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Development, Vol 115, Issue 1 221-237, Copyright © 1992 by Company of Biologists
JOURNAL ARTICLES |
C Sardet, J Speksnijder, M Terasaki and P Chang
Unite de Biologie Cellulaire Marine, URA 671 CNRS/Universite Paris VI, Villefranche-sur-Mer, France.
The unfertilized ascidian egg displays a visible polar organization along its animal-vegetal axis. In particular, the myoplasm, a mitochondria-rich subcortical domain inherited by the blastomeres that differentiate into muscle cells, is mainly situated in the vegetal hemisphere. We show that, in the unfertilized egg, this vegetal domain is enriched in actin and microfilaments and excludes microtubules. This polar distribution of microfilaments and microtubules persists in isolated cortices prepared by shearing eggs attached to a polylysine-coated surface. The isolated cortex is further characterized by an elaborate network of tubules and sheets of endoplasmic reticulum (ER). This cortical ER network is tethered to the plasma membrane at discrete sites, is covered with ribosomes and contains a calsequestrin-like protein. Interestingly, this ER network is distributed in a polar fashion along the animal-vegetal axis of the egg: regions with a dense network consisting mainly of sheets or tightly knit tubes are present in the vegetal hemisphere only, whereas areas characterized by a sparse tubular ER network are uniquely found in the animal hemisphere region. The stability of the polar organization of the cortex was studied by perturbing the distribution of organelles in the egg and depolymerizing microfilaments and microtubules. The polar organization of the cortical ER network persists after treatment of eggs with nocodazole, but is disrupted by treatment with cytochalasin B. In addition, we show that centrifugal forces that displace the cytoplasmic organelles do not alter the appearance and polar organization of the isolated egg cortex. These findings taken together with our previous work suggest that the intrinsic polar distribution of cortical membranous and cytoskeletal components along the animal-vegetal axis of the egg are important for the spatial organization of calcium-dependent events and their developmental consequences.
This article has been cited by other articles:
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  F. Prodon, P. Dru, F. Roegiers, and C. Sardet Polarity of the ascidian egg cortex and relocalization of cER and mRNAs in the early embryo J. Cell Sci., June 1, 2005; 118(11): 2393 - 2404. [Abstract] [Full Text] [PDF]
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 C. Sardet, H. Nishida, F. Prodon, and K. Sawada Maternal mRNAs of PEM and macho 1, the ascidian muscle determinant, associate and move with a rough endoplasmic reticulum network in the egg cortex Development, December 1, 2003; 130(23): 5839 - 5849. [Abstract] [Full Text] [PDF]
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R. Dumollard and C. Sardet Three different calcium wave pacemakers in ascidian eggs J. Cell Sci., January 7, 2001; 114(13): 2471 - 2481. [Abstract] [Full Text] [PDF]
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F Roegiers, C Djediat, R Dumollard, C Rouviere, and C Sardet Phases of cytoplasmic and cortical reorganizations of the ascidian zygote between fertilization and first division Development, January 6, 1999; 126(14): 3101 - 3117. [Abstract] [PDF]
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F Roegiers, A McDougall, and C Sardet The sperm entry point defines the orientation of the calcium-induced contraction wave that directs the first phase of cytoplasmic reorganization in the ascidian egg Development, January 10, 1995; 121(10): 3457 - 3466. [Abstract] [PDF]
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 H. Iwasaki, K. Chiba, T. Uchiyama, F. Yoshikawa, F. Suzuki, M. Ikeda, T. Furuichi, and K. Mikoshiba Molecular Characterization of the Starfish Inositol 1,4,5-Trisphosphate Receptor and Its Role during Oocyte Maturation and Fertilization J. Biol. Chem., January 18, 2002; 277(4): 2763 - 2772. [Abstract] [Full Text] [PDF]
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