Relation of Nodal expression to the specification of the dorsal-ventral axis and tissue patterning in the starfish Patiria pectinifera.

In this study, we attempted to reveal fundamental aspects of starfish embryogenesis, particularly embryonic axis specification or determination, in Patiria pectinifera. We first cloned PpNodal, which is known to play an important role in the specification of the embryonic axis in a wide range of animals, and studied its expression profile. PpNodal expression was first detected at the mid-blastula stage and showed a single peak around the onset of gastrulation.

Novel population of embryonic secondary mesenchyme cells in the keyhole sand dollar Astriclypeus manni.

We have found a novel embryonic cell population in the keyhole sand dollar Astriclypeus manni, which we refer to as lucent fluorescent cells (LFCs). Live LFCs are transparent, but emit autofluorescence after formaldehyde fixation. LFCs become noticeable in the vegetal plate of early gastrulae immediately after the appearance of pigment cells.

Involvement of Delta and Nodal signals in the specification process of five types of secondary mesenchyme cells in embryo of the sea urchin, Hemicentrotus pulcherrimus.

Secondary mesenchyme cells (SMCs) of the sea urchin embryo are composed of pigment cells, blastocoelar cells, spicule tip cells, coelomic pouch cells and muscle cells. To learn how and when these five types of SMCs are specified in the veg₂ descendants, Notch or Nodal signaling was blocked with γ-secretase inhibitor or Nodal receptor inhibitor, respectively. All types of SMCs were decreased with DAPT, while sensitivity to this inhibitor varied among them.

Specification process of animal plate in the sea urchin embryo.

The most animal part of the ciliated band of sea urchin larvae, the animal plate, is a specialized region in which elongated cells form long and non-beating cilia. To learn how this region is specified, animal halves were isolated from the early cleavage to pregastrulation stages. As is well known, the animal half that is isolated at the eight-cell stage develops into a 'dauerblastula', which forms long and non-beating cilia all around the surface.

Initial observation of potential factors involved in the specification process of oral-aboral axis in the sand dollar Scaphechinus mirabilis.

To elucidate factors involved in the oral-aboral axis specification, several observations and experiments were undertaken using the sand dollar Scaphechinus mirabilis. Unlike in Strongylcentrotus purpuratus, localization of mitochondria was not detected in unfertilized eggs. After fertilization, however, the bulk of mitochondria became localized to the opposite side of sperm entry.

Subequatorial cytoplasm plays an important role in ectoderm patterning in the sea urchin embryo.

To gain information on the process of ectoderm patterning, the animal halves of sea urchin embryos were isolated at various stages, and their morphology was examined when control embryos developed into pluteus larvae. The animal halves separated at the 8-cell stage developed into 'dauerblastula', without showing any conspicuous ectoderm differentiation. In contrast, some of the animal halves isolated at the 60-cell stage (after the sixth cleavage) formed a ciliated band and oral opening, suggesting that some patterning signal was transmitted from the vegetal to animal hemisphere during early cleavage.

Behavior of pigment cells closely correlates the manner of gastrulation in sea urchin embryos.

To know whether behavior of pigment cells correlates the process of gastrulation or not, gastrulating embryos of several species of regular echinoids (Anthocidaris crassispina, Mespilia globulus and Toxopneustes pileolus) and irregular echinoids (Clypeaster japonicus and Astriclypeus manni) were examined. In M. globulus and A.

Gastrulation in the sea urchin embryo: a model system for analyzing the morphogenesis of a monolayered epithelium.

Processes of gastrulation in the sea urchin embryo have been intensively studied to reveal the mechanisms involved in the invagination of a monolayered epithelium. It is widely accepted that the invagination proceeds in two steps (primary and secondary invagination) until the archenteron reaches the apical plate, and that the constituent cells of the resulting archenteron are exclusively derived from the veg2 tier of blastomeres formed at the 60-cell stage. However, recent studies have shown that the recruitment of the archenteron cells lasts as late as the late prism stage, and some descendants of veg1 blastomeres are also recruited into the archenteron.

Pigment cells trigger the onset of gastrulation in tropical sea urchin Echinometra mathaei.

In the tropical sea urchin Echinometra mathaei, pigment cells are just detectable before the onset of gastrulation, owing to an early accumulation of red pigment granules. Taking advantage of this feature, behavior of pigment cells was studied in relation to the processes of gastrulation. Before the initiation of primary invagination, pigment cells were arranged in a hemi-circle in the dorsal half of the vegetal plate.

Behavior and differentiation process of pigment cells in a tropical sea urchin Echinometra mathaei.

The behavior and differentiation processes of pigment cells were studied in embryos of a tropical sea urchin Echinometra mathaei, whose egg volume was one half of those of well-known sea urchin species. Owing to earlier accumulation of pigments, pigment cells could be detected in the vegetal plate even before the onset of gastrulation, distributed dorsally in a hemi-circle near the center of the vegetal plate. Although some pigment cells left the archenteron during gastrulation, most of them remained at the archenteron tip.

Timing of early developmental events in embryos of a tropical sea urchin Echinometra mathaei.

Egg volume of a tropical sea urchin Echinometra mathaei is about one half that of other well-known species. We asked whether such a small size of eggs affected the timings of early developmental events or not. Cleavages became asynchronous from the 7th cleavage onward, and embryos hatched out before completion of the 9th cleavage.

Specification of secondary mesenchyme-derived cells in relation to the dorso-ventral axis in sea urchin blastulae.

To learn how the dorso-ventral (DV) axis of sea urchin embryos affects the specification processes of secondary mesenchyme cells (SMC), a fluorescent dye was injected into one of the macromeres of 16-cell stage embryos, and the number of each type of labeled SMC was examined at the prism stage. A large number of labeled pigment cells was observed in embryos in which the progeny of the labeled macromere were distributed in the dorsal part of the embryo. In contrast, labeled pigment cells were scarcely noticed when the descendants of the labeled macromere occupied the ventral part.

In situ screening for genes expressed preferentially in secondary mesenchyme cells of sea urchin embryos.

In sea urchin embryos, four types of non-skeletogenic mesodermal cells are derived from secondary mesenchyme cells (SMCs). Although determining the complete lineage of SMCs is currently a high-priority goal, specific markers for each type of SMC-derived cell in Hemicentrotus pulcherrimus are unavailable. To identify genes preferentially expressed in the various types of SMC-derived cells, we constructed a cDNA library of the archenteron isolated from late gastrulae.

Cell adhesion and the negative cell surface charges in embryonic cells of the starfish Asterina pectinifera.

Spherical blastomeres of starfish embryos begin to adhere to neighboring blastomeres and to become columnar in shape from the 7(th) or 8(th) cleavage onward. Studying development of embryos in the presence of LiCl, we found that developmental changes in cell-cell contacts were accelerated by LiCl. In order to learn why LiCl increased the adhesiveness between blastomeres, the negative surface charge density was estimated by the method of cell electrophoresis.

Role of cell contact in the specification process of pigment founder cells in the sea urchin embryo.

Effects of LiCl on the specification process of pigment founder cells were examined in the sea urchin Hemicentrotus pulcherrimus. If embryos were treated with 30 mM LiCl during 4-7 or 7-10 hours postfertilization, pigment cells increased significantly. Aphidicolin treatment indicated that this increase was due to the increase in the pigment founder cells.

Specification and differentiation processes of secondary mesenchyme-derived cells in embryos of the sea urchin Hemicentrotus pulcherrimus.

Four types of mesoderm cells (pigment cells, blastocoelar cells, coelomic pouch cells and circumesophageal muscle cells) are derived from secondary mesenchyme cells (SMC) in sea urchin embryos. To gain information on the specification and differentiation processes of SMC-derived cells, we studied the exact number and division cycles of each type of cell in Hemicentrotus pulcherrimus. Numbers of blastocoelar cells, coelomic pouch cells and circumesophageal muscle fibers were 18.

Process of pigment cell specification in the sand dollar, Scaphechinus mirabilis.

The process of pigment cell specification in the sand dollar Scaphechinus mirabilis was examined by manipulative methods. In half embryos, which were formed by dissociating embryos at the 2-cell stage, the number of pigment cells was significantly greater than half the number of pigment cells observed in control embryos. This relative increase might have been brought about by the change in the arrangement of blastomeres surrounding the micromere progeny.

A cyto-embryological study of gastrulation in the sand dollar, Scaphechinus mirabilis.

Processes of gastrulation in the sand dollar Scaphechinus mirabilis were compared with those in the sea urchin Hemicentrotus pulcherrimus, which seemed to show a typical pattern of gastrulation. Measurement of the archenteron length clearly demonstrated that invagination processes in H. pulcherrimus are divided into two phases, the primary and secondary invagination.

Timers in Early Development of Sea Urchin Embryos: (sea urchin/timing mechanism/temperature dependency/mid-blastula transition/cytoplasmic clock).

To elucidate the timing mechanisms in the early development of sea urchin embryos, we measured the times of initiation of the first four cleavages, of ciliary movement, of primary mesenchyme cell ingression, and of gastrulation at four temperatures ranging from 11 to 20°C. The times of cleavage and of initiation of ciliary movement showed similar temperature dependency, indicating that these events may be controlled by a common timer (the first timer). Although batches of eggs often showed variation in the period between fertilization and the first cleavage, their subsequent cleavages were more regular.

Changes in the Pattern of Intercellular Junctions during Early Embryogenesis of the Starfish, Asterias amurensis: (starfish/cell adhesion/embryogenesis/dye transfer/carboxyfluorescein).

Changes in the cellular adhesion pattern during the early embryogenesis of a starfish Asterias amurensis were examined using carboxyfluorescein (CF) dye as a probe. CF that was injected into one of the blastomeres at the 2- or 4-cell stage was in all cases restricted to the progeny cells of the CF-labelled blastomere. With the advancement of gastrulation, however, the injected dye was distributed not only to the progeny of the labelled blastomere, but also to cells that originated from non-injected blastomeres.

The Role of Cell Adhesion in the Differentiation of Mesendodermal Tissues in the Starfish, Asterina pectinifera: (starfish/cell adhesion/ConA/mesendodermal tissue/cell number).

The role of cell-to-cell adhesion in the early embryogenesis of the starfish Asterina pectinifera was studied by using concanvalin A (ConA), an agent known to weaken cellular contact by binding to glycosides at the cell surface. The major change in morphology was a diminution in the volume of the endodermal tissues (the digestive tract) of the treated larvae. It was found by pulse treatment that this effect of ConA was stage-specific, and that the effective period corresponded to the stage when blastomeres become more cohesive.