Common Cytoplasmic Mass Research Articles

Morphology of Mitochondria in Syncytial Annelid Female Germ-Line Cyst Visualized by Serial Block-Face SEM.

Mitochondria change their morphology and distribution depending on the metabolism and functional state of a cell. Here, we analyzed the mitochondria and selected structures in female germ-line cysts in a representative of clitellate annelids – the white worm Enchytraeus albidus in which each germ cell has one cytoplasmic bridge that connects it to a common cytoplasmic mass. Using serial block-face scanning electron microscopy (SBEM), we prepared three-dimensional ultrastructural reconstructions of the entire selected compartments of a cyst at the advanced stage of oogenesis, i.e. the nurse cell, cytophore, and cytoplasmic bridges of all 16 cells (15 nurse cells and oocyte). We revealed extensive mitochondrial networks in the nurse cells, cytophore and mitochondria that pass through the cytoplasmic bridges, which indicates that a mitochondrial network can extend throughout the entire cyst. The dynamic hyperfusion state was suggested for such mitochondrial aggregations. We measured the mitochondria distribution and revealed their polarized distribution in the nurse cells and more abundant accumulation within the cytophore compared to the nurse cell. A close association of mitochondrial networks with dispersed nuage material, which seems to be the structural equivalent of a Balbiani body, not described in clitellate annelids so far, was also revealed.

An ultrastructural study of the ovary cord organization and oogenesis in Erpobdella johanssoni (Annelida, Clitellata: Hirudinida)

The aims of the present study were to analyze the ovary cord structure and oogenesis in Erpobdella johanssoni under light, fluorescent and transmission electron microscopy and to compare the obtained results with other clitellate annelids, especially with other arhynchobdellid leeches. Each of the paired ovaries is composed of the ovary wall (ovisac) and several (7–8) short, cone-shaped ovary cords. The ovary cords are of the “Erpobdella” type, i.e. they are short and polarized and five zones containing germ cells at consecutives stages of their development can be distinguished along their long axis. One, huge somatic cell (the apical cell), oogonia and premeiotic germ cells occur at the tip of the apical part of the ovary cord – zone I. Below, in zone II germ cells enter meiosis, whereas in zone III only a few cells continue meiosis and gather nutrients (oocytes), while the rest become nurse cells. In zone IV, huge vitellogenic oocytes form protuberances on the surface of the cord, and degenerating germ cells were observed at the base of the ovary cord (zones IV and V). The germline cells form syncytial cysts in zones I–III. The germline cysts have broadly the same architecture as in the ovaries of all of the clitellate annelids that have been described to date. Each germ cell in a cyst has only one cytoplasmic bridge connecting it to the common cytoplasmic mass – the cytophore. The cytophore is poorly developed, and it has the form of thin, long cytoplasmic strands. The presence of two categories of germ cells suggests a meroistic mode of oogenesis. The germline cysts are closely associated with somatic, follicular cells. There are two subpopulations of follicular cells: one envelops the growing oocytes, while the second is distributed between other germ cells. The entire ovary cord is additionally enveloped by a layer of somatic cells with a spongy appearance – the spongiosa cells. A characteristic feature of vitellogenic oocytes is the condensation of the chromosomes into a karyosome. Fully grown oocytes are excluded from the ovary cords and float freely in the ovisac lumen.

Ultrastructure of Spermatogenesis of Atriaster heterodus (Platyhelminthes, Monogenea, Polyopisthocotylea)

The development of spermatozoa in the Polyopisthocotylea Atriaster heterodus was studied by transmission electron microscopy. Spermatogonia were undifferentiated, with irregular nuclei and little cytoplasm. Primary spermatocytes had sparse chromatin and typical synaptonemal complexes. The nuclear chromatin of secondary spermatocytes was in patches along the nuclear envelope and throughout the nucleoplasm. The complete process of fusion of the early spermatids to a common cytoplasmic mass forming a rosette was elucidated. Nuclei migrated to the center of the mass and changed from round to lamellar or tubular in shape. At the borders of the common cytoplasmic mass, the irregular zones of differentiation had microtubules, mitochondria, nuclei, centrioles, and intercentriolar bodies that give rise to 2 flagella. The spermatozoa presented a continuous row of cortical microtubules surrounding 2 parallels axonemes of the 9+1 type.

Spermiogenesis and spermatozoon of Echinostoma caproni ( Platyhelminthes, Digenea): transmission and scanning electron microscopy, and tubulin immunocytochemistry

Spermiogenesis and the spermatozoon of Echinostoma caproni (from experimentally infested laboratory mice) were investigated by several methods. Transmission electron microscopy shows that spermiogenesis consists of a proximo-distal fusion of three processes followed by elongation of the spermatid. Scanning electron microscopy shows that the spermatozoon is a filiform cell, 235 μm in length, with a cylindrical anterior extremity and a broader posterior extremity. Epifluorescence microscopy, including immunocytochemistry of tubulin and labelling of nucleus with specific dyes, has provided valuable additional information. Migration of the nuclei from the common cytoplasmic mass of spermatids to the distal part of the elongating spermatids is visualized, and centrioles demonstrated in the proximal, anterior region, and the nucleus in the distal, posterior region of the spermatozoon. One axoneme has a distal extremity which in the mature spermatozoon extends 30 μm more distally than the other, with the result that the posterior part of the spermatozoon contains a single axoneme and the nucleus. Immunocytochemistry experiments show that a region, 15 μm in length, not labelled by the anti-tubulin antibodies with certain fixation-permeabilization procedures, corresponds to a region which, by transmission electron microscopy, shows external ornamentation on the membrane. This region has a bilaterally asymmetric pattern (in TEM), forms angles or coils according to the fixation used, and marks the boundary between two distinct patterns of movement. Spermiogenesis and the spermatozoon in E. caproni correspond to the general pattern found in the digeneans, with the exception of this asymmetric region. It is emphasized that the use of various methods provides a better understanding of sperm structure than transmission electron microscopy alone, particularly in the case of long, filiform spermatozoa.

Spermiogenesis in a Scutariellid (Platyhelminthes)

AbstractSpermiogenesis and spermatozoa were studied by transmission and scanning electron microscopy in Troglocaridicolasp., a scutariellid epizoic on a cavernicolous freshwater shrimp. Spermiogenesis involves elongation of the spermatid in which the nucleus elongates, but remains close to the common cytoplasmic mass. Flagella first grow in opposite direction and at a right angle to the cytoplasmic shaft, and centrioles show associate structures. Later, the two centrioles rotate and the flagella emerge parallel, but still perpendicular to the shaft. An apical process elongates at the extremity of the spermatid shaft. The spermatozoon shows active flagellar beating and undulations of the sperm body. The spermatozoon comprises an anterior ‘corkscrew’ region, the flagellar insertion region, a cytoplasmic region and a posterior nuclear region. The corkscrew contains an electron dense structure, not membrane‐bound, originating from the apical process of the spermatid. The flagella show the 9+‘1’ pattern, usual in Platyhelminthes. The cytoplasmic and nuclear regions show a cortical row of about 50 twisted longitudinal microtubules surrounding a row of electron dense, and not membrane‐bound, 25‐nm granules. These granules are original structures and seem to be known only in a few Platyhelminthes species in which a non‐flagellar movement of the spermatozoon occurs. Thus, it is hypothesised that the 25‐nm granules play a role in cellular motility. Sperm ultrastructure in Troglocaridicolashows major differences to that in the temnocephalids. It is therefore concluded that the phylogenetic position of the scutariellids within the Temnocephalidea should be reinvestigated.

Ultrastructure of spermatogenesis and sperm ofMulticotyle purvisi (Plathelminthes, Aspidogastrea)

The ultrastructure of spermatogenesis is described for the first time in an aspidogastrean. The zone of differentiation which is usually formed during digenean spermiogenesis was not observed inMulticotyle purvisi. Instead, spermatid components are assembled within the common cytoplasmic mass before the outgrowth of spermatids. Microtubules, mitochondrion, nucleus and axonemes including their basal body regions, migrate from the cytoplasm into the spermatid which is pinched off at the level of the arching membrane. An unusual, complex structure of the basal body region is described. Intercentriolar bodies and striated rootlets are left behind and quickly disappear from the residual cytoplasm. Despite these atypical aspects, spermiogenesis results in the formation of mature sperm with the ‘classical’ structure common to Digenea and Monogenea Polyopisthocotylea with the addition of some extra, non-cortical microtubules and a dense rod along part of the length of the sperm.

Ultrastructural Study of Spermatogenesis and Mature Spermatozoa of Paravortex cardii (Platyhelminthes, Dalyellioida)

AbstractThe spermatogenesis and mature spermatozoon of Paravortex cardii were studied by transmission electron microscopy. Meiotic divisions occur without cytokinesis and the spermatid nuclei appear embedded in a common cytoplasmic mass. The mature spermatozoon is filiform, very regular in contour and circular in cross‐section. A tubular lining of microtubules lying close to the plasma membrane is found along the spermatozoon. Rows of spherical glycogen particles with helical arrangement lay internal to the cortical microtubules. The spermatozoon of P. cardii may be divided into two regions, nuclear and cytoplasmic regions. The nuclear region contains an elongated nucleus with a densely packed nuclear material. The mitochondria are distributed throughout the cytoplasmic region; they pack tightly together and often fuse to form one large one. This spermatozoon lacks both acrosome and the so‐called dense bodies. A ciliary or centriolar apparatus was not observed. Accordingly, the spermatozoon of P. cardii is considered to be aflagellate in type. Spermatozoa are compared among flatworms, and some considerations on the significance of their ultrastructure for phylogeny in the Platyhelminthes are tentatively given.

Phylogenetic relationships between the families Capsalidae and Dionchidae (Platyhelminthes, Monogenea, Monopisthocotylea) indicated by the comparative ultrastructural study of spermiogenesis

Comparative ultrastructural observations were carried out on the spermiogenesis of the capsalid Caballerocotyla manteri Price and the dionchid Dionchus remorae MacCallum. At the beginning of spermiogenesis the zones of differentiation (ZD) jut out in all directions. A large mitochondrion shaped like a perforated bead, and through which the elongated nucleus passes, is found facing each ZD. Later the ZD become parallel and are embedded within the common cytoplasmic mass. Cortical longitudinal microtubules are present in the ZD at the outset of spermiogenesis, but they later disappear. The spermatozoon is long and filiform. It shows two parallel axonemes of the 9 +“1” flatworm pattern, the nucleus and mitochondrion, and no cortical microtubule. The ultrastructure of spermiogenesis and spermatozoon is remarkably similar in the two species studied, as in other capsalids previously described. Two characteristics, the perforated bead shape of the spermatid mitochondrion and the progressive disappearance of the microtubules of the ZD, may be considered as synapomorphies which indicate close phylogenetic relationships between the families Dionchidae and Capsalidae. This interpretation coincides with Llewellyn's (1971) scheme of the evolution of the monogeneans.

Comparative ultrastructural study of spermiogenesis in monogeneans (flatworms): 4. Diplectanum (Monopisthocotylea diplectanidae)

In Diplectanum sp., the common cytoplasmic mass, which contains 64 fused spermatids, is starshaped at the outset of spermiogenesis, but is globular and shows 64 parallel canals at the end. The zone of differentiation of each spermatid juts laterally into the inner enlarged part of each of these canals. The zone of differentiation contains a single centriole oriented perpendicular to its axis. After differentiation within a canal, separation of the spermatozoon occurs laterally to its anterior region. The mature spermatozoon is filiform, uniflagellate, about 20 μ m long, and shows (a) an anterior pointed centriolar adjunct; (b) a single centriole made up of nine singlets; (c) a 9 — “1”-type flagellum; (d) the distal tip of the axoneme, made up of only eight long singlets aligned along the cell membrane and associated with the filiform mitochondrion; (e) the nucleus, without any accompanying element. The spermatozoon pattern, with anterior flagellum and posterior nucleus, is inverted : it shows some resemblance to that of Acanthocephala.

Etude ultrastructurale comparée de la spermiogenènes des monogènes: I. Megalocotyle (Monopisthocotylea Capsalidae)

In Megalocotyle the zones of differentiation (ZD) are short and incomplete; there is no median cytoplasmic process or free flagella. Some peripheral microtubules are present in early ZD, but they disappear. Each nucleus of the common cytoplasmic mass inserts one extremity into a ZD. The mitochondria fuse around this extremity and form a beadlike perforated sphere. Later this sphere slides along the nucleus away from the plasmic membrane like a bead on a string. Each mitochondrial bead (MB), as it moves, trails part of its bulk in the form of a solid streamer; two parallel centrioles follow the MB, each generating a trailing 9+“1” flagellum. The result is a four-part ensemble extending from each MB to each ZD: the two axonemes, the streamer, and the nucleus, with no membrane separating it from the surrounding cytoplasm. Subsequently a cytoplasmic canal (CC) is formed. The arching membranes, originally located at the base of the ZD, migrate along the four-part ensembles as far as the MB, leaving behind two membranes which define the CC. This formation of the CC is remarkable in that it occurs after migration of the centrioles. At the end of spermiogenesis, the cytoplasmic mass reveals 64 parallel CC each containing an immature spermatozoid whose free rear extremity lengthens out. Each spermatozoid is then detached at its anterior extremity set in the cytoplasmic mass. As in most monopisthocotylean monogeneans, the mature spermatozoid of Megalocotyle lacks peripheral microtubules, although its early ZD has microtubules which subsequently disappear. This feature distinguishes it from trematodes and polyopisthocotylean monogeneans, whose mature spermatozoid keep their ZD microtubules.

Oogenesis in the annelid Enchytraeus albidus with special reference to the origin and cytochemistry of yolk

AbstractIn the annelid Enchytraeus albidus the ovary is composed of packets containing eight synchronously developing oocytes. Each oocyte in the packet is connected, via a bridge, to a common cytoplasmic mass. Developmental synchrony of oocytes within individual packets is probably related to the ooplasmic continuity.The young previtellogenic oocyte contains many polysomes, a few cisternae of smooth and rough endoplasmic reticulum, small Golgi complexes, and mitochondria. Many of the mitochondria are dumbbell‐shaped and may thus represent division stages.Vitellogenesis is marked by the appearance of peripherally located lipid yolk and small, densely staining granules scattered throughout the ooplasm. There is an increase of smooth endoplasmic reticulum, mitochondria, and enlarged Golgi elements. Small multivesicular‐like bodies, the early stages of developing yolk, are derived from the Golgi complex. The mature yolk sphere is bipartite and consists of (a) a variable number of dense spheres, the core bodies, which are produced in the ooplasm by the Golgi complex and which become embedded in (b) a dense matrix. The electron opaque tracer, horseradish peroxidase is incorporated into the oocyte and deposited in the matrix suggesting that this component of the yolk sphere is obtained by micropinocytosis. Enzyme digestions and various cytochemical techniques suggest that the core bodies are rich in carbohydrate, probably as glyco‐ or mucoproteins, and that the matrix is rich in lipid.

The Integumentary Mucous Secretions of the Ophiuroid Ophiocomina Nigra

The general histology of the integument of the ophiuroid Ophiocomina nigra is outlined. Two types of integumentary mucous glands are described in detail for the first time. The first is a multicellular gland, the basal end of which is located deep within the calcareous layer of the integument. The source of the secretion is a variable number of nuclei embedded in a common cytoplasmic mass filled with fine basiphil granules. These cells contributed their secretion to a duct which pursues a tortuous course through the integument. The ducts frequently branch and anastomose so that any one exit pore may extrude mucin derived from a number of separate, polynuclear sources. The structure so formed is, thus, a massive, multicellular gland. Histochemical studies demonstrate that the mucin is a highly sulphated acid mucopolysaccharide. The second type of mucus-secreting unit is a unicellular gland usually located superficially in the calcareous layer or sometimes restricted to the epidermis and distributed universally over the body. The secretion product of these cells is shown histochemically to be a simple acid mucopolysaccharide. The mucin secreted by the tube-foot glands is demonstrated also to be a highly sulphated acid mucopolysaccharide.The function of these secretions has been investigated to some extent. The massive glands secrete only under conditions of alarm and it is suggested that this mucus serves as a defence against predation. The unicellular glands secrete in a periodic fashion correlated with the act of feeding. This secretion is probably utilized in a suspension-feeding mechanism.