Distribution and role of microfilaments during early events of sheep fertilization

Abstract

The distribution of actin was studied during early events of sheep fertilization by fluorescence microscopy after staining with 7-nitrobenz-2-oxal-1.3 diazole (NBD)-phallacidin and anti-actin antibody and by electron microscopy after heavy meromyosin labelling. unfertilized and fertilized eggs exhibited a continuous band of fluorescence with both NBD-phallacidin and anti-actin antibody. Unlike in mice, no high concentration of actin overlying the spindle was detected in ovulated sheep oocytes. At the site of sperm head incorporation, the fertilization cone developed above the decondensing male chromatin and was underlined by a submembranous area rich in microfilaments. A similar actin network was observed in the cortex of the second polar body. Cytochalasin D was used to investigate the role of actin during the fertilization process. This drug did not prevent sperm fusion and incorporation but inhibited polar body abstriction and fertilization cone development and retarded sperm tail incorporation. Moreover, in the presence of the drug, the anchorage of the metaphase II spindle at the surface of the egg was destroyed. The role of microfilaments in these early events is discussed.

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elongated and tapered [5,23] with a length of 26.4 ± 0.3 µm in the mouse [23] and 16.4 ± 0.7 µm in the hamster (our unpublished observation).…”

“…During oocyte aging, peripheral microfilaments, which are involved in anchorage of the spindle to the oocyte cortex [8,[12][13][14][15]26], drastically reduced in density as observed here. Kim et al [11] observed that the meiotic plate was frequently located outside of the microfilament-rich domain in aged pig oocytes.…”

“…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].…”

Centrioles in the beginning of human development.

“…(v) Remnants of sperm tails and midpieces were seen in the vicinity of centrioles at spindle poles. (vW) Furthermore, the presence of centrioles associated with the flagellar'neck piece of spermatozoa in pronuclear stage oocytes has also been reported in the human (25), pig, and sheep (26,27).…”

Dynamics and unexpected localization of the plakin binding protein, kazrin, in mouse eggs and early embryos

“…Furthermore, each cytoskeletal system (i.e., actin, microtubules, and intermediate filaments) has adapted specialized features to allow them to push through the developmental transition. For example, at fertilization, a loose actin-based network of filaments intimately associates with the head and neck of a sperm for normal, efficient sperm penetration; a specialized function for actin that occurs only once in the lifetime of an organism (Maro et al, 1985;Le Guen at al., 1989;Webster and McGaughey, 1990). Our data suggest that kaz also has adapted a specialized role during these early transitions.…”