DNA synthesis in the early embryo of the nematode Ascaris suum

Azzaria, Marie; McGhee, James D.

doi:10.1016/0012-1606(92)90158-d

Cited by 12 publications

(6 citation statements)

References 24 publications

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“…1A). After 24 hr of development at 30°C, the two pronuclei fuse and the first division occurs at around 36 hr [19]. Subsequent cell divisions occur every ~13 hr on average and development of the L1 and L2 occurs over an extended period of 10 and 21 days, respectively.…”

Section: Resultsmentioning

confidence: 99%

“…These differences in the requirement for transcription in early cleavages have been suggested to be a function of variation in maternal contributions to the embryos in different nematodes [29]. The duration of the C. elegans cell cycle during early development is on average 15–20 min [29, 31], whereas it is ~ 150 min in A. nanus [29], and ~13 hr in A. suum [19]. In addition, A. suum zygotes undergo an extended period of maturation in the uterus (~ 12 – 24 hr).…”

Section: Discussionmentioning

confidence: 99%

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Transcription in Pronuclei and One- to Four-Cell Embryos Drives Early Development in a Nematode

2014

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Summary Background A long-standing view of development is that transcription is silenced in the oocyte until early divisions in the embryo. The point at which major transcription is reactivated varies between organisms, but is usually after the 2-cell stage. However, this model may not be universal. Results We used RNA-seq and exploited the protracted development of the parasitic nematode Ascaris suum, to provide a comprehensive time course of mRNA expression, degradation, and translation during early development. Surprisingly, we find that ~4,000 genes are transcribed prior to pronuclear fusion and in the 1–4 cell embryos. Intriguingly, we do not detect maternal contribution of many orthologs of maternal C. elegans mRNAs, but instead find these are newly transcribed in the A. suum zygote prior to pronuclear fusion. Ribosome profiling demonstrates that, in general, early embryonic mRNAs are not stored for subsequent translation, but are directly translated following their synthesis. The role of maternally contributed and zygotically transcribed genes differs between the nematodes A. suum and C. elegans despite the fact that the two nematodes appear to exhibit highly similar morphological patterns during early development. Conclusions Our study indicates that major transcription can occur immediately after fertilization and prior to pronuclear fusion in metazoa, suggesting that newly transcribed genes appear to drive A. suum early development. Furthermore, the mechanisms used for controlling the timing of the expression of key conserved genes has been altered between the two nematodes, illustrating significant plasticity in the regulatory networks that play important roles in developmental outcomes in nematodes.

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Section: Resultsmentioning

confidence: 99%

Section: Discussionmentioning

confidence: 99%

Transcription in Pronuclei and One- to Four-Cell Embryos Drives Early Development in a Nematode

2014

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“…Fertilized zygotes arrest before pronuclear fusion, allowing storage of large numbers of embyos for years at 4°, which can then be synchronously released by exposure to an acidic environment that mimics the host stomach (R. E. Davis, personal communication). Postfertilization cell cycles are slow (13 hr, compared to 30 min in C. elegans ) ( Azzaria and McGhee 1992 ), allowing for excellent temporal resolution of early development. Although pigs are needed to maintain the lifecycle, embryonic and early larval development can be studied in vitro , and migration from the intestine to the liver and lungs can be studied in rabbits, mice, or rats ( Campbell and Timinski 1965 ; Galvin 1968 ; Enobe et al 2006 ).…”

Section: Existing Technologies In Parasitesmentioning

confidence: 99%

Rendering the Intractable More Tractable: Tools from Caenorhabditis elegans Ripe for Import into Parasitic Nematodes

Ward

2015

Genetics

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Recent and rapid advances in genetic and molecular tools have brought spectacular tractability to Caenorhabditis elegans, a model that was initially prized because of its simple design and ease of imaging. C. elegans has long been a powerful model in biomedical research, and tools such as RNAi and the CRISPR/Cas9 system allow facile knockdown of genes and genome editing, respectively. These developments have created an additional opportunity to tackle one of the most debilitating burdens on global health and food security: parasitic nematodes. I review how development of nonparasitic nematodes as genetic models informs efforts to import tools into parasitic nematodes. Current tools in three commonly studied parasites (Strongyloides spp., Brugia malayi, and Ascaris suum) are described, as are tools from C. elegans that are ripe for adaptation and the benefits and barriers to doing so. These tools will enable dissection of a huge array of questions that have been all but completely impenetrable to date, allowing investigation into host–parasite and parasite–vector interactions, and the genetic basis of parasitism.

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“…In the 4-cell embryo, two cells (ABa and ABp) simultaneously undergo PDE, followed by PDE in the EMS cell (39). Notably, Ascaris early embryos have a long cell cycle of ∼15 hours (40), compared to ∼20-30 minutes in the free-living nematodes C. elegans and O. tipulae . The long cell cycle allowed us to identify and examine DSBs and their resection at 11 time points between 50 to 98 hours of embryo development.…”

Section: Resultsmentioning

confidence: 99%

End resection and telomere healing of DNA double-strand breaks during nematode programmed DNA elimination

Estrem,

Davis,

Wang

2024

Preprint

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Most DNA double-strand breaks (DSBs) are harmful to genome integrity. However, some forms of DSBs are essential to biological processes, such as meiotic recombination and V(D)J recombination. DSBs are also required for programmed DNA elimination (PDE) in ciliates and nematodes. In nematodes, the DSBs are healed with telomere addition. While telomere addition sites have been well-characterized, little is known regarding the DSBs that fragment nematode chromosomes. Here, we used embryos from the nematode Ascaris to study the timing of PDE breaks and examine the DSBs and their end processing. Using END-seq, we characterize the DSB ends and demonstrate that DNA breaks are introduced before mitosis, followed by extensive end resection. The resection profile is unique for each break site, and the resection generates 3' overhangs before the addition of telomeres. Interestingly, telomere healing occurs much more frequently on retained DSB ends than on eliminated ends. This biased repair of the DSB ends in Ascaris may be due to the sequestration of the eliminated DNA into micronuclei, preventing their ends from telomere healing. Additional DNA breaks occur within the eliminated DNA in both Ascaris and Parascaris, ensuring chromosomal breakage and providing a fail-safe mechanism for nematode PDE.

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DNA synthesis in the early embryo of the nematode Ascaris suum

Cited by 12 publications

References 24 publications

Transcription in Pronuclei and One- to Four-Cell Embryos Drives Early Development in a Nematode

Transcription in Pronuclei and One- to Four-Cell Embryos Drives Early Development in a Nematode

Rendering the Intractable More Tractable: Tools from Caenorhabditis elegans Ripe for Import into Parasitic Nematodes

End resection and telomere healing of DNA double-strand breaks during nematode programmed DNA elimination

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