The blastocoelic fluid of sea urchin embryo induces exogastrulation

Abstract

The exogastrula-inducing activity of the blastocoelic fluid of sea urchin embryo was demonstrated by adding it to the culture medium of the late blastula stage. The active substance was separated by gel filtration and ultrafiltration, and its molecular weight was found to be in the range from 10,000 to 50,000. The activity was destroyed by trypsin and heat treatment. Since the treated embryos developed normally into pluteus larvae, except for the extrusion of archenteron toward the outside, the morphogenetic activity of the blastocoelic fluid was assumed to be exerted on the endoderm. Close examination of the exogastrulation process suggests that the evagination was due to some force pushing the endodermal plate toward the outside of the embryo.Gastrulation is the first remarkable morphogenetic event in the embryonic development of sea urchins. The mechanism of this process has not been sufficiently elucidated. Normal gastrulation of sea urchin embryos can easily be disturbed by vegetalizing agents such as lithium (Herbst, 1892; cf. Gustafson, '65) and chloramphenicol (Horstadius, '63; Fujiwara and Yasumasu, '74) and by chilling (Waterman, '34; Takahashi et al., '77), resulting in exogastrulation. These disturbances in normal development elicited by foreign srbstances suggest that there may possibly be some intrinsic controlling factorb), which can be affected by the external environment. In this regard, some morphogenetic factors have been reported in the unfertilized egg homogenate of sea urchin (Horstadius et al., '67; Josefsson and Horstadius, '69).On the other hand, Dan and Okazaki ('56) pointed out the importance of pseudopodia protruding from the secondary mesenchyme cells in the second step of gastrulation, by causing exogastrulation by affecting the attachment of pseudopodia to the roof of the blastocoel by either Ca deficiency or protease treatment. The same results were also reported independently by Gustafson and Kinnader ('56) from the cinematographic studies. Recently, it was reported by Berg and Akin ('71) that the blastocoelic fluid of blastula may have a special role in gastrulation. According to these authors, the gastrulation of sea urchin embryos reared in a culture medium containing blastocoelic fluid was arrested; permanent blastulae were maintained, and occasionally exogastrulae were formed as the blastocoelic fluid was made more dilute.It is thus conceivable that the blastocoelic fluid as an intrinsic factor may have an effect on the growth of secondary mesenchyme cells or on the movement of the invaginating cells of the endodermal plate. In this preliminary experiment, we attempted to isolate the active component(s) of blastocoelic fluid that induces exogastrulation, so as to characterize the intrinsic factors affecting gastrulation in sea urchin embryos, and also tried to analyze the process of exogastrulation. MATERIALS AND METHODSThe eggs of Anthocidaris crassispina obtained by introducing 0.53 M KC1 into the coelom were cultured after fertilization in normal sea water in th...

Generation of Aggregates of Mouse Embryonic Stem Cells that Show Symmetry Breaking, Polarization and Emergent Collective Behaviour <em>In Vitro</em>

“…A report by Marikawa et al 14 , whilst working with aggregates of mouse P19 Embryo Carcinoma (EC) cells formed by the hanging-drop method, reported the emergence of elongated structures of mesodermal origin reminiscent of the elongations that are observed with exogastrulae in amphibian and sea urchin embryos and Keller explants [15][16][17][18] . As this had not been observed with mouse embryonic stem cells (mESCs), we attempted to reproduce the behaviour observed with P19 EC cells using aggregates of mESCs 19 and we report culture conditions that lead to their symmetry breaking and axial elongation.…”

Localization of an Exogastrula‐Inducing Peptide (EGIP) in Embryos of the Sea Urchin Anthocidaris crassispina

“…However, EGIP-vesicles were scattered in mesenchyme Celts that had inclined before the inward movement of mesodermal cells at the blastula stage. The significance of EGIPvesicles in mesenchyme cells is unknown and we are investigating whether EGlPs in mesenchyme cells actually secrete into the blastocoel of the blastula, as proposed in an earlier report (12) …”

“…They induce the extrusion of the archenteron toward the outside of the embryo, which leads to exogastrulation, when they are added exogenously to embryos (12,19).…”

A Protein That Binds an Exogastrula‐Inducing Peptide, EGIP‐D, in the Hyaline Layer of Sea Urchin Embryos

“…Exogastrula-inducing activities were examined by monitoring the morphological changes that followed the addition of EGIP-D to the culture medium, as previously reported (6). In brief, 0.2-ml test samples were added to 0.2 ml of a suspension of embryos (which contained about 100 embryos) at the mesenchyme blastula stage.…”

“…They induce the extrusion of the archenteron toward the outside of the embryo and cause exogastrulation when they are added exogenously to embryos (6,12). Four EGIPs, designated A-D, were purified from mesenchyme blastulae and the amino acid sequences of all four peptides were determined (12)(13)(14).…”