scholarly journals Three in one: evolution of viviparity, coenocytic placenta and polyembryony in cyclostome bryozoans

2021 ◽  
Vol 21 (1) ◽  
Author(s):  
U. A. Nekliudova ◽  
T. F. Schwaha ◽  
O. N. Kotenko ◽  
D. Gruber ◽  
N. Cyran ◽  
...  
Keyword(s):  
Ultrastructural Study ◽  
Main Part ◽  
Structural Diversity ◽  
Early Embryo ◽  
Unique Combination ◽  
Nutritive Tissue ◽  
Pore Cells ◽  
Secondary Embryos ◽  
Cytoplasmic Bridges ◽  
Hydrostatic System

Abstract Background Placentation has evolved multiple times among both chordates and invertebrates. Although they are structurally less complex, invertebrate placentae are much more diverse in their origin, development and position. Aquatic colonial suspension-feeders from the phylum Bryozoa acquired placental analogues multiple times, representing an outstanding example of their structural diversity and evolution. Among them, the clade Cyclostomata is the only one in which placentation is associated with viviparity and polyembryony—a unique combination not present in any other invertebrate group. Results The histological and ultrastructural study of the sexual polymorphic zooids (gonozooids) in two cyclostome species, Crisia eburnea and Crisiella producta, revealed embryos embedded in a placental analogue (nutritive tissue) with a unique structure—comprising coenocytes and solitary cells—previously unknown in animals. Coenocytes originate via nuclear multiplication and cytoplasmic growth among the cells surrounding the early embryo. This process also affects cells of the membranous sac, which initially serves as a hydrostatic system but later becomes main part of the placenta. The nutritive tissue is both highly dynamic, permanently rearranging its structure, and highly integrated with its coenocytic ‘elements’ being interconnected via cytoplasmic bridges and various cell contacts. This tissue shows evidence of both nutrient synthesis and transport (bidirectional transcytosis), supporting the enclosed multiple progeny. Growing primary embryo produces secondary embryos (via fission) that develop into larvae; both the secondary embyos and larvae show signs of endocytosis. Interzooidal communication pores are occupied by 1‒2 specialized pore-cells probably involved in the transport of nutrients between zooids. Conclusions Cyclostome nutritive tissue is currently the only known example of a coenocytic placental analogue, although syncytial ‘elements’ could potentially be formed in them too. Structurally and functionally (but not developmentally) the nutritive tissue can be compared with the syncytial placental analogues of certain invertebrates and chordates. Evolution of the cyclostome placenta, involving transformation of the hydrostatic apparatus (membranous sac) and change of its function to embryonic nourishment, is an example of exaptation that is rather widespread among matrotrophic bryozoans. We speculate that the acquisition of a highly advanced placenta providing massive nourishment might support the evolution of polyembryony in cyclostomes. In turn, massive and continuous embryonic production led to the evolution of enlarged incubating polymorphic gonozooids hosting multiple progeny.

Intercellular communication in the early embryo of the ascidian Ciona intestinalis

Development ◽  
1988 ◽  
Vol 102 (1) ◽  
pp. 55-63 ◽  
Author(s):  
F. Serras ◽  
C. Baud ◽  
M. Moreau ◽  
P. Guerrier ◽  
J.A.M. Van den Biggelaar
Keyword(s):  
Intercellular Communication ◽  
Lucifer Yellow ◽  
Ciona Intestinalis ◽  
Early Embryo ◽  
Cell Stage ◽  
Early Embryos ◽  
Junctional Conductance ◽  
Voltage Dependent ◽  
Cytoplasmic Bridges ◽  
Series Of Experiments

We have studied the intercellular communication pathways in early embryos of the ascidian Ciona intestinalis. In two different series of experiments, we injected iontophoretically the dyes Lucifer Yellow and Fluorescein Complexon, and we analysed the spread of fluorescence to the neighbouring cells. We found that before the 32-cell stage no dye spread occurs between nonsister cells, whereas sister cells are dye-coupled, possibly via cytoplasmic bridges. After the 32-cell stage, dye spread occurs throughout the embryo. However, electrophysiological experiments showed that nonsister cells are ionically coupled before the 32-cell stage. We also found that at the 4-cell stage junctional conductance between nonsister cells is voltage dependent, which suggests that conductance is mediated by gap junctions in a way similar to that observed in other embryos.

Etude par cytochimie ultrastructurale des corpuscules périnucléaires présents dans les jeunes oocytes de Ilyanassa obsoleta Say (Mollusca gastéropode)

Development ◽  
1971 ◽  
Vol 25 (3) ◽  
pp. 423-438
Author(s):  
Yves Gerin
Keyword(s):  
Nuclear Envelope ◽  
Variable Thickness ◽  
Ultrastructural Study ◽  
Main Part ◽  
The Other ◽  
Perinuclear Region ◽  
Ilyanassa Obsoleta ◽  
Cytochemical Study ◽  
Ultrathin Sections

An ultrastructural cytochemical study of the perinuclear corpuscles found in young oocytes of Ilyanassa obsoleta Say (molluscan gastropod) Ultrastructural study of the perinuclear region of young oocytes of Ilyanassa obsoleta shows the existence of numerous corpuscles which we have called ‘perinuclear corpuscles’. These are composed of filaments, of variable thickness (15–45 nm) and frequently show contacts with the nuclear envelope. With the development of the oocyte, they scatter in the cytoplasm and then disappear. Treatment of ultrathin sections by pronase or by pepsin provokes the disappearance of the main part of the perinuclear corpuscle. The residual structures of these corpuscles are not digested either by RNase or by DNase. However, if a digestion is carried out with DNase and pronase together, it increases the contrast of the residual structures. On the other hand, the contrast of the perinuclear corpuscles is not altered by specific techniques for polysaccharides. The constitution and the role of the perinuclear corpuscles is discussed.

Germ line of Tetrodontophora bielanensis (Insecta, Collembola). Ultrastructural study on the origin of primordial germ cells

Development ◽  
1982 ◽  
Vol 72 (1) ◽  
pp. 183-195
Author(s):  
Jerzy Klag
Keyword(s):  
Germ Cells ◽  
Ultrastructural Study ◽  
Germ Line ◽  
Primordial Germ Cells ◽  
Early Embryo ◽  
The Other ◽  
Annulate Lamellae ◽  
Yolk Mass

In the early embryo of Tetrodontophora bielanensis (up to the stage of 500 blastomeres) nuage granules occur in two different locations: (1) in areas where the invaginating cleavage furrows have pushed fragments of the oosome into the yolk mass, and (2) in the oosome proper. In the first areas the granules are few in number and certain cells that have enclosed them in their cytoplasm eventually degenerate. The remaining cells arising in these areas are devoid of any nuage granules and differentiate into yolk cells. A different situation is observed in the other areas, where certain cells resulting from tangential divisions of the superficial blastomeres contain many nuage granules and represent primordial germ cells (PGCs). The incipient PGCs differ from the other cells of the embryo in possessing nuage granules associated with mitochondria and in lacking any annulate lamellae.

An ultrastructural study of the marine diatom Licmophora hyalina and its parasite Ectrogella perforans. II. Development of the fungus in its host

1980 ◽  
Vol 58 (24) ◽  
pp. 2557-2574 ◽  
Author(s):  
Chandralata Raghu Kumar
Keyword(s):  
Plasma Membrane ◽  
Host Cell ◽  
Ultrastructural Study ◽  
Typical Feature ◽  
Golgi Body ◽  
Marine Diatom ◽  
Host Plasma Membrane ◽  
Cytoplasmic Bridges ◽  
Dense Vesicles

The thallus of the fungus Ectrogella perforans Petersen inside its host, the diatom Licmophora hyalina Agardh, is surrounded initially by two electron-dense membranes, of which the outer one is the invaginated host plasma membrane and the inner one, the fungal plasma membrane. Later, new membranes are added between these two membranes and the fungal envelope consists of four to six membranes. When the fungal thallus is mature, all the membranes except the fungal plasmalemma break down and it secretes an amorphous wall around itself. This coincides with the breakdown of host organelles followed by death of the host cell. Zoosporogenesis begins after the sporangium becomes multinucleate. A peculiar "multitubular body" is always observed in the multinucleate sporangium. A typical feature of the multinucleate sporangium prior to zoosporogenesis is the presence of a ring of tubular cisternae around the nuclei, electron-dense vesicles, and granular vesicles.The tubular cisternae found around the nuclei move away and act as cleavage cisternae. The cleavage cisternae run perpendicular to the sporangial plasma membrane and delimit the sporangial mass into uninucleate units at the time of zoosporogenesis. Simultaneously, vesicles are pinched off from the Golgi body which act as cleavage vesicles. These cleavage vesicles fuse with each other and form cleavage furrows. The cleavage cisternae fuse with the plasma membrane outside and with the cleavage vesicles inside and thus deepen the cleavage furrows. The sporangial mass is thus divided into zoospore units and the units are connected only by narrow cytoplasmic bridges. The zoospores have their flagella developed already. The structure of primary zoospores, encysted primary zoospores, and encysted secondary zoospores is described here.

Reference Coordinate System Requirements for Geophysics

1975 ◽  
Vol 26 ◽  
pp. 87-92
Author(s):  
P. L. Bender
Keyword(s):  
Coordinate System ◽  
Polar Motion ◽  
Main Part ◽  
Measurement Techniques ◽  
Reference Points ◽  
Angular Motion ◽  
Coordinate Systems ◽  
Axis Of Rotation ◽  
The Earth ◽  
Fixed System

AbstractFive important geodynamical quantities which are closely linked are: 1) motions of points on the Earth’s surface; 2)polar motion; 3) changes in UT1-UTC; 4) nutation; and 5) motion of the geocenter. For each of these we expect to achieve measurements in the near future which have an accuracy of 1 to 3 cm or 0.3 to 1 milliarcsec.From a metrological point of view, one can say simply: “Measure each quantity against whichever coordinate system you can make the most accurate measurements with respect to”. I believe that this statement should serve as a guiding principle for the recommendations of the colloquium. However, it also is important that the coordinate systems help to provide a clear separation between the different phenomena of interest, and correspond closely to the conceptual definitions in terms of which geophysicists think about the phenomena.In any discussion of angular motion in space, both a “body-fixed” system and a “space-fixed” system are used. Some relevant types of coordinate systems, reference directions, or reference points which have been considered are: 1) celestial systems based on optical star catalogs, distant galaxies, radio source catalogs, or the Moon and inner planets; 2) the Earth’s axis of rotation, which defines a line through the Earth as well as a celestial reference direction; 3) the geocenter; and 4) “quasi-Earth-fixed” coordinate systems.When a geophysicists discusses UT1 and polar motion, he usually is thinking of the angular motion of the main part of the mantle with respect to an inertial frame and to the direction of the spin axis. Since the velocities of relative motion in most of the mantle are expectd to be extremely small, even if “substantial” deep convection is occurring, the conceptual “quasi-Earth-fixed” reference frame seems well defined. Methods for realizing a close approximation to this frame fortunately exist. Hopefully, this colloquium will recommend procedures for establishing and maintaining such a system for use in geodynamics. Motion of points on the Earth’s surface and of the geocenter can be measured against such a system with the full accuracy of the new techniques.The situation with respect to celestial reference frames is different. The various measurement techniques give changes in the orientation of the Earth, relative to different systems, so that we would like to know the relative motions of the systems in order to compare the results. However, there does not appear to be a need for defining any new system. Subjective figures of merit for the various system dependon both the accuracy with which measurements can be made against them and the degree to which they can be related to inertial systems.The main coordinate system requirement related to the 5 geodynamic quantities discussed in this talk is thus for the establishment and maintenance of a “quasi-Earth-fixed” coordinate system which closely approximates the motion of the main part of the mantle. Changes in the orientation of this system with respect to the various celestial systems can be determined by both the new and the conventional techniques, provided that some knowledge of changes in the local vertical is available. Changes in the axis of rotation and in the geocenter with respect to this system also can be obtained, as well as measurements of nutation.

Transmission Electron Microscopy Studies of Pore Cells in Limax Maximus

1977 ◽  
Vol 35 ◽  
pp. 656-657
Author(s):  
B. S. Beltz
Keyword(s):  
Electron Microscopy ◽  
Cell Periphery ◽  
Salivary Duct ◽  
Terrestrial Mollusc ◽  
Buccal Ganglia ◽  
Transmission Electron ◽  
Pore Cells ◽  
Gland Tissue ◽  
Storage Area ◽  
Limax Maximus

The cells which are described in this study surround the salivary nerve of the terrestrial mollusc, Limax maximus. The salivary system of Limax consists of bilateral glands, ducts, and nerves. The salivary nerves originate at the buccal ganglia, which are situated on the posterior face of the buccal mass, and run along the salivary duct to the gland. The salivary nerve branches several times near the gland, and eventually sends processes into the gland.The pore cells begin to appear at the first large branch point of the salivary nerve, near the gland (Figure 1). They follow the nerve distally and eventually accompany the nerve branches into the gland tissue. The cells are 20-50 microns in diameter and contain very small nuclei (1-5 microns) (Figure 2).The cytoplasm of the pore cells is segregated into a storage area of glycogen and an organelle region located in a band around the cell periphery (Figure 3).

Tumor Diagnosis

1982 ◽  
Vol 40 ◽  
pp. 262-265
Author(s):  
Bruce Mackay
Keyword(s):  
Electron Microscopy ◽  
Transmission Electron Microscopy ◽  
Differential Diagnosis ◽  
Light Microscopy ◽  
Clinical Examination ◽  
Ultrastructural Study ◽  
Diagnostic Procedures ◽  
Specific Diagnosis ◽  
Transmission Electron ◽  
Microscopic Diagnosis

The broadest application of transmission electron microscopy (EM) in diagnostic medicine is the identification of tumors that cannot be classified by routine light microscopy. EM is useful in the evaluation of approximately 10% of human neoplasms, but the extent of its contribution varies considerably. It may provide a specific diagnosis that can not be reached by other means, but in contrast, the information obtained from ultrastructural study of some 10% of tumors does not significantly add to that available from light microscopy. Most cases fall somewhere between these two extremes: EM may correct a light microscopic diagnosis, or serve to narrow a differential diagnosis by excluding some of the possibilities considered by light microscopy. It is particularly important to correlate the EM findings with data from light microscopy, clinical examination, and other diagnostic procedures.

Further Observations on the Virus of Epizootic Diarrhea of Infant Mice. An Electron Microscopic Study

1967 ◽  
Vol 25 ◽  
pp. 110-111
Author(s):  
W. G. Banfield ◽  
G. Kasnic ◽  
J. H. Blackwell
Keyword(s):  
Electron Microscope ◽  
Infected Cell ◽  
Microscopic Study ◽  
Intestinal Epithelium ◽  
Ultrastructural Study ◽  
Osmium Tetroxide ◽  
Lead Citrate ◽  
Electron Microscopic ◽  
Virus Particles ◽  
Infected Cells

An ultrastructural study of the intestinal epithelium of mice infected with the agent of epizootic diarrhea of infant mice (EDIM virus) was first performed by Adams and Kraft. We have extended their observations and have found developmental forms of the virus and associated structures not reported by them.Three-day-old NLM strain mice were infected with EDIM virus and killed 48 to 168 hours later. Specimens of bowel were fixed in glutaraldehyde, post fixed in osmium tetroxide and embedded in epon. Sections were stained with uranyl magnesium acetate followed by lead citrate and examined in an updated RCA EMU-3F electron microscope.The cells containing virus particles (infected) are at the tips of the villi and occur throughout the intestine from duodenum through colon. All developmental forms of the virus are present from 48 to 168 hours after infection. Figure 1 is of cells without virus particles and figure 2 is of an infected cell. The nucleus and cytoplasm of the infected cells appear clearer than the cells without virus particles.

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