The Problem of Germ Cell Determinants

Beams, H. W.; Kessel, Richard G.

doi:10.1016/s0074-7696(08)60944-4

Cited by 172 publications

(61 citation statements)

References 113 publications

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“…During early cleavage divisions of a variety of organisms a process called chromatin diminution can be observed: portions of chromatin are eliminated from the presumptive somatic cells thus leading to somatic cells which contain less genetic material than germ line cells (see [1][2][3], for review). The phenomenon, which was first described by Theodor Boveri (4) for Parascaris equorum, has since been found to occur in phylogenetically widespread species of nematodes, insects, crustaceans and hypotrichous ciliates (1)(2)(3).…”

Section: Introductionmentioning

confidence: 99%

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Nucleotide sequence of satellite DNA contained in the eliminated genome ofAscaris lumbricoides

et al. 1982

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Section: Introductionmentioning

confidence: 99%

“…The phenomenon, which was first described by Theodor Boveri (4) for Parascaris equorum, has since been found to occur in phylogenetically widespread species of nematodes, insects, crustaceans and hypotrichous ciliates (1)(2)(3). In Ascaris lumbricoides var.…”

Section: Introductionmentioning

confidence: 99%

Nucleotide sequence of satellite DNA contained in the eliminated genome ofAscaris lumbricoides

et al. 1982

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“…In many animal groups, maternal factors required for germ-line formation are localized in a histologically remarkable region in egg cytoplasm, or germ plasm, and are inherited in the germ-line progenitors (1,2). In Drosophila, the germ-line progenitors known as pole cells are first formed at the posterior pole of the blastoderm embryos.…”

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confidence: 99%

“…In Drosophila, the germ-line progenitors known as pole cells are first formed at the posterior pole of the blastoderm embryos. During later embryogenesis, the pole cells pass through midgut epithelium into hemocoel and migrate within the embryos to reach the embryonic gonads, where they differentiate as functional germ line (1)(2)(3)(4). Previous works have demonstrated that none of the pole cells becomes incorporated into any somatic tissues and contributes to somatic development during embryogenesis (5,6).…”

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confidence: 99%

Nanos suppresses somatic cell fate in Drosophila germ line

Hayashi

Hayashi²,

Kobayashi³

2004

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

132

157

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Nanos (Nos) is one of the evolutionarily conserved proteins known to direct germ-line development. In Drosophila, maternal Nos protein maintains transcriptional quiescence in the germ-line progenitors or pole cells to repress ectopic expression of somatic genes. Here we show that maternal Nos is required to establish and maintain germ-line identity by preventing apoptosis and somatic cell fate. The pole cells lacking maternal Nos were degraded by apoptosis during mid to late embryogenesis. When apoptosis was suppressed by Df(3L)H99, some pole cells lacking Nos adopted somatic cell fates. These pole cells expressed somatic markers ectopically and lost the germ-line marker Vasa. We further found that some Nos-negative pole cells were able to migrate into the gonads, but they failed to develop as functional germ cells during postembryonic stages. We propose a model in which Nos establishes germ-line͞soma dichotomy and is also required to maintain germ-line fate.T he mechanism underlying the segregation of germ line from somatic line is a century-old issue in developmental biology. In many animal groups, maternal factors required for germ-line formation are localized in a histologically remarkable region in egg cytoplasm, or germ plasm, and are inherited in the germ-line progenitors (1, 2). In Drosophila, the germ-line progenitors known as pole cells are first formed at the posterior pole of the blastoderm embryos. During later embryogenesis, the pole cells pass through midgut epithelium into hemocoel and migrate within the embryos to reach the embryonic gonads, where they differentiate as functional germ line (1-4). Previous works have demonstrated that none of the pole cells becomes incorporated into any somatic tissues and contributes to somatic development during embryogenesis (5, 6). However, it remains elusive how the developmental fate of pole cells is regulated by germ plasm components.One of the germ plasm components, Nanos (Nos), is evolutionarily conserved and has a widespread role in germ-line development (7-13). Maternal nos mRNA is enriched in germ plasm, and its protein product is partitioned into pole cells when they are formed and remains detectable in these cells throughout embryogenesis (14). Nos is required in pole cells for their proper migration into the embryonic gonads (15, 16). Within pole cells, Nos is involved in maintaining transcriptional quiescence (17) and is also required for maintenance of a germ-line-specific chromatin status that correlates with transcriptional inactivity (18). In the absence of maternal Nos activity, ectopic expression of somatic genes is detectable in pole cells (17). These results led us to speculate that pole cells lacking Nos may adopt somatic cell fate.Here, we show that pole cells are able to adopt both germ-line and somatic cell fates and undergo apoptosis. Nos is required to repress the pathway leading to somatic differentiation and apoptosis. Thus, we conclude that Nos is essential for germline͞soma dichotomy and for germ-line maintenance. H99-PLH⌬23͞TM3...

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“…Such conspicuous "extra DNA bodies" have not only been observed in dytiscid beetles but also in other beetles [24,25,33,48,49] and in taxonomic ally rather distant insect species (for refs. see Introduction and I.…”

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confidence: 94%

Frequencies of Circular Units of Nucleolar DNA in Oocytes of Two Insects, Acheta domesticus and Dytiscus marginalis, and Changes of Nucleolar Morphology during Oogenesis

1977

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The organization of the extrachromosomal nucleolar material in oocytes of two insect species with different ovary types, the house cricket Acheta domesticus (panoistic ovary) and the water beetle Dytiscus marginalis (meroistic ovary), was studied with light and electron microscopic techniques. Stages early in oogenesis were compared with fully vitellogenic stages (mid-to-Iate diplotene). The arrangement of the nucleolar material undergoes a marked change from a densely aggregated to a dispersed state. The latter was characterized by high transcriptional activity. In spread and positively stained preparations of isolated nucleolar material, a high frequency of small circular units of transcribed rDNA was observed and rings with small numbers (1-5) of pre-rRNA genes were predominant. The observations suggest that the "extra DNA body" observed in early oogenic stages of both species represents a dense aggregate of numerous short circular units of nucleolar chromatin, with morphological subcomponents identifiable in ultrathin sections. These apparently remain in close association with the chromosomal nucleolar organizer(s). The observations further indicate that the individual small nucleolar subunit circles dissociate and are dispersed as actively transcribed rDNA units later in diplotene. The results are discussed in relation to principles of the ultrastructural organization of nucleoli in other cell types as well as in relation to possible mechanisms of gene amplification.

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The Problem of Germ Cell Determinants

Cited by 172 publications

References 113 publications

Nucleotide sequence of satellite DNA contained in the eliminated genome ofAscaris lumbricoides

Nucleotide sequence of satellite DNA contained in the eliminated genome ofAscaris lumbricoides

Nanos suppresses somatic cell fate in Drosophila germ line

Frequencies of Circular Units of Nucleolar DNA in Oocytes of Two Insects, Acheta domesticus and Dytiscus marginalis, and Changes of Nucleolar Morphology during Oogenesis

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