ニホンアマガエル(Hyla arborea japonica)卵の受精能力とゼリー層変化

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The change of the jelly envelopes of the egg of Hyla arborea japonica was studied in relation to the maintenace of its fertilizability. The egg is surrounded by a viteline membrane and 4 layers of jelly envelopes. In the present paper, the jelly layers are designated as J_1, jelly membrane, J_2 and J_3, from the inner to the outer ones (Fig. 1). When inseminated, spermatozoa penetrating into the jelly come to a standstill upon contact with the jelly membrane. After a short pause of 1-2 seconds, they again start to penetrate through J_1 and reach the viteline membrane. Fertilizability of the egg can be retained for a considerable time, at least 6 hours, in De Boer's solution, whereas in tap water it is retained at longest for 30 minutes and is completely lost within 45 minutes after immersion (Fig. 2). It was found that spermatozoa cannot penetrate through the jelly membrane of the eggs pretreated for a long time with tap water (Figs. 4 & 5). The fertilizability of these eggs, however, can be completely recovered when the jelly membrane is dissected off mechanically (Table 1). Some experiments were then performed in order to ascertain the nature of the change in the jelly membrane to prevent sperm penetration. When the egg is treated with tap water containing 0.2% EDTA, the change of the membrane occurring in water is inhibited. The maintenace of egg fertilizability also occurs when the egg is pretereated with isotonic Na_2-oxalate or 0.2% EDTA and then immersed in Ca-free 1/(20) De Boer's solution. On the other hand, the eggs merely washed with Ca-free De Boer's solution become completely unfertilizable upon immersion in Ca-free 1/(20) De Boer's solution (Table 2). Further, once the change of the jelly membrane occurs in tap water, it cannot be reversed even when Ca-precipitant or chelating agent as mentioned above is applied. Observations by polarizing microscope showed that the vitelline membrane is strongly birefringent either in De Boer's solution or in tap water. None of the 4 layers of jelly envelopes show birefringence in De Boer's solution. When immersed in tap water, however, the jelly membrane gradually becomes birefringent and its brightness becomes almost comparable with that of the vitelline membrane after 1.5 hours' immersion. Observations in various media proved that the occurrence of birefringence in jelly membrane is entirely parallel with that of the change which prevents the sperm penetration (Table 3). The vital staining of jelly envelopes with toluidine blue showed that the jelly membrane is the only layer which shows metachromasia with the dye, in contrast to the other jelly layers and vitelline membrane which are stained only faintly and orthochromatically. The results presented above were discussed in connection with the description of Balaillon & Tchou (1930) in Hyla egg, and with the results obtained in the otehr anuran species (Katagiri 1962). Emphasis was laid on the point that Ca is one of the factors responsible for the change of the jelly membrane in question. Further, this change may essentially be based on the denaturation of the protein composing the membrane.
1963-01-15

ニホンアマガエル(Hyla arborea japonica)卵の受精能力とゼリー層変化

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