Eggs Of Psammechinus Miliaris Research Articles

Fertilization acid production in Psammechinus eggs under pH clamp conditions, and the effects of some pyrazine derivatives

The production of fertilisation acid in eggs of Psammechinus miliaris, fertilised with sperm, was studied under pH clamp conditions. The more usual procedure, in which acid production is recorded as a fall in pH of the external medium, can give reliable information about acid release, but the method is cumbersome compared with pH clamping. Inhibition of acid production by two pyrazines (amiloride and benzamil) was studied, as it has been reported that amiloride blocks acid formation in some species. No change in acid production was seen, although generation was slowed by amiloride. It is concluded that sodium-proton exchange following fertilisation does not occur through amiloride-sensitive channels.

Some comparative remarks on the transient change in lactic acid content in sea urchin eggs following fertilization

During the first few minutes following fertilization a transient increase in the concentration of lactic acid occurs in the eggs of Arbacia lixula, whereas no change at all is observed in the eggs of Paracentrotus liuidus. In the eggs of Psammechinus miliaris there is a transient decrease, soon followed by a recovery so that the level of the unfertilized egg is again reached.

Microelectrode experiments on unfertilized sea urchin eggs

A microelectrode inserted into an egg of Psammechinus miliaris is found to exhibit 5–10 mV positivity to an indifferent electrode. With two microelectrodes inserted into an egg, a current flow through one of them does not usually shift the potential of the other. It is concluded that the tips of the electrodes have not penetrated the membrane. The membrane resistance was measured after passing a comparatively strong current through two electrodes inserted into the egg, probably resulting in local destruction of the part of the membrane in contact with the tip of the electrodes. The mean value of membrane resistance was 1350 ohm. cm 2 in eggs from the surface form, and 1700 in eggs from the deep-water form. It is concluded that plasma membrane resistance of the unfertilized egg is of this order of magnitude or possibly somewhat higher.

Heavy metals, fertilization and cleavage in the eggs of Psammechinus miliaris

Heavy metals, fertilization and cleavage in the eggs of Psammechinus miliaris

The activation of the egg of the sea urchin Psammechinus miliaris by periodate

Sodium periodate in concentration 6.10 −5–9.10 −5 N has an activating effect on the eggs of Psammechinus miliaris. A membrane elevation occurred and cleavage started. It did not proceed beyond the 2–8 cell stage. The eggs activated subsequent to the periodate treatment exhibited the angular plasmolysis characteristic of fertilized eggs when immersed in a hypertonic medium. Even non activated periodate treated eggs behave differently from non pretreated eggs. The latter are often somewhat elongated in one direction and show a fine wrinkling on the surface. The former are spherical with a smooth surface. This behaviour indicates that the eggs have taken a step towards activation. Eggs activated subsequent to periodate treatment are as strongly stained with methylene blue as are fertilized eggs. In contrast the non activated pretreated or the non pretreated unfertilized eggs are very weakly or not at all stained with methylene blue. Iodate of corresponding concentrations has a much lower activating effect than sodium periodate. The activation of the eggs by periodate occurred even in absence of Ca. After transfer to Ca-containing medium the eggs underwent a contraction and the membrane became much more refractile.

Respiration during cell division in the egg of the sea urchin psammechinus miliaris.

The later divisions in the egg of Psammechinus miliaris are accompanied by variations in oxygen uptake. As in the embryo more and more cells divide simultaneously, the respiratory variations become more and more pronounced. The phenomenon is interpreted as an extra O2-uptake correlated with the mitosis. During the four divisions nos. 58 proportionality is approximated between number of cells dividing and extra O2 taken up. Thus, for the division period considered, the extra O2 consumed by a dividing cell approximates constancy, viz.: it is independent of the size of the dividing blastomere.

Action of periodate on the surface reactions attending the activation of the egg of the sea urchin, Psammechinus miliaris

A solution of jelly coat substance inhibits a normal differentiation of the fertilization membrane in eggs of Psammechinus miliaris. The contraction of the egg surface does not occur, the coagulation of the vitelline membrane and the merging of the cortical material with this membrane are impeded. Furthermore the eggs present a varying degree of di- or plurispermy in presence of jelly coat solution. All the effects of the jelly coat solutions which have been mentioned in the preceding paragraph are removed by addition of 5 × 10 −5N sodium periodate. Periodate has also a certain activating effect on the ripe eggs. Particularly it sensitizes the egg to the activating effect of brief exposures to hypertonic medium. Pretreatment of underripe eggs with periodate has a most striking improving effect on membrane formation and further development. The jelly coats of periodate pretreated eggs are more weakly precipitated upon addition of clupein than are eggs not pretreated. Periodate treatment has a harmful effect on the oocytes. They elongate and a deep constriction separates the oocyte into one nucleated and one non nucleated part. Numerous bulges and appendages are formed from the latter (Fig. 11). It is inferred that underripeness is caused by the predominance of an inhibitor having a character similar to that of the jelly coat substance. The belief is expressed that the inhibitory agent is deeply engaged in the whole activation process.

Studies on the surface layers and the formation of the fertilization membrane in sea urchin eggs

Studies were carried out on the surface layers and the formation of the fertilization membrane in the eggs of Psammechinus miliaris, Echinocardium cordatum and Strongylocentrotus droebachiensis. The sign of birefringence and the retardation of the cortical layer were determined. No perceptible change of retardation occurred on fertilization. The birefringence of the cortex is due chiefly to ordered lipoid layers. The cortical granules have no influence on the birefringence of the cortex. They are formed at the maturation of the egg. By means of a number of different experiments and observations, it was rendered probable that the cortical granules, along with a matrix, merge with the vitelline membrane to form the fertilization membrane. A granular membrane gives a low retardation. Only on incorporation of the cortical granules and their matrix did the retardation of the membrane attain its normal value (about 12.5 mμ). An attempt was made to combine numerous data to a consistent picture of the mechanism of the membrane formation, cf. above under “Discussion.”

Mechanism of Formation of the Fertilization Membrane in the Sea Urchin Egg

THE mechanism of formation of the fertilization membrane in the sea urchin egg has long been a matter of discussion. Runnstrom, Monne and Broman1 recently reviewed the essential points in this discussion. They also resumed, on the eggs of Psammechinus miliaris and Echinocardium cordatum, the study of the birefringence of the membrane first described by Runnstrom2.