Control of cell division and cell differentiation by deoxynucleotides in the early embryo of Xenopus laevis

Landström, Ulf; Løvtrup-Rein, Huguette; Løvtrup, S

doi:10.1016/0045-6039(75)90016-0

Cited by 34 publications

(9 citation statements)

References 22 publications

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“…The coincidence between the time at which maternal pools of dNTPs are exhausted and the MBT, as well as our novel result that dATP pools are diminished around the time of the MBT, support an old idea that the MBT is triggered by declining dNTP pools [7],[30]. In this model, the MBT occurs when dNTP pools and the biosynthetic capacity of RNR are outpaced by the exponentially increasing demands for dNTPs at replication forks.…”

Section: Resultssupporting

confidence: 79%

“…One significant problem with the limiting dNTP model is how difficult it has been to definitively test. Newport and Dasso were unable to repeat the results of Lovtrup and colleagues, who claimed that injecting dNTPs could increase the number of sychronous cleavage cycles in X.laevis [28], [30]. When we attempted this experiment, we consistently found that injecting dNTPs to 100–300 µM, or ∼2.5–7.5 fold their endogenous concentration, slowed the cleavage cycles relative to control siblings.…”

Section: Resultsmentioning

confidence: 75%

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Remodeling of the Metabolome during Early Frog Development

et al. 2011

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A rapid series of synchronous cell divisions initiates embryogenesis in many animal species, including the frog Xenopus laevis. After many of these cleavage cycles, the nuclear to cytoplasmic ratio increases sufficiently to somehow cause cell cycles to elongate and become asynchronous at the mid-blastula transition (MBT). We have discovered that an unanticipated remodeling of core metabolic pathways occurs during the cleavage cycles and the MBT in X.laevis, as evidenced by widespread changes in metabolite abundance. While many of the changes in metabolite abundance were consistently observed, it was also evident that different female frogs laid eggs with different levels of at least some metabolites. Metabolite tracing with heavy isotopes demonstrated that alanine is consumed to generate energy for the early embryo. dATP pools were found to decline during the MBT and we have confirmed that maternal pools of dNTPs are functionally exhausted at the onset of the MBT. Our results support an alternative hypothesis that the cell cycle lengthening at the MBT is triggered not by a limiting maternal protein, as is usually proposed, but by a decline in dNTP pools brought about by the exponentially increasing demands of DNA synthesis.

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Section: Resultssupporting

confidence: 79%

Section: Resultsmentioning

confidence: 75%

Remodeling of the Metabolome during Early Frog Development

et al. 2011

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“…However, the effects on zygotic transcription were moderate (Collart et al, 2013), consistent with the likely existence of multiple titrated molecules, with some having greater influence on replication and others—such as histones—perhaps having greater influence on transcription (Amodeo et al, 2015; Joseph et al, 2017). In addition to histones and replication factors, other candidate titrated molecules include the phosphatase PP2A-B55 (Murphy and Michael, 2013), maternal histone variants (Yue et al, 2013), the DNA methyl transferase xDnmt1 (Dunican et al, 2008), and dNTPs (Landström et al, 1975; Vastag et al, 2011). …”

Section: Nuclear-to-cytoplasmic Ratio Mechanismsmentioning

confidence: 99%

Zygotic Genome Activation in Vertebrates

2017

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The first major developmental transition in vertebrate embryos is the maternal-to-zygotic transition (MZT) when maternal mRNAs are degraded and zygotic transcription begins. During the MZT, the embryo takes charge of gene expression to control cell differentiation and further development. This spectacular organismal transition requires nuclear reprogramming and the initiation of RNAPII at thousands of promoters. Zygotic genome activation (ZGA) is mechanistically coordinated with other embryonic events including changes in the cell cycle, chromatin state, and nuclear-to-cytoplasmic component ratios. Here, we review progress in understanding vertebrate ZGA dynamics in frogs, fish, mice, and humans to explore differences and emphasize common features.

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“…The (20), they themselves block cleav-age after the 12th cycle. Thus, the primary inhibitory effect of spinach thioredoxin m is probably not on ribonucleotide reduction, a suggestion fitting the fact that Xenopus eggs store sufficient deoxynucleotides for 12 rounds of DNA synthesis (18).…”

Section: Resultsmentioning

confidence: 99%

Spinach thioredoxin m inhibits DNA synthesis in fertilized Xenopus eggs.

Hartman

Buchanan

et al. 1993

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

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A role for thioredoxin in metazoan DNA synthesis has been assessed by injecting rapidly dividing Xenopus eggs with purified heterologous thioredoxins, which might act as inhibitors if they were to replace resident thioredoxins in some but not all reaction steps. Of 10 tested proteins, spinach chloroplast thioredoxin m is the most potent inhibitor. Eggs cleave and produce cells lacking nuclei. DNA synthesis is severely reduced. Development arrests before gastrulation. In egg extracts, thioredoxin m inhibits incorporation of radioactive dCTP into DNA of sperm nuclei and M13 phage. Inhibition exceeds 90% when thioredoxin m and M13 DNA are preincubated together. The data support the interpretation that thioredoxins normally participate in initiation of metazoan DNA synthesis.Thioredoxins are a widely distributed group of proteins that mediate both redox and nonredox reactions in prokaryotic and eukaryotic cells (1)(2)(3)(4). In the latter capacity, thioredoxin functions as an essential subunit of phage T7 DNA polymerase (5, 6) and in the maturation of DNA filamentous phages Fl and M13 (7,8 (12), and each was injected with 30 nl of the specified thioredoxin in TB at the stock concentrations indicated in the figure legends and tables or with TB (buffer) alone 40-60 min postfertilization-that is, prior to first cleavage. Embryos were allowed to develop in MMR/5 medium at 21°C (see ref.12 for composition of MMR medium). The progress of development was scored at various intervals. Arrested blastulae were identified as eggs that had cleaved to numerous cells but did not form a blastopore and did not initiate gastrulation. Arrested gastrulae were identified as those that initiated gastrulation but failed to close the blastopore (large yolk plug remaining) and did not initiate neurulation. Arrested neurulae closed the blastopore and raised neural folds but did not complete closure of the folds or differentiate specific tissues such as eyes or muscle. DNA Staining and Microscopic Analysis of Nuclei. Eggswere injected and allowed to develop in MMR/5 medium at 21°C for 8 hr to reach the midblastula transition (13). They were fixed in 4% formaldehyde in MMR/5 for 1 hr. Animal caps were cut off and transferred to MMR/5 containing Hoechst dye 33258 (bisbenzimide), flattened under a coverslip, and observed with Zeiss fluorescence optics. Preparation of Xenopus Sperm Nuclei and Egg Extracts.Xenopus sperm nuclei were prepared by the method ofLohka and Masui (14) and were demembranated by the inclusion of 400 pg of lysolecithin per ml of sperm heads (=106 sperm heads per ml). Extracts from unfertilized Xenopus eggs were also prepared by published methods (14, 15), with a final centrifugation at 10,000 x g for 5 min in a microcentrifuge at a 900 angle. DNA Replication by Sperm Nuclei. Egg extract (20 I1) was added to 2 ,l of sperm nuclei, 1 1.l of [a-32P]

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Control of cell division and cell differentiation by deoxynucleotides in the early embryo of Xenopus laevis

Cited by 34 publications

References 22 publications

Remodeling of the Metabolome during Early Frog Development

Remodeling of the Metabolome during Early Frog Development

Zygotic Genome Activation in Vertebrates

Spinach thioredoxin m inhibits DNA synthesis in fertilized Xenopus eggs.

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