Microtubule arrays of the zebrafish yolk cell: organization and function during epiboly

Development ◽  
1994 ◽  
Vol 120 (9) ◽  
pp. 2443-2455 ◽  
Author(s):  
L. Solnica-Krezel ◽  
W. Driever
Keyword(s):  
Danio Rerio ◽  
Developmental Changes ◽  
Microtubule Network ◽  
Cell Stage ◽  
Yolk Syncytial Layer ◽  
Animal Pole ◽  
Yolk Cell ◽  
Vegetal Pole ◽  
Cell Organization ◽  
And Function

In zebrafish (Danio rerio), meroblastic cleavages generate an embryo in which blastomeres cover the animal pole of a large yolk cell. At the 500–1000 cell stage, the marginal blastomeres fuse with the yolk cell forming the yolk syncytial layer. During epiboly the blastoderm and the yolk syncytial layer spread toward the vegetal pole. We have studied developmental changes in organization and function during epiboly of two distinct microtubule arrays located in the cortical cytoplasm of the yolk cell. In the anuclear yolk cytoplasmic layer, an array of microtubules extends along the animal-vegetal axis to the vegetal pole. In the early blastula the yolk cytoplasmic layer microtubules appear to originate from the marginal blastomeres. Once formed, the yolk syncytial layer exhibits its own network of intercrossing mitotic or interphase microtubules. The microtubules of the yolk cytoplasmic layer emanate from the microtubule network of the syncytial layer. At the onset of epiboly, the external yolk syncytial layer narrows, the syncytial nuclei become tightly packed and the network of intercrossing microtubules surrounding them becomes denser. Soon after, there is a vegetal expansion of the blastoderm and of the yolk syncytial layer with its network of intercrossing microtubules. Concomitantly, the yolk cytoplasmic layer diminishes and its set of animal-vegetal microtubules becomes shorter. We investigated the involvement of microtubules in epiboly using the microtubule depolymerizing agent nocodazole and a stabilizing agent taxol. In embryos treated with nocodazole, microtubules were absent and epibolic movements of the yolk syncytial nuclei were blocked. In contrast, the vegetal expansion of the enveloping layer and deep cells was only partially inhibited. The process of endocytosis, proposed to play a major role in epiboly of the yolk syncytial layer (Betchaku, T. and Trinkaus, J. P. (1986) Am. Zool. 26, 193–199), was still observed in nocodazole-treated embryos. Treatment of embryos with taxol led to a delay in all epibolic movements. We propose that the yolk cell microtubules contribute either directly or indirectly to all epibolic movements. However, the epibolic movements of the yolk syncytial layer nuclei and of the blastoderm are not coupled, and only movements of the yolk syncytial nuclei are absolutely dependent on microtubules. We hypothesize that the microtubule network of the syncytial layer and the animal-vegetal set of the yolk cytoplasmic layer contribute differently to various aspects of epiboly. Models that address the mechanisms by which the two microtubule arrays might function during epiboly are discussed.

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.

Memoirs: The Direct Development of a New Zealand Ophiuroid

1941 ◽  
Vol s2-82 (327) ◽  
pp. 377-440
Author(s):  
H. BARRACLOUGH FELL
Keyword(s):  
Bilateral Symmetry ◽  
Ventral Surface ◽  
Radial Symmetry ◽  
Early Ontogeny ◽  
Body Cavity ◽  
Cell Stage ◽  
Animal Pole ◽  
Early Stages ◽  
Vegetal Pole ◽  
Primitive Structure

1. The first cleavage may be either equal, or markedly unequal; when it is equal the next segmentation affects both blastomeres; when it is unequal the larger blastomere is believed to give rise to three cells, and the smaller remains undivided till the next cleavage. 2. At the eight-cell stage there are two quartets of blastomeres. The upper quartet, micromeres, occupy the animal pole. The lower quartet, macromeres, occupy the vegetal pole. 3. The blastula comprises micromeres and macromeres, and the blastocoel is small and becomes eccentric. No cilia are developed. 4. The gastrula is formed by the shallow imagination of the macromeres, accompanied by an extensive process of epiboly affecting the micromeres. More marked epiboly of cells on two sides of the blastomere produces in the early stages two crests which later disappear. These may indicate a trace of bilateral symmetry. Epiblast comes to lie on solid mes-hypoblast. The archenteron is transient, and gives rise to no structures. The blastopore occupies the position of the definitive mouth. 5. No larva ever forms, nor is there any vestige of a larval stage. 6. The solid gastrula is converted into the adult by assuming a radial symmetry directly, with no intermediate bilaterally symmetrical form, unless the two epibolic crests are regarded as vestiges of larval symmetry. 7. The podia appear as solid outgrowths, in which the hydrocoelic cavity develops by splitting. 8. The definitive enteron appears as a split extending upward from the ventral surface through the solid hypoblast. 9. The young ophiuroid leaves the egg before the appearance of the general body cavity, and moves about, but does not at first take food. 10. The general coelomic body cavity and the perihaemal cavity develop by splitting in a mass of mesenchyme derived from the outer layers of mes-hypoblast. 11. The formation of the skeletal system is delayed till the stage of between two and three arm-segments. 12. The development of the skeleton follows closely that described for Amphiura squamata. 13. The tooth is shown to originate independently of the torus angularis; its rudiments comprise nine symmetrically disposed spicules. 14. The terminal plate arises later than the radials, and has a distinctive ‘primitive structure’. 15. The spine is shown to have a different development to that of the tooth, and therefore would seem to have no connexion with the latter in phylogeny or ontogeny. 16. It is suggested that the aberrant early stages are to be correlated with the retarding effect of the yolk mass present in the egg during ontogeny. The aberrant features may have had a different origin in phylogeny. 17. It is suggested that the simultaneous appearance in ontogeny of homologous organs situated at equal radial distances from the centre is to be explained in terms of hormonic activity. 18. It is concluded that evolution has considerably affected the early ontogeny without leaving its mark on phylogeny. The adult thus conforms to its class, the young form does not.

scholarly journals Changes in γ-Tubulin Protein Distribution in Zebrafish (Danio rerio) Oocytes and the Early Cleavage-Stage Embryo

2013 ◽  
Vol 2013 ◽  
pp. 1-11
Author(s):  
Jianxiong Liu ◽  
Charles A. Lessman
Keyword(s):  
Nuclear Division ◽  
Protein Distribution ◽  
Early Cleavage ◽  
Cell Stage ◽  
Animal Pole ◽  
Yolk Cell ◽  
Cleavage Stage Embryo ◽  
Tubulin Antibodies ◽  
Stage Embryo ◽  
Tubulin Protein

We investigated the distribution of γ-tubulin in zebrafish oocytes and embryos using epifluorescent or confocal microscopy and γ-tubulin antibodies. During meiotic maturation of zebrafish oocytes, γ-tubulin begins redistribution from oocyte ooplasm and cortex to the future blastodisc region at the animal pole. In activated eggs, γ-tubulin was uniformly distributed in the enlarging blastodisc with label emanating from the yolk cell. In newly fertilized eggs, γ-tubulin was evenly distributed in blastomere cytoplasm, with the presence of pronuclei but initially lacking discernable centrosomes. During early cleavage, especially at the eight-cell stage, striking arc-shaped/rings (A/R) of putative centrosomes were detected. Decreasing γ-tubulin was seen in yolk cells while early cleavage blastomeres had strong cytoplasmic label along with obvious A/R arrays. In addition, we found the orientation of the A/R array and nuclear division alternated by about 90 degrees for each cell cycle along with alternation of punctate and A/R arrays.

scholarly journals Analysis of mitochondrial morphology and function with novel fixable fluorescent stains.

1996 ◽  
Vol 44 (12) ◽  
pp. 1363-1372 ◽  
Author(s):  
M Poot ◽  
Y Z Zhang ◽  
J A Krämer ◽  
K S Wells ◽  
L J Jones ◽  
...  
Keyword(s):  
Membrane Potential ◽  
Mitochondrial Membrane Potential ◽  
Mitochondrial Membrane ◽  
Epifluorescence Microscopy ◽  
Mitochondrial Morphology ◽  
Microtubule Network ◽  
Multiple Features ◽  
Permeabilized Cells ◽  
Dye Staining ◽  
And Function

Investigation of mitochondrial morphology and function has been hampered because photostable, mitochondrion-specific stains that are retained in fixed, permeabilized cells have not been available. We found that in live cell preparations, the CMXRos and H2-CMXRos dyes were more photostable than rhodamine 123. In addition, fluorescence and morphology of mitochondria stained with the CMXRos and CMXRos-H2 dyes were preserved even after formaldehyde fixation and acetone permeabilization. Using epifluorescence microscopy, we showed that CMXRos and H2-CMXRos dye fluorescence fully co-localized with antibodies to subunit I of cytochrome c oxidase, indicating that the dyes specifically stain mitochondria. Confocal microscopy of these mitochondria yielded colored banding patterns, suggesting that these dyes and the mitochondrial enzyme localize to different suborganellar regions. Therefore, these stains provide powerful tools for detailed analysis of mitochondrial fine structure. We also used poisons that decrease mitochondrial membrane potential and an inhibitor of respiration complex II to show by flow cytometry that the fluorescence intensity of CMXRos and H2-CMXRos dye staining responds to changes in mitochondrial membrane potential and function. Hence, CMXRos has the potential to monitor changes in mitochondrial function. In addition, CMXRos staining was used in conjunction with spectrally distinct fluorescent probes for the cell nucleus and the microtubule network to concomitantly evaluate multiple features of cell morphology.

scholarly journals Network-based approaches to quantify multicellular development

2017 ◽  
Vol 14 (135) ◽  
pp. 20170484 ◽  
Author(s):  
Matthew D. B. Jackson ◽  
Salva Duran-Nebreda ◽  
George W. Bassel
Keyword(s):  
Structure Function ◽  
Spatial Relations ◽  
Higher Order ◽  
Cellular Interaction ◽  
Cellular Organization ◽  
Multicellular Development ◽  
Cell Organization ◽  
Function Relationship ◽  
And Function ◽  
The Relationship

Multicellularity and cellular cooperation confer novel functions on organs following a structure–function relationship. How regulated cell migration, division and differentiation events generate cellular arrangements has been investigated, providing insight into the regulation of genetically encoded patterning processes. Much less is known about the higher-order properties of cellular organization within organs, and how their functional coordination through global spatial relations shape and constrain organ function. Key questions to be addressed include: why are cells organized in the way they are? What is the significance of the patterns of cellular organization selected for by evolution? What other configurations are possible? These may be addressed through a combination of global cellular interaction mapping and network science to uncover the relationship between organ structure and function. Using this approach, global cellular organization can be discretized and analysed, providing a quantitative framework to explore developmental processes. Each of the local and global properties of integrated multicellular systems can be analysed and compared across different tissues and models in discrete terms. Advances in high-resolution microscopy and image analysis continue to make cellular interaction mapping possible in an increasing variety of biological systems and tissues, broadening the further potential application of this approach. Understanding the higher-order properties of complex cellular assemblies provides the opportunity to explore the evolution and constraints of cell organization, establishing structure–function relationships that can guide future organ design.

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).

Anteroposterior patterning in the zebrafish, Danio rerio: an explant assay reveals inductive and suppressive cell interactions

Development ◽  
1996 ◽  
Vol 122 (6) ◽  
pp. 1873-1883 ◽  
Author(s):  
C.G. Sagerstrom ◽  
Y. Grinblat ◽  
H. Sive
Keyword(s):  
Danio Rerio ◽  
Neural Induction ◽  
Active Role ◽  
Cell Number ◽  
Type I ◽  
Animal Pole ◽  
Anteroposterior Patterning ◽  
Embryonic Shield ◽  
Low Levels ◽  
Neural Markers

We report the first extended culture system for analysing zebrafish (Danio rerio) embryogenesis with which we demonstrate neural induction and anteroposterior patterning. Explants from the animal pole region of blastula embryos ('animal caps') survived for at least two days and increased in cell number. Mesodermal and neural-specific genes were not expressed in cultured animal caps, although low levels of the dorsoanterior marker otx2 were seen. In contrast, we observed strong expression of gta3, a ventral marker and cyt1, a novel type I cytokeratin expressed in the outer enveloping layer. Isolated ‘embryonic shield’, that corresponds to the amphibian organizer and amniote node, went on to express the mesodermal genes gsc and ntl, otx2, the anterior neural marker pax6, and posterior neural markers eng3 and krx20. The expression of these genes defined a precise anteroposterior axis in shield explants. When conjugated to animal caps, the shield frequently induced expression of anterior neural markers. More posterior markers were rarely induced, suggesting that anterior and posterior neural induction are separable events. Mesodermal genes were also seldom activated in animal caps by the shield, demonstrating that neural induction did not require co-induction of mesoderm in the caps. Strikingly, ventral marginal zone explants suppressed the low levels of otx2 in animal caps, indicating that ventral tissues may play an active role in axial patterning. These data suggest that anteroposterior patterning in the zebrafish is a multi-step process.

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.

scholarly journals Cell-matrix adhesion controls Golgi organization and function by regulating Arf1 activation in anchorage dependent cells

2018 ◽  
Author(s):  
Vibha Singh ◽  
Chaitanya Erady ◽  
Nagaraj Balasubramanian
Keyword(s):  
Membrane Trafficking ◽  
Microtubule Network ◽  
Matrix Adhesion ◽  
Cell Matrix ◽  
Summary Statement ◽  
Golgi Fragmentation ◽  
And Function ◽  
Golgi Organization ◽  
Cell Matrix Adhesion ◽  
Constitutively Active

AbstractCell-matrix adhesion regulates membrane trafficking to control anchorage-dependent signaling. While a dynamic Golgi complex can contribute to this pathway, its control by adhesion remains untested. We find the loss of adhesion rapidly disorganizes the Golgi in mouse and human fibroblast cells, its integrity restored rapidly on re-adhesion to fibronectin (but not poly-l-lysine coated beads) along the microtubule network. Adhesion regulates the trans-Golgi more prominently than the cis /cis-medial Golgi, though they show no fallback into the ER making this reorganization distinct from known Golgi fragmentation. This is controlled by an adhesion-dependent drop and recovery of Arf1 activation, mediated through the Arf1 GEF BIG1/2 over GBF1. Constitutively active Arf1 disrupts this regulation and prevents Golgi disorganization in non-adherent cells. Adhesion regulates active Arf1 binding to the microtubule minus-end motor protein dynein to control Golgi reorganization, which ciliobrevin blocks. This regulation by adhesion controls Golgi function, promoting cell surface glycosylation on the loss of adhesion that constitutively active Arf1 blocks. This study hence identifies cell-matrix adhesion to be a novel regulator of Arf1 activation, controlling Golgi organization and function in anchorage-dependent cells.Summary StatementThis study identifies a role for cell-matrix adhesion in regulating organelle (Golgi) architecture and function which could have implications for multiple cellular pathways and function.

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