Targeted Deletion of the Lens Fiber Cell–Specific Intermediate Filament Protein Filensin

2003 ◽  
Vol 44 (12) ◽  
pp. 5252 ◽  
Author(s):  
Azita Alizadeh ◽  
John Clark ◽  
Teri Seeberger ◽  
John Hess ◽  
Tom Blankenship ◽  
...  
Keyword(s):  
Intermediate Filament ◽  
Fiber Cell ◽  
Intermediate Filament Protein ◽  
Lens Fiber ◽  
Lens Fiber Cell ◽  
Targeted Deletion ◽  
Filament Protein

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 The 47-kD lens-specific protein phakinin is a tailless intermediate filament protein and an assembly partner of filensin.

1993 ◽  
Vol 123 (6) ◽  
pp. 1507-1516 ◽  
Author(s):  
A Merdes ◽  
F Gounari ◽  
S D Georgatos
Keyword(s):  
Intermediate Filament ◽  
Specific Protein ◽  
Cytokeratin 19 ◽  
Intermediate Filament Protein ◽  
Type I ◽  
Lens Fiber ◽  
Tail Domain ◽  
Lens Fiber Cell ◽  
Significant Similarity ◽  
Helical Domain

In previous studies we have characterized a lens-specific intermediate filament (IF) protein, termed filensin. Filensin does not self-assemble into regular IFs but is known to associate with another 47-kD lens-specific protein which has been suggested to represent its assembly partner. To address this possibility, we cloned and sequenced the cDNA coding for the bovine 47-kD protein which we have termed phakinin (from the greek phi alpha kappa omicron sigma = phakos = lens). The predicted sequence comprises 406 amino acids and shows significant similarity (31.3% identity over 358 residues) to type I cytokeratins. Phakinin possesses a 95-residue, non-helical domain (head) and a 311 amino acid long alpha-helical domain punctuated with heptad repeats (rod). Similar to cytokeratin 19, phakinin lacks a COOH-terminal tail domain and it therefore represents the second known example of a naturally tailless IF protein. Confocal microscopy on frozen lens sections reveals that phakinin colocalizes with filensin and is distributed along the periphery of the lens fiber cells. Quantitative immunoblotting with whole lens fiber cell preparations and fractions of washed lens membranes suggest that the natural stoichiometry of phakinin to filensin is approximately 3:1. Under in vitro conditions, phakinin self-assembles into metastable filamentous structures which tend to aggregate into thick bundles. However, mixing of phakinin and filensin at an optimal ratio of 3:1 yields stable 10-nm filaments which have a smooth surface and are ultrastructurally indistinguishable from "mainstream" IFs. Immunolabeling with specific antibodies shows that these filaments represent phakinin/filensin heteropolymers. Despite its homology to the cytokeratins, phakinin does not coassemble with acidic (type I), or basic (type II) cytokeratins. From these data we conclude that filensin and phakinin are obligate heteropolymers which constitute a new membrane-associated, lens-specific filament system related to, but distinct from the known classes of IFs.

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.

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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