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Biochemical heterogeneity, migration, and pre-fertilization release of mouse oocyte cortical granules.

Liu M, Sims D, Calarco P, Talbot P - Reprod. Biol. Endocrinol. (2003)

Bottom Line: A second cortical granule free domain developed following pre-fertilization exocytosis and subsequently continued to increase in area as both, LCA and LCA/ ABL2-binding granules near the spindle became redistributed toward the equator of the oocyte.The pre-fertilization release of cortical granules did not affect binding of sperm to the overlying zona pellucida.The observations indicate that the functions of the cortical granules are more complex than previously realized and include events occurring prior to gamete membrane fusion.

View Article: PubMed Central - HTML - PubMed

Affiliation: Department of Cell Biology & Neuroscience, University of California Riverside, California 92521, USA. corticalgranules@hotmail.com

ABSTRACT

Background: Oocyte cortical granules are important in the fertilization of numerous species including mammals. Relatively little is known about the composition, migration, and pre-fertilization release of mammalian oocyte cortical granules.

Results: Results obtained with confocal scanning laser microscopy indicated that mouse oocytes have at least two populations of cortical granules, one that bound both the lectin LCA and the antibody ABL2 and one that bound only LCA. Both types of granules were synthesized at the same time during oocyte maturation suggesting that the ABL2 antigen is targeted to specific granules by a sorting sequence. The distribution of both populations of cortical granules was then studied during the germinal vesicle to metaphase II transition. As the oocytes entered metaphase I, the first cortical granule free domain, which was devoid of both populations of cortical granules, formed over the spindle. During first polar body extrusion, a subpopulation of LCA-binding granules became concentrated in the cleavage furrow and underwent exocytosis prior to fertilization. Granules that bound ABL2 were not exocytosed at this time. Much of the LCA-binding exudate from the release at the cleavage furrow was retained in the perivitelline space near the region of exocytosis and was deduced to contain at least three polypeptides with approximate molecular weights of 90, 62, and 56 kDa. A second cortical granule free domain developed following pre-fertilization exocytosis and subsequently continued to increase in area as both, LCA and LCA/ ABL2-binding granules near the spindle became redistributed toward the equator of the oocyte. The pre-fertilization release of cortical granules did not affect binding of sperm to the overlying zona pellucida.

Conclusions: Our data show that mouse oocytes contain at least two populations of cortical granules and that a subset of LCA-binding cortical granules is released at a specific time (during extrusion of the first polar body) and place (around the cleavage furrow) prior to fertilization. The observations indicate that the functions of the cortical granules are more complex than previously realized and include events occurring prior to gamete membrane fusion.

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Three-dimensional projection showing an ovulated unfertilized metaphase II zona intact oocyte collected 14 hours after the hCG injection and stained with ABL2 and LCA. arrowhead = equator; asterisk = cortical granule free domain; arrow = perivitelline space. ZP = indicates the zona pellucida which does not actually show as it is not fluorescently labeled. Entire oocyte was optically sectioned, and all optical sections were used to compile the 3D projection, which was animated. A movie of this oocyte can be viewed by double clicking the movie file Fig5Movie.avi ("see Additional file 1").
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Figure 5: Three-dimensional projection showing an ovulated unfertilized metaphase II zona intact oocyte collected 14 hours after the hCG injection and stained with ABL2 and LCA. arrowhead = equator; asterisk = cortical granule free domain; arrow = perivitelline space. ZP = indicates the zona pellucida which does not actually show as it is not fluorescently labeled. Entire oocyte was optically sectioned, and all optical sections were used to compile the 3D projection, which was animated. A movie of this oocyte can be viewed by double clicking the movie file Fig5Movie.avi ("see Additional file 1").

Mentions: As a result of this final redistribution, the density of cortical granules around the equator increased in ovulated metaphase II mature oocytes. This increase in density of granules was best visualized by rotating three-dimensional reconstructions of metaphase II oocytes (Fig. 5, "see Additional file 1"). The belt of granules around the equator was particularly rich in LCA/ABL2-binding granules, while granules that bound only LCA were also present in areas away from the equator. This polar distribution of cortical granules established in metaphase II oocytes was maintained until the oocytes were fertilized and the remaining granules underwent exocytosis. The three-dimensional reconstructions of zona intact metaphase II oocytes recovered from oviduct also showed that the LCA-binding cortical granule components released prior to fertilization were present in the perivitelline space in the area adjacent to the cortical granule-free domain (Fig. 5). These results do not preclude the possibility that some of the pre-fertilization exudate entered and modified the zona.


Biochemical heterogeneity, migration, and pre-fertilization release of mouse oocyte cortical granules.

Liu M, Sims D, Calarco P, Talbot P - Reprod. Biol. Endocrinol. (2003)

Three-dimensional projection showing an ovulated unfertilized metaphase II zona intact oocyte collected 14 hours after the hCG injection and stained with ABL2 and LCA. arrowhead = equator; asterisk = cortical granule free domain; arrow = perivitelline space. ZP = indicates the zona pellucida which does not actually show as it is not fluorescently labeled. Entire oocyte was optically sectioned, and all optical sections were used to compile the 3D projection, which was animated. A movie of this oocyte can be viewed by double clicking the movie file Fig5Movie.avi ("see Additional file 1").
© Copyright Policy
Related In: Results  -  Collection

Show All Figures
getmorefigures.php?uid=PMC305340&req=5

Figure 5: Three-dimensional projection showing an ovulated unfertilized metaphase II zona intact oocyte collected 14 hours after the hCG injection and stained with ABL2 and LCA. arrowhead = equator; asterisk = cortical granule free domain; arrow = perivitelline space. ZP = indicates the zona pellucida which does not actually show as it is not fluorescently labeled. Entire oocyte was optically sectioned, and all optical sections were used to compile the 3D projection, which was animated. A movie of this oocyte can be viewed by double clicking the movie file Fig5Movie.avi ("see Additional file 1").
Mentions: As a result of this final redistribution, the density of cortical granules around the equator increased in ovulated metaphase II mature oocytes. This increase in density of granules was best visualized by rotating three-dimensional reconstructions of metaphase II oocytes (Fig. 5, "see Additional file 1"). The belt of granules around the equator was particularly rich in LCA/ABL2-binding granules, while granules that bound only LCA were also present in areas away from the equator. This polar distribution of cortical granules established in metaphase II oocytes was maintained until the oocytes were fertilized and the remaining granules underwent exocytosis. The three-dimensional reconstructions of zona intact metaphase II oocytes recovered from oviduct also showed that the LCA-binding cortical granule components released prior to fertilization were present in the perivitelline space in the area adjacent to the cortical granule-free domain (Fig. 5). These results do not preclude the possibility that some of the pre-fertilization exudate entered and modified the zona.

Bottom Line: A second cortical granule free domain developed following pre-fertilization exocytosis and subsequently continued to increase in area as both, LCA and LCA/ ABL2-binding granules near the spindle became redistributed toward the equator of the oocyte.The pre-fertilization release of cortical granules did not affect binding of sperm to the overlying zona pellucida.The observations indicate that the functions of the cortical granules are more complex than previously realized and include events occurring prior to gamete membrane fusion.

View Article: PubMed Central - HTML - PubMed

Affiliation: Department of Cell Biology & Neuroscience, University of California Riverside, California 92521, USA. corticalgranules@hotmail.com

ABSTRACT

Background: Oocyte cortical granules are important in the fertilization of numerous species including mammals. Relatively little is known about the composition, migration, and pre-fertilization release of mammalian oocyte cortical granules.

Results: Results obtained with confocal scanning laser microscopy indicated that mouse oocytes have at least two populations of cortical granules, one that bound both the lectin LCA and the antibody ABL2 and one that bound only LCA. Both types of granules were synthesized at the same time during oocyte maturation suggesting that the ABL2 antigen is targeted to specific granules by a sorting sequence. The distribution of both populations of cortical granules was then studied during the germinal vesicle to metaphase II transition. As the oocytes entered metaphase I, the first cortical granule free domain, which was devoid of both populations of cortical granules, formed over the spindle. During first polar body extrusion, a subpopulation of LCA-binding granules became concentrated in the cleavage furrow and underwent exocytosis prior to fertilization. Granules that bound ABL2 were not exocytosed at this time. Much of the LCA-binding exudate from the release at the cleavage furrow was retained in the perivitelline space near the region of exocytosis and was deduced to contain at least three polypeptides with approximate molecular weights of 90, 62, and 56 kDa. A second cortical granule free domain developed following pre-fertilization exocytosis and subsequently continued to increase in area as both, LCA and LCA/ ABL2-binding granules near the spindle became redistributed toward the equator of the oocyte. The pre-fertilization release of cortical granules did not affect binding of sperm to the overlying zona pellucida.

Conclusions: Our data show that mouse oocytes contain at least two populations of cortical granules and that a subset of LCA-binding cortical granules is released at a specific time (during extrusion of the first polar body) and place (around the cleavage furrow) prior to fertilization. The observations indicate that the functions of the cortical granules are more complex than previously realized and include events occurring prior to gamete membrane fusion.

Show MeSH
Related in: MedlinePlus