Epicytic Folds Research Articles

Freeze-fracture studies on the pellicle of the eugregarine, Gregarina garnhami (Eugregarinida, Protozoa)

Ultrastructural studies reveal that the structure of the epicyte of eugregarines is highly ordered. In Gregarina garnhami the epicyte pellicle consists of an outer plasma membrane, beneath which there is a membrane complex consisting of two closely opposed membranes, the middle and inner membranes. The whole of the outer surface of the animal is thrown into a series of longitudinal epicyte folds which are separated from the rest of the body by a basal lamina. Between the folds, pores emerge for release of mucus while restricted to their tips are two sets of filaments which run longitudinally. The first set of filaments is situated between the outer plasma membrane and the middle membrane, in closer association with the middle membrane E face. In replicas the middle membrane E face possesses linear alignments of grooves and intramembranous particles (IMPs). The second set of filaments, which are more electron dense and smaller, are closely associated with the inner face of the inner membrane which is characterized by rows of IMPs, again limited to the fold tips. The interaction of these filaments via their insertion in the membrane of the tip folds at the IMP sites is discussed as a possible mechanism for the gliding motion these organisms exhibit.

Substrate Contact, Mucus, and Eugregregarine Gliding1

ABSTRACT. Experiments have been carried out on Gregarina garnhami to examine some of the factors that may be significant in gliding. Suspension of gregannes in Ficoll showed that substrate contact is essential. Reflection interference microscopy shows that there are fluctuating surface/substrate contacts, but it is not necessary for the whole of the undersurface of the cell to be in close contact with the substrate. Gliding is always accompanied by the formation of a mucus trail. The effects of the drugs amphetamine and ephedrine on mucus trail formation and gliding have been examined. Lateral undulations of the epicyte folds have previously been implicated in grcgarinc gliding, but G. garnhami does not exhibit lateral undulations of the epicyte folds as it moves. The folds are predominantly straight with indications of varicosities or swellings along the length of the folds. These observations are discussed in relation to gliding movement.

Freeze-fracture study of the Gregarine trophozoite: II. Evidence of “rosette” organization on cytomembranes in relation with micropore structure

Abstract Conventional transmission electron microscopy (TEM) and freeze-fracture technique have been carried out on the trophozoite of Gregarina sp. to examine the ultrastructural modifications of the membrane organization during the sequence of events characterizing exocytosis. Electron microscopical observations revealed that exocytosis is accompanied by the break of the inner and middle membranes, constituents of the three “unit membrane complex”, which form the pellicle of this organism, and by their fusion at the site of the successive micropore formation. Freeze fracturing showed internal membrane organization of these complexes. Along the lateral surface of the epicytic folds numerous aggregates of rosette-shaped IMPs (intramembrane particles) were evident. These are specialized points of the membrane organized to make contact possible between the secretory vesicle and the membrane complex. Freeze-fracture images give also evidence of progressive membrane modifications in relation with the secretory process.

Freeze-fracture study of the Gregarine trophozoite: I the top of the epicyte folds

Abstract The fine organization of the “membrane complex” present at the tip of the epicyte folds in the sporozoan Gregarina trophozoite has been studied. Electron microscopy revealed bundles of intermediate filaments (8–10 nm) in the interspace between plasma and middle membrane. Doublets of filaments are present in the cytoplasm adhering to the inner membrane. The narrow space between the inner and middle membrane exhibits electron dense dots arranged in pairs. Freeze-fracture replicas reveal a different organization in each of the three membranes. The plasma membrane shows the P-face rich in particles and E-face with a few clusters of intramembrane particles (IMPs). Parallel ridges are present on the E-face and parallel grooves on the P-face of the intermediate membrane. The P-face of the inner membrane shows double longitudinal arrays of IMPs and the E-face has large grooves alternating with rows of ridges. The rows of particles on the P-face of the inner membrane are in register with the clusters of f...

Electron microscope investigation of the evolutionary stages of the trophozoite of Didymophyes gigantea (Sporozoa, Gregarinida). III. The fine structure of the epicyte with emphasis on the contractile elements (author's transl)

The fine structure of the epicyte of D. gigantea was investigated. The motility of the gregarine and the contractile elements are described. Four essential types of movements can be observed in this gregarine: (1) rolling up and pendular movements, (2) locomotion by gliding forward, (3) cytoplasmic streaming (Fig. 1), (4) peristaltic contractions (Fig. 2) which seem to be accompanied by the contraction of annular myonemes (Fig. 2). The epicyte is formed by the folding of the parasitic cell wall which is made from three membranes (Figs. 3 and 4). At the top of each fold one can see apical struts between the outer and middle membrane and apical filaments under the inner membrane (Fig. 3). In addition, the epicytic folds are covered by a cell coat which is made from tubular structures (Fig. 5). At the base of the epicytic folds can be observed the basal lamina (Fig. 3) composed of very fine fibrillar material with an average thickness of 2.5 nm (Fig. 6). These fibrils are oriented in the longitudinal axis of the gregarine. Beneath the epicytic fold in the ectoplasm are found the annular myonemes with a width of up to 0.5 micrometers (Fig. 7). They are composed of many fine fibrils with an average thickness of 5 nm. In young trophozoites, the myonemes also contain microtubuli (Fig. 8). Between the epicytic folds, the cell wall is interrupted by three different types of vesicles: the vesicles with an electrondense content (Fig. 9), the three-membranous vesicles (Fig. 10), and the hose-shaped vesicles (Fig. 11). Glycerol-extraction of the parasites was performed in order to define the contractile structures. After extraction the annular myonemes are difficult to recognize (Fig. 13). When ATP is added, the gregarine does not contract but the myonemes reappear after 3 to 4 min (Fig. 14). Differences can also be observed in the myoneme structure using electron microscopy: After extraction, the myonemes are composed of a very limp fibrillar network (Fig. 15) which becomes very dense after the action of ATP (Fig. 16). Glycerol extraction does not disturb either the apical struts and apical filaments or the fibrils of the basal lamina (Figs. 15--17). In addition, cytoplasmic fibrillar structures appear after glycerol extraction (Figs. 15 and 16). The experimental and electron microscope results indicate that the motility of the gregarine depends upon four different systems: (1) the ectoplasmic annular myonemes, (2) the apical structures in the undulating epicytic folds, (3) the cytoplasmic fibrils, and (4) the basal lamina.

Beitrag zur Zytologie der Gregarinen: Endo-, Exozytose, Organelle des Stoffwechsels

Summary 1. Endocytosis of compact particles in gregarines has to be distinguished well from already known cytological models. The exocytosis of plasma portions gets on in a simple splitting of the epicyte folds. 2. It seems that the pores of pinocytosis are continuous. Microtubules approach both sides of the syzygial connection between two gamonts. 3. The species' degree of parasitism depends on the figures of epimerits, their durability and equipment with organells. 4. The reduced number and simplified inner structure of mitochondria in gregarines of the family Gregarinidae express a changed kind of metabolism. 5. Polyribosomal complexes are not bound with the endoplasmic reticulum. This reticulum itself is rather small developped. The small number of dictyosomes seems to produce glycogen.

A Study of the Structure and Gliding Movement of Gregarina garnhami

SYNOPSIS The structure and gliding movement of Gregarina garnhami Canning, a eugregarine found in the midgut of the desert locust, Schistocerca gregaria, have been studied by light microscopy and transmission and scanning electron microscopy (EM). Ultrastructural studies revealed that the cytoplasm of G. garnhami is separated from the epicyte folds by a basal lamina. The pellicle consists of 3 membrane layers. At the tips of the epicyte folds there are 2 sets of longitudinally oriented filaments. An ectoplasmic network is present in the ectoplasm and the endoplasm contains numerous paraglycogen granules. The effect of cytochalasin B on G. garnhami was studied. Examination of scanning EM preparations of gliding and stationary gregarines yielded inconclusive results. In some instances the epicyte folds were thrown into waves; in others the folds were straight, regardless of treatment before fixation. Gregarina garnhami glides through its environment without any apparent deformation in shape. As it moves, a mucus trail is left behind it. Phase‐contrast observations were made of centrifuged gregarines in which the endoplasm was displaced. Centrifuged gregarines continued to glide. Displacement of the endoplasm allows visualization of the epicyte folds in gliding animals. No lateral waves were seen in the epicyte folds of gliding centrifuged animals.

Chronologie des Modifications Ultrastructurales au Cours de la Croissance de Gregarina blaberae*

In an ultrastructural study the development of the sporozoite as well as the growth and development of the trophozoite of Gregarina blaberae were followed in the course of experimental infections of larvae of the cokroach Blaberus craniifer. The spectacular growth involved the transformation within 18 days of the sporozoite, measuring 15 X 1 micronm, to a cephaline--trophozoite affixed to the intestinal epithelium--of 250 micronm length and 65 micronm diameter. The sporozoite's ultrastructure is not different from that of sporozoites of other Sporozoa studies to date--the conoid and dense bodies are present. The pellicle consists of 3 membranes, but there are some interruptions in the internal membrane complex. The first dictyosomes are formed from the nuclear envelope. The migration of the nucleus and of the dense bodies, followed by the regression of all the structures characteristic of the sporozoites, and the establishment of a cortical zone that comes to cover the epimerite, take place within 48 h after infection and mark the transformation of the sporozoite into the trophozoite. Development of the cephaline involves the formation of the epicytic folds, which occurs at the base of the deutomerite, starting on the 3rd day of development. A regular system of longitudinal or epicytic folds is formed over the entire surface of the gregarine. On the 4th and 5th days of development, a vacuolar system and a chondriome become differentiated in the epimerite, while a fibrillar septum separates the protomerite from the deutomerite. The next stage, starting on the 6th day, is characterized by distribution of polysaccharide reserves between these 2 segments. The model studied allows us to determine the role of the epimerite in the parasite's nutrition, as well as the development of the chondriome and of the cortical membranes in the course of the vegetative growth phase of the cephaline gregarine.

A contribution to the physiology of movement of gregarines: elements and modus of cellular movement (author's transl)

1. Cytochalasin B (= CCB, Phomin) in several concentrations inhibits the visible movement of gregarines. The fine structure of the cell is simultaneously changed, fibrillar bundles are desorganized. These fibrils are regarded as myonemes. 2. These myonemes are directed peripherally of the cell longitudinal and transverse to its axis. The longitudinal myonemes are organized in separated strings stretching along the top of the epicyte folds, between the plasmalemm and the secondary membranous layer. Fibrils under this layer serve as skeleton and as thus antagonist. The skeleton fibrils remain unaltered after CCB inhibition. They are located in a parallel direction to the myonemes. Their number corresponds together in one epicyte fold. The transverse myonemata surround the central plasma nearby the basal lamella, which cannot be found in some of the regarded species. 3. The co-work of skeleton-fibrils, stiff pellicle and myonemes allows to describe the modus of all known types of movement. Only change of coordination yields the multitude of these kinds of movement.

A scanning electron microscope study on Gregarina sp. from Udeopsylla nigra.

SYNOPSISScanning electron microscope studies on Gregarina sp. from the cricket Udeopsylla nigra revealed that the epicytic folds of the younger gamonts are undulatory, whereas those of the older gamonts are relatively straight. The protomerite of the primite is conical with a mammiliform structure at the anterior tip, where the epicytic folds originate from a disc‐like structure. The protomerite of the satellite is flattened.