Active chromatin of oocytes injected with somatic cell nuclei or cloned DNA

Weisbrod, Stuart; Wickens, Marvin; Whytock, Sue; Gurdon, J. B.

doi:10.1016/0012-1606(82)90085-9

Cited by 24 publications

(12 citation statements)

References 31 publications

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“…Although nucleoplasmin has not been reported in mammalian oocytes, similar molecules might be involved in the H1 removal in mammalian oocytes as the responsible factor(s) seems to be accumulated in the bovine oocyte nuclei as with Xenopus nucleoplasmin. In contrast, core histones of somatic nuclei are not removed and nucleosomal spacing is not altered when entire chromatin was tested as bulk [6]. These results are consistent with recent studies using fluorescence recovery after photobleaching (FRAP) in living cells.…”

supporting

confidence: 90%

Chromatin remodeling in nuclear cloning

Wade¹,

Kikyo²

2002

European Journal of Biochemistry

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Nuclear cloning is a procedure to create new animals by injecting somatic nuclei into unfertilized oocytes. Recent successes in mammalian cloning with differentiated adult nuclei strongly indicate that oocyte cytoplasm contains unidentified remarkable reprogramming activities with the capacity to erase the previous memory of cell differentiation. At the heart of this nuclear reprogramming lies chromatin remodeling as chromatin structure and function define cell differentiation through regulation of the transcriptional activities of the cells. Studies involving the modification of chromatin elements such as selective uptake or release of binding proteins, covalent histone modifications including acetylation and methylation, and DNA methylation should provide significant insight into the molecular mechanisms of nuclear dedifferentiation and redifferentiation in oocyte cytoplasm.Keywords: nuclear cloning; chromatin remodeling; linker histone; histone acetylation; histone methylation; DNA methylation. I N T R O D U C T I O NDifferentiated somatic nuclei have the flexibility to dedifferentiate in oocyte cytoplasm and redifferentiate into other multiple lineages during the subsequent embryogenesis. This drastic nuclear plasticity has been repeatedly confirmed by successful nuclear cloning in frogs and several mammalian species over the past half a century (reviewed in [1][2][3]). Although generally only less than 1% of cloned mice survive to adulthood [1], many of the aborted embryos still contain terminally differentiated tissues derived from the injected somatic nuclei establishing that highly efficient reprogramming mechanisms exist in oocyte cytoplasm. Currently, the identities of these activities are ill defined. The toad Xenopus laevis and the mouse represent two of the complementary model organisms for nuclear cloning. Because of its large and abundant oocytes, Xenopus has been used for nuclear cloning since the 1950s, providing a great amount of valuable information regarding a wide range of cell biological and biochemical events that take place in the injected nuclei [2]. On the other hand, mouse cloning is more suitable for genetic studies such as the modification of DNA methylation, genomic imprinting and telomere length. Although these two species display distinct early developmental processes, these nuclei share common features upon injection into each oocyte including nuclear swelling, chromatin dispersal and loss of linker histone H1 (see below). In this minireview, we will highlight some of the selected topics on the chromatin modification in Xenopus and mammalian nuclear cloning, followed by a discussion about newly identified histone methylation and heterochromatin formation as an entirely unexplored field of chromatin modification involved in nuclear cloning. E X C H A N G E O F C H R O M A T I N P R O T E I N SEarly reports demonstrated that Xenopus or human somatic nuclei injected into Xenopus oocytes lose 80-90% of the preradiolabelled nuclear proteins accompanied with significant incorporation o...

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supporting

confidence: 90%

Chromatin remodeling in nuclear cloning

Wade¹,

Kikyo²

2002

European Journal of Biochemistry

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“…Histone B4 and HMG1/2 in the Xenopus sperm nucleus The presence of HMG 1/2-like molecules has been reported previously in X.laevis oocytes (Weisbrod et al, 1982;Kleinschmidt et al, 1983) and eggs . Condensed Xenopus sperm chromatin is deficient in HMGI/2, and these proteins(s) only accumulate as sperm chromatin is decondensed during nuclear assembly in the egg extract (Figure 1 D).…”

Section: Discussionsupporting

confidence: 52%

Evidence for a shared structural role for HMG1 and linker histones B4 and H1 in organizing chromatin.

et al. 1996

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The high mobility group proteins 1 and 2 (HMG1/2) and histone B4 are major components of chromatin within the nuclei assembled during the incubation of Xenopus sperm chromatin in Xenopus egg extract. To investigate their potential structural and functional roles, we have cloned and expressed Xenopus HMG1 and histone B4. Purified histone B4 and HMG1 form stable complexes with nucleosomes including Xenopus 5S DNA. Both proteins associate with linker DNA and stabilize it against digestion with micrococcal nuclease, in a similar manner to histone H1. However, neither histone B4 nor HMG1 influence the DNase I or hydroxyl radical digestion of DNA within the nucleosome core. We suggest that HMG1/2 and histone B4 have a shared structural role in organizing linker DNA in the nucleosome.

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“…Preformation of nucleosome cores on DNA before microinjection was found previously to inhibit transcription {Weisbrod et al 1982;Gargiulo et al 1984). Remarkably however, chromatin assembly using dsDNA templates, when occurring in the oocyte nucleus, has never been found to efficiently repress basal transcription from either class III or class II genes (Miller and Mertz 1982;Weisbrod et al 1982;Gargiulo and Worcel 1983;Gargiulo et al 1984}. Our results therefore provide the first evidence that chromatin assembly can actually be repressive in the Xenopus oocyte nucleus.…”

Section: Chromatin Assembly Coupled To Replication a Mechanism To Essupporting

confidence: 51%

“…This approach has been used for the initial definition of gene regulatory elements (Brown and Gurdon 1977;McKnight and Kingsbury 1982): the assembly of chromatin on exogenous DNA (Wyllie et al 1978;Ryoji and Worcel 1984); the examination of chromatin-mediated gene repression (Weisbrod et al 1982); and the determination of the influence of DNA topology on transcription (Harland et al 1983). In every instance, results in oocyte nuclei have been substantiated by later experiments in somatic cells [Gurdon and Wickens 1983;Gurdon and Wakefield 1986).…”

mentioning

confidence: 99%

Replication-coupled chromatin assembly is required for the repression of basal transcription in vivo.

Almouzni¹,

Wolffe²

1993

Genes Dev.

158

124

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The chromatin assembly process coupled to DNA synthesis in the Xenopus oocyte nucleus is significantly more repressive toward basal transcription than chromatin assembly on duplex DNA. We show that chromatin assembly concurrent with DNA synthesis over the promoter region itself is causal for repression.However, the trans-activator GaI4-VP16 both relieves repression and activates transcription regardless of the chromatin assembly pathway. This activation is independent of whether GaI4-VP16 addition occurs before or after chromatin assembly. We propose that replication-coupled chromatin assembly represents a general mechanism to direct the efficient repression of basal transcription. However transcription induction by a specific activator, GaI4-VP16, occurs independent of this chromatin-mediated repression.

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Active chromatin of oocytes injected with somatic cell nuclei or cloned DNA

Cited by 24 publications

References 31 publications

Chromatin remodeling in nuclear cloning

Chromatin remodeling in nuclear cloning

Evidence for a shared structural role for HMG1 and linker histones B4 and H1 in organizing chromatin.

Replication-coupled chromatin assembly is required for the repression of basal transcription in vivo.

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