Biomedical subjects

Sergio Moreno

Publications and source records attributed to Sergio Moreno.

13 recordsLinked to original sources

PubMed2025

Nrm1 is a bistable switch connecting cell cycle progression to transcriptional control.

Entry into the cell cycle requires activation of G1 cyclin-dependent kinases (CDKs) and the G1/S transcriptional program. In fission yeast, the MBF complex is the main transcription factor driving early cell-cycle gene expression. MBF-dependent transcription is activated in metaphase and repressed at the end of S phase by a feedback loop involving the cyclin Cig2 and co-repressors Nrm1 and Yox1. While replicative stress inactivates Yox1 via phosphorylation, the mechanism that activates MBF during an unperturbed cell cycle remains unclear. Here, we identify Nrm1 as the key target of cell cycle regulation in a two-step control mechanism. First, CDK1 phosphorylates Nrm1 in metaphase, leading to its release-along with Yox1-from chromatin. Second, unphosphorylated Nrm1, generated either by dephosphorylation or de novo synthesis, is degraded during anaphase, preventing its re-association with MBF until the end of the next S phase. Together, these parallel pathways create a precisely timed window of MBF activation, ensuring proper cell cycle progression and preserving genomic stability.

Schizosaccharomyces↗

PubMed2006

Fission yeast Tor2 promotes cell growth and represses cell differentiation.

The fission yeast Schizosaccharomyces pombe is an excellent model system in which to study the coordination of cell growth and cell differentiation. In the presence of nutrients, fission yeast cells grow and divide; in the absence of nutrients, they stop growing and undergo cell differentiation. The molecular mechanisms underlying this response are not fully understood. Here, we demonstrate that Tor2, a fission yeast member of the TOR protein kinase family, is central to controlling the switch between cell growth and cell differentiation in response to nutrient availability. Tor2 controls cell growth and ribosome biogenesis by regulating ribosomal protein gene expression. We have found that Tor2 has an additional function in repressing sexual differentiation. Tor2 overexpression strongly represses mating, meiosis and sporulation efficiency, whereas Tor2 inactivation has the opposite effect, leading to cell differentiation, regardless of the nutritional conditions. This newly revealed function of Tor2 appears to operate by interfering with the functions of the transcription factor Ste11 and the meiosis-promoting RNA-binding protein Mei2. Thus, our data reveal a unique regulatory function of the Tor pathway - ensuring that growth and cell differentiation become mutually exclusive and that the choice between them depends on environmental conditions.

Blotting, Northern↗

PubMed2006

Cross-talk between nucleotide excision and homologous recombination DNA repair pathways in the mechanism of action of antitumor trabectedin.

Trabectedin (Yondelis) is a potent antitumor drug that has the unique characteristic of killing cells by poisoning the DNA nucleotide excision repair (NER) machinery. The basis for the NER-dependent toxicity has not yet been elucidated but it has been proposed as the major determinant for the drug's cytotoxicity. To study the in vivo mode of action of trabectedin and to explore the role of NER in its cytotoxicity, we used the fission yeast Schizosaccharomyces pombe as a model system. Treatment of S. pombe wild-type cells with trabectedin led to cell cycle delay and activation of the DNA damage checkpoint, indicating that the drug causes DNA damage in vivo. DNA damage induced by the drug is mostly caused by the NER protein, Rad13 (the fission yeast orthologue to human XPG), and is mainly repaired by homologous recombination. By constructing different rad13 mutants, we show that the DNA damage induced by trabectedin depends on a 46-amino acid region of Rad13 that is homologous to a DNA-binding region of human nuclease FEN-1. More specifically, an arginine residue in Rad13 (Arg961), conserved in FEN1 (Arg314), was found to be crucial for the drug's cytotoxicity. These results lead us to propose a model for the action of trabectedin in eukaryotic cells in which the formation of a Rad13/DNA-trabectedin ternary complex, stabilized by Arg961, results in cell death.

Antineoplastic Agents, Alkylating↗

PubMed2006

The fission yeast APC activator Ste9 is regulated by mRNA decay.

Fission yeast Ste9/Srw1 is a family member of the Fizzy-related APC activators that promote the ubiquitination and degradation of mitotic cyclins and other substrates at the end of mitosis and G1. These proteins are highly regulated during the cell cycle at the level of gene transcription and protein phosphorylation in order to guarantee the correct order of events during the cell cycle. Here we propose mRNA decay as a novel mechanism that regulates ste9+ gene expression during the cell cycle. We have characterized the elements in the 3'UTR of the ste9 mRNA responsible for this mechanism. Moreover, we demonstrate that the instability of ste9 mRNA is important for downregulating Ste9 levels in G2, allowing appropriate cyclin B accumulation to promote timely entry into mitosis.

3' Untranslated Regions↗

PubMed2005

A large-scale screen in S. pombe identifies seven novel genes required for critical meiotic events.

Meiosis is a specialized form of cell division by which sexually reproducing diploid organisms generate haploid gametes. During a long prophase, telomeres cluster into the bouquet configuration to aid chromosome pairing, and DNA replication is followed by high levels of recombination between homologous chromosomes (homologs). This recombination is important for the reductional segregation of homologs at the first meiotic division; without further replication, a second meiotic division yields haploid nuclei. In the fission yeast Schizosaccharomyces pombe, we have deleted 175 meiotically upregulated genes and found seven genes not previously reported to be critical for meiotic events. Three mutants (rec24, rec25, and rec27) had strongly reduced meiosis-specific DNA double-strand breakage and recombination. One mutant (tht2) was deficient in karyogamy, and two (bqt1 and bqt2) were deficient in telomere clustering, explaining their defects in recombination and segregation. The moa1 mutant was delayed in premeiotic S phase progression and nuclear divisions. Further analysis of these mutants will help elucidate the complex machinery governing the special behavior of meiotic chromosomes.

Chromosome Segregation↗

PubMed2005

Cdh1/Hct1-APC is essential for the survival of postmitotic neurons.

Cell division at the end of mitosis and G1 is controlled by Cdh1/Hct1, an activator of the E3-ubiquitin ligase anaphase-promoting complex (APC) that promotes the ubiquitylation and degradation of mitotic cyclins and other substrates. Cdh1-APC is active in postmitotic neurons, where it regulates axonal growth and patterning in the developing brain. However, it remains unknown whether Cdh1-APC is involved in preventing cell-cycle progression in terminally differentiated neurons. To address this issue, we used the small hairpin RNA strategy to deplete Cdh1 in postmitotic neurons. We observed that Cdh1 silencing rapidly triggered apoptotic neuronal death. To investigate the underlying mechanism, we focused on cyclin B1, a major Cdh1-APC substrate. Our results demonstrate that Cdh1 is required to prevent the accumulation of cyclin B1 in terminally differentiated neurons. Moreover, by keeping cyclin B1 low, Cdh1 prevented these neurons from entering an aberrant S phase that led to apoptotic cell death. These results provide an explanation for the mechanism of cyclin B1 reactivation that occurs in the brain of patients suffering from neurodegenerative diseases, such as Alzheimer's disease.

Animals↗

PubMed2005

Etd1p is a novel protein that links the SIN cascade with cytokinesis.

In animal cells, cytokinesis occurs by constriction of an actomyosin ring. In fission yeast cells, ring constriction is triggered by the septum initiation network (SIN), an SPB-associated GTPase-regulated kinase cascade that coordinates exit from mitosis with cytokinesis. We have identified a novel protein, Etd1p, required to trigger actomyosin ring constriction in fission yeasts. This protein is localised at the cell tips during interphase. In mitosis, it relocates to the medial cortex region and, coincident with cytokinesis, it assembles into the actomyosin ring by association to Cdc15p. Relocation of Etd1p from the plasma membrane to the medial ring is triggered by SIN signalling and, reciprocally, relocation of the Sid2p-Mob1p kinase complex from the SPB to the division site, a late step in the execution of the SIN, requires Etd1p. These results suggest that Etd1p coordinates the mitotic activation of SIN with the initiation of actomyosin ring constriction. Etd1p peaks during cytokinesis and is degraded by the ubiquitin-dependent 26S-proteasome pathway at the end of septation, providing a mechanism to couple inactivation of SIN to completion of cytokinesis.

Actomyosin↗

PubMed2004

A role for the Cdc14-family phosphatase Flp1p at the end of the cell cycle in controlling the rapid degradation of the mitotic inducer Cdc25p in fission yeast.

The Schizosaccaromyces pombe protein Flp1p belongs to a conserved family of serine-threonine-phosphatases. The founding member of this family, Saccharomyces cerevisiae Cdc14p, is required for inactivation of mitotic CDKs and reversal of CDK mediated phosphorylation at the end of mitosis, thereby bringing about the M-G1 transition. Initial studies of Flp1p suggest that it may play a different role to Cdc14p. Here we show that Flp1p is required for rapid degradation of the mitotic inducer Cdc25p at the end of mitosis, and that Cdc25p is a substrate of Flp1p in vitro. Down-regulation of Cdc25p activity by Flp1p may ensure a prompt inactivation of mitotic CDK complexes to trigger cell division. Our results suggest a regulatory mechanism, and a universal role, for Cdc14p like proteins in coordination of cytokinesis with other cell cycle events.

Cell Cycle↗

PubMed2003

Synthesis, structural determination and dynamic behavior of 2-chloro-4,6-bis(pyrazolylamino)-1,3,5-triazines.

A series of 2-chloro-4,6-bis(pyrazolylamino)-1,3,5-triazines with applications in crystal engineering have been prepared. At low temperature, the presence of two or three isomers has been detected and these assigned to 4,6-diamino-1,3,5-triazine structures on the basis of comparison with model compounds. 2D-Exchange spectroscopy studies in various solvents and at different temperatures have been used to determine the equilibrium constants and the activation free energies of the restricted rotation about the amino-triazine bond. A plot of the activation free energy versus temperature showed a good linear correlation and confirmed that the same process is present in all of the compounds under investigation. Comparison with model compounds also confirmed both the occurrence of the restricted rotation and the 4,6-diamino-1,3,5-triazine tautomerism for triazines 1-4 in solution. The structure of compound 1 has been determined in the solid state by X-ray crystallography and consists ofa 4,6-diamino- 1,3,5-triazine structure stabilized by intra and intermolecular hydrogen bonds.

Crystallography, X-Ray↗

PubMed2003

Regulated mRNA stability of the Cdk inhibitor Rum1 links nutrient status to cell cycle progression.

BACKGROUND: The survival of a cell depends on continuous sensing of the nutritional environment and appropriate coordination of the cell cycle. The fission yeast Schizosaccharomyces pombe is an excellent model system in which to study these processes. In the presence of nutrients, fission yeast cells grow and divide, spending most of their time in G2; when nutrients are limiting, they are promoted into mitosis and arrest the cell cycle in G1. The molecular mechanisms underlying this response are currently unknown. RESULTS: Here, we show that expression of the fission yeast Cdk inhibitor Rum1, a key regulator of Cdc2/cyclin B in G1, is subject to regulated mRNA stability in response to nutrient deprivation. In complete minimal medium, rum1 mRNAs are very unstable. Following nitrogen starvation, rum1 mRNAs are rapidly stabilized, allowing the accumulation of Rum1 protein to delay the G1 phase of the subsequent cell cycle. Instability of rum1 mRNAs in complete minimal medium depends on the presence of AU-rich elements in the 3'UTR. We also show that lack of this mechanism has consequences in the mitotic cell cycle, in meiosis, and in the control of ploidy. CONCLUSION: We propose that mRNA stability is an important mechanism to fine tune the expression of the rum1 gene, in order to allow the production of appropriate levels of Rum1 protein in response to changes in the nutritional environment.

Base Sequence↗

PubMed2003

Systematic functional analysis of the Caenorhabditis elegans genome using RNAi.

A principal challenge currently facing biologists is how to connect the complete DNA sequence of an organism to its development and behaviour. Large-scale targeted-deletions have been successful in defining gene functions in the single-celled yeast Saccharomyces cerevisiae, but comparable analyses have yet to be performed in an animal. Here we describe the use of RNA interference to inhibit the function of approximately 86% of the 19,427 predicted genes of C. elegans. We identified mutant phenotypes for 1,722 genes, about two-thirds of which were not previously associated with a phenotype. We find that genes of similar functions are clustered in distinct, multi-megabase regions of individual chromosomes; genes in these regions tend to share transcriptional profiles. Our resulting data set and reusable RNAi library of 16,757 bacterial clones will facilitate systematic analyses of the connections among gene sequence, chromosomal location and gene function in C. elegans.

Animals↗

PubMed2003

Regulation of meiotic progression by the meiosis-specific checkpoint kinase Mek1 in fission yeast.

During the eukaryotic cell cycle, accurate transmission of genetic information to progeny is ensured by the operation of cell cycle checkpoints. Checkpoints are regulatory mechanisms that block cell cycle progression when key cellular processes are defective or chromosomes are damaged. During meiosis, genetic recombination between homologous chromosomes is essential for proper chromosome segregation at the first meiotic division. In response to incomplete recombination, the pachytene checkpoint (also known as the meiotic recombination checkpoint) arrests or delays meiotic cell cycle progression, thus preventing the formation of defective gametes. Here, we describe a role for a meiosis-specific kinase, Mek1, in the meiotic recombination checkpoint in fission yeast. Mek1 belongs to the Cds1/Rad53/Chk2 family of kinases containing forkhead-associated domains, which participate in a number of checkpoint responses from yeast to mammals. We show that defects in meiotic recombination generated by the lack of the fission yeast Meu13 protein lead to a delay in entry into meiosis I owing to inhibitory phosphorylation of the cyclin-dependent kinase Cdc2 on tyrosine 15. Mutation of mek1(+) alleviates this checkpoint-induced delay, resulting in the formation of largely inviable meiotic products. Experiments involving ectopic overexpression of the mek1(+) gene indicate that Mek1 inhibits the Cdc25 phosphatase, which is responsible for dephosphorylation of Cdc2 on tyrosine 15. Furthermore, the meiotic recombination checkpoint is impaired in a cdc25 phosphorylation site mutant. Thus, we provide the first evidence of a connection between an effector kinase of the meiotic recombination checkpoint and a crucial cell cycle regulator and present a model for the operation of this meiotic checkpoint in fission yeast.

Amino Acid Sequence↗

PubMed2002

Mental models in deductive reasoning.

We report research investigating the role of mental models in deduction. The first study deals with conjunctive inferences (from one conjunction and two conditional premises) and disjunctive inferences (from one disjunction and the same two conditionals). The second study examines reasoning from multiple conditionals such as: If e then b; If a then b; If b then c; What follows between a and c? The third study addresses reasoning from different sorts of conditional assertions, including conditionals based on if then, only if, and unless. The paper also presents research on figural effects in syllogistic reasoning, on the effects of structure and believability in reasoning from double conditionals, and on reasoning from factual, counterfactual, and semifactual conditionals. The findings of these studies support the model theory, pose some difficulties for rule theories, and show the influence on reasoning of the linguistic structure and the semantic content of problems.

Cognition↗