Cleavage and gastrulation in the egg-brooding, marsupial frog, Gastrotheca riobambae

Development ◽  
1985 ◽  
Vol 90 (1) ◽  
pp. 223-232
Author(s):  
Richard P. Elinson ◽  
Eugenia M. Del Pino
Keyword(s):  
Vital Staining ◽  
Yolk Sac ◽  
Small Cells ◽  
Size Difference ◽  
Animal Pole ◽  
Embryonic Disc ◽  
Slow Development ◽  
Vegetal Pole ◽  
Egg Brooding ◽  
Marginal Region

The marsupial frog Gastrotheca riobambae has several reproductive adaptations, most prominent of which is the incubation of the embryo in a pouch on the mother's back. We have followed cleavage and gastrulation by microscopical observation and by vital staining, and have found several alterations in these processes which may reflect the reproductive adaptations. The large, yolky egg has a cap of yolk-poor cytoplasm at the animal pole which is incorporated into a translucent blastocoel roof consisting of a single cell layer. The epithelium of the yolk sac is derived from the roof. The inconspicuous blastoporal lips form near the vegetal pole from cells of the marginal region. Gastrulation movements include the epibolic stretching of the surface towards the blastopore and a contraction of the vegetal surface. The blastoporal lips close over a small archenteron, and the cells of the lips become the embryonic disc, a discrete group of small cells which give rise to most of the embryo's body. The great size difference between animal and vegetal blastomeres during cleavage, the single-celled blastocoel roof, the dissociation in time between archenteron formation and its expansion, the embryonic disc and the slow development distinguish G. riobambae embryos from those of other frogs. The importance of the marginal region which produces the embryonic disc and the unimportance of the most animal region whose fate is primarily yolk sac emphasizes the role of the marginal region in amphibian development.

Ultrastructural changes in the avian vitelline membrane during embryonic development

Development ◽  
1969 ◽  
Vol 21 (3) ◽  
pp. 467-484
Author(s):  
Cynthia Jensen
Keyword(s):  
Embryonic Development ◽  
Mechanical Strength ◽  
Dual Role ◽  
Early Embryonic Development ◽  
Ultrastructural Changes ◽  
Vitelline Membrane ◽  
Entire Surface ◽  
Animal Pole ◽  
The Third ◽  
Vegetal Pole

The vitelline (yolk) membrane of the avian egg plays a dual role during early embryonic development; it encloses the yolk and provides a substratum for expansion of the embryo (Fig. 1). Expansion appears to be dependent upon the movement of cells at the edge of the blastoderm which is intimately associated with the inner layer of the vitelline membrane (New, 1959; Bellairs, 1963). The blastoderm (embryonic plus extraembryonic cells) has almost covered the entire surface of the yolk by the third and fourth days of incubation, and when this stage has been reached the vitelline membrane ruptures over the embryo and slips toward the vegetal pole. Rupture of the membrane during development appears to be the consequence of a decrease in its mechanical strength (Moran, 1936), which changes most rapidly at the animal pole (over the embryo).

GSK3beta/shaggy mediates patterning along the animal-vegetal axis of the sea urchin embryo

Development ◽  
1998 ◽  
Vol 125 (13) ◽  
pp. 2489-2498 ◽  
Author(s):  
F. Emily-Fenouil ◽  
C. Ghiglione ◽  
G. Lhomond ◽  
T. Lepage ◽  
C. Gache
Keyword(s):  
Sea Urchin ◽  
Wnt Pathway ◽  
Dominant Negative ◽  
Early Gene ◽  
Expression Domain ◽  
Animal Pole ◽  
Axial Patterning ◽  
Sea Urchin Embryo ◽  
Vegetal Pole ◽  
Dominant Negative Activity

In the sea urchin embryo, the animal-vegetal axis is defined before fertilization and different embryonic territories are established along this axis by mechanisms which are largely unknown. Significantly, the boundaries of these territories can be shifted by treatment with various reagents including zinc and lithium. We have isolated and characterized a sea urchin homolog of GSK3beta/shaggy, a lithium-sensitive kinase which is a component of the Wnt pathway and known to be involved in axial patterning in other embryos including Xenopus. The effects of overexpressing the normal and mutant forms of GSK3beta derived either from sea urchin or Xenopus were analyzed by observation of the morphology of 48 hour embryos (pluteus stage) and by monitoring spatial expression of the hatching enzyme (HE) gene, a very early gene whose expression is restricted to an animal domain with a sharp border roughly coinciding with the future ectoderm / endoderm boundary. Inactive forms of GSK3beta predicted to have a dominant-negative activity, vegetalized the embryo and decreased the size of the HE expression domain, apparently by shifting the boundary towards the animal pole. These effects are similar to, but even stronger than, those of lithium. Conversely, overexpression of wild-type GSK3beta animalized the embryo and caused the HE domain to enlarge towards the vegetal pole. Unlike zinc treatment, GSK3beta overexpression thus appeared to provoke a true animalization, through extension of the presumptive ectoderm territory. These results indicate that in sea urchin embryos the level of GSKbeta activity controls the position of the boundary between the presumptive ectoderm and endoderm territories and thus, the relative extent of these tissue layers in late embryos. GSK3beta and probably other downstream components of the Wnt pathway thus mediate patterning both along the primary AV axis of the sea urchin embryo and along the dorsal-ventral axis in Xenopus, suggesting a conserved basis for axial patterning between invertebrate and vertebrate in deuterostomes.

Fertilization and ooplasmic movements in the ascidian egg

Development ◽  
1989 ◽  
Vol 105 (2) ◽  
pp. 237-249 ◽  
Author(s):  
C. Sardet ◽  
J. Speksnijder ◽  
S. Inoue ◽  
L. Jaffe
Keyword(s):  
Polar Body ◽  
Surface Velocity ◽  
Second Phase ◽  
Animal Pole ◽  
Male Pronucleus ◽  
Vegetal Pole ◽  
Female Pronucleus ◽  
Ooplasmic Segregation ◽  
Second Polar Body ◽  
Sperm Aster

Using light microscopy techniques, we have studied the movements that follow fertilization in the denuded egg of the ascidian Phallusia mammillata. In particular, our observations show that, as a result of a series of movements described below, the mitochondria-rich subcortical myoplasm is split in two parts during the second phase of ooplasmic segregation. This offers a potential explanation for the origin of larval muscle cells from both posterior and anterior blastomeres. The first visible event at fertilization is a bulging at the animal pole of the egg, which is immediately followed by a wave of contraction, travelling towards the vegetal pole with a surface velocity of 1.4 microns s-1. This wave accompanies the first phase of ooplasmic segregation of the mitochondria-rich subcortical myoplasm. After this contraction wave has reached the vegetal pole after about 2 min, a transient cytoplasmic lobe remains there until 6 min after fertilization. Several new features of the morphogenetic movements were then observed: between the extrusion of the first and second polar body (at 5 and 24–29 min, respectively), a series of transient animal protrusions form at regular intervals. Each animal protrusion involves a flow of the centrally located cytoplasm in the animal direction. Shortly before the second polar body is extruded, a second transient vegetal lobe (‘the vegetal button’) forms, which, like the first, resembles a protostome polar lobe. Immediately after the second polar body is extruded, three events occur almost simultaneously: first, the sperm aster moves from the vegetal hemisphere to the equator. Second, the bulk of the vegetally located myoplasm moves with the sperm aster towards the future posterior pole, but interestingly about 20% remains behind at the anterior side of the embryo. This second phase of myoplasmic movement shows two distinct subphases: a first, oscillatory subphase with an average velocity of about 6 microns min-1, and a second steady subphase with a velocity of about 26 microns min-1. The myoplasm reaches its final position as the male pronucleus with its surrounding aster moves towards the centre of the egg. Third, the female pronucleus moves towards the centre of the egg to meet with the male pronucleus. Like the myoplasm, the migrations of both the sperm aster and the female pronucleus shows two subphases with distinctly different velocities. Finally, the pronuclear membranes dissolve, a small mitotic spindle is formed with very large asters, and at about 60–65 min after fertilization, the egg cleaves.

The Effect of a Temperature Gradient on the Early Development of the Frog

1928 ◽  
Vol 5 (4) ◽  
pp. 309-336
Author(s):  
I. L. DEAN ◽  
M. E. SHAW ◽  
M. A. TAZELAAR
Keyword(s):  
Cell Size ◽  
Small Cells ◽  
Tail Bud ◽  
Animal Cells ◽  
Differential Growth ◽  
Experimental Conditions ◽  
Animal Pole ◽  
Stage Of Development ◽  
Permanent Effect ◽  
Two Sides

1. Temperature gradients were passed through the developing frog's egg and embryos. These gradients were applied either (a) apico-basally, when they were either (i) adjuvant, or (ii) antagonistic to the egg's own main gradient; or (b) transversely to the egg's main axis--lateral gradients. 2. (a) By this means considerable modification of segmentation and of cell size was induced, and was especially marked in the mid-blastula. Adjuvant gradients accentuated the normal differences in cell size between the animal and vegetative poles. Antagonistic gradients produced a double gradient in cell size, the smallest cells being in the region of the equator, and animal cells, in extreme cases, larger than yolk cells. (b) Several cases of the non-formation or obliteration of the blastocoel were obtained by all methods of treatment. (c) Too high temperature with adjuvant gradient produced inhibition at the animal pole, the large retarded cells being very sharply marked off from the surrounding small cells. (d) Lateral gradients produced a great difference in cell size on the two sides of the eggy and, as in the cases of "inhibition," a sharp line of demarcation may appear between the large cells of the cooled side and the small cells of the heated side. (e) When two sets of exactly similar eggs were treated simultaneously in opposite ways, then those subjected to the adjuvant gradient were always, at the close of the experiment, at a more advanced stage of development than those subjected to an antagonistic gradient. Because of this the yolk cells of the "adjuvant" eggs were smaller than those of the "antagonistic" eggs, although the former were cooled and the latter heated. (f) There seems to be a slight permanent effect of the gradient applied during segmentation. Eggs treated with antagonistic gradient tend to develop into microcephalous tadpoles and vice versa. 3. (a) Antagonistic gradients during gastrulation cause a reduction of the gastrular angle. (For definition see Bellamy (1919).) (b) Antagonistic gradient causes the eggs to gastrulate sooner than adjuvant eggs under exactly similar experimental conditions. (c) In the neurula stage the differential effect of the gradient is seen in the inhibition of the head and dorsal region in those subjected to antagonistic gradient, and inhibition of tail and ventral region in those subjected to adjuvant gradient. (d) Whether this alteration of relative sizes of head and tail regions is maintained in later development has not yet been ascertained. (e) Eggs exposed to lateral gradients in all stages of gastrulation showed marked asymmetries, some of which were apparently regulated later, while others persisted till the death of the tadpole. 4. Side-to-side treatment in the tail bud stage caused the development of marked asymmetry as the result of differential growth of the two sides. As in the case of 3 (e) some tadpoles appeared to regulate back to normal, whereas others remained markedly asymmetrical till death.

Scanning electron microscopy of gastrulation in a sea urchin (Anthocidaris crassispina)

Development ◽  
1982 ◽  
Vol 67 (1) ◽  
pp. 27-35
Author(s):  
Shonan Amemiya ◽  
Koji Akasaka ◽  
Hiroshi Terayama
Keyword(s):  
Electron Microscopy ◽  
Scanning Electron Microscopy ◽  
Cell Formation ◽  
Cell Movement ◽  
Animal Pole ◽  
Vegetal Pole ◽  
Mesenchyme Cell ◽  
Major Motive ◽  
Mesenchyme Cells ◽  
Scanning Electron

Gastrulation in Anthocidaris was investigated by observing the inside and the outside of embryos by scanning electron microscopy. Furrows which possibly rėflect changes in intercellular interactions were observed on the outer surface (hyaline layer side) of embryos twice in development: firstly at the time of primary mesenchyme cell formation, and secondly at the time of vegetal plate indentation. In the latter case, the cells within and surrounding the vegetal plate appeared to change their shapes differently; the former (within the plate) having broader surfaces on the blastocoel side whereas the latter (surrounding the plate) having broader surfaces on the hyaline layer side. This suggests that the first phase of indentation may be mediated by the autonomous change of cell shape and intercellular adhesiveness, accompanied by an autonomous cell movement in the vegetal pole region. Although some pseudopodial linkages were observed between secondary mesenchyme cells on the top of the invaginating archenteron and the animal pole in the mid-gastrula and later stage embryos, they were thinner and smaller in number as compared to those in the Pseudocentrotus embryos. The rate of invagination appeared rather constant throughout gastrulation in contrast to the accelerated invagination in other embryos with larger blastocoel cavities. Moreover, the number of columnar cells on the dissected surface of embryos remained unaltered. These findings suggest that the secondary mesenchyme cells may act as a linker between the archenteron tip and the animal pole, but they may not generate major motive forces for archenteron invagination at least in the Anthocidaris embryos.

Specification of endoderm and mesoderm in the sea urchin

Zygote ◽  
1999 ◽  
Vol 8 (S1) ◽  
pp. S41-S41 ◽  
Author(s):  
David R. McClay
Keyword(s):  
Sea Urchin ◽  
Wnt Pathway ◽  
Special Significance ◽  
Nuclear Entry ◽  
Cell Stage ◽  
Animal Pole ◽  
Secondary Axis ◽  
Sea Urchin Embryo ◽  
Vegetal Pole

It has long been recognized that micromeres have special significance in early specification events in the sea urchin embryo. Micromeres have the ability to induce a secondary axis if transferred to the animal pole at the 16-cell stage of sea urchin embryos (Hörstadius, 1939). Without micromeres an isolated animal hemisphere develops into an ectodermal ball called a dauer blastula. Addition of micromeres to an animal half rescues a normal pluteus larva, including endoderm (Hörstadius, 1939). Despite these well-known experiments, however, neither the molecular basis of that induction nor the endogenous inductive role of micromeres in development was known. In recent experiments we learned that if one eliminates micromeres from the vegetal pole at the 16-cell stage the resulting embryo makes no secondary mesenchyme. Earlier it had been found that β-catenin is crucial for specification events that lead to mesoderm and endoderm (Wikra-manayake et al., 1998; Emily-Fenouil et al., 1998; Logan et al., 1999). We noticed that at the 16-cell stage β-catenin enters the nuclei of micromeres, then enters the nuclei of macromeres at the 32-cell stage (Logan et al., 1999). Since nuclear entry of β-catenin is known to be important for its signalling function in the Wnt pathway, we asked whether β-catenin functions in the micromere induction pathway.

Meiosis-associated calcium waves in ascidian oocytes are correlated with the position of the male centrosome

Zygote ◽  
2000 ◽  
Vol 8 (4) ◽  
pp. 285-293 ◽  
Author(s):  
Martin Wilding ◽  
Marcella Marino ◽  
Vincenzo Monfrecola ◽  
Brian Dale
Keyword(s):  
Intracellular Calcium ◽  
Calcium Release ◽  
Polar Body ◽  
Calcium Transients ◽  
Calcium Waves ◽  
Oocyte Activation ◽  
Animal Pole ◽  
Vegetal Pole ◽  
Sperm Penetration ◽  
Oocyte Cytoplasm

We have used confocal microscopy to measure calcium waves and examine the distribution of tubulin in oocytes of the ascidian Ciona intestinalis during meiosis. We show that the fertilisation calcium wave in these oocytes originates in the vegetal pole. The sperm penetration site and female meiotic apparatus are found at opposite poles of the oocyte at fertilisation, confirming that C. intestinalis sperm enter in the vegetal pole of the oocyte. Following fertilisation, ascidian oocytes are characterised by repetitive calcium waves. Meiosis I-associated waves originate at the vegetal pole of the oocyte, and travel towards the animal pole. In contrast, the calcium waves during meiosis II initiate at the oocyte equator, and cross the oocyte cytoplasm perpendicular to the point of emission of the polar body. Immunolocalisation of tubulin during meiosis II reveals that the male centrosome is also located between animal and vegetal poles prior to initiation of the meiosis II-associated calcium waves, suggesting that the male centrosome influences the origin of these calcium transients. Ascidians are also characterised by an increase in sensitivity to intracellular calcium release after fertilisation. We show that this is not simply an effect of oocyte activation. The data strongly suggest a role for the male centrosome in controlling the mechanism and localisation of post-fertilisation intracellular calcium waves.

Oxidation of

1993 ◽  
Vol 5 (2) ◽  
pp. 201 ◽  
Author(s):  
RG Wales ◽  
EE Waugh
Keyword(s):  
Yolk Sac ◽  
Metabolic Energy ◽  
Embryonic Tissue ◽  
Co2 Production ◽  
Acetate Metabolism ◽  
Embryonic Disc ◽  
Extraembryonic Membranes

Acetate metabolism by the sheep conceptus was assessed by measuring CO2 production during a 2.5-h incubation of embryos and samples of the extraembryonic membranes in HEPES-buffered media containing 1.12 mM [U-14C]acetate. The rate of oxidation of acetate by embryonic tissue showed little change between Days 13 and 15 of pregnancy but greatly decreased by Days 17 and 19. By contrast, oxidation of the substrate by the trophoblast increased substantially with development and was five times the early rate by Day 19. Oxidation of acetate by the yolk sac also increased 4-fold between Days 17 and 19. The addition of glucose to incubations of extraembryonic membranes resulted in some reduction in the oxidation of acetate by the yolk sac and allantois but had little effect on the trophoblast. At Days 13 and 15, the rate of oxidation of acetate by the embryonic disc was 6-7 times that by the trophoblast. As development progressed, this situation was reversed and by Day 19 the trophoblast metabolized more than five times the amount of acetate per microgram than did the Day-19 embryo. Although acetate metabolism by yolk sac and allantois on Day 17 was low, its metabolism by the yolk sac increased to values similar to those for the trophoblast at Day 19 but its utilization by the allantoic membrane remained low. Comparison of the estimates of ATP generated from acetate by these tissue with those published for glucose demonstrates that acetate is much less effective than glucose for the provision of metabolic energy.

scholarly journals Oriented cell divisions and cellular morphogenesis in the zebrafish gastrula and neurula: a time-lapse analysis

Development ◽  
1998 ◽  
Vol 125 (6) ◽  
pp. 983-994 ◽  
Author(s):  
M.L. Concha ◽  
R.J. Adams
Keyword(s):  
Cell Division ◽  
Time Lapse ◽  
Ventral Surface ◽  
Neural Plate ◽  
Common Mechanism ◽  
Gradual Transition ◽  
Animal Pole ◽  
Dorsal Midline ◽  
Vegetal Pole ◽  
The Central Nervous System

We have taken advantage of the optical transparency of zebrafish embryos to investigate the patterns of cell division, movement and shape during early stages of development of the central nervous system. The surface-most epiblast cells of gastrula and neurula stage embryos were imaged and analysed using a computer-based, time-lapse acquisition system attached to a differential interference contrast (DIC) microscope. We find that the onset of gastrulation is accompanied by major changes in cell behaviour. Cells collect into a cohesive sheet, apparently losing independent motility and integrating their behaviour to move coherently over the yolk in a direction that is the result of two influences: towards the vegetal pole in the movements of epiboly and towards the dorsal midline in convergent movements that strengthen throughout gastrulation. Coincidentally, the plane of cell division becomes aligned to the surface plane of the embryo and oriented in the anterior-posterior (AP) direction. These behaviours begin at the blastoderm margin and propagate in a gradient towards the animal pole. Later in gastrulation, cells undergo increasingly mediolateral-directed elongation and autonomous convergence movements towards the dorsal midline leading to an enormous extension of the neural axis. Around the equator and along the dorsal midline of the gastrula, persistent AP orientation of divisions suggests that a common mechanism may be involved but that neither oriented cell movements nor shape can account for this alignment. When the neural plate begins to differentiate, there is a gradual transition in the direction of cell division from AP to the mediolateral circumference (ML). ML divisions occur in both the ventral epidermis and dorsal neural plate. In the neural plate, ML becomes the predominant orientation of division during neural keel and nerve rod stages and, from late neural keel stage, divisions are concentrated at the dorsal midline and generate bilateral progeny (C. Papan and J. A. Campos-Ortega (1994) Roux's Arch. Dev. Biol. 203, 178–186). Coincidentally, cells on the ventral surface also orient their divisions in the ML direction, cleaving perpendicular to the direction in which they are elongated. The ML alignment of epidermal divisions is well correlated with cell shape but ML divisions within the neuroepithelium appear to be better correlated with changes in tissue morphology associated with neurulation.

Roles of Cortical and Subcortical Components in Cleavage Furrow Formation in Amphibia

1972 ◽  
Vol 11 (2) ◽  
pp. 543-556
Author(s):  
TSUYOSHI SAWAI
Keyword(s):  
Surface Layer ◽  
Xenopus Laevis ◽  
Species Specificity ◽  
Cleavage Furrow ◽  
Entire Surface ◽  
Animal Pole ◽  
The Future ◽  
Vegetal Pole ◽  
Triturus Pyrrhogaster

In the eggs of the newt, Triturus pyrrhogaster, 2 separate factors are recognized which take part in cleavage furrow formation. (1) The inductive capacity for the furrow formation by the cytoplasm lying under the cortex along the cleavage furrow (FIC); and (2) the reactivity of the overlying cortex to form a furrow in response to FIC. (1) FIC. The inductive capacity is shown by the fact that FIC induces a furrow on whichever part of the surface under which FIC is transplanted. FIC is distributed along the cleavage furrow and even extends along the future furrow plane ahead of the furrow tip. The distance FIC precedes the furrow tip is about 1.0 mm in the animal hemisphere and is less in the vegetal hemisphere. In the direction at right angles to the furrow plane, FIC does not spread more than 0.1 mm. FIC is also present in the eggs of Xenopus laevis. Species specificity of FIC for induction is not found between Triturus and Xenopus. (2) Surface layer. At the onset of the first cleavage, the reactivity of the cortex to form the furrow in answer to FIC induction is localized on the animal pole region. The reactivity of the cortex propagates medially as a belt along the surface towards the vegetal pole with the advancing tip of the cleavage furrow. After the furrow is completed, the reactivity begins to be lost from the animal pole region, and eventually over the entire surface. The reactivity, however, reappears on the animal pole region simultaneously with the second cleavage.

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