Biomedical subjects

S Tamm

Publications and source records attributed to S Tamm.

24 records · Page 2Linked to original sources

PubMed1984

Alternate patterns of doublet microtubule sliding in ATP-disintegrated macrocilia of the ctenophore Beroë.

We have used the unique properties of macrocilia from the lips of the ctenophore Beroë to test whether the ciliary beat cycle is caused by sequential activation of doublet sliding on opposite sides of the axoneme (Satir, P., 1982, Soc. Exp. Biol. Symp., 35: 179-201; Sugino, K., and Y. Naitoh, 1982, Nature (Lond.), 295: 609-611; Wais-Steider, J., and P. Satir, 1979, J. Supramol. Struct., 11:339-347). Macrocilia contain several hundred axonemes linked into rows by lamellae between doublets 3 and 8. These connections provide morphological markers for numbering the doublet microtubules in thin sections. Demembranated, detached macrocilia undergo ATP-induced sliding disintegration by extrusion of thick fragments and finer fibers from the proximal end. Disintegration can easily be followed with low-magnification brightfield or phase-contrast optics. Sliding occurs with or without added elastase, and is reversibly inhibited by vanadate. Thin sections through 16 ATP-disintegrated macrocilia showed two mutually exclusive patterns of doublet extrusion with equal frequency. Doublets 9, 1, and 2 or doublets 5, 6, and 7 were usually extruded, but not both groups. We conclude that both subsets of doublets slide by their own active arms, and that the two extrusion patterns represent alternate activation and inactivation of doublet sliding on opposite halves of the axoneme. These findings provide the first direct experimental support for a switching mechanism regulating microtubule sliding in cilia.

Adenosine Triphosphate↗

PubMed1983

Distribution of sterol-specific complexes in a continually shearing region of a plasma membrane and at procaryotic-eucaryotic cell junctions.

A narrow zone of plasma membrane between the head and body of a protozoan from termites undergoes continual in-plane shear because the head rotates continuously in the same direction relative to the cell body (Tamm, S.L., and S. Tamm, 1974, Proc. Natl. Acad. Sci. USA 71:4589-4593). Using filipin and digitonin as cytochemical probes for cholesterol and related 3-beta-hydroxysterols, we found a high level of sterol-specific complexes, visible as membrane lesions in thin sections, in both shearing and nonshearing regions of the membrane, indicating no difference in sterol content. This confirmed previous observations that any region of the fluid membrane can undergo shear, but that this occurs only at certain locations due to cell geometry and proximity to rotating cytoskeletal structures. Filipin and digitonin did not disrupt the plasma membrane at the junctions with ectosymbiotic rod and fusiform bacteria (i.e., membrane pockets and ridges). However, pepsin degradation of dense material coating the junctional membranes resulted in a positive response of these regions to filipin. Fluorescence microscopy revealed a bright halo around each rod bacterium, due to filipin-sterol binding in the sides of the membrane pockets, but no fluorescence at the bottom of the pockets; the same fluorescence pattern was found in pepsin-treated cells despite the presence of sterols throughout the pocket membrane, as shown by electron microscopy. These findings indicate that (a) regional constraints may restrict the ability of filipin to interact with sterols or form visible membrane lesions, and (b) a negative response to filipin, assayed by either electron or fluorescence microscopy, is not sufficient to demonstrate low membrane sterol concentration, particularly in membrane domains characterized by closely associated proteins.

Animals↗

PubMed1981

Ciliary reversal without rotation of axonemal structures in ctenophore comb plates.

We have used a newly discovered reversal response of ctenophore comb plates to investigate the structural mechanisms controlling the direction of ciliary bending. High K+ concentrations cause cydippid larvae of the ctenophore Pleurobrachia to swim backward. High-speed cine films of backward-swimming animals show a 180 degree reversal in beat direction of the comb plates. Ion substitution and blocking experiments with artificial seawaters demonstrate that ciliary reversal is a Ca++-dependent response. Comb plate cilia possess unique morphological markers for numbering specific outer-doublet microtubules and identifying the sidedness of the central pair. Comb plates of forward- and backward-swimming ctenophores were frozen in different stages of the beat cycle by an "instantaneous fixation" method. Analysis of transverse and longitudinal sections of instantaneously fixed cilia showed that the assembly of outer doublets does not twist during ciliary reversal. This directly confirms the existence of radial switching mechanism regulating the sequence of active sliding on opposite sides of the axoneme. We also found that the axis of the central pair always remains perpendicular to the plane of bending; more importantly, the ultrastructural marker showed that the central pair does not rotate during a 180 degree reversal in beat direction. Thus, the orientation of the central pair does not control the direction of ciliary bending (i.e., the pattern of active sliding around the axoneme). We discuss the validity of this finding for three-dimensional as well as two-dimensional ciliary beat cycles and conclude that models of central-pair function based on correlative data alone must now be re-examined in light of these new findings on causal relations.

Calcium↗

PubMed1980

Origin and development of free kinetosomes in the flagellates Deltotrichonympha and Koruga.

The formation of more than half a million free (non-flagellated) kinetosomes in post-mitotic Deltotrichonympha and Koruga from Mastotermes is described. Ladder-like configurations of prokinetosomes extend from the 2 fibrous walls of the centriolar apparatus in the rostrum. The prokinetosomes within the ladders are arranged side by side in 2 layers. Because the fibrous walls are oriented perpendicular to each other, the 2 groups of prokinetosomal ladders are also mutually perpendicular. The prokinetosomes arise continuously next to the fibrous walls, and migrate outward along the ladders as they develop. Consequently, progressive stages in kinetosome formation occur sequentially along the ladders in a polarized fashion. A cartwheel-structure appears first. This is followed by the formation of A tubules, B tubules and C tubules in an orderly sequence around the cartwheel (counter-clockwise, viewed from the distal end). The cartwheel ring disappears after the triplets have formed. The new free kinetosomes accumulate in a disorganized mass at the ends of the ladders. Later, the kinetosomes become organized end to end into the polarized chains found in interphase cells. The fibrous wall of the centriolar apparatus is thus a new type of intermediate structure associated with the mass production of basal bodies. It appears to determine the spatial organization of the 'assembly lines' of developing kinetosomes.

Animals↗

PubMed1976

Rotary movements and fluid membranes in termite flagellates.

We previously described a remarkable type of cell motility that provided direct, visual evidence for the fluid nature of cell membranes. The movement involved continual, unidirectional rotation of one part of a protozoan, including the plasma membrane and cytoplasmic organelles, in relation to a neighbouring part. The cell membrane in the 'shear zone' appeared continuous with that of the rest of the cell. The rotary motor consisted, at least in part, of a non-contractile, microtubular axostyle which extended centrally through the cell. The protozoan was a devescovinid flagellate found in the hindgut of a Florida termite. In this paper, we have confirmed earlier reports of this type of motility in other kinds of devescovinids from Australian termites. By demonstrating continuity of the plasma membrane in the shear zone of the Australian devescovinids as well, we have obtained additional examples that provide direct, visual evidence for fluid membranes. A comparative analysis of rotational motility in various devescovinids revealed 2 different kinds of rotary mechanisms. Hyperdevescovina probably have an internal motor, in which one part of the cell exerts forces against another part, as in the Florida termite devescovinid. Devescovina species, on the other hand, have an external motor, in which flagellar and/or papillar movements exert forces against the surrounding medium. The structure of the axostyle in different devescovinids was compared, and its role in rotational motility discussed with respect to the behavioural data.

Animals↗

PubMed1974

Direct evidence for fluid membranes.

We describe a new kind of cell motility that provides direct, visual evidence for the fluid nature of cell membranes. The movement involves continual, unidirectional rotation of one part of a devescovinid flagellate in relation to a neighboring part, at speeds up to one rotation/1.5 sec (room temperature). Rotation includes the plasma membrane, using the flagellar bases and ectosymbiotic bacteria embedded in pockets of the membrane as visible markers. The plasma membrane between the rotating and stationary surfaces is continuous, without fusions with other membranes, and has the typical trilaminar structure of other cell membranes. The nucleus, helical Golgi complex, and stiff central axostyle also rotate. The head of the flagellate always rotates clockwise (as viewed from the anterior end) in relation to the body, but when the head becomes stuck to debris, the body rotates counterclockwise. Evidence suggests that the microtubular axostyle generates the motive force for rotation.

Animals↗