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Development, Vol 124, Issue 11 2213-2223, Copyright © 1997 by Company of Biologists
JOURNAL ARTICLES |
CY Logan and DR McClay
Department of Zoology, Duke University, Durham, NC 27708, USA.
During sea urchin development, a tier-to-tier progression of cell signaling events is thought to segregate the early blastomeres to five different cell lineages by the 60-cell stage (E. H. Davidson, 1989, Development 105, 421-445). For example, the sixth equatorial cleavage produces two tiers of sister cells called 'veg1' and 'veg2,' which were projected by early studies to be allocated to the ectoderm and endoderm, respectively. Recent in vitro studies have proposed that the segregation of veg1 and veg2 cells to distinct fates involves signaling between the veg1 and veg2 tiers (O. Khaner and F. Wilt, 1991, Development 112, 881-890). However, fate-mapping studies on 60-cell stage embryos have not been performed with modern lineage tracers, and cell interactions between veg1 and veg2 cells have not been shown in vivo. Therefore, as an initial step towards examining how archenteron precursors are specified, a clonal analysis of veg1 and veg2 cells was performed using the lipophilic dye, DiI(C16), in the sea urchin species, Lytechinus variegatus. Both veg1 and veg2 descendants form archenteron tissues, revealing that the ectoderm and endoderm are not segregated at the sixth cleavage. Also, this division does not demarcate cell type boundaries within the endoderm, because both veg1 and veg2 descendants make an overlapping range of endodermal cell types. The allocation of veg1 cells to ectoderm and endoderm during cleavage is variable, as revealed by both the failure of veg1 descendants labeled at the eighth equatorial division to segregate predictably to either tissue and the large differences in the numbers of veg1 descendants that contribute to the ectoderm. Furthermore, DiI-labeled mesomeres of 32-cell stage embryos also contribute to the endoderm at a low frequency. These results show that the prospective archenteron is produced by a larger population of cleavage-stage blastomeres than believed previously. The segregation of veg1 cells to the ectoderm and endoderm occurs relatively late during development and is unpredictable, indicating that later cell position is more important than the early cleavage pattern in determining ectodermal and archenteron cell fates.
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C. A. Bradham and D. R. McClay p38 MAPK is essential for secondary axis specification and patterning in sea urchin embryos Development, January 1, 2006; 133(1): 21 - 32. [Abstract] [Full Text] [PDF]
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D. R. Sherwood and D. R. McClay LvNotch signaling plays a dual role in regulating the position of the ectoderm-endoderm boundary in the sea urchin embryo Development, June 15, 2001; 128(12): 2221 - 2232. [Abstract] [Full Text] [PDF]
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D. McClay, R. Peterson, R. Range, A. Winter-Vann, and M. Ferkowicz A micromere induction signal is activated by beta-catenin and acts through notch to initiate specification of secondary mesenchyme cells in the sea urchin embryo Development, January 12, 2000; 127(23): 5113 - 5122. [Abstract] [PDF]
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L. Angerer, D. Oleksyn, C. Logan, D. McClay, L Dale, and R. Angerer A BMP pathway regulates cell fate allocation along the sea urchin animal-vegetal embryonic axis Development, January 3, 2000; 127(5): 1105 - 1114. [Abstract] [PDF]
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H. Sweet, P. Hodor, and C. Ettensohn The role of micromere signaling in Notch activation and mesoderm specification during sea urchin embryogenesis Development, January 12, 1999; 126(23): 5255 - 5265. [Abstract] [PDF]
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D. Sherwood and D. McClay LvNotch signaling mediates secondary mesenchyme specification in the sea urchin embryo Development, January 4, 1999; 126(8): 1703 - 1713. [Abstract] [PDF]
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C. Logan, J. Miller, M. Ferkowicz, and D. McClay Nuclear beta-catenin is required to specify vegetal cell fates in the sea urchin embryo Development, January 1, 1999; 126(2): 345 - 357. [Abstract] [PDF]
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M Zernicka-Goetz Fertile offspring derived from mammalian eggs lacking either animal or vegetal poles Development, January 12, 1998; 125(23): 4803 - 4808. [Abstract] [PDF]
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E. Davidson, R. Cameron, and A Ransick Specification of cell fate in the sea urchin embryo: summary and some proposed mechanisms Development, January 9, 1998; 125(17): 3269 - 3290. [Abstract] [PDF]
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F Emily-Fenouil, C Ghiglione, G Lhomond, T Lepage, and C Gache GSK3beta/shaggy mediates patterning along the animal-vegetal axis of the sea urchin embryo Development, January 7, 1998; 125(13): 2489 - 2498. [Abstract] [PDF]
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H Benink, G Wray, and J Hardin Archenteron precursor cells can organize secondary axial structures in the sea urchin embryo Development, January 9, 1997; 124(18): 3461 - 3470. [Abstract] [PDF]
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