Cytoskeletal organization during stages 4-5...
MT sidebar Microtubules: During stage IV-V, the oocyte MT array and the distribution of cortical g-tubulin become progressively more polarized along the animal vegetal axis (see below). In the animal hemisphere, MTs are organized into loose, radially-oriented, bundles (JPEG: 46 KB) . A large fraction of the MTs in these radial bundles are acetylated (not shown). MTs in the vegetal cortex appear less ordered (JPEG: 66 KB), and fewer are acetylated. Numerous MTs are also apparent in the perinuclear cap of yolk-free cytoplasm found at the base of the GV (JPEG: 32 KB). In the animal cortex, g-tubulin appears evenly distributed in the form of numerous small foci. g-Tubulin in the vegetal cortex appears organized into short linear aggregates (see description of stage VI oocytes).
St4_actin low F-actin: During stages IV-VI, substantial concentration of Factin is seen in the GV (JPEG: 15 KB). In addition,  a complex network of actin cables extends throughout the subcortical (JPEG: 19 KB) and deeper cytoplasm (see description of stage VI oocytes).
S4 early ck1 Keratin filaments: The transition from stage III to stage IV of oogenesis is marked by the polarization of the distribution of pigment in the oocyte cortex. However, no polarity is evident in the of KFs at this stage. Extensive interlinked, radially-organized networks of KFs are apparent in the animal (JPEG: 47 kB; AVI or QT: 2.0 MB), equatorial (JPEG: 46 kB; AVI or QT: 2.0 MB), or vegetal (JPEG: 43 kB; AVI or QT: 2.0 MB) cytoplasm (all three stereo images, JPEG: 133 KB). The cortical and cytoplasmic KF network of Xenopus oocytes becomes visibly polarized during late stage IV - stage V of oogenesis (JPEG: 65 KB). Polarization of the cortical KF network occurs in an animal to vegetal direction, as the KF network of the animal cortex first adopts the final thickness and mesh size seen later in stage VI. The network of KFs in the vegetal cortex remains thickened during stage IV, adopting its final thickness and mesh size during late stage V-VI.