Cytoskeletal organization in Xenopus oogonia...
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Microtubules: During interphase, oogonia contain a relatively sparse array of cytoplasmic MTs radiating from a central MTOC or centrosome (JPEG: 32 KB). Mitotic oogonia are typically found in clusters of two, four, or eight cells (JPEG: 45 KB), corresponding to the second, third, and fourth oogonial divisions (it is difficult to distinguish the single oogonia in the first mitosis from mitotic follicle cells). Dividing oogonia contain typical mitotic spindles, with well focused poles containing g-tubulin, and sparse astral MT arrays.
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F-Actin: Individual interphase oogonia were not readily identifiable in our examination of fluorescent-phalloidin-stained ovaries from juvenile frogs. However, the absence of cytoplasmic cables or GV-staining during stage 0 (JPEG: 43 KB) suggests that F-actin is restricted to the cortex of oogonia, as it is during stage 0 of oogenesis.

ck-sidebar Keratin filaments: Interphase oogonia were not readily identifiable in our examination of ovaries from juvenile frogs by confocal immunofluorescence microscopy. However, KFs are conspicuously absent from mitotic oogonia (JPEG: 40 KB; AVI or QT) and stage 0 oocytes lack KFs (see below), suggesting that they appear later in oogenesis.
Cytoskeletal organization in stage 0 oocytes...Secondary oogonia undergo four synchronous mitotic divisions (JPEG), giving rise to a "nest" of 16 post-mitotic oocytes. To convey the distinct morphological and cytoskeletal differences between these pre-diplotene post-mitotic oocytes and larger, stage I oocytes, we have suggested that young post-mitotic oocytes be referred to as "stage 0" oocytes.
MT_S0_sidebar Microtubules: confocal immunofluorescence microscopy revealed that stage 0 oocytes contain a dense array of MTs concentrated in the cap of cytoplasm located at the narrow end of these pear-shaped cells (JPEG: 35 KB). Antibodies to g-tubulin stain a single focus within the MT array of each oocyte (JPEG: 45 kB; JPEG:27 KB), electron microscopy reveals that stage 0 oocytes contain centrioles (JPEG), and MT regrowth assays reveal a single focus of MT nucleation activity in each oocyte (JPEG: 35 KB). Together, these results indicate that stage 0 oocytes contain a typical centrosome that functions as a microtubule-organizing center (MTOC). In contrast to oogonia, many of the MTs in stage 0 oocytes stain brightly with antibodies to acetylated a-tubulin, a marker for stable MTs (JPEG: 28 KB). Acetylated MTs are concentrated in the cap of cytoplasm at the narrow end of stage 0 oocytes (JPEG: 32 KB).
actin-sidebar F-actin: Confocal microscopy of stage 0 oocytes stained with fluorescent phalloidin reveals that F-actin is restricted to the oocyte cortex. Nests of stage 0 oocytes can be recognized as clusters of oval or pear-shaped cells with prominent staining of the cortical cytoplasm  (JPEG: 44 KB).
Kfs Keratin filaments: KFs are conspicuously absent from the cytoplasm of stage 0 (post-mitotic) oocytes. Nests of small stage 0 oocytes (JPEG: 56 KB), and larger individual stage 0 oocytes (JPEG: 45 KB; AVI or QT:   0.6 MB), are surrounded by follicle cells which stain brightly with antibodies to keratins (counter-stained with a DNA dye to reveal oocyte nuclei).