The restructuring of the flagellar base and the flagellar necklace during spermatogenesis of Ephestia kuehniella Z. (Pyralidae,Lepidoptera)

Summary Transmission electron microscopy was used to study the development of the flagellar base and the flagellar necklace during spermatogenesis in a moth (Ephestia kuehniella Z.). Until mid-pachytene, two basal body pairs without flagella occur per cell. The basal bodies, which contain a cartwheel complex, give rise to four flagella in late prophase I. The cartwheel complex appears to be involved in the nucleation of the central pair of axonemal microtubules. In spermatids, there is one basal body; this is attached to a flagellum. At this stage, the nine microtubular triplets of the basal body do not terminate at the same proximal level. The juxtanuclear triplets are shifted distally relative to the triplets distant from the nuclear envelope. Transition fibrils and a flagellar necklace are formed at the onset of axoneme elongation. The flagellar necklace includes Y-shaped elements that connect the flagellar membrane and the axonemal doublets. In spindle-containing spermatocytes, the flagellar necklace is no longer detectable. During spermatid differentiation, the transition fibrils move distally along the axoneme and a prominent middle piece appears. Our observations and those in the literature indicate certain trends in sperm structure. In sperms with a short middle piece, we expect the presence of a flagellar necklace. The distal movement of the transition fibrils or equivalent structures is prevented by the presence of radial linkers between the flagellar membrane and the axonemal doublets. On the other hand, the absence of a flagellar necklace at the initiation of spermiogenesis enables the formation of a long middle piece. Thus, in spermatozoa possessing an extended middle piece, a flagellar necklace may be missing.     

SPERMIOGENESIS OF THE TELEOST,ORYZIAS LATIPES,WITH SPECIAL REFERENCE TO THE FORMATION OF FLAGELLAR MEMBRANE *

In the early stage of Oryzias spermiogenesis, an axonemal bud appears at the distal end of a centriole characterized by its electron dense accessories. When the axoneme begins to grow in the cytoplasm, small vesicles come to surround it. These vesicles are similar to those produced by the Golgi apparatus which lies close to the growing axoneme. At this stage, the spermatid cell membranes disappear, causing transformation of the mononuclear spermatids into a multinucleated syncytium. As each axoneme elongates in the syncytium, it is enveloped by a cylindrical array of vesicles which are most likely derived from the Golgi apparatus. Shortly after this stage, the syncytium is again partitioned by cell membranes, restoring the existence of mononuclear spermatids. The arrayed vesicles fuse with each other to form two concentric membranes surrounding the axoneme. The inner membrane becomes the flagellar membrane and the outer one, the membrane of a flagellar sheath. These observations lead to the conclusion that the formation of the flagellar membrane is due to the fusion of vesicles surrounding the axoneme which are derived from the Golgi apparatus. In the course of spermiogenesis, no indication of an acrosomal structure is observed.     

Spermiogenesis and sperm ultrastructure in Cylindrostoma fingalianum (Platyhelminthes,Prolecithophora) with notes on a protozoan (kinetoplastid) symbiont closely associated with allosperm

Summary

The only positive synapomorphy uniting members of the platyhelminth turbellarian taxon, Prolecithophora, is a peculiar membranous system present in much of the shaft of the sperm. This investigation followed the development of this membrane system during spermiogenesis in Cylindrostoma fingalianum and its appearance in the mature sperm. Formation begins with invaginations of the early spermatid shaft outer cell membrane. The invaginations enlarge and the membrane becomes increasingly folded. They appear to be subsequently supplemented with membranous material supplied by an extensive vacuolar system originating from the Golgi apparatus in the main cytoplasmic mass of the spermatid. Throughout development, and in mature sperm, the membranous system forms a part of the outer cell membrane and is also intimately associated with the elongate mitochondrion that lies between the membranous column and the nucleus. The nucleus is highly lobed and the sperm cell lacks flagella or axonemes or the dense bodies found in most other turbellarian taxonomic divisions. A kinetoplastid protozoon present in considerable numbers amongst allosperm is also described.     

Spermiogenesis and sperm in Mesostoma viaregginum (Plathelminthes, Rhabdocoela): an ultrastructural study to infer sperm orientation

Spermiogenesis in Mesostoma viaregginum begins with the formation of a zone of differentiation containing striated rootlets, two centrioles, and an intercentriolar body in-between. These centrioles generate two parallel free-flagella with the 9+“1” pattern of the Trepaxonemata growing out in opposite directions. Spermatid differentiation is characterised by a 90° latero-ventral rotation of flagella and a subsequent disto-proximal centriolar rotation, with a distal cytoplasmic projection. The former rotation involves the compression of a row of cortical microtubules and allows recognising a flagellar side and an aflagellar side in the late spermatid and in the mature spermatozoon. At the end of the differentiation, centrioles and microtubules lie parallel to the spermatid axis. The disto-proximal centriolar rotation is proposed as a synapomorphy for the Rhabdocoela. The modifications of the intercentriolar body during spermiogenesis and the migration of the nucleus and the centrioles towards the cytoplasmic distal projection are also described. The mature spermatozoon of M. viaregginum is filiform and tapered at both ends and presents many features found in the Rhabdocoela gametes. The nucleus disappears before the flagellar insertion and a density gradient of mitochondria is observed along the sperm axis. The anterior end of the spermatozoon of M. viaregginum is characterised by a tapering capped by a membrane expansion. This study has enabled us to describe precisely the orientation of spermatozoa in the Rhabdocoela in general: the centriolar extremity is proposed as the anterior one for the Rhabdocoela.     

FINE STRUCTURE OF THE ZOOSPORE OF OEDOCLADIUM CAROLINIANUM (CHLOROPHYTA) WITH SPECIAL REFERENCE TO THE FLAGELLAR APPARATUS1, 2

Ultrastructure of the motile zoospore has been investigated in Oedocladium catolinianum & Hoffman. An unwalled zoospore is usually produced from the contents of a terminal vegetative cell and consists of two principal regions: a small anterior dome and a larger body region; a ring of flagella marks the juncture of these two areas. Chloroplast inclusions consist of thylakoids, mature and incipient pyrenoids, starch and striated microtubules; no eyespot has been observed. Zoospores appear to possess permanent contractile vacuoles with numerous accessory vacuoles, coated vesicles and occasionally coated tubules. The cytoplasm of the dome contains numerous mitochondria ER and golgi bodies, as well as two distinct types of vesicles. The first contains an electron-dense; granular core and is surrounded by a loose, sinuate membrane. The second vesicle is electron-opaque and is found at the apex of the dome: it contains mucopolysaccharides employed during zoospore adhesion. A complex flagellar apparatus encircles the lower region of the dome. It consists of ca. 30–65 flagella, a ring-shaped fibrous band, flagella roots and additional supporting material. The flagella and roots alternate with one another beneath the fibrous band. The compound flagellar roots consist of two superimposed components: an outer ribbon-like unit composed of three microtubular elements and a single striated inner component. A band of support material lies beneath the proximal end of the basal bodies. It is a continuous fibrous band, although it often appears as three distinct, repetitive units.     

Membrane specializations in flagellar ribbons of elasmobranch fish

Specialized epithelial cells lining the elasmobranch nephron bear numerous flagella which are organized into closely-packed, parallel rows forming ribbons (Lacy et al., 1989a). The compact arrangement of the adjacent flagella comprising each ribbon suggests they are structurally bound together, forming a single unit which functions to force urine along the nephric tubule. In the present study, the structural basis of the interflagellar connections was investigated by scanning electron microscopy (SEM) and by transmission electron microscopy (TEM) of thin sections and freeze fracture replicas. Various fixatives and histochemical stains were used to elucidate the structure and composition of the interflagellar adhesive material. SEM of the luminal cell surface showed the organization of the flagella in ribbons. In TEM, fixation in a solution containing glutaraldehyde and tannic acid, Ruthenium red or Alcian blue, or postfixation in reduced OsO(4) revealed that the plasma membrane of each flagellum of a ribbon was surrounded by a thin layer of surface coat composed of very short filaments more prominent at sites where adjacent flagella were in close apposition. In comparable locations, freeze-fracture replicas disclosed small aggregates or plaques of particles arranged in an irregular, discontinuous line on both faces P and E of the flagellar membrane. In areas where the flagella were not arranged into ribbons (most frequently after immersion fixation), the surface coat was thick and expanded and, in replicas, the intramembranous particles were randomly scattered. All of these plasma membrane specializations appear to function in binding adjacent flagella and thus facilitate a coordinated flagellar ribbon beat.     

The flagellar apparatus of the golden algaSynura uvella: Four absolute orientations

Summary Flagellated vegetative cells of the colonial golden algaSynura uvella Ehr, were examined using serial sections. The two flagella are nearly parallel as they emerge from a flagellar pit near the apex of the cell. The photoreceptor is restricted to swellings on the flagella in the region where they pass through the apical pore in the scale case and the swellings are not associated with the cell membrane or an eyespot. A unique ring-like structure surrounds the axonemes of both flagella at a level just above the transitional helix. The basal bodies are interconnected by three striated, fibrous bands. Four short (<100 nm) microtubules lie between the basal bodies at their proximal ends. Two rhizoplasts extend down from the basal bodies and separate into numerous fine striated bands which lie over the nucleus. Three- and four-membered microtubular roots arise from the rhizoplasts and extend apically together. As the roots reach the cell anterior, the three-membered root bends and curves clockwise to form a large loop around the flagella; the four-membered root bends anticlockwise and terminates under the distal end of the three-membered root as it completes the loop. There are four absolute orientations, termed Types 1–4, in which the flagellar apparatus can occur. With each orientation type the positions of the Golgi body, nucleus, rhizoplasts, chloroplasts and microtubular roots change with respect to the flagella, basal bodies and photoreceptor. Two new basal bodies appear in pre-division cells, and three short microtubules appear in a dense substance adjacent to each new basal body. Based upon the positions of new pre-division basal bodies, a hypothesis is proposed to explain why there are four orientations and how they are maintained through successive cell divisions.     

Cytoplasmic bridges,intercellular junctions,and individualization of germ cells during spermatogenesis in Dermatobia hominis (Diptera: Cuterebridae)

During mitotic and meiotic divisions in Dermatobia hominis spermatogenesis, the germ cells stay interlinked by cytoplasmic bridges as a result of incomplete cytokinesis. By the end of each division, cytoplasmic bridges flow to the center of the cyst, forming a complex, called the fusoma. During meiotic prophase I, spermatocytes I present desmosome-like junctions and meiotic cytoplasmic bridges. At the beginning of spermiogenesis, the fusoma moves to the future caudal end of the cyst, and at this time the early spermatids are linked by desmosome-like junctions. Throughout spermiogenesis, new and sometimes broad cytoplasmic bridges are formed among spermatids at times making them share cytoplasm. In this case the individualization of cells is assured by the presence of smooth cisternae that outline their structures. The more differentiated spermatids have in addition to narrow cytoplasmic bridges, plasmic membranes junctions. By the end of spermiogenesis, the excess cytoplasmic mass is eliminated leading to spermatid individualization. Desmosome-like junctions of spermatocytes I and early spermatids appear during the fusoma readjustment and segregations; on the other hand, plasmic membrane junctions appear in differentiating spermatids and are eliminated along with the cytoplasmic excess. These circumstances suggest that belt desmosome-like and plasmic membrane junctions are involved in the maintenance of the relative positions of male germ cells in D. hominis while they are inside the cysts. © 1996 Wiley-Liss, Inc.     

MICROMORPHOLOGY OF A SMALL DINOFLAGELLATE PROROCENTRUM MARIAE-LEBOURIAE (PARKE & BALLATINE) COMB. NOV.1,2,3

The surface structures of the bivalvate dinoflagellate Prorocentrum mariae-lebouriae are described in detail. It has an almost spheroidal shape in face-view, a compressed saucer-shape in side view, with a distinct striated band at the edge of the cell. Its surface is covered with small spines in a regular pattern, with 450 nm distance between pairs. The spines are 100–120 nm wide and 200–300 nm long. There are 600–700 spines on each valve. At the anterior cell end, one of the values has a V-shaped depression which contains a specialized structure accommodating the 2 flagellar pores. The flagellar pores are-enclosed by 8 small, thick plates held together and to the values by sutures. The flagellar pore area consists of 2 distinct structures: an apical collar possessing a curved forked plate and a larger structure composed of an unbranched, plate. There are 2 flagellar canals located between the flagellar pore plates. Beneath each flagellar canal lies a row of 11 microtubules. A row of microtubules forming a microtubular cylinder is situated adjacent to the oblong flagellar canal near a simple pusule. The microtubular cylinder encircles electron dense bodies. The bases of the longitudinal and transverse flagella appear to lie at an angle to each other. The above features are illustrated with transmission and scanning electron micrographs.     

Golgi apparatus activity and membrane flow during scale biogenesis in the green flagellateScherffelia dubia (Prasinophyceae). I: Flagellar regeneration

Summary Cells ofScherffelia dubia regenerate flagella with a complete scale covering after experimental flagellar amputation. Flagellar regeneration was used to study Golgi apparatus (GA) activity during flagellar scale production. By comparing the number of scales present on mature flagella with the flagellar regeneration kinetics, it is calculated that each cell produces ca. 260 scales per minute during flagellar regeneration. Flagellar scales are assembled exclusively in the GA and abstricted from the rims of thetrans-most GA cisternae into vesicles. Exocytosis of scales occurs at the base of the anterior flagellar groove. The central portion of thetrans-most cisterna, containing no scales, detaches from the stack of cisternae and develops a coat to become a coated polygonal vesicle. Scale biogenesis involves continuous turnover of GA cisternae, and scale production rates indicate maturation of four cisternae per minute from each of the cells two dictyosomes. A possible model of membrane flow routes during flagellar regeneration, which involves a membrane recycling loop via the coated polygonal vesicles, is presented.     

Ultrastructural analysis of the aberrant axoneme morphogenesis in thrips (Thysanoptera, Insecta)

Thrips spermiogenesis is characterized by unusual features in the differentiating spermatid cells. Three centrioles from which three individual short flagella are initially assembled, make the early spermatid a tri-flagellated cell. Successively, during spermatid maturation, the three basal bodies maintain a position close to the most anterior end of the elongating nucleus, so that the three axonemes are progressively incorporated in the spermatid cytoplasm, where they run in parallel to the main nuclear axis. Finally, the three axonemes amalgamate to form a microtubular bundle. The process starts with the formation of rifts at three specific points in each axonemal circumference, corresponding to sites 1,3,7 and leads to the formation of 9 microtubular rows of different length, i.e. 3 "dyads", 3 "triads" and 3 "tetrads". In the spermatozoon, the nucleus, the mitochondrion and the bundle of microtubules are arranged in a helicoidal pattern. The elongation of the spermatozoon is allowed by the deep anchorage of the spermatid to the cyst cell through a dense mass of material which, at the end of spermiogenesis, becomes a long anterior cylindrical structure. This bizarre "axoneme" does not show any trace of progressive movement but it is able to beat. According to the presence of dynein arms, sliding can take place only within each row and not between the rows. The possible molecular basis underlying the peculiar instability of thrips axonemes is discussed in light of the present knowledge on the organization of the axoneme in mutant organisms carrying alterations of the tubulin molecule.     

Membrane glycoproteins of Chlamydomonas eugametos flagella

The flagellar glycoproteins exposed on Chlamydomonas eugametos gametes were labeled by means of lactoperoxidase, diiodosulfanilic acid and chloramine T, and characterised in SDS-electrophoresis gels. The medium from gamete cultures contains particles (isoagglutinins) that agglutinate gametes of the opposite mating type. When crude preparations of these particles were subjected to isopycnic centrifugation in a caesium chloride gradient, two bands of particles were found. The lighter, active band consisted of membrane vesicles. The denser, inactive band consisted of cell wall material. The active band had the same glycoprotein composition as membrane vesicles artificially made from isolated flagella. Preparations of glagella were also separated on a caesium chloride cushion into pure flagella and cell wall material. The flagella, but not the cell wall material, isoagglutinated opposite gametes. Again the glycoprotein composition of pure flagella was similar to that of pure isoagglutinin vesicles. No difference was detected between the protein and glycoprotein compositions of flagella and isoagglutinins from both mating types.Abbreviations LPO lactoperoxidase - PB phosphate buffer - DISA diazotized ¹²⁵I-iodo-sulfanilic acid - SDS sodium dodecyl sulphate - CBD coomassie Brilliant Blue - PAS periodic acid Schiff     

FLAGELLAR DEVELOPMENT AND REGENERATION IN VOLVOX CARTERI (CHLOROPHYTA)1

The biflagellate somatic cells of Volvox carteri f. nagariensis lyengar exhibit an asymmetric pattern of flagellar development. Initiallt each somatic cell has two short (4 μm) flagella but after several hours one flagellum on each cell elongates unitl it reaches a length of 12 μm. Due to the regular arrangement of somatic cells in the Volvox spheroid it is apparent that the same flagellum on each somatic is the first to elongale. The asymmetric flagellar length is maintained for about 8 h after which the second flagellum on each somatic cell elongates. When the second flagellum attains the same length (12 μm) as the first flagellum, both flagella elongale at the same rate until reaching a final length of 22 μm. Experimental removal of somatic cell flagella results in their regeneration. Somatis cells regenerate both flagella simultaneously and full length flagella are produced in about 2 h. The intial rate of flagellar regeneration is about ten times faster than the intial rate of flagllar growth in development. Cycloheximide, an inhibitor of protein synthesis, has no effect on the initial rate of flagellar regeneration but the flagella produced in the presence of the drug are half the length of flagella produced in its absence. Somatic cells are able to regenerate flagella up to the time of α and β tubulin, the major structural proteins of the flagellar axoneme, and other cellular proteins.     

Spermiogenesis in the Flatworm, Notoplana Japonica with Special Attention to the Organization of an Acrosome and Flagella

Ultrastructural changes during spermiogenesis in the flatworm, Notoplana japonica were studied with special attention to organizing process of an acrosome and flagella. During spermiogenesis, the G olgi complex develops conspicuously but it fails to organize the structure of an acrosomal vesicle. Consequently, no acrosome is formed at the apex of the sperm. As a substitute for an acrosomal structure, the slender process at the tip of the mature sperm is prominently occupied with glycogen granules.
The axoneme of the flagellum is formed from the basal body in the protrusion which is juxtaposed to the nucleus of the early spermatid. Two flagella associated with an electron-dense structure (EDS) extend superficially from the spermatid body in opposite directions. Progressively, they take an acute angle to each other and finally run alongside the sperm body. The axoneme consits of nine peripheral doublets with arms, a central cylinder containing an electron dense core, a less dense intermediate zone and fine spokes between the cylinder and doublets.     

Spermatogenesis inPlatynereis massiliensis (Polychaeta: Nereidae)

Stage 1 of spermatogenesis in the protandrous polychaetePlatynereis massiliensis is represented by clusters of about 60 spermatogonia which appear in the coelomic cavity. There are no testes inP. massiliensis. The origin of the spermatogonial clusters is not known. Subclusters of approximately 20 primary spermatocytes each represent stage 2. The appearance of synaptonemal figures in the spermatocyte nuclei marks the beginning of stage 3. Cells tend to lose their tight packing during stage 3 but interdigitate with cellular processes. Then very small subclusters of 4 to 8 spermatocytes appear. Meiosis is completed during stage 4, giving rise to secondary spermatocytes and then to spermatid tetrads. Spermatogonia and primary spermatocytes are interconnected by structurally specialized fusomes while secondary spermatocytes and spermatids, which are also in cytoplasmic continuity, show rather simple cell bridges. Synthesis of acrosomal material starts during stage 2. During spermiogenesis the proacrosomal vesicles of Golgi origin travel from the posterior part of the cell to its anterior part to form the acrosome proper. Acrosome formation, nuclear condensation, shaping of the long and slender sperm nucleus, and development of the sperm tail are the main events during spermiogenesis. Sperm morphology is briefly discussed wity respect to its phylogenetic bearings.     

A STUDY OF CELL WALL AND FLAGELLA FORMATION DURING CELL DIVISION IN THE SCALY GREEN ALGA,SCHERFFELIA DUBIA (CHLOROPHYTA)1

The thecate green flagellate Scherffelia dubia (Perty) Pascher divides within the parental cell wall into two progeny cells. It sheds all four flagella before cell division, and the maturing progeny cells regenerate new walls and flagella. By synchronizing cell division, we observed mitosis, cytokinesis, cell maturation, flagella extension, and cell wall formation via differential interference contrast microscopy of live cells and serial thin‐section EM. Synthesis of thecal and flagellar scales is spatially and temporally strictly separated. Flagellar scales are collected in a pool during late interphase. Before prophase, Golgi stacks divide, flagella are shed, the parental theca separates from the plasma membrane, and flagellar scales are deposited on the plasma membrane near the flagellar bases. At prophase, Golgi bodies start to synthesize thecal scales, continuing into interphase after cytokinesis. During cytokinesis, vesicles containing thecal scales coalesce near the cell posterior, forming a cleavage furrow that is initially oriented slightly diagonal to the longitudinal cell axis but later becomes transverse. After the progeny nuclei have moved into opposite directions, resulting in a “head to tail” orientation of the progeny cells, theca biogenesis is completed and flagellar scale synthesis resumes. Progeny cells emerge through a hole near the posterior end of the parental theca with four flagella of about 8 μm long. The precise timing of flagellar and thecal scale synthesis appears to be an evolutionary adaptation in a scaly green flagellate for the thecal condition, necessary for the evolution of the phycoplast and thus multicellularity in the Chlorophyta.     

SPERMIOGENESIS IN THE PULMONATE SNAIL,EUHADRA HICKONIS III. FLAGELLUM FORMATION*

The formation of the flagellum in the spermatid of the Japanese land snail, Euhadra hickonis, is introduced by the appearance of a central indentation in the differentiated posterior side of the spherical nucleus early in spermiogenesis. One centriole moves to this part of the cell, changes in several structural respects and acquires a short-lived “centriole adjunct”. At first it lies tangential to the nuclear surface as it begins to induce formation of the flagellar axoneme; then it turns so that its proximal end fits into the deepening nuclear indentation (“implantation fossa”). Cytoplasmic tubules appear to mediate this shift in direction. Internal changes in the centriolar components begin as it initiates formation of the axoneme, and continue throughout spermiogenesis. First, a dense “cap” forms at its proximal end, the microtubular triplets become doublets and a pair of singlets occupies the center of the complex. All these microtubules extend from the dense cap and are continuous with those of the axoneme. As the basal body (modified centriole) becomes set in the implantation fossa, the material of the centriole adjunct forms 9 strands, which are continuous with the peripheral coarse fibers when these develop. The microtubular doublets of the basal body are visible for a short time between the fiber strands; in the mature spermatozoon they are found embedded in the basal body portions of the coarse fibers in a degenerated form. Posterior to the basal body, however, they separate from the inner sides of the striated coarse fibers and become the doublets of the axoneme. The proximal part of the elongating axoneme lies in a posterior extension of the cell, in which glycogen particles and mitochondria are conspicuous. As the mitochondria unite into a sheath tightly surrounding the axoneme, the structure of their cristae changes to form a paracrystal-line “mitochondria derivative”, which consists of many layers close to the nucleus and progressively fewer posteriorly. Outside of this “primary sheath”, more modified mitochondria unite to form a “secondary sheath” of paracrystalline lamellae which encloses a compartment, filled with glycogen particles, that extends in a low-pitched helix nearly to the end of the flagellum. In the late spermatid, microtubules become arranged at regular intervals around the nucleus and secondary sheath of the flagellum for a short period while the remaining cytoplasm and spermatid organelles such as the Golgi complex are being discarded. The flagellum of the mature spermatozoon is 250–300 μm in length, tapering gradually from a diameter of ca 1 μm just behind the nucleus to less than 0.3 μm at its tip, as the result of reduction in the amount of stored glycogen, the number of paracrystalline lamellae and the diameter of the peripheral fibers.     

Spermatogenesis and sperm ultrastructure in the polychaete genusOphryotrocha (Dorvilleidae)

The details of spermatogenesis and spermiogenesis are described forOphryotrocha puerilis. The ultrastructure of mature sperm is shown forO. puerilis, O. hartmanni, O. gracilis, O. diadema, O. labronica, andO. notoglandulata. Clusters of sixteen cells each are proliferated by two stem cells in each setigerous segment ofO. puerilis representing the very early stages of both oogenesis and spermatogenesis. In each spermatocyte-I cluster, the cells are interconnected by cytoplasmic bridges. Early, clusters are enveloped by peritoneal sheath cells. These transient gonad walls break down prior to meiosis. The meiotic processes may start in the clusters with the cells still interconnected, or during breakdown of the original cluster, giving rise to smaller subclusters of both spermatocytes I and spermatocytes II with various numbers of cells. Finally, spermatid tetrads are present. As spermiogenesis progresses, the tetrads disintegrate. Golgi vesicles in both spermatocytes and spermatids contain electron-dense material, presumably preacrosomal. The acrosome is formed by such vesicles. In the six species studied here, the acrosomes appear to be of a similar overall structure but are of different shape. Centrioles are usually located beneath the acrosome. The distal centriole forms the basal body of a flagellum-like cytoplasmic process. The microtubules of these flagellar equivalents do not show a normal ciliar arrangement. The flagellar equivalent appears to be non-motile. InO. hartmanni and inO. notoglandulata, a flagellar equivalent is missing. Microtubules originating from the proximal end of the distal centriole stretch to the nuclear envelope. This feature appears to be especially conspicuous inO. puerilis and inO. labronica. InO. labronica and inO. notoglandulata, bundles of microtubules paralleling the cell perimeter appear to stabilise the sperm. Various numbers of mitochondria are either randomly distributed around the nucleus or accumulate on one side, often directly under the acrosome. Parts of the present paper were presented at the 2^nd International Polychaete Conference, Copenhagen 1986 and at the 3^rd International Polychaete Conference, Long Beach, Ca. 1989.     

Partial purification of presynaptic plasma membrane by immunoadsorption

Chlamydomonas flagella exhibit force transduction in association with their surface. This flagellar surface motility is probably used both for whole cell gliding movements (flagella-substrate interaction) and for reorientation of flagella during mating (flagella-flagella interaction). The present study seeks to identify flagellar proteins that may function as exposed adhesive sites coupled to a motor responsible for their translocation in the plane of the plasma membrane. The principal components of the flagellar membrane are a pair of glycoproteins (approximately 350,000 mol wt), with similar mobility on SDS polyacrylamide gels. A rabbit IgG preparation has been obtained which is specific for these two glycoproteins; this antibody preparation binds to and agglutinates cells by their flagellar surfaces only. Treatment of cells with 0.1 mg/ml pronase results in a loss of motility-coupled flagellar membrane adhesiveness. This effect is totally reversible, but only in the presence of new protein synthesis. The major flagellar protein modified by this pronase treatment is the faster migrating of the two high molecular weight glycoproteins; the other glycoprotein does not appear to be accessible to external proteolytic digestion. Loss and recovery of flagella surface binding sites for the specific antibody parallels the loss and recovery of the motility-coupled flagellar surface adhesiveness, as measured by the binding and translocation of polystyrene microspheres. These observations suggest, but do not prove, that the faster migrating of the major high molecular weight flagellar membrane glycoproteins may be the component which provides sites for substrate interaction and couples these sites to the cytoskeletal components responsible for force transduction.     

Desmosomes and hemidesmosomes in the flagellate Crithidia fasciculata

Summary The flagellum of the trypanosomatid flagellate Crithidia fasciculata expands asymmetrically as it emerges from the reservoir. Where the flagellar memhrane approaches the membrane lining the reservoir, desmosomes are found. These structures are arranged in several slightly curved lines and have many features in common with vertebrate desmosomes.In cultures, the flagellates stick to each other by their flagella and form rosettes. In these bundles of cells, probable sites of adhesion between flagella, or between flagella and pieces of debris, are marked by a dense filamentous tract which passes posteriorly along the flagellum and by a thick band lying just below the flagellar membrane. It is suggested that similar adhesions are found in the insect host where the flagellate attaches itself to the gut wall.