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• W2002245752 abstract "A study was made of the effect of pretreatment with cryst. trypsin (and chymotrypsin) on eggs of the sea urchin, Paracentrotus lividus . After the pretreatment the eggs were fertilized and the changes of the eggs after fertilization were followed in different stages of development. Pretreatment with a low concentration of trypsin alters the eggs so that, on fertilization, the fertilization membrane remains adherent to the surface of the egg. Moreover a high percentage of the eggs remains uncleaved. The concentration giving the maximum effect was found to be in the range 5.0 × 10 −5 –1.3 × 10 −4 per cent cryst. trypsin at an exposure time of 15 minutes (cf. Figs. 33–34). The concentrations in question corresponded to about 2–4 × 10 −10 Hultin units or roughly to 10 −8 Anson units [1]. When the concentration was further increased, the vitelline membrane broke down with the consequence that no adherent fertilization membrane was formed. Nevertheless the cortical granules were expelled and converted into rods or plates (cf. Fig. 15). Sometimes these kept together to a certain extent and formed fenestrated membranes (cf. Figs. 16–18). The eggs with broken-up vitelline membrane developed in a manner which may be equal to that of the control eggs. As found previously by Sugawara [46], a variation in time of pretreatment gives a gamut of phenomena from failure of membrane elevation and block of cleavage to disappearance of the fertilization membrane and normal development without membrane. A variation in time of exposure to trypsin thus acts as a variation in concentration of the enzyme (cf. Fig. 34). At least within a certain range there is a dose effect which is dependent on the product of concentration and time (cf. also [29]). The blockage of cleavage or impairment of development was thus bound to a comparatively low dose of trypsin and it was relieved at higher doses. A description is given of eggs with blocked cleavage. The eggs remained spherical, even in telophase. The spindle could elongate further than in normal cleavage and a bending of the spindle was sometimes observed. Dense blisters often appeared at the sites of abortive furrow formation. Sometimes a number of protrusions appeared on the surface of the blocked eggs (Figs. 3–9). These pierced the hyaline layer and the fertilization membrane. They were furnished with finger-like smaller processes. In other cases, one or two bulges appeared in a region of the egg (Figs. 10–12) devoid of hyaline layer and fertilization membrane. The broad bulges could appear also in eggs with a completely broken-up vitelline membrane. The protrusions appeared after pretreatment with a somewhat higher dose of trypsin than that giving smooth eggs with adhering membrane. The broader bulges appeared following pretreatment with different concentrations of trypsin, which cause a partial break-up of the vitelline membrane. Fixation of the eggs in 4 per cent formaldehyde in sea water (pH 7.6) preserved the cytoplasmic structure well but entailed certain changes reminiscent of those observed under the action of hypertony. Control eggs, fixed 10 minutes after fertilization, exhibited an angular shape and hyaline blisters appeared in the perivitelline space. In eggs pretreated with the cleavage-blocking dose of trypsin the egg surface was smooth, sometimes dense flattened blisters appeared in the perivitelline space. In the eggs with blocked cleavage the division of the nuclei continued; these gathered in a subcortical layer. Within 4–6 hours the return of the chromosomes to the dispersed resting state became more difficult (Fig. 24 a, b ). Finally they formed blocks or strings of condensed basophilic substance. A separation of phase occurred at the same time in the cytoplasm (Fig. 25). The fixation in formalin caused an elevation of the hyaline layer which began about the time of the initiation of the first mitosis. In eggs pretreated with trypsin the elevation failed to occur. This applies primarily to blocked eggs but also to eggs that underwent development, viz. in eggs with an adhering hyaline layer. In these the cytoplasmic structure was disturbed and the cleavage delayed or atypical to a varying extent and bulges were formed. The eggs with elevated hyaline layer underwent a normal cleavage. The bulges could be nucleated and undergo cell division. They could remain in contact with the main embryo; under certain conditions they were reintegrated into the embryo. They could also be detached and develop into dwarf blastulae. In tests with a high percentage of blockage of cleavage the minority of developing eggs showed a tendency to animalization and at the most plutei of reduced size appeared. The measure indicated in Fig. 26 was used as an index of growth of the pluteus. The effects of trypsin pretreatment described for fertilized eggs were found also in eggs artificially activated by the butyric acid method. A polarity prevails with respect to elevation and properties of the fertilization membrane and of the hyaline layer, formation of bulges etc. and its axis is approximately perpendicular to the axis of the animal-vegetal polarity in both fertilized and artificially activated eggs. This induces the assumption that two systems of polar organization are present as early as in the unfertilized egg. The data tend to show that the pretreatment with the blocking doses of trypsin and chymotrypsin brings about the activation of an enzyme which causes a gelation of the egg cytoplasm. An increased dose acts more in the direction of hydrolysis with reversal of the blocking gelation and a break-up of the vitelline membrane. Ca 2+ favors the activation of both kinds of enzymes. It seems possible to relate the gelating and the hydrolytic effects to the group of proteolytic enzymes which have been distinguished in the Paracentrotus egg by Lundblad [22–28]." @default.
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• W2002245752 title "Effect of pretreatment of the sea urchin egg with trypsin of different doses with respect to cortical changes, cleavage and further development" @default.
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• W2002245752 doi "https://doi.org/10.1016/0014-4827(61)90134-3" @default.
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