19 citations found in entrez
Mech Dev 60 (1): 3-12 (1996)
Expression of S9 and actin CyIIa mRNAs reveals dorso-ventral polarity
and mesodermal sublineages in the vegetal plate of the sea urchin embryo
Miller RN, Dalamagas DG, Kingsley PD, Ettensohn CA
Department of Biological Sciences, Carnegie Mellon University, Pittsburgh,
PA 15213, USA.
We have used whole amount in situ hybridization to analyze the patterns
of expression of two genes, S9 and actin CyIIa, during the development
of the sea urchin, Strongylocentrotus purpuratus. We demonstrate that at
the late blastula stage, these two mRNAs are expressed specifically by
cells of the vegetal plate. Their domains of expression, however, are different.
S9 mRNA is broadly distributed within most of the vegetal plate except
for the central region, while CyIIa expression is restricted to a population
of 10-15 cells in the ventral region of the plate. S9-expressing secondary
mesenchyme cells (SMCs) migrate from the vegetal plate into the blastocoel
early in gastrulation and later populate the dorsal ectoderm. The numbers,
morphology, and migratory behavior of these cells strongly suggest that
they are pigment cells. Throughout gastrulation, CyIIa mRNA is expressed
by a population of presumptive SMCs at the ventral aspect of the archenteron
tip. The pattern of expression of this mRNA is dynamic, however, and by
the early pluteus stage, CyIIa mRNA accumulates in primary mesenchyme cells
(PMCs), SMCs, and endodermal cells of the gut. When embryos are treated
with NiCl2, a compound that has been shown to ventralize other embryonic
tissues, CyIIa mRNA is expressed by an increased number of cells in the
vegetal plate in a radially symmetrical pattern. The spatial pattern of
CyIIa expression provides the first direct molecular evidence that the
vegetal plate is polarized along the dorso-ventral (D-V) axis of the embryo.
This gene product should be a valuable marker in future studies of D-V
axis specification, as it can be detected at earlier developmental stages
than existing molecular markers of this axis. Our observations show that
the vegetal plate consists of subterritories of gene expression, and provide
further support for the view that diversification of the presumptive, non-skeletogenic
mesoderm begins prior to the onset of invagination.
J Biol Chem 271 (8): 4468-4476 (1996)
A large family of putative transmembrane receptors homologous to the
product of the Drosophila tissue polarity gene frizzled.
Wang Y, Macke JP, Abella BS, Andreasson K, Worley P, Gilbert DJ, Copeland
NG, Jenkins NA, Nathans J
Department of Molecular Biology, Howard Hughes Medical Institute, The Johns
Hopkins University School of Medicine, Baltimore, Maryland 21205, USA.
In Drosophila melanogaster, the frizzled gene plays an essential role in
the development of tissue polarity as assessed by the orientation of cuticular
structures. Through a combination of random cDNA sequencing, degenerate
polymerase chain reaction amplification, and low stringency hybridization
we have identified six novel frizzled homologues from mammals, at least
11 from zebrafish, several from chicken and sea urchin, and one from Caenorhabditis
elegans. The complete deduced amino acid sequences of the mammalian and
nematode homologues share with the Drosophila frizzled protein a conserved
amino-terminal cysteine-rich domain and seven putative transmembrane segments.
Each of the mammalian homologues is expressed in a distinctive set of tissues
in the adult, and at least three are expressed during embryogenesis. As
hypothesized for the Drosophila frizzled protein, the frizzled homologues
are likely to act as transmembrane receptors for as yet unidentified ligands.
These observations predict the existence of a family of signal transduction
pathways that are homologous to the pathway that determines tissue polarity
in Drosophila.
Anal Biochem 232 (1): 43-46 (1995)
Determination of microtubule polarity in vitro by the use of video-enhanced
differential-interference contrast light microscopy and Chlamydomonas flagellar
axonemal pieces.
Gamblin TC, Williams RC Jr
Department of Molecular Biology, Vanderbilt University, Nashville, Tennessee
37235, USA.
Microtubules nucleated by sea urchin sperm-tail axonemes have polar ends
that differ both functionally and structurally but cannot be distinguished
from one another when viewed by light microscopy. Ambiguity and circularity
surround any classification of microtubule polarity by conventional methods.
Chlamydomonas flagellar axonemal pieces have distinct morphological differences
at their plus- and minus-ends, and microtubules nucleated from these pieces
can be distinguished as plus- or minus-ended based on the morphological
differences present in the Chlamydomonas flagellar axonemal pieces. Plus-
and minus-ended microtubules were polymerized in this fashion and analyzed
for differences in growth rates, shortening rates, and frequencies of transitions.
The results were in good agreement with similar data generated by the more
time-consuming and difficult use of kinesin-coated beads (R. J. Kowalski,
and R. C. Williams, Jr. (1993) Cell Motil. Cytoskeleton 26, 282-290) to
determine microtubule polarity. This is a relatively simple and effective
method for determining the polarity of microtubules in vitro by video-enhanced
differential-interference contrast light microscopy.
Dev Biol 171 (1): 195-211 (1995)
Characterization of the SpHE promoter that is spatially regulated along
the animal-vegetal axis of the sea urchin embryo.
Wei Z, Angerer LM, Gagnon ML, Angerer RC
Department of Biology, University of Rochester, New York 14627, USA.
To understand how the maternally determined animal-vegetal polarity of
the sea urchin embryo is established, we have begun to examine the regulatory
apparatus of the gene encoding the Strongylocentrotus purpuratus hatching
enzyme (SpHE). Previous studies have shown that the pattern of SpHE mRNA
accumulation reflects the animal-vegetal developmental axis in that transcription
is strongly upregulated during early cleavage in more animal blastomeres,
but not in those around the maternally specified vegetal pole of the 16-cell
embryo [Reynolds et al., Development 114, 769-786 (1992)]. Tests of SpHE
promoter function in vivo using chloramphenicol acetyltransferase and beta-galactosidase
enzymatic reporters define a regulatory region within several hundred nucleotides
of the transcription initiation site. This region is sufficient to mediate
both strong expression in the early blastula and spatially correct transcription.
However, neither this region nor longer upstream sequences are sufficient
to reproduce the transcriptional downregulation after very early blastula
stage that is observed for endogenous genes. Biochemical assays of protein-DNA
interactions within the regulatory region identify at least nine sites
binding at least six different factors. These cis elements include Otx
(an orthodenticle homologue), CCAAT, ets-related, and three unidentified
motifs. Deletions and/or replacements of these cis-elements, alone and
in combination, indicate that no single factor is essential for SpHE promoter
activity, but instead that various combinations of subsets of these elements
are capable of eliciting levels of transcription similar to those of the
unaltered regulatory region. This density of regulatory elements is consistent
with the intense transcription of endogenous SpHE genes during cleavage.
Biophys J 68 (3): 739-748 (1995)
Spatiotemporal relationships among early events of fertilization in
sea urchin eggs revealed by multiview microscopy.
Suzuki K, Tanaka Y, Nakajima Y, Hirano K, Itoh H, Miyata H, Hayakawa
T, Kinosita K Jr
Department of Physics, Faculty of Science and Technology, Keio University,
Yokohama, Japan.
Four early events of egg fertilization, changes in intracellular calcium
concentration and intracellular pH, reorientation of the surface membrane,
and the elevation of the fertilization envelope, were imaged in real time
and in pairs in single sea urchin eggs. The paired imaging allowed the
correlation of the four events spatially and temporally. Three of them
propagated as waves starting at the sperm entry site. The earliest was
the calcium wave, visualized with fluorescent indicator dyes. After a delay
of 10 s there followed a large decrease in the fluorescence polarization
of membrane-bound dyes, which we interpret as arising from membrane reorientation
as a result of cortical granule exocytosis and microvillar elongation.
With a further delay of 15 s the fertilization envelope was seen to rise
in transmitted light. All three waves propagated with similar velocities
of approximately 10 microns/s, supporting the view that calcium triggers
the latter two events. The fluorescence polarization changed in two steps
with a clear pause of 10-20 s in between. The second step, which also propagated
as wave, reflects either further elongation of microvilli or straightening
of irregular microvilli. This second step was abolished by cytochalasin
B and was coincident with an increase in cytoplasmic pH, suggesting that
pH-induced actin reorganization may play a role. The cytoplasmic alkalinization,
imaged with a fluorescent probe, was quite different from the other events
in that it took place homogeneously throughout the egg and slowly (over
100 s). Apparently, the alkalinization is not on a direct downstream pathway
of calcium origin. An opposing possibility, that the alkalinization may
in fact be triggered by the traveling calcium wave, is also discussed.
J Cell Biol 119 (6): 1641-1648 (1992)
Phorbol esters alter cell fate during development of sea urchin embryos.
Livingston BT, Wilt FH
School of Biological Sciences, University of Missouri, Kansas City 64110-2499.
Protein kinase C (PKC) has been implicated as important in controlling
cell differentiation during embryonic development. We have examined the
ability of 12-O-tetradecanoyl phorbol-13-acetate (TPA), an activator of
PKC, to alter the differentiation of cells during sea urchin development.
Addition of TPA to embryos for 10-15 min during early cleavage caused dramatic
changes in their development during gastrulation. Using tissue-specific
antibodies, we have shown that TPA causes the number of cells that differentiate
as endoderm and mesoderm to increase relative to the number that differentiate
as ectoderm. cDNA probes show that treatment with TPA causes an increase
in accumulation of RNAs specific to endoderm and mesoderm with a concomitant
decrease in RNAs specific to ectoderm. Treatment of isolated prospective
ectodermal cells with TPA causes them to differentiate into endoderm and
mesoderm. The critical period for TPA to alter development is during early
to mid cleavage, and treatment of embryos with TPA after that time has
little effect. These results indicate that PKC may play a key role in determining
the fate of cells during sea urchin development.
Development 116 (3): 671-685 (1992)
Commitment along the dorsoventral axis of the sea urchin embryo is
altered in response to NiCl2.
Hardin J, Coffman JA, Black SD, McClay DR
Department of Zoology, University of Wisconsin, Madison 53706.
Few treatments are known that perturb the dorsoventral axis of the sea
urchin embryo. We report here that the dorsoventral polarity of the sea
urchin embryo can be disrupted by treatment of embryos with NiCl2. Lytechinus
variegatus embryos treated with 0.5 mM NiCl2 from fertilization until the
early gastrula stage appear morphologically normal until the midgastrula
stage, when they fail to acquire the overt dorsoventral polarity characteristic
of untreated siblings. The ectoderm of normal embryos possesses two ventrolateral
thickenings just above the vegetal plate region. In nickel-treated embryos,
these become expanded as a circumferential belt around the vegetal plate.
The ectoderm just ventral to the animal pole normally invaginates to form
a stomodeum, which then fuses with the tip of the archenteron to produce
the mouth. In nickel-treated embryos, the stomodeal invagination is expanded
to become a circumferential constriction, and it eventually pinches off
as the tip of the archenteron fuses with it to produce a mouth. Primary
mesenchyme cells form a ring in the lateral ectoderm, but as many as a
dozen spicule rudiments can form in a radial pattern. Dorsoventral differentiation
of ectodermal tissues is profoundly perturbed: nickel-treated embryos underexpress
transcripts of the dorsal (aboral) gene LvS1, they overexpress the ventral
(oral) ectodermal gene product, EctoV, and the ciliated band is shifted
to the vegetal margin of the embryo. Although some dorsoventral abnormalities
are observed, animal-vegetal differentiation of the archenteron and associated
structures seems largely normal, based on the localization of region-specific
gene products. Gross differentiation of primary mesenchyme cells seems
unaffected, since nickel-treated embryos possess the normal number of these
cells. Furthermore, when all primary mesenchyme cells are removed from
nickel-treated embryos, some secondary mesenchyme cells undergo the process
of "conversion" (Ettensohn, C. A. and McClay, D. R. (1988) Dev. Biol. 125,
396-409), migrating to sites where the larval skeleton would ordinarily
form and subsequently producing spicule rudiments. However, the skeletal
pattern formed by the converted cells is completely radialized. Our data
suggest that a major effect of NiCl2 is to alter commitment of ectodermal
cells along the dorsoventral axis. Among the consequences appears to be
a disruption of pattern formation by mesenchyme cells.
Cell Motil Cytoskeleton 21 (3): 223-234 (1992)
Fertilization alters the orientation of pigment granule saltations
in Arbacia eggs.
Allen PG, Baltz JM, Begg DA
Department of Anatomy and Cellular Biology, Harvard Medical School, Boston,
Massachusetts.
Unfertilized eggs of the sea urchin Arbacia punctulata contain pigment
granules distributed throughout their cytoplasm. During the first 15 minutes
after fertilization, these vesicles move out to the cortex where they become
firmly anchored. We have used time-lapse video differential interference
microscopy to analyze the motility of these organelles in unfertilized
and fertilized Arbacia eggs. Pigment granules exhibit saltatory movement
in both unfertilized and fertilized eggs. Quantitation of vesicle saltations
before and after fertilization demonstrates that while there is no significant
difference in the speed or path-length of vesicle movement, there is a
dramatic change in the orientation of these saltations. Saltations in the
unfertilized egg are very non-radial and are as likely to be directed toward
the cortex as away. In contrast, saltations in the fertilized egg are more
radially oriented and more likely to be cortically directed. This transition
must reflect underlying changes in the cellular structures necessary for
pigment granule saltations. The change in the orientation of pigment granule
saltations following fertilization requires both a transient increase in
the cytoplasmic concentration of Ca2+ and an elevation of cytoplasmic pH.
Similarly, the ability of pigment granules to adhere to the cortex requires
both the transient elevation of cytoplasmic Ca2+ and the alkalinization
of the cytoplasm. As the reorganization of cortical actin at fertilization
is regulated by these ionic fluxes, and both movement and adhesion are
sensitive to cytochalasins, we hypothesize that the alterations in directed
motility and adhesion reflect underlying changes in the actin cytoskeleton.
Biochim Biophys Acta 1028 (2): 117-140 (1990)
Membrane fractions display different lipid and enzyme content in three
cell types in 16-cell stage embryos of sea urchins.
Sparling ML, Kruszewska B
Biology Department, California State University, Northridge 91330.
Three cell types were isolated from dissociated 16-cell sea urchin embryos.
Four membrane density fractions from discontinuous gradients have different
proportions of lipids, surfacer markers and enzymes for the three cell
types. Assays of lipid content, CH/PLIPID and SPH/PC ratios, acyl chain
length, level of unsaturation by proton NMR and assays of enzyme activity
revealed variation at the same density between the three cell types and
among different densities from one cell type. There were also differences
between whole embryos and dissociated embryo cells. There was no typical
membrane domain at a particular density common to the cell types. Cell
surface characteristics and polarity of adult cells rely on which lipid
domains and enzymes are present, their association with cytoskeleton and
how they are localized. At the 16-cell stage these characteristics are
still very dynamic as revealed by cytochemical localization of Na+/K(+)-ATPase
which varied with cell type and suggests endocytosis at set times in the
division cycle. Polarity has not been permanently set for Na+/K(+)-ATPase
yet. Membrane enzyme and lipid distributions unique to the three cell types
seen in this study suggest parcelling out or insertion of new membrane
domains occurs during early sea urchin cleavage. Perturbation of membrane
density distribution and lipid content occurs after treatment of embryos
with animalizing and vegetalizing teratogens which alter development.
Gene 76 (1): 181-185 (1989)
Gene arrangement in sea star mitochondrial DNA demonstrates a major
inversion event during echinoderm evolution.
Smith MJ, Banfield DK, Doteval K, Gorski S, Kowbel DJ
Institute of Molecular Biology and Biochemistry, Department of Biological
Sciences, Simon Fraser University, Burnaby, BC, Canada.
The mitochondrial (mt) DNA from the sea star Pisaster ochraceus has been
isolated, restriction-mapped, and cloned into plasmid vectors. Both ribosomal
RNA genes, the genes for 12 of the 13 mitochondrial proteins, and 11 of
the tRNA genes have been localized by DNA sequence analyses. The sequence
arrangement of the genes is markedly different from that seen in sea urchin
mitochondrial DNA. A segment of the DNA molecule extending from tRNA(pro),
including the tRNA cluster, ND1, ND2, and 16S genes, is inverted in relation
to the sea urchin genome. The resulting gene order in the sea star is 12S,
16S, ND2, tRNA cluster, COI. As a result of the inversion, the transcriptional
polarity of ND1, ND2, and 16S genes are opposite to that of the 12S and
COI genes. The arrangement and transcriptional polarity of the other genes
mapped here is the same as seen in urchin.
Genes Dev 3 (3): 370-383 (1989)
Progressively restricted expression of a homeo box gene within the
aboral ectoderm of developing sea urchin embryos.
Angerer LM, Dolecki GJ, Gagnon ML, Lum R, Wang G, Yang Q, Humphreys
T, Angerer RC
Department of Biology, University of Rochester, New York 14627.
A homeo box-containing gene, Hbox1 is expressed in an unusual and highly
conserved spatial pattern in embryos of two different species of sea urchin,
Tripneustes gratilla and Strongylocentrotus purpuratus. Hybridization in
situ shows that this mRNA accumulates initially throughout the aboral ectoderm;
however, between blastula and pluteus stages, the region containing Hbox1
mRNA retracts gradually until only a small area around the vertex is labeled
in pluteus larvae. Aboral ectoderm appears cytologically uniform and also
accumulates uniform levels of other tissue-specific mRNAs. Therefore, the
Hbox1 pattern reveals a previously unsuspected heterogeneity of aboral
ectoderm cells and a polarity within this tissue. In S. purpuratus, the
Hbox1 gene product probably is not involved in initial specification of
cell fate, as this message does not achieve a significant fraction of its
peak abundance until almost hatching blastula stage, well after the time
aboral ectoderm cells have initiated a tissue-specific program of gene
expression. RNA blot and RNase protection analyses revealed low levels
of Hbox1 mRNA in all adult tissues examined. However, this message was
not detectable in mature eggs, suggesting that the Hbox1 gene does not
have a maternal function. In addition to highly conserved spatial and temporal
patterns of expression, the homeo box genes of these two urchin species
also are conserved highly in sequences outside the homeo domain, despite
the divergence of these two species (30-45 my). Two notable features of
the protein shared with several vertebrate homeo proteins are a short conserved
sequence encoded by an exon upstream of that encoding the homeo domain
and a large region of high serine and proline content.
Dev Biol 130 (1): 57-66 (1988)
Sea urchin primary mesenchyme cells: relation of cell polarity to the
epithelial-mesenchymal transformation.
Anstrom JA, Raff RA
Department of Anatomy, Bowman Gray School of Medicine, Wake Forest University,
Winston-Salem, North Carolina 27103.
In euechinoid sea urchin embryos, a subset of epithelial cells in the wall
of the blastula become pulsatile, elongate, lose connections with their
neighboring cells, and move into the blastocoel to form the primary mesenchyme
cells. The Golgi apparatus and microtubule organizing center (MTOC) are
located at the apical end of these epithelial cells. We show that as primary
mesenchyme cells begin to move into the blastocoel, the Golgi apparatus
and MTOC move to a new position adjacent to the apical side of the nucleus.
They do not move to a position between the nucleus and the leading (i.e.,
basal) end of the cell as they do in cultured fibroblasts undergoing directed
migration. In addition, we have inhibited the movement of membranous vesicles
to the cell surface by incubating embryos in the ionophore monensin. We
have used antibodies to msp130, a primary mesenchyme cell surface-specific
glycoprotein, to demonstrate that monensin inhibits the movement of msp130-containing
vesicles to the cell surface. Despite the inhibition of membrane shuttling
by monensin, primary mesenchyme cells ingress on schedule and display normal
cell-shape changes. We draw two conclusions from our data. First, the cellular
elongation that characterizes ingression is not due to the local insertion
of membrane at the leading (basal) end of the cell. Second, ingression
does not depend upon establishment of the same cell polarity required for
fibroblasts to carry out directed cell migration.
Dev Biol 127 (2): 235-247 (1988)
Cell polarity in sea urchin embryos: reorientation of cells occurs
quickly in aggregates.
Nelson SH, McClay DR
Department of Zoology, Duke University, Durham, North Carolina 27706.
Four apical components were used as markers for the apical end of the cell
in studies centering on cell polarity in the early blastula stage of sea
urchin embryos and in aggregates of cleavage stage cells. Cells were observed
to maintain their polarity for several hours if dissociated and cultured
in suspension. Orientation of cells in aggregates initially is random;
however, within 3 hr the cells have reoriented so that their apical-basal
axis corresponds to the correct inside-outside position in the aggregate.
This reorientation occurs before formation of a basal lamina or a new hyalin
layer in the aggregate, and appears to take place by a rotation or other
movement of individual cells. The polarity within each cell is maintained
during reorientation. An apical surface antigen is colocalized with concentrations
of filamentous actin. Treatment of isolated cells with cytochalasin B causes
the antigen to lose its apical position and eventually become distributed
around the outside of the cell. Microtubules are visible radiating from
two foci closely associated with the nucleus in untreated cells. Treatment
of isolated cells with nocodazole leaves the apical cell surface marker
and its associated actin undisturbed, but causes the nucleus to lose its
apical position. Cytochalasin B and colchicine both prevent reorientation
of cells in aggregates. Thus polarity appears to be a constant for the
cells, and their reorientation in aggregates occurs prior to the polarized
release of extraembryonic matrix and basal lamina.
Dev Biol 125 (2): 255-264 (1988)
Contact-independent polarization of the cell surface and cortex of
free sea urchin blastomeres.
Schroeder TE
Friday Harbor Laboratories, University of Washington, Friday Harbor 98250.
In a normal, intact sea urchin embryo blastomeres are structurally polarized
so that all microvilli and cortical "pigment granules" are situated at
the apical surfaces facing the hyaline layer and are absent from basolateral
surfaces facing adjacent blastomeres and the internal embryonic cavity.
To test the roles of intercellular contacts and the hyaline layer in the
process of establishing this blastomere polarity, these two factors were
experimentally eliminated; sea urchin eggs of four species were denuded
of the nascent hyaline layer soon after fertilization and then cultured
in calcium-free artificial seawater to prevent subsequent intercellular
adhesion and contact. Such free blastomeres divided normally and still
developed polarized distributions of microvilli and pigment granules resembling
those of the corresponding blastomeres in intact embryos. These results
indicate that the process of polarization is intrinsic to individual blastomeres
(self-polarization) and that neither intercellular contacts nor adhesion
of microvilli to the hyaline layer is necessary. The precise temporal and
spatial coincidence of the patterns of polarization and the division cycles
further suggests that a mechanistic link is maintained among cell division,
blastomere polarization, and probably also a heritable component of the
animal-vegetal axis.
Development 100 (4): 559-576 (1987)
Determination and morphogenesis in the sea urchin embryo.
Wilt FH
Department of Zoology, University of California, Berkeley 94720.
The study of the sea urchin embryo has contributed importantly to our ideas
about embryogenesis. This essay re-examines some issues where the concerns
of classical experimental embryology and cell and molecular biology converge.
The sea urchin egg has an inherent animal-vegetal polarity. An egg fragment
that contains both animal and vegetal material will produce a fairly normal
larva. However, it is not clear to what extent the oral-aboral axis is
specified in embryos developing from meridional fragments. Newly available
markers of the oral-aboral axis allow this issue to be settled. When equatorial
halves, in which animal and vegetal hemispheres are separated, are allowed
to develop, the animal half forms a ciliated hollow ball. The vegetal half,
however, often forms a complete embryo. This result is not in accord with
the double gradient model of animal and vegetal characteristics that has
been used to interpret almost all defect, isolation and transplantation
experiments using sea urchin embryos. The effects of agents used to animalize
and vegetalize embryos are also due for re-examination. The classical animalizing
agent, Zn2+, causes developmental arrest, not expression of animal characters.
On the other hand, Li+, a vegetalizing agent, probably changes the determination
of animal cells. The stability of these early determinative steps may be
examined in dissociation-reaggregation experiments, but this technique
has not been exploited extensively. The morphogenetic movements of primary
mesenchyme are complex and involve a number of interactions. It is curious
that primary mesenchyme is dispensable in skeleton formation since in embryos
devoid of primary mesenchyme, the secondary mesenchyme cells will form
skeletal elements. It is likely that during its differentiation the primary
mesenchyme provides some of its own extracellular microenvironment in the
form of collagen and proteoglycans. The detailed form of spicules made
by primary mesenchyme is determined by cooperation between the epithelial
body wall, the extracellular material and the inherent properties of primary
mesenchyme cells. Gastrulation in sea urchins is a two-step process. The
first invagination is a buckling, the mechanism of which is not understood.
The secondary phase in which the archenteron elongates across the blastocoel
is probably driven primarily by active cell repacking. The extracellular
matrix is important for this repacking to occur, but the basis of the cellular-environmental
interaction is not understood.
Exp Cell Res 160 (1): 73-82 (1985)
A marker of animal-vegetal polarity in the egg of the sea urchin Paracentrotus
lividus. The pigment band.
Sardet C, Chang P
We have examined the subequatorial accumulation of pigment granules (the
so-called 'pigment band') in the egg of the sea urchin Paracentrotus lividus,
which constitutes an unambiguous marker of animal-vegetal polarity. Most
of the reddish pigment granules are situated at the periphery of the egg.
They exhibit occasional saltatory movements and can aggregate into large
patches. Pigment granules are retained as a band in the isolated cortex
when the egg surface complex is isolated by shearing eggs attached to polylysine-coated
surfaces with calcium-free isotonic solutions. Pigment granules remain
as the main vesicular component of fertilized egg cortices or of unfertilized
egg cortices perfused with calcium to provoke cortical granule exocytosis.
They may be anchored to the isolated cortex through associations with the
plasma membrane and with an extensive subsurface network of rough endoplasmic
reticulum (rough ER). Pigment granules contain antimonate-precipitable
calcium and, in this respect and many others, resemble acidic vesicles
recently identified in the cortex of unpigmented sea urchin eggs. We discuss
the similarities observed between granules and acidic vesicles in various
urchin egg species and their possible functions.
J Embryol Exp Morphol 75: 87-100 (1983)
Establishment of embryonic axes in larvae of the starfish, Asterina
pectinifera.
Kominami T
In order to clarify the relationships between the first cleavage plane
and the embryonic axes, early cleavage pattern of the fertilized eggs of
the starfish. Asterina pectinifera was reexamined. It was ascertained that
the polar bodies were formed at the site to which the germinal vesicle
had closely located before the initiation of the meiotic division, and
that the first cleavage plane passed near this site of polar body formation.
While some of the early embryos of this starfish were observed to show
various cleavage patterns during early cleavage stage, more than 70% of
the embryos developed according to, so to say, the 'typical' cleavage pattern.
Next, horseradish peroxidase (HRP) was injected into one of the blastomeres
of the 2-cell- or 8-cell-stage embryos. The embryos were allowed to develop
up to either the early gastrula or the early bipinnaria stage and stained
to detect the descendants of the blastomere injected with HRP. In early
gastrulae still retaining radial symmetry, the activity of HRP injected
at the 2-cell stage was found only in one side of the embryo partitioned
by one of the symmetrical planes. When one of the four blastomeres lying
nearer to the polar bodies at the 8-cell stage was marked with HRP, its
descendants constituted one quarter of the anterior part of the gastrula,
and descendants of a blastomere opposite the polar bodies were found in
the posterior region of the embryo. It was concluded that the animal-vegetal
(AV) axis was pre-existing in the fertilized egg and that the first cleavage
plane contained this primary axis. In early bipinnariae with their dorsoventral
(DV) axes already established, the region of activity of the HRP injected
at the 2-cell stage was still demarcated by a plane which passed through
the AV axis, but the plane of the boundary had no fixed relation to the
DV axis. The results indicate that the first cleavage plane does not necessarily
correspond to the median plane of the starfish larva, unlike the case in
sea-urchin eggs (Horstadius & Wolsky, 1936). In other words, the DV
axis of the starfish embryo is not predetermined in the fertilized egg,
and might be established in the course of development through cell-to-cell
interactions, while the AV axis is established mainly according to the
pre-existing egg polarity.
Exp Cell Res 128 (2): 490-494 (1980)
The jelly canal marker of polarity for sea urchin oocytes, eggs, and
embryos.
Schroeder TE
Acta Embryol Exp (Palermo) 1: 47-57 (1978)
Research on the polarity of sea urchin (Paracentratus lividus) eggs
Lallier R