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J M Corless

Publications and source records attributed to J M Corless.

17 recordsLinked to original sources
PubMed1989

Modulation of disk margin structure during renewal of cone outer segments in the vertebrate retina.

In the process of disk renewal in retinal cone outer segments (COSs), apical displacement of disks must be coupled to systematic reductions in disk area and perimeter in order to retain overall conical geometry. We have quantified these changes in disk area and perimeter segment lengths by morphometric analyses of cross sections of fully formed disks taken from basal to apical ends of COSs. Specifically excluded from these analyses are data arising from partial or incomplete disks within the COS, which do not conform to the conical geometry and which constitute a minor fraction of the COS disk population. Thus, our results address the long-range pattern of structural changes affecting the major population of disks along the length of the COS. Our data indicate that decreases in total disk margin length associated with apical displacement of fully formed disks are due to decreases in the length of the margin opposite the cilium, i.e., the open margin segment. In contrast, the average length of the closed margin segment remains constant or increases slightly in the apical direction. The open margins of frog COS disks have recently been shown to possess a distinctive lattice of membrane-associated components (Fetter and Corless: Invest. Ophthalmol. Vis. Sci. 28:646-657, '87). We have also examined COSs by the freeze-fracture, deep-etch technique for evidence of a mechanism whereby measured changes in open margin length may be accommodated while maintaining the overall organization of the open margin segments. In regions of membrane continuity between open margins and the COS plasma membrane, we have observed elevated ridges on the plasma membrane that 1) tend to lie parallel to the open margin segments, 2) have a similar axial spacing, 3) occasionally demonstrate interconnecting filaments similar to those of the open margin lattice, and 4) appear to have a particulate substructure. The mechanism proposed for reducing open margin length involves tangential displacement of the lateral edges of the open margin lattice to the adjacent plasma membrane. These shifted lattice domains initially give rise to the plasmalemmal ridges, which subsequently disassemble, and whose components become redistributed in the COS plasma membrane. These structural features of COS open margins suggest several revisions of our earlier model of disk morphogenesis (Corless and Fetter: J. Comp. Neurol. 257:24-38, '87), which was based on the margin structure of ROS disks alone. Eckmiller (J. Cell Biol. 105:2267-2277, '87) has recently proposed that partial-disks observed within the COS represent sites of new disk formation.(ABSTRACT TRUNCATED AT 400 WORDS)

Animals↗
PubMed1987

Structural features of the terminal loop region of frog retinal rod outer segment disk membranes: I. Organization of lipid components.

We have applied thin sectioning and freeze-fracture techniques to investigate the terminal loop structure of photoreceptive disks in frog retinal rod outer segments. Our studies of this region demonstrate a highly curved terminal loop bilayer that is continuous with both lamellar bilayers of the disk, and equivalent to them in dimensions and staining properties. Rhodopsin, however, appears to be excluded from this region of high curvature.

Animals↗
PubMed1987

Structural features of the terminal loop region of frog retinal rod outer segment disk membranes: II. Organization of the terminal loop complex.

In addition to a lipid bilayer component (Corless, Fetter, and Costello: J. Comp. Neurol. 257:1-8, '87), the terminal loop region of frog rod outer segment (ROS) disks displays a clustering of discrete elements referred to as the terminal loop complex. It consists of (1) semicircular or crescentic densities within the terminal loop, (2) linear interdisk densities spanning the cytoplasm near terminal loops, and (3) distinctive freeze-fracture particles associated with the terminal loop, located between 1 and 2. The linear interdisk densities are organized on a two-dimensional lattice that appears to ensheath completely the lamellar domains of all ROS disks. Indirect evidence is presented for a net axial alignment of intraloop densities. We interpret the large freeze-fracture particles of the terminal loop region to reflect transmembrane components that connect the interdisk and intraloop densities. Thus, we propose that the entire terminal loop (TL) complex is organized on a two-dimensional net. We further infer that each TL complex is organized as a dimeric unit and that such dimers interact axially and laterally to generate the observed lattice structure. It is suggested that one component of the terminal loop complex is the high molecular weight protein localized along the disk perimeter by Papermaster, Schneider, Zorn, and Kraehenbuhl (J. Cell. Biol. 78:415-425, '78).

Animals↗
PubMed1987

Structural features of the terminal loop region of frog retinal rod outer segment disk membranes: III. Implications of the terminal loop complex for disk morphogenesis, membrane fusion, and cell surface interactions.

The perimeter of rod outer segment (ROS) disks displays a two-dimensional lattice of components referred to as the terminal loop complex (Corless, Fetter, Zampighi, Costello, and Wall-Buford: J. Comp. Neurol. 257:9-23, '87b). We take the view that this pattern of structural organization reflects the mechanism(s) whereby the disk perimeter is defined and constructed. Herein we develop and partially evaluate a generalized template mechanism of disk perimeter development, to account for the structure and the axial alignment of both marginal and incisural domains. Components of the terminal loop complex are conceived as the morphogens that determine the location and guide the differentiation of the disk perimeter. Briefly, we postulate that transmembranous components of the terminal loop complex are present within the reflection of plasmalemma that forms the base of the rod outer segment. These components interact with the cytoplasmic template provided by the perimeter lattice present along the lower surface of the most basal disk, thereby propagating the lattice and creating an extracellular template. The latter is then available to interact with corresponding elements distributed within the apical surface of the adjacent disk precursor evagination. The progressive interaction and alignment of these extracellular domains form the scaffolding that guides the restructuring of the plasmalemma, to form the mature disk margin topology. Successive repetitions of this process are seen to produce an axial stacking of disks whose perimeters are aligned and ensheathed by a two-dimensional net.

Animals↗
PubMed1987

Patterns of interdisk connections within the lamellar domains of retinal rod outer segment disks: observations relevant to the axial propagation of incisures.

In rod outer segments (ROSs) of the Congo eel salamander (Amphiuma), we have observed a system of cytoplasmic filaments that interconnect the lamellar domains of adjacent disks. In longitudinal sections, these filaments occur in pairs, spaced 18-20 nm apart. Each filament is 9-11 nm in length, and perpendicular to the disk membrane. Such filament pairs display extended axial alignment through the lamellar domains of successive disks, indicating the involvement of trans-membranous elements. In cross-sectional views, these filaments appear as a row of paired, punctate densities with a periodic spacing of 14-16 nm. Such views indicate that these filaments are organized on a two-dimensional crystalline lattice, oriented perpendicular to the disk lamellae. The linear interdisk densities of the terminal loop complex appear to be identical to these cytoplasmic filaments: both are equal in length, and both are organized as two-dimensional assemblies with equivalent orientations and lattice parameters. These shared features suggest a common subset of molecular components and lattice determinants. Where the paired filament assemblies intersect the disks, one observes a characteristic dilatation of the intradisk space. In these regions, the disk is 3-6 nm wider than adjacent lamellar regions, and tends to approximate the width of the terminal loop expansion along the disk perimeter. Within such dilatations, we have not been able to demonstrate crescentic densities corresponding to those found within the terminal loop region. Paired filament arrays are not randomly located within the lamellar domains, but lie parallel to the local disk perimeter. Both single and multiple arrays are commonly observed. Single arrays are recessed about 80 nm from the disk edge. When more than one array is present, the additional arrays lie parallel to the first and are spaced at intervals of about 70 nm. Thus, in three dimensions, the multiple arrays appear as regularly spaced sheets of filaments, parallel to the local disk perimeter and perpendicular to the lamellar domains. The characteristic interval between such filament arrays suggests the presence of 'spacer' molecules that organize the two-dimensional filament lattices in the third dimension. Such a spacing mechanism may also account for the minimum width observed for disk lobule segments defined by extended parallel incisures. The potential role of paired filament arrays in the axial propagation of incisures is discussed.

Animals↗
PubMed1987

Morphological components associated with frog cone outer segment disc margins.

The two margin morphologies of frog retinal cone outer segment (COS) discs were examined by thin sectioning, freeze-fracture, and deep-etch, rotary shadowing techniques. The disc margin adjacent to the connecting cilium, which morphologically resembles the terminal loop of rod outer segment (ROS) discs, exhibited a distinctive staining density tightly apposed to the membrane surface facing the lumen. This density was crescent-shaped in longitudinal sections, and a continuous band in cross-sections. Associated with the disc margin opposite the cilium, two additional extracellular structures were observed: a globular staining density located at the outer edge of the membrane loop forming the margin, and filaments axially interconnecting adjacent margins. The globular densities and filaments were spaced at regular intervals along the margin. Where these margins were adjacent to calycal processes, the globular densities appeared to span the extracellular gap and interconnect the membranes of the COS discs and the calycal process. Distinctive intramembrane particles were observed along both margins by freeze-fracture. The distribution of the globular and filamentous elements suggests that they may have a role in maintaining the radial dimensions and axial spacing of the associated disc margin by forming an extracellular framework.

Animals↗
PubMed1986

Crystalline arrays of the Escherichia coli sn-glycerol-3-phosphate acyltransferase, an integral membrane protein.

The gene encoding the Escherichia coli sn-glycerol-3-phosphate acyltransferase, plsB, was inserted into hybrid plasmids under transcriptional control of the lambda PL and tac promoters. Enzymatic activities 35-50-fold above wild type and a large increase in glycerol-P acyltransferase polypeptide were obtained. Thin section electron microscopy of the cells overproducing the glycerol-P acyltransferase revealed 235-245-A diameter tubular structures associated with the cytoplasmic membrane. These structures were released from the cell by osmotic lysis and purified on Matrex Gel Green A. Subsequent sodium dodecyl sulfate-polyacrylamide gel electrophoresis demonstrated that the dominant protein constituent of the tubules was the glycerol-P acyltransferase. Analysis of tubule-enriched fractions isolated by differential centrifugation revealed a decreased phospholipid to protein ratio as compared to total and cytoplasmic membrane fractions. At high magnification, negative stained tubules displayed ordered arrays of stain-excluding components projecting 50-60 A from the cytoplasmic surface. Optical diffraction patterns from the micrographs contained intense layer lines at (1/78 A) and (1/39 A) along the tubule axis and a prominent spot at (1/62 A) near the equator. From compositional and structural data, 18-37% of the polypeptide volume is estimated to lie within the hydrophobic domain of the tubule membrane.

Acyltransferases↗
PubMed1982

Two-dimensional rhodopsin crystals from disk membranes of frog retinal rod outer segments.

Two-dimensional crystals of rhodopsin have been prepared from purified frog disk membranes by using the detergent Tween 80. The space group of the orthorhombic crystals is p22121; the unit cell dimensions are 47 X 151 A. Projection maps of negatively stained preparations have been calculated to a resolution of approximately 22 A. The rhodopsin molecules are associated as dimers that appear to be slightly sigmoidal and are 20-25 A in width and 70-80 A in length.

Animals↗
PubMed1980

The carbohydrates in frog retinal rod outer segments.

Frog retinal rod outer segments appear to contain uncharacterized chemical components whose mass is roughly equivalent to 12--51% of the rhodopsin mass. Available data suggest that such components include soluble proteins and complex polysaccharides, and that hyaluronic acid accounts for a substantial fraction of this mass. Electron microscopic histochemical staining studies suggest that these polysaccharide components are located within the ROS disks. The oligosaccharide moieties of rhodopsin also appear localized within the disks. The interdisk cytoplasm may contain carbohydrates, but their quantity and identity are uncertain. Rhodopsin oligosaccharides as well as some fraction of the intradisk polysaccharide appear to have extended saccharide chains preferentially oriented perpendicular to the surface of the disk membrane. Possible roles for these polysaccharides in disk development and photoexcitation are discussed. The immediate need for complete rod outer segment chemical composition data is emphasized.

Animals↗
PubMed1980

On gap junction structure.

We have studied the stain distribution within rat liver gap junctions for specimens prepared by thin sectioning and negative staining. Pools of stain molecules exist in two specific locations with respect to the distinctive morphological units (connexons) of the junction. One pool of stain surrounds the connexons and is restricted to the extracellular space in the gap between the adjacent plasma membranes. The other pool of stain is located along in the central axis of each connexon, measures 1-2 nm in diameter and 4-5 nm in length, and is restricted to the gap region. On rare occasions, barely discernible linear densities seem to extend from this latter pool of stain and traverse the entire width of the junction. The data indicate the existence of a hydrophilic cavity along the central axis of te connexon which, in most instances, is restricted to the gap region. However, the precise depth to which this cavity may further extend along the connexon axis is still uncertain.

Animals↗
PubMed1979

Structural interpretation of the birefringence gradient in retinal rod outer segments.

The birefringence of frog retinal rod outer segments is analyzed in terms of a three-dielectric layer model. The possibility that the birefringence gradient found in such cells is due to changes in the disk membrane-pair spacing is investigated using previously published glycerol imbibition data (Kaplan et al., 1978. Biophys. J. 23: 59-70). The higher net birefringence of the basal end compared to the midpoint of rod outer segments can be accounted for by a smaller negative form birefringence term due to either a smaller or larger intradiskal space, depending upon the assumed relative solids contents of the intradiskal and cytoplasmic spaces.

Animals↗
PubMed1978

Orientation of acidic polysaccharides and rhodopsin-oligosaccharides in frog retinal rod outer segments.

Using topo-optical staining reactions, the presence and molecular order of three structural components of outer segments of frog retina were studied. These components included (1) an acidic polysaccharide texture, (2) free aldehyde groups which arise during formalin fixation and (3) the oligosaccharide chains of rhodopsin. Quantitative measurements of the dye binding and birefringence effects arising from the individual structural components in rod outer segments were made. Results indicated that all three structural components had a rather well-defined orientation within the ROS. The spherulites phagocytized from the apical ends of ROSs by the pigment epithelium also demonstrate preferred orientation of the three structural components investigated.

Aldehydes↗
PubMed1978

The direct measurement of temperature changes within freeze-fracture specimens during rapid quenching in liquid coolants.

We have evaluated the cooling rates of specimens mounted in a variety of freeze-fracture holders when plunged into a series of liquid coolants. these rates were measured using miniature thermocouples placed within the mounted specimens. The most rapid cooling rates were obtained using propane at 83 K as the coolant. When mounted on a newly devised 'copper sandwich' holder, specimen cooling rates in excess of 4500 K/s have been recorded. A simple guillotine-like device for quenching freeze-fracture specimens under reproducible conditions is presented.

Chlorofluorocarbons, Methane↗