. The Biological bulletin. Biology; Zoology; Biology; Marine Biology. FIGURE 12. The Jeffery and Meier model for the first phase of ooplasmic segregation. A. An unfertilized egg. The vertical arrow indicates the focal point for segregation. B-D. Fertilized eggs in the process of ooplasmic segregation. The arrows represent the directions of ooplasmic movement: arrows with solid lines for the myoplasm and arrows with broken lines for the endoplasm. E. A zygote which has completed the first phase of ooplasmic segregation. In each diagram the thick egg boundaries represent parts of the plasma memb
. The Biological bulletin. Biology; Zoology; Biology; Marine Biology. FIGURE 12. The Jeffery and Meier model for the first phase of ooplasmic segregation. A. An unfertilized egg. The vertical arrow indicates the focal point for segregation. B-D. Fertilized eggs in the process of ooplasmic segregation. The arrows represent the directions of ooplasmic movement: arrows with solid lines for the myoplasm and arrows with broken lines for the endoplasm. E. A zygote which has completed the first phase of ooplasmic segregation. In each diagram the thick egg boundaries represent parts of the plasma membrane with PML underneath, and the thin egg boundaries represent parts of the plasma membrane without the PML. The structures attached to the inside of the PML in the myoplasm represent the filaments of the DFL and its associated components, pigment granules and localized mRNA molecules of the myoplas- mic cytoskeletal domain. AP, animal pole; VP, vegetal pole. From Jeffery and Meier (1983). traction of the PML may be the reason for restriction of microvilli to this region (Fig. 4) (Sawada and Osanai, 1981). The contraction of the PML into the vegetal hemisphere is also proposed as the force that displaces most of the endoplasmic yolk platelets into the animal hemisphere. The PML is thought to form a contractile ring at its upper margin, and this ring coupled with a weakening of the plasma membrane (possibly due to the depletion of integral membrane proteins), would lead to the bulging of endoplasm in the animal hemisphere. Further tightening of the contractile ring, shortening of the PML, and endoplasmic bulging in the animal hemisphere could also make the vegetal hemisphere appear to protrude a cytoplasmic lobe (Fig. 7), as is usually seen during ooplasmic segregation (Fig. 3). A significant question which arises from the models is whether the force generating the movement of the PML is an active, energy-dependent process, such as that based on an actomyosin system, or the rec
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Keywords: ., bookauthorlilliefrankrat, booksubjectbiology, booksubjectzoology
