Cytoskeletal organization of rat oocytes during metaphase II arrest and following abortive activation: A study by confocal laser scanning microscopy

Abstract

In metaphase II arrested rat oocytes (M II), microtubules were found in the taper-shaped meiotic spindle and in the cytoplasm as asters and free microtubules. Whereas spindle microtubules were acetylated, those located in the cytoplasm were not. Cytoplasmic microtubules were also labile as assessed by mild cooling. In contrast to mouse oocytes, rat microtubule organizing centers (MTOCs) did not react with MPM-2 antibody by immunofluorescence despite the fact that this antibody reacts with several proteins as shown by immunoblot. However, cytoplasmic MTOCs in M II-arrested rat oocytes could be detected by their nucleating capacity in the presence of taxol, a drug that induced the formation of numerous cytoplasmic asters. In addition, taxol caused a change in the spindle shape and the formation of astral microtubules at the spindle poles. Meiotic spindles (as well as chromosomes devoid of microtubules after nocodazole-treatment) were overlaid by an actin-rich domain. Spontaneous abortive activation led to the extrusion of the second polar body followed by another metaphase arrest--metaphase III; however, normal spindles did not form and dispersed chromosomes surrounded by microtubules were observed. Electron microscopic studies confirmed these observations and revealed that the kinetochores, are located deep within the chromosomes in contrast to mouse kinetochores, and this might be responsible for the absence of a metaphase III spindle in the rat oocyte. Induced activation caused transition to interphase with the formation of a characteristic microtubule network. This study shows that there are several significant differences in the cytoskeletal organization of rat and mouse oocytes.

Cytoskeletal Organization of Porcine Oocytes Aged and Activated Electrically or by Sperm.

“…The present results showed that the meiotic spindle of the porcine oocyte is peripherally located and radially oriented with its long axis as seen in other domestic species [6,8,10] and humans [16], and no rotation of the meiotic spindle occurred unlike in laboratory rodents [3,5]. Further, the meiotic spindle is barrel-shaped in the pig ( [11] and this study) and cattle [10], and is approximately 10 µm long, whereas in laboratory rodents it is much more elongated and tapered [5,23] with a length of 26.4 ± 0.3 µm in the mouse [23] and 16.4 ± 0.7 µm in the hamster (our unpublished observation).…”

“…Further, the meiotic spindle is barrel-shaped in the pig ( [11] and this study) and cattle [10], and is approximately 10 µm long, whereas in laboratory rodents it is much more elongated and tapered [5,23] with a length of 26.4 ± 0.3 µm in the mouse [23] and 16.4 ± 0.7 µm in the hamster (our unpublished observation). In the present study, the pole-to-pole length of the meiotic spindle increased significantly during oocyte aging, as reported for the aged bovine oocyte [24].…”

“…These include the resumption of meiosis, chromosome condensation, spindle formation, polar body emission, sperm incorporation and pronuclear formation and migration. Cytoskeleton organization is well known to be important for the progression of these events in mammals such as the mouse [1][2][3][4], rat [5], rabbit [6], sheep [7,8], cattle [9,10], pig [11][12][13][14][15] and human [16]. Our previous studies showed that cytoskeletal alteration is involved in the dynamic change of the cumulus-oocyte cell communication during oocyte maturation, and that the cumulus mass condition affects oocyte maturation in the pig [17,18].…”

Organisation of the cytoskeleton during in vitro maturation of horse oocytes

“…The distribution of micro®laments during mammalian oocyte maturation has also been investigated. In short, in matured oocytes recovered from mice (Maro et al, 1984;Schatten et al, 1986), rats (Zernicka-Goetz et al, 1993), pigs (Kim et al, 1996a), and women (Kim et al, 1998), the micro®laments are concentrated in the cell cortex, although, a secondary aggregation has been described overlying the meiotic spindle and has been proposed to maintain the spindle and the chromosomes in a peripheral position (Kim et al, 1996a).…”

Imaging Mitochondrial Organization in Living Primate Oocytes and Embryos using Multiphoton Microscopy

“…For example, mitochondria in mouse oocytes are asymmetrically localized but become homogeneously distributed during fertilization (Van Blerkom and Runner, 1984;Muggleton-Harris and Brown, 1988;Calarco, 1995). Similarly, organelles in rat oocytes exhibit a perinuclear aggregation which subsequently disperses into the cell cortex (Zernicka-Goetz et al, 1993). In contrast, mitochondria in hamster embryos undergo a reorganization from a homogeneous distribution in the oocyte and early pronucleate stage to a distinct perinuclear organization late in the pronucleate stage and at the two-cell stage (Barnett et al, 1996).…”