Biomedical subjects

Cyril Berthet

Publications and source records attributed to Cyril Berthet.

7 recordsLinked to original sources

PubMed2006

Cdk2 and Cdk4 cooperatively control the expression of Cdc2.

Progression through the mammalian cell cycle is associated with the activity of four cyclin dependent kinases (Cdc2/Cdk1, Cdk2, Cdk4, and Cdk6). Knockout mouse models have provided insight into the interplay of these Cdks. Most of these models do not exhibit major cell cycle defects revealing redundancies, and suggesting that a single Cdk might be sufficient to drive the cell cycle, similar as in yeast. Recent work on Cdk2/Cdk4 double knockouts has indicated that these two Cdks are required to phosphorylate Rb during late embryogenesis. The lack of Rb phosphorylation is progressive and associated with reduced E2F-inducible gene expression. Cdk2 and Cdk4 share the essential function of coupling the G1/S transition with mitosis. However, proliferation in early embryogenesis appears to be independent of Cdk2 and Cdk4. We discuss these observations and propose molecular mechanisms that establish the requirement for Cdk2 and Cdk4 at the G1/S transition. We are considering that the balance between proliferation and differentiation is disturbed, which affects especially heart development and leads to embryonic lethality in Cdk2-/- Cdk4-/- mutants. We also discuss the specific functions of Cdk4 and Cdk6, which ironically do not compensate for each other.

Journal Article↗

PubMed2006

Combined loss of Cdk2 and Cdk4 results in embryonic lethality and Rb hypophosphorylation.

Mouse knockouts of Cdk2 and Cdk4 have demonstrated that, individually, these genes are not essential for viability. To investigate whether there is functional redundancy, we have generated double knockout (DKO) mice. Cdk2-/- Cdk4-/- DKOs die during embryogenesis around E15 as a result of heart defects. We observed a gradual decrease of Retinoblastoma protein (Rb) phosphorylation and reduced expression of E2F-target genes, like Cdc2 and cyclin A2, during embryogenesis and in embryonic fibroblasts (MEFs). DKO MEFs are characterized by a decreased proliferation rate, impaired S phase entry, and premature senescence. HPV-E7-mediated inactivation of Rb restored normal expression of E2F-inducible genes, senescence, and proliferation in DKO MEFs. In contrast, loss of p27 did not rescue Cdk2-/- Cdk4-/- phenotypes. Our results demonstrate that Cdk2 and Cdk4 cooperate to phosphorylate Rb in vivo and to couple the G1/S phase transition to mitosis via E2F-dependent regulation of gene expression.

Animals↗

PubMed2004

CCR4-associated factor CAF1 is an essential factor for spermatogenesis.

The CCR4-associated protein CAF1 has been demonstrated to play several roles in the control of transcription and of mRNA decay. To gain further insight into its physiological function, we generated CAF1-deficient mice. They are viable, healthy, and normal in appearance; however, mCAF1(-/-) male mice are sterile. The crossing of mCAF1(+/-) mice gave a Mendelian ratio of mCAF1(+/+), mCAF1(+/-), and mCAF1(-/-) pups, indicating that haploid mCAF1-deficient germ cells differentiate normally. The onset of the defect occurs during the first wave of spermatogenesis at 19 to 20 days after birth, during progression of pachytene spermatocytes to haploid spermatids and spermatozoa. Early disruption of spermatogenesis was evidenced by Sertoli cell vacuolization and tubular disorganization. The most mature germ cells were the most severely depleted, but progressively all germ cells were affected, giving Sertoli cell-only tubes, large interstitial spaces, and small testes. This phenotype could be linked to a defect(s) in germ cells and/or to inadequate Sertoli cell function, leading to seminiferous tubule disorganization and finally to a total disappearance of germ cells. The mCAF1-deficient mouse provides a new model of failed spermatogenesis in the adult that may be relevant to some cases of human male sterility.

Animals↗

PubMed2004

Cdk2 as a master of S phase entry: fact or fake?

It has long been believed that Cdk2 and its activator cyclin E play essential roles in the progression of the mitotic cell cycle. However, recent studies using knockout mouse models revealed that neither Cdk2 nor cyclin E are essential in vivo. The purpose of this Perspective is to compare both Cdk2 and cyclin E knockout mice models and to discuss potential mechanisms driving the cell cycle in the absence of Cdk2 or cyclin E. Particular emphasis is placed on possible non-catalytic roles of cyclin E, the expression and activity of the second cyclin binding partner of Cdk2, cyclin A, as well as on the expression and degradation of the Cdk2 inhibitor p27Kip1 in the absence of Cdk2.

Animals↗

PubMed2003

Cdk2 knockout mice are viable.

BACKGROUND: Cyclin-dependent kinases (Cdks) and their cyclin regulatory subunits control cell growth and division. Cdk2/cyclin E complexes are thought to be required because they phosphorylate the retinoblastoma protein and drive cells through the G1/S transition into the S phase of the cell cycle. In addition, Cdk2 associates with cyclin A, which itself is essential for cell proliferation during early embryonic development. RESULTS: In order to study the functions of Cdk2 in vivo, we generated Cdk2 knockout mice. Surprisingly, these mice are viable, and therefore Cdk2 is not an essential gene in the mouse. However, Cdk2 is required for germ cell development; both male and female Cdk2(-/-) mice are sterile. Immunoprecipitates of cyclin E1 complexes from Cdk2(-/-) spleen extracts displayed no activity toward histone H1. Cyclin A2 complexes were active in primary mouse embryonic fibroblasts (MEFs), embryo extracts and in spleen extracts from young animals. In contrast, there was little cyclin A2 kinase activity in immortalized MEFs and spleen extracts from adult animals. Cdk2(-/-) MEFs proliferate but enter delayed into S phase. Ectopic expression of Cdk2 in Cdk2(-/-) MEFs rescued the delayed entry into S phase. CONCLUSIONS: Although Cdk2 is not an essential gene in the mouse, it is required for germ cell development and meiosis. Loss of Cdk2 affects the timing of S phase, suggesting that Cdk2 is involved in regulating progression through the mitotic cell cycle.

Animals↗

PubMed2002

Interaction of PRMT1 with BTG/TOB proteins in cell signalling: molecular analysis and functional aspects.

BACKGROUND: Several recent reports have connected protein methylation with differentiation. Furthermore, the BTG/TOB proteins have also been implicated in such control. BTG1 and 2 have been shown to interact with PRMT1 (predominant cellular arginine N-methyltransferase of type I). RESULTS: First, we have studied the interaction between PRMT1 and the proteins of the BTG/TOB family. We show that boxC, a sequence present only in BTG1 and BTG2, is essential for this association. Using boxC peptide, we have investigated the importance of PRMT1/BTG protein association during type I protein methylation reactions. Finally, we show that the addition of boxC fused to penetratin interferes with the neuronal differentiation of PC12 cells and ES cell-derived neurones. CONCLUSIONS: Taken together, these results indicate that PRMT1/BTG proteins could play a key role in the arginine methylation-mediated signalling pathway as well as in neuronal differentiation.

Animals↗

PubMed2002

Epigenetic marks at BRCA1 and p53 coding sequences in early human embryogenesis.

In the vertebrate genome, methylation of deoxycytosine residues of CpGs dinucleotide has been associated with transcriptional silencing of genes, parental imprinting, X-inactivation and chromatin remodelling. In human somatic tissues, the 5' end of the BRCA1 CpG island is methylated, whereas this region is unmethylated in mature germ cells and early embryos. In gametes, as in somatic tissues, the CpG sites in the coding region are methylated. We took advantage of this bimodal distribution as a model to analyse the epigenetic reprogramming of coding regions during early human embryogenesis using the bisulphite-based genomic sequencing method. During preimplantation divisions, exon 11 of BRCA1 was slowly demethylated and retained approximately 30% of its methylated residues at the blastocyst stage. Moreover, the change in the distribution of methylated residues was not restricted to the BRCA1 gene, since for another gene, p53, a relatively high level of methylation (50%) of exon 4 was observed in blastocysts. Taken together, these data suggest that a significant part of the methylated residues of coding sequences might be conserved during preimplantation development.

Animals↗