CHANGE IN THE ACTIVITY OF LIPASE IN SEA URCHIN EGGS AND EMBRYOS DURING EARLY DEVELOPMENT*

During the early development of the sea urchin, Anthocidaris crassispina, the activity of lipase was maintained at the same level as in unfertilized eggs until the mesenchymal blastula stage (20 hr culture at 20°C) and then increased gradually after gastrulation. The activity in the embryos kept in SO^2?₄-free artificial sea water changed in a similar manner to that in those kept in normal sea water, during the development until 36 hr of fertilization. At 48 hr, the activity in the embryos, which had developed to the permanent blastulae in SO^2?₄-free sea water, was markedly lower than in normal plutei and was similar to that in unfertilized eggs. The lipase activity in fertilized eggs 30 min after fertilization, which was almost the same as that in unfertilized eggs was found mainly to be localized in the precipitate fraction obtained by the centrifugation at 12,000 x g for 20 min, whereas the activity in unfertilized eggs was found in the precipitate by the centrifugation at 105,000 x g for 60 min. Ca²⁺, adenosine 3′, 5′-cyclic monophosphate (cAMP) and guanosine 3′, 5′-cyclic monophosphate (cGMP) had no effect on the lipase activity.     

Effect of α,α'-dipyridyl on Exogut Formation in Vegetalized Embryos of the Sea Urchin

In presumptive vegetalized embryos, obtained by 3-hr treatment with chloramphenicol at the 16–32 cell stage, the rates of [¹⁴C]proline incorporation into the collagen fraction and production of the [¹⁴C]hydroxyproline residues increased during development between 16 hr (equivalent to mesenchyme blastula stage) and 40 hr (the early pluteus stage) after fertilization at 20°C. In presumptive vegetalized embryos, the radioactivity of [¹⁴C]hydroxyproline residues was higher at the mesenchyme blastula stage (16 hr after fertilization), but lower at the post-gastrula stage than in normal embryos. In normal embryos at the post-gastrula stage, [¹⁴C]hydroxyproline residues were mainly found in isolated spicules, and the amounts of [¹⁴C]hydroxyproline residues in other parts were much lower than in vegetalized embryos, which had few, if any, spicules. α, α'-Dipyridyl, an inhibitor of prolyl hydroxylase, inhibited the hydroxylation of [¹⁴C]proline residues in presumptive vegetalized and normal embryos, and blocked the formation of the archenteron and exogut.     

CONCANAVALIN A-INDUCED AGGLUTINATION AND BINDING OF CON A TO THE DIFFERENTIATING CELLS OF DICTYOSTELIUM DISCOIDEUM

Changes in agglutinability of Dictyostelium discoideum cells with Concanavalin A (Con A) during the course of development were investigated. The agglutinability of the cells was assayed under conditions where no spontaneous cell agglutination occurred. It was found that there was a progressive decrease in Con A-induced agglutinability during development: a decrease to half from exponentially growing cells to preaggregation cells, and to sixth in disaggregated slug cells. Pronase-BAL treatment of preaggregation cells did not enhance their agglutinability with Con A. The amounts of sites available for binding Con A were determined with preaggregation and slug cells. Cells were incubated at 4°C and in the presence of NaN₃ to avoid possible endocytosis of Con A. No significant differences in numbers of Con A-binding sites per unit area of cell surface was detected among preaggregation cells, those treated with pronase and BAL and cells disaggregated from slugs by similar treatment. It was thus concluded that the decrease in Con A-induced agglutinability during development is not attributable to changes in the numbers of Con A-binding sites.     

Changes in Activities of Glucose Metabolising Enzymes in Germ Cells during Spermatogenesis in Rats

The rate of ¹⁴CO₂, liberation from [¹⁴C-1]glucose was identical to that from [¹⁴C-6]glucose in spermatids, but more than the latter in spermatogonia. Rotenone (1 μM) completely inhibited ¹⁴CO₂ release from [¹⁴C-1]glucose in spermatids, but decreased it only 30% in spermatogonia. The activity of glucose-6-phosphate dehydrogenase, but not 6-phosphogluconate dehydrogenase, was markedly lower in spermatocytes and spermatids than in spermatogonia. The activities of the glycolytic enzymes, glucosephosphate isomerase, fructose diphosphatase, glyceraldehyde-3-phosphate dehydrogenase and enolase, differed only slightly in spermatids and spermatogonia. It is concluded that the low glucose-6-phosphate dehydrogenase activity may contribute to the low activity of the pentose cycle in spermatocytes and spermatids.     

Intercellular Contacts Between the Embryonic or Extraembryonic Ectoderm and the Primitive Endoderm in Rat Egg Cylinders Prior to the Formation of Primitive Streak

In pre-primitive streak-stage rat egg cylinders, both the embryonic and extraembryonic ectodermal cells projected cytoplasmic protrusions through gaps in the basal lamina and formed intimate cell-to-cell contact with the primitive endodermal cells. The 70 Å microfilaments were considered to participate in the production of these cytoplasmic protrusions. However, direct cell contact mediated by adherent junctions was occasionally found between the embryonic or extraembryonic ectodermal cells and the primitive endodermal cells. It has been proposed that these cell-to-cell contacts may play a role either in the supporting effect of primitive endodermal cells in the maintenance of cellular organization of the ectodermal cells, or in the facilitation of transport of nutritive materials from the primitive endodermal cells to both types of ectodermal cells.     

Role of Cell Sorting in Pattern Formation in Dictyostelium discoideum

To examine the relationship between cell sorting and cell differentiation in the development of Dictyostelium discoideum , labeled cells grown in the absence of glucose [G(–) cells] and unlabeled cells grown in its presence [G(+) cells] were mixed and either allowed to undergo normal morphogenesis or cultured under submerged conditions. Changes in the distributions within a cell aggregate of labeled cells and cells stained with the conjugated antispore serum (prespore cells) were followed on the same sections by the methods of autoradiography and immunohistochemistry. In normal morphogenesis, differentiation of prespore cells apparently initiated and proceeded coincident with sorting out between G(+) and G(–) cells, during formation of a standing slug. By contrast, within an aggregate formed under submerged conditions, prespore cells began to differentiate long before G(+) and G(–) cells were sorted out, indicating that the cell sorting is not a prerequisite for the cell differentiation. The sorting out, however, brought about an accumulation of prespore cells in a hemisphere, thus producing a prestalk-prespore pattern within the aggregate.