The origins and consequences of fragmentation in mammalian eggs and embryos

Mammalian eggs and embryos contain an elaborate cytoskeletal network of “sheets” which are distributed throughout the entire cell cytoplasm. Cytoskeletal sheets are long, planar structures unlike the cytoskeletal networks typical of somatic cells (actin filaments, microtubules, and intermediate filaments), which are filamentous. These sheets are not found in mammalian somatic cells nor are they found in nonmammalian eggs or embryos. Evidence that they are, indeed, cytoskeletal in nature is derived from studies demonstrating that 1) the sheets are retained in the detergent-resistant cytoskeleton fraction; 2) there are no associated membranes (determined by freeze-fracture); and 3) the sheets dissociate into filaments at the blastocyst stage of embryogenesis. Embedment-free sections of hamster eggs viewed at 60 kV show sheets running across the egg cytoplasm (Fig. 1). Although this approach provides excellent global views of the sheets and their reorganization during development, the mechanism of image formation for embedment-free sections does not permit evaluation of the sheets at high resolution.

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Composition regulation and function of the cytoskeleton in mammalian eggs and embryos

Frontiers in Bioscience ◽

10.2741/a672 ◽

2001 ◽

Vol 6 (3) ◽

pp. d1089-1108

Author(s):

G. Ian Gallicano

Keyword(s):

And Function ◽

Mammalian Eggs

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Selective and Continuous Elimination of Mitochondria Microinjected Into Mouse Eggs From Spermatids, but Not From Liver Cells, Occurs Throughout Embryogenesis

Genetics ◽

10.1093/genetics/156.3.1277 ◽

2000 ◽

Vol 156 (3) ◽

pp. 1277-1284 ◽

Cited By ~ 8

Author(s):

Hiroshi Shitara ◽

Hideki Kaneda ◽

Akitsugu Sato ◽

Kimiko Inoue ◽

Atsuo Ogura ◽

...

Keyword(s):

Early Stage ◽

Liver Mitochondria ◽

Blastocyst Stage ◽

Mus Musculus Domesticus ◽

Newborn Mice ◽

Selective Elimination ◽

Specific Factors ◽

Pcr Method ◽

Mammalian Eggs ◽

Mouse Eggs

Abstract Exclusion of paternal mitochondria in fertilized mammalian eggs is very stringent and ensures strictly maternal mtDNA inheritance. In this study, to examine whether elimination was specific to sperm mitochondria, we microinjected spermatid or liver mitochondria into mouse embryos. Congenic B6-mtspr strain mice, which are different from C57BL/6J (B6) strain mice (Mus musculus domesticus) only in possessing M. spretus mtDNA, were used as mitochondrial donors. B6-mtspr mice and a quantitative PCR method enabled selective estimation of the amount of M. spretus mtDNA introduced even in the presence of host M. m. domesticus mtDNA and monitoring subsequent changes of its amount during embryogenesis. Results showed that M. spretus mtDNA in spermatid mitochondria was not eliminated by the blastocyst stage, probably due to the introduction of a larger amount of spermatid mtDNA than of sperm mtDNA into embryos on fertilization. However, spermatid-derived M. spretus mtDNA was eliminated by the time of birth, whereas liver-derived M. spretus mtDNA was still present in most newborn mice, even though its amount introduced was significantly less than that of spermatid mtDNA. These observations suggest that mitochondria from spermatids but not from liver have specific factors that ensure their selective elimination and resultant elimination of mtDNA in them, and that the occurrence of elimination is not limited to early stage embryos, but continues throughout embryogenesis.

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Different Ca2+-releasing abilities of sperm extracts compared with tissue extracts and phospholipase C isoforms in sea urchin egg homogenate and mouse eggs

Biochemical Journal ◽

10.1042/bj3460743 ◽

2000 ◽

Vol 346 (3) ◽

pp. 743-749 ◽

Cited By ~ 32

Author(s):

Keith T. JONES ◽

Miho MATSUDA ◽

John PARRINGTON ◽

Matilda KATAN ◽

Karl SWANN

Keyword(s):

Phospholipase C ◽

Sea Urchin ◽

Tissue Extracts ◽

Sea Urchin Egg ◽

Boar Sperm ◽

Specific Activities ◽

Mammalian Eggs ◽

Mouse Eggs

A soluble phospholipase C (PLC) from boar sperm generates InsP3 and hence causes Ca2+ release when added to sea urchin egg homogenate. This PLC activity is associated with the ability of sperm extracts to cause Ca2+ oscillations in mammalian eggs following fractionation. A sperm PLC may, therefore, be responsible for causing the observed Ca2+ oscillations at fertilization. In the present study we have further characterized this boar sperm PLC activity using sea urchin egg homogenate. Consistent with a sperm PLC acting on egg PtdIns(4,5)P2, the ability of sperm extracts to release Ca2+ was blocked by preincubation with the PLC inhibitor U73122 or by the addition of neomycin to the homogenate. The Ca2+-releasing activity was also detectable in sperm from other species and in whole testis extracts. However, activity was not observed in extracts from other tissues. Moreover recombinant PLCβ1, -γ1, -γ2, -∆1, all of which had higher specific activities than boar sperm extracts, were not able to release Ca2+ in the sea urchin egg homogenate. In addition these PLCs were not able to cause Ca2+ oscillations following microinjection into mouse eggs. These results imply that the sperm PLC possesses distinct properties that allow it to hydrolyse PtdIns(4,5)P2 in eggs.

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Immunological Aspects of Sperm Receptors on the Zona Pellucida of Mammalian Eggs

Immunological Communications ◽

10.3109/08820137609033855 ◽

1976 ◽

Vol 5 (5) ◽

pp. 375-385 ◽

Cited By ~ 12

Author(s):

Bonnie S. Dunbar ◽

C. Alex Shivers

Keyword(s):

Zona Pellucida ◽

Mammalian Eggs

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Effects of proteolytic enzymes on the zona pellucida of fertilized and unfertilized mammalian eggs

Experimental Cell Research ◽

10.1016/0014-4827(56)90128-8 ◽

1956 ◽

Vol 11 (2) ◽

pp. 497-499 ◽

Cited By ~ 46

Author(s):

M CHANG ◽

D HUNT

Keyword(s):

Zona Pellucida ◽

Proteolytic Enzymes ◽

Mammalian Eggs

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Profile of a mammalian sperm receptor

Development ◽

10.1242/dev.108.1.1 ◽

1990 ◽

Vol 108 (1) ◽

pp. 1-17 ◽

Cited By ~ 2

Author(s):

P.M. Wassarman

Keyword(s):

Gene Expression ◽

Zona Pellucida ◽

Specific Gene ◽

Mammalian Development ◽

Unique Nature ◽

Mammalian Fertilization ◽

Species Specific ◽

Available Information ◽

Mammalian Eggs ◽

Sperm Receptor

Complementary molecules on the surface of eggs and sperm are responsible for species-specific interactions between gametes during fertilization in both plants and animals. In this essay, several aspects of current research on the mouse egg receptor for sperm, a zona pellucida glycoprotein called ZP3, are addressed. These include the structure, synthesis, and functions of the sperm receptor during oogenesis and fertilization in mice. Several conclusions are drawn from available information. These include (I) ZP3 is a member of a unique class of glycoproteins found exclusively in the extracellular coat (zona pellucida) of mammalian eggs. (II) ZP3 gene expression is an example of oocyte-specific and, therefore, sex-specific gene expression during mammalian development. (III) ZP3 is a structural glycoprotein involved in assembly of the egg extracellular coat during mammalian oogenesis. (IV) ZP3 is a sperm receptor involved in carbohydrate-mediated gamete recognition and adhesion during mammalian fertilization. (V) ZP3 is an inducer of sperm exocytosis (acrosome reaction) during mammalian fertilization. (VI) ZP3 participates in the secondary block to polyspermy following fertilization in mammals. (VII) The extracellular coat of other mammalian eggs contains a glycoprotein that is functionally analogous to mouse ZP3. The unique nature, highly restricted expression, and multiple roles of ZP3 during mammalian development make this glycoprotein a particularly attractive subject for investigation at both the cellular and molecular levels.

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