition of primary fiber cell differentiation can be detected at E13.5. Interestingly, the observed inhibition of primary fiber cell development was asymmetrical and appeared only on the nasal side of the lens in the ventral half. Expression of the inhibitory form of Alk6 was driven either by the αA-cystallin promoter or the ectoderm enhancer from the Pax6 gene in two different transgenes. These expression units drive transgene expression in distinct patterns that overlap in the equatorial cells of the lens vesicle at E12.5. Despite the distinctions between the transgenes, they caused primary fiber cell differentiation defects that were essentially identical, which implied that the equatorial lens vesicle cells were responding to Bmp signals in permitting primary fiber cells to develop. Importantly, E12.5 equatorial lens vesicle cells showed cell-surface immunoreactivity for bone-morphogenetic protein receptor type 2 and nuclear immunoreactivity for the active, phosphorylated form of the Bmp responsive Smads. This indicated that these cells had the machinery for Bmp signaling and were responding to Bmp signals. We conclude that Bmp signaling is required for primary lens fiber cell differentiation and, given the asymmetry of the differentiation inhibition, that distinct differentiation stimuli may be active in different quadrants of the eye.

Bone morphogenetic protein signaling and the initiation of lens fiber cell differentiation

Development ◽  
2002 ◽  
Vol 129 (16) ◽  
pp. 3795-3802 ◽  
Author(s):  
Teri Louise Belecky-Adams ◽  
Ruben Adler ◽  
David C. Beebe
Keyword(s):  
Cell Differentiation ◽  
Growth Factor ◽  
Cell Elongation ◽  
Chicken Embryo ◽  
Vitreous Humor ◽  
Fiber Cell ◽  
Lens Fiber ◽  
Lens Fiber Cell ◽  
Fiber Cells ◽  
Bmp Receptors

Previous studies showed that the retina produces factors that promote the differentiation of lens fiber cells, and identified members of the fibroblast growth factor (FGF) and insulin-like growth factor (IGF) families as potential fiber cell differentiation factors. A possible role for the bone morphogenetic proteins (BMPs) is suggested by the presence of BMP receptors in chicken embryo lenses. We have now observed that phosphorylated SMAD1, an indicator of signaling through BMP receptors, localizes to the nuclei of elongating lens fiber cells. Transduction of chicken embryo retinas and/or lenses with constructs expressing noggin, a secreted protein that binds BMPs and prevents their interactions with their receptors, delayed lens fiber cell elongation and increased cell death in the lens epithelium. In an in vitro explant system, in which chicken embryo or adult bovine vitreous humor stimulates chicken embryo lens epithelial cells to elongate into fiber-like cells, these effects were inhibited by noggin-containing conditioned medium, or by recombinant noggin. BMP2, 4, or 7 were able to reverse the inhibition caused by noggin. Lens cell elongation in epithelial explants was stimulated by treatment with FGF1 or FGF2, alone or in combination with BMP2, but not to the same extent as vitreous humor. These data indicate that BMPs participate in the differentiation of lens fiber cells, along with at least one additional, and still unknown factor.

scholarly journals Fibroblast growth factor receptor signaling is essential for lens fiber cell differentiation

2008 ◽  
Vol 318 (2) ◽  
pp. 276-288 ◽  
Author(s):  
Haotian Zhao ◽  
Tianyu Yang ◽  
Bhavani P. Madakashira ◽  
Cornelius A. Thiels ◽  
Chad A. Bechtle ◽  
...  
Keyword(s):  
Cell Differentiation ◽  
Growth Factor ◽  
Fibroblast Growth Factor ◽  
Fibroblast Growth Factor Receptor ◽  
Growth Factor Receptor ◽  
Fiber Cell ◽  
Fibroblast Growth ◽  
Lens Fiber ◽  
Lens Fiber Cell ◽  
Growth Factor Receptor Signaling
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