Association of an ultraviolet irradiation sensitive cytoplasmic localization with the future dorsal side of the amphibian egg

Malacinski, George M.; Benford, Helen H.; Chung, Hae-Moon

doi:10.1002/jez.1401910110

Cited by 66 publications

(12 citation statements)

References 19 publications

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“…2). Occasionally, anterior neural structures such as the eyes are reduced but sections reveal that the amount of notochord is unaffected (data not shown (12,25). These ventralized embryos can be rescued by several methods, including injection of Xwnt-8 RNA.…”

Section: Resultsmentioning

confidence: 94%

“…In contrast, overexpression of Xwnt-5A affects morphogenetic movements without producing a duplication of the axis (17). UV irradiation of Xenopus embryos blocks formation of the embryonic blastula organizer, the Nieuwkoop center, and results in an embryo lacking dorsal axial structures (12,25). In such embryos, overexpression of Xwnt-8 (26,27) but not Xwnt-5A (17) mimics the Nieuwkoop center and restores normal development, rescuing expression of the putative transcription factor goosecoid (28).…”

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confidence: 99%

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Identification of Distinct Classes and Functional Domains of Wnts through Expression of Wild-Type and Chimeric Proteins in Xenopus Embryos

Purcell

Christian

et al. 1995

Molecular and Cellular Biology

296

209

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Wnts are secreted signaling factors which influence cell fate and cell behavior in developing embryos. Overexpression in Xenopus laevis embryos of a Xenopus Wnt, Xwnt-8, leads to a duplication of the embryonic axis. In embryos ventralized by UV irradiation, Xwnt-8 restores expression of the putative transcription factor goosecoid, and rescues normal axis formation. In contrast, overexpression of Xwnt-5A in normal embryos generates defects in dorsoanterior structures, without inducing goosecoid or a secondary axis. To determine whether Xwnt-4 and Xwnt-11 fall into one of these two previously described classes of activity, synthetic mRNAs were introduced into animal caps, normal embryos, and UV-treated embryos. The results indicate that Xwnt-4, Xwnt-5A, and Xwnt-11 are members of a single functional class with activities that are indistinguishable in these assays. To investigate whether distinct regions of Xwnt-8 and Xwnt-5A were sufficient for eliciting the observed effects of overexpression, we generated a series of chimeric Xwnts. RNAs encoding the chimeras were injected into normal and UV-irradiated Xenopus embryos. Analysis of the embryonic phenotypes and goosecoid levels reveals that chimeras composed of carboxy-terminal regions of Xwnt-8 and amino-terminal regions of Xwnt-5A are indistinguishable from the activities of native Xwnt-8 and that the reciprocal chimeras elicit effects indistinguishable from overexpression of native Xwnt-5A. We conclude that the carboxy-terminal halves of these Xwnts are candidate domains for specifying responses to Xwnt signals.

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Section: Resultsmentioning

confidence: 94%

mentioning

confidence: 99%

Identification of Distinct Classes and Functional Domains of Wnts through Expression of Wild-Type and Chimeric Proteins in Xenopus Embryos

Purcell

Christian

et al. 1995

Molecular and Cellular Biology

296

209

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“…For instance, ultraviolet irradiation during the first two thirds of the first cell cycle after fertilisation inhibits a superficial cytoplasmic rotation that leads immediately to grey crescent formation and subsequently to positioning of the future dorsal side and the anterior end of the embryo (Malacinski et al, 1975). The result of this rotational process is that molecules are in some way activated on the future dorsal side of the vegetal hemisphere, leading to the production of a signal inducing the dorsal mesoderm of the future or-ganiser (reviewed by Kimelman et al, 1992).…”

Section: Introductionmentioning

confidence: 99%

N-acetyl-cysteine causes a late re-specification of the anteroposterior axis in theXenopus embryo

Gatherer

Woodland

1996

Dev. Dyn.

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“…The only previous example of a specific cytoplasmic component localized in amphibian eggs is the germ plasm. It has been known for some time that the dorso-vegetal surface of amphibian eggs is especially sensitive to ultraviolet irradiation (17,18), but it now seems likely that this treatment inhibits a general cytoplasmic rearrangement that normally follows fertilization and not that it destroys a specific cytoplasmic substance (19,20).…”

Section: Discussionmentioning

confidence: 99%

All components required for the eventual activation of muscle-specific actin genes are localized in the subequatorial region of an uncleaved amphibian egg.

Gurdon¹,

Mohun²,

Fairman³

et al. 1985

Proc. Natl. Acad. Sci. U.S.A.

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Fertilized Xenopus eggs have been ligated with a hair loop into separate fragments before the first cleavage. The plane of the ligation was varied in relation to the animal-vegetal and dorso-ventral axes. The fragments that contained a nucleus were cultured for 24 hr until controls reached the neurula stage; they were then analyzed by S1 nuclease protection for their content of muscle-specific actin mRNA, using a gene-specific probe. We find that all egg components required for the eventual activation of these actin genes are localized, already at the 1-cell stage, in a region below the equator, and mostly on the dorsal (grey crescent) side. This material subsequently occupies the equivalent position in 8-cell and 32-cell embryos. We interpret our results, in combination with the previous work of others, to mean that mesoderm (including muscle) formation in Amphibia depends both on cytoplasmic substances already localized in the egg as well as on inductive cell interactions during cleavage.An important question in embryology is whether a fertilized but uncleaved egg contains substances already localized in a way that is related to future cell differentiation, or whether such substances first appear and become localized at a later multicellular stage. The question is significant because the localization of materials in a single cell, the egg, is most likely to depend on large molecules or complexes, whereas cell interactions may well involve small molecules capable of passing rapidly from cell to cell.There are several examples in invertebrate animals in which one region of egg cytoplasm seems to be related to a particular type of differentiation. The most celebrated cases are insect pole plasm (1) (related to egg and sperm formation) and the yellow cytoplasm in ascidian eggs (related to tail muscle formation) (reviewed in refs. 2 and 3). A more common situation is that in which a particular region of egg cytoplasm becomes localized within a certain cell lineage by asymmetric early cleavage divisions, as in the photocyteand cilia-forming cells of Ctenophores (4). In the vertebrates, the only definite example of either kind is the germ plasm of Amphibia (5), which appears to be functionally equivalent to the pole plasm of insects. Here we describe egg ligation experiments in Xenopus and the use of a gene-specific probe to investigate the localization of materials required for the activation of muscle-specific a-actin genes. Rather surprisingly, we find that these materials are already localized in a particular region of the uncleaved egg. MATERIALS AND METHODSEggs and Embryos. Eggs laid after hormone injection were artificially fertilized as described (6). Developmental stages are those of Nieuwkoop and Faber (7).Hair-Loop Ligations. Eggs were dejellied in saline containing 2% cysteine (pH 8.0), washed, and the vitelline membrane was removed manually with forceps. Eggs were ligated with a thin brunette hair-loop in the desired orientation in modified Barth saline (MBS) (8), between 30 and 60 min after fert...

show abstract

Association of an ultraviolet irradiation sensitive cytoplasmic localization with the future dorsal side of the amphibian egg

Cited by 66 publications

References 19 publications

Identification of Distinct Classes and Functional Domains of Wnts through Expression of Wild-Type and Chimeric Proteins in Xenopus Embryos

Identification of Distinct Classes and Functional Domains of Wnts through Expression of Wild-Type and Chimeric Proteins in Xenopus Embryos

N-acetyl-cysteine causes a late re-specification of the anteroposterior axis in theXenopus embryo

All components required for the eventual activation of muscle-specific actin genes are localized in the subequatorial region of an uncleaved amphibian egg.

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