Synthesis of nucleic acid purines in the sea urchin embryo

Embryos of the sea urchin, Arbacia punctulata, were shown to utilize carboxyl labeled acetate and glycine for the synthesis of nucleic acids and protein.The hypothesis that DNA must arise exclusively from the pre-formed RNA of the virgin egg is unlikely since the specific activities of DNA and its isolated purines from the blastula were at least 10 times greater than the corresponding values for RNA.The specific activities of adenine and guanine of RNA formed from glycine-1-C¹⁴ were identical, whereas in DNA the specific activity of adenine was less than half that of guanine.Comparison of the specific activities of the DNA purines with the glycine in the medium indicated that a large part of the newly formed DNA arose from unlabeled endogenous precursor.     

Proteins, nucleic acids and acid hydrolases in the chick embryo tail bud

During the 3d and 4th days of incubation the tail bud displays cell degeneration which result in the complete involution of both postanal gut and primitive streak. In spite of the degenerations the amounts of DNA, RNA and proteins are still growing. Over this period the activities of acid phosphatase and cathepsin are changing. The specific activity of phosphatase reaches a maximum when the tissue resorption is most intensive. The specific activity of cathepsin is then at its lowest level but it has passed earlier through a maximum.     

Morphogenesis in the amphibian embryo fertilization and blastula formation

Summary The morphology of the cortex of the amphibian egg is discussed, with special reference to the hyaline membrane.The physical properties of the cortex are reviewed, especially those evidenced by the wound healing reaction. The participation of the hyaline membrane in this process is particularly emphasized.An analysis of the activation processes normally associated with fertilization indicates that they may be accounted for by three cortical contractions, two radially symmetrical, with center at the animal pole, and one asymmetrical (or bilaterally symmetrical) originating at the point of sperm entrance. The contractions may be spatially correlated with three wounds normally afflicted on the cortex, viz., the expulsion of the polar bodies and penetration of the sperm. The first cortical contraction leads to separation between egg surface and vitelline membrane, and consequently to rotation of orientation, the second leads to formation of the perivitelline space, and the third to grey crescent formation.The mechanisms of blastula formation and of volume regulation are finally discussed. The strong adhesion between the cells and the hyaline membrane are of special importance in the former process. The hydrostatic pressure exerted through the cortex tension of the individual cells is suggested to account for the transport of water against the osmotic pressure difference from cells to blastocoele. The tension in the hyaline membrane developing in the late blastula and early gastrula is suggested to control the volume of the embryo.     

Heterogeneity of liver acid phosphatases in developing chick embryo

1. The development, localization and heterogeneity of acid phosphatase and a Zn(2+)-activated acid phosphatase in cellular fractions of developing chick liver were studied. 2. Acid phosphatase is distributed abundantly in the particulate and soluble fractions. The soluble fraction is rich in Zn(2+)-activated acid phosphatase, which attains its peak activity at about 15 days of incubation. 3. The particulate acid phosphatase activity is inhibited by fluoride but not by sodium l(+)-tartrate or cysteine. On the other hand, the soluble Zn(2+)-activated acid phosphatase activity is inhibited by sodium l(+)-tartrate and cysteine but not by fluoride. 4. The pH optimum of these two enzymes is similar at about 5.6. 5. The soluble Zn(2+)-activated acid phosphatase activity appears to be thermally stabilized by the treatment with Triton X-100 or bovine serum albumin.     

Phospholipid turnover in hamster and chick embryo fibroblasts

The stability of the glycerol backbone of phosphatidyl choline, phosphatidyl ethanolamine and phosphatidyl serine was measured in growing and non-growing hamster and chick embryo fibroblasts. Major differences were found for the rates of degradation of the individual glycerophospholipids in both hamster and chick embryo fibroblasts: considerable degradation of phosphatidyl choline was detected over a 24 h period while at the same time no degradation of the glycerol backbone of phosphatidyl ethanolamine and phosphatidyl serine was observed. The patterns of stability of these glycerophospholipids were similar in growing and non-growing cells.     

Morphological differentiation of mitochondria in the early amphibian embryo

Three different cell types (epidermal cells, fibroblast-like Ruffini cells and undifferentiated cells) may be observed in cultures of cells isolated from the blastula of Ambystoma mexicanum. Electron micrographs show that the mitochondria in the two kinds of differentiated cells have the orthodox conformation; those in the undifferentiated cells the condensed conformation. Measurements of the area and the form factor demonstrate that the mitochondria in the differentiated cells are considerably larger than those in the undifferentiated cells, and that the three populations of mitochondria differ significantly from each other.     

Rayleigh instability of the inverted one-cell amphibian embryo

The one-cell amphibian embryo is modeled as a rigid spherical shell containing equal volumes of two immiscible fluids with different densities and viscosities and a surface tension between them. The fluids represent denser yolk in the bottom hemisphere and clearer cytoplasm and the germinal vesicle in the top hemisphere. The unstable equilibrium configuration of the inverted system (the heavier fluid on top) depends on the value of the contact angle. The theoretically calculated normal modes of perturbation and the instability of each mode are in agreement with the results from ComFlo computational fluid dynamic simulations of the same system. The two dominant types of modes of perturbation give rise to axisymmetric and asymmetric sloshing of the cytoplasm of the inverted embryos, respectively. This work quantifies our hypothesis that the axisymmetric mode corresponds to failure of development, and the asymmetric sloshing mode corresponds to development proceeding normally, but with reversed pigmentation, for inverted embryos.