. The Biological bulletin. Biology; Zoology; Biology; Marine Biology. UREA-ACTIVATED EGGS 343 100 o LJ o LU cr 2 Z> ^P. 20 10 100 200 TIME (sec) 300 FIGURE 3. Effect of exposure time on incidence of cortical reaction in eggs activated by urea. The eggs ( ml) were exposed to ml of isotonic urea and fixed at indicated times. The incidence of reacted and unreacted eggs was scored from thick sections observed by light microscopy. Morphological (Endo, 1961; Anderson, 1968) and biochemical (Kane, 1970) observations suggest that hyalin, the major structural protein of the hyaline layer (Ste
. The Biological bulletin. Biology; Zoology; Biology; Marine Biology. UREA-ACTIVATED EGGS 343 100 o LJ o LU cr 2 Z> ^P. 20 10 100 200 TIME (sec) 300 FIGURE 3. Effect of exposure time on incidence of cortical reaction in eggs activated by urea. The eggs ( ml) were exposed to ml of isotonic urea and fixed at indicated times. The incidence of reacted and unreacted eggs was scored from thick sections observed by light microscopy. Morphological (Endo, 1961; Anderson, 1968) and biochemical (Kane, 1970) observations suggest that hyalin, the major structural protein of the hyaline layer (Stephens and Kane, 1970; Citkowitz, 1971), is secreted by the cortical granules during fertilization (reviewed by Schuel, 1978). In addition a secondary cytoplasmic reservoir that normally is slowly released during embryogenesis also is present in unfertilized eggs (Kane, 1973). These concepts have become controversial because McBlaine and Carroll (1980) claimed to show that hyalin is a cryptic protein on the surface of unfertilized eggs. The issue has been resolved by recent immunocyto- chemical studies using monospecific antibodies against pure hyalin (Hylander, 1981; Hylander and Summers, 1982; McClay and Fink, 1982). They found that hyalin is not detectable on the surface of eggs prior to secretion of the cortical granules, and is sequestered within cortical granules of unfertilized eggs. At the ultrastructural level hyalin is localized to the amorphous component of Strongylocentrotus cortical granules (Hylander, 1981; Hylander and Summers, 1982). The secondary hyalin reservoir is stored in small cytoplasmic vesicles (Hylander, 1981; Hylander and Summers, 1982). In the present study the hyaline layer formed by eggs that are fertilized subsequent to urea activation must have been secreted by the secondary reservoir, since the cortical granule store was discharged and dispersed while the eggs were being pretreated with urea. Hence this treatment could be used to collect hyalin f
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