. The Biological bulletin. Biology; Zoology; Biology; Marine Biology. 220 M. MATSUNAGA ET Figure 7. Effects of cytochalasin D on the fixing processes. Eggs were fertilized at 40 min after 1-MeAde treatment. (A) Ten minutes after application of 3 fj-M cytochalasin D {Sigma-Aldrich, St. Louis. MO), which is applied to the fertilized eggs at 90 min after fertilization. (B) Fertilized eggs were pulse-treated with the cytochalasin (3 juA/l tor 10 nun after the third cleavage. Each blastomere lost its contact with the fertilization membrane, and transformed its flattened shape into a globular o
. The Biological bulletin. Biology; Zoology; Biology; Marine Biology. 220 M. MATSUNAGA ET Figure 7. Effects of cytochalasin D on the fixing processes. Eggs were fertilized at 40 min after 1-MeAde treatment. (A) Ten minutes after application of 3 fj-M cytochalasin D {Sigma-Aldrich, St. Louis. MO), which is applied to the fertilized eggs at 90 min after fertilization. (B) Fertilized eggs were pulse-treated with the cytochalasin (3 juA/l tor 10 nun after the third cleavage. Each blastomere lost its contact with the fertilization membrane, and transformed its flattened shape into a globular one. Scale bar: 100 j^m. which the tips of the fixing processes were joined (Fig. 6D, G). Near the cleavage furrows (Fig. 9), the inner layer was occasionally seen detached from the fertilization envelope and was linked with a number of fixing processes (arrows). Discussion In the early cleavage stages before the establishment of some mechanism, such as desmosomes, to directly bind blastomeres, animal embryos devise various means to keep the blastomeres together and maintain their spatial positions relative to each other. In sea urchin eggs, a hyaline layer is formed by the exocytosis of cortical granules immediately after fertilization (Endo, 1961). Microvilli are embedded into the hyaline layer, thus fixing the surface of fertilized eggs to the hyaline layer. Each blastomere produced by cleavage is therefore held in place by the hyaline layer (Dan and Ono, 1952) by means of microvilli, thereby maintaining the three-dimensional spatial relationship among the blas- tomeres. In sea urchin embryos, even if the fertilization envelope is removed, normal morphogenesis continues as long as the hyaline layer remains (Showman and Foerder. 1979). In this study, we found that in Astropectcn \ci>iicihn\ embryos, which lack a hyaline layer, the relative positions among blastomeres are maintained by the fertilization en- velope and the cytoplasmic threads (fixing processes) at- tached to
Size: 2298px × 1087px
Photo credit: © Library Book Collection / Alamy / Afripics
License: Licensed
Model Released: No
Keywords: ., bookauthorlilliefrankrat, booksubjectbiology, booksubjectzoology
