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Asymmetric p38 activation in zebrafish: its possible role in symmetric and synchronous cleavage.

Fujii R, Yamashita S, Hibi M, Hirano T - J. Cell Biol. (2000)

Bottom Line: When a dominant negative (DN) form of p38 was uniformly expressed, blastomere cleavage was impaired on one side of the blastodisc, resulting in the formation of blastomeres with a large mass of cytoplasm and an enlarged nucleus on the affected side.The area affected by the DN-p38 expression did not correlate with the initial cleavage plane, but coincided with the side where dharma/bozozok, a dorsal-specific zygotic gene, was expressed (Yamanaka et al. 1998).Our findings suggest that asymmetric p38 activation is required for symmetric and synchronous cleavage, and may be regulated by the same machinery that controls the initiation of dorsalizing signals.

View Article: PubMed Central - PubMed

Affiliation: Division of Molecular Oncology, Biomedical Research Center (C-7), Osaka University Graduate School of Medicine, Suita, Osaka 565-0871 Japan.

ABSTRACT
Cleavage is one of the initial steps of embryogenesis, and is characterized by a series of symmetric and synchronous cell divisions. We showed that p38 MAP kinase (p38) is asymmetrically activated on one side of the blastodisc during the early cleavage period in zebrafish (Danio rerio) embryos. When a dominant negative (DN) form of p38 was uniformly expressed, blastomere cleavage was impaired on one side of the blastodisc, resulting in the formation of blastomeres with a large mass of cytoplasm and an enlarged nucleus on the affected side. The area affected by the DN-p38 expression did not correlate with the initial cleavage plane, but coincided with the side where dharma/bozozok, a dorsal-specific zygotic gene, was expressed (Yamanaka et al. 1998). Furthermore, UV irradiation and removal of the vegetal yolk mass before the first cleavage, both of which inhibit the initiation of the dorsalizing signals, abolished the asymmetric p38 activation. Our findings suggest that asymmetric p38 activation is required for symmetric and synchronous cleavage, and may be regulated by the same machinery that controls the initiation of dorsalizing signals.

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The asymmetric p38 activation is required for symmetric and synchronous cleavage in zebrafish. “X,” unknown factor(s) transported from the vegetal pole through the vegetal microtubule array. DD, dorsal determinants; and “Z,” putative signal(s) transported from the vegetal pole through the vegetal microtubule array that compete with p38. V, ventral side; D, dorsal side.
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Figure 10: The asymmetric p38 activation is required for symmetric and synchronous cleavage in zebrafish. “X,” unknown factor(s) transported from the vegetal pole through the vegetal microtubule array. DD, dorsal determinants; and “Z,” putative signal(s) transported from the vegetal pole through the vegetal microtubule array that compete with p38. V, ventral side; D, dorsal side.

Mentions: Next, we examined whether p38 activation depends on factors located in the vegetal yolk region. When the vegetal yolk mass was removed as early as the one-cell stage, the embryos displayed a completely ventralized phenotype with no dorsal and anterior structures (data not shown) as previously reported (Mizuno et al. 1999b). In these yolk-depleted embryos, no expression of dharma was detected at any developmental stage (30/30; Fig. 9 A, compare with controls on which no operation was performed) and the p38 asymmetric activation at the early cleavage stages was completely missing (20/20; Fig. 9 C), although the p38 protein was evenly distributed (Fig. 9 B). These results suggest that the asymmetrical activation of p38 is dependent on unknown factors (Fig. 10, “X”) located in the vegetal yolk hemisphere, just as the dorsalizing signals are dependent on the dorsal determinants located there.


Asymmetric p38 activation in zebrafish: its possible role in symmetric and synchronous cleavage.

Fujii R, Yamashita S, Hibi M, Hirano T - J. Cell Biol. (2000)

The asymmetric p38 activation is required for symmetric and synchronous cleavage in zebrafish. “X,” unknown factor(s) transported from the vegetal pole through the vegetal microtubule array. DD, dorsal determinants; and “Z,” putative signal(s) transported from the vegetal pole through the vegetal microtubule array that compete with p38. V, ventral side; D, dorsal side.
© Copyright Policy
Related In: Results  -  Collection

Show All Figures
getmorefigures.php?uid=PMC2150708&req=5

Figure 10: The asymmetric p38 activation is required for symmetric and synchronous cleavage in zebrafish. “X,” unknown factor(s) transported from the vegetal pole through the vegetal microtubule array. DD, dorsal determinants; and “Z,” putative signal(s) transported from the vegetal pole through the vegetal microtubule array that compete with p38. V, ventral side; D, dorsal side.
Mentions: Next, we examined whether p38 activation depends on factors located in the vegetal yolk region. When the vegetal yolk mass was removed as early as the one-cell stage, the embryos displayed a completely ventralized phenotype with no dorsal and anterior structures (data not shown) as previously reported (Mizuno et al. 1999b). In these yolk-depleted embryos, no expression of dharma was detected at any developmental stage (30/30; Fig. 9 A, compare with controls on which no operation was performed) and the p38 asymmetric activation at the early cleavage stages was completely missing (20/20; Fig. 9 C), although the p38 protein was evenly distributed (Fig. 9 B). These results suggest that the asymmetrical activation of p38 is dependent on unknown factors (Fig. 10, “X”) located in the vegetal yolk hemisphere, just as the dorsalizing signals are dependent on the dorsal determinants located there.

Bottom Line: When a dominant negative (DN) form of p38 was uniformly expressed, blastomere cleavage was impaired on one side of the blastodisc, resulting in the formation of blastomeres with a large mass of cytoplasm and an enlarged nucleus on the affected side.The area affected by the DN-p38 expression did not correlate with the initial cleavage plane, but coincided with the side where dharma/bozozok, a dorsal-specific zygotic gene, was expressed (Yamanaka et al. 1998).Our findings suggest that asymmetric p38 activation is required for symmetric and synchronous cleavage, and may be regulated by the same machinery that controls the initiation of dorsalizing signals.

View Article: PubMed Central - PubMed

Affiliation: Division of Molecular Oncology, Biomedical Research Center (C-7), Osaka University Graduate School of Medicine, Suita, Osaka 565-0871 Japan.

ABSTRACT
Cleavage is one of the initial steps of embryogenesis, and is characterized by a series of symmetric and synchronous cell divisions. We showed that p38 MAP kinase (p38) is asymmetrically activated on one side of the blastodisc during the early cleavage period in zebrafish (Danio rerio) embryos. When a dominant negative (DN) form of p38 was uniformly expressed, blastomere cleavage was impaired on one side of the blastodisc, resulting in the formation of blastomeres with a large mass of cytoplasm and an enlarged nucleus on the affected side. The area affected by the DN-p38 expression did not correlate with the initial cleavage plane, but coincided with the side where dharma/bozozok, a dorsal-specific zygotic gene, was expressed (Yamanaka et al. 1998). Furthermore, UV irradiation and removal of the vegetal yolk mass before the first cleavage, both of which inhibit the initiation of the dorsalizing signals, abolished the asymmetric p38 activation. Our findings suggest that asymmetric p38 activation is required for symmetric and synchronous cleavage, and may be regulated by the same machinery that controls the initiation of dorsalizing signals.

Show MeSH