Cinquin Lab

Cinquin O. J. Pathol. 217, pp186-198 (2009)

Abstract

Stem cells are expected to play a key role in the development and maintenance of organisms, and hold great therapeutical promises. However, a number of questions must be answered to achieve an understanding of stem cells and put them to use. Here I review some of these questions, and how they relate to the model system provided by the C. elegans germ line, which is exceptional by its thorough genetic characterization and experimental accessibility under in vivo conditions. A fundamental question is how to define a stem cell; different definitions can be adopted that capture different features of interest. In the C. elegans germ line, stem cells can be defined by cell lineage or by cell commitment (”commitment” must itself be carefully defined). These definitions are associated with two other important questions about stem cells: their functions (which must be addressed following a systems approach based on an evolutionary perspective) and their regulation. I review possible functions and their evolutionary groundings, including genome maintenance and powerful regulation of cell proliferation and differentiation, and possible regulatory mechanisms, including asymmetrical division and control of transit amplification by a developmental timer. I draw parallels between Drosophila and C. elegans germline stem cells; such parallels raise intriguing questions about Drosophila stem cells. I conclude by showing that the C. elegans germ line bears similarities with a number of other stem cell systems, which underscores its relevance to the understanding of stem cells.

Cinquin O. Mech. Dev. 124(7-8), pp501-517 (2007)

Abstract

The segmentation of vertebrate embryos depends on a complex genetic network that generates highly dynamic gene expression. Many of the elements of the network have been identified, but their interaction and their influence on segmentation remain poorly understood. A few mathematical models have been proposed to explain the dynamics of subsets of the network, but the mechanistic bases remain controversial. This review focuses on outstanding problems with the generation of somitogenesis clock oscillations, and the ways they could regulate segmentation. Proposals that oscillations are generated by a negative feedback loop formed by Lunatic fringe and Notch signaling are weighed against a model based on positive feedback, and the experimental basis for models of simple negative feedback involving Her/Hes genes or Wnt targets is evaluated. Differences are then made explicit between the many ‘clock and wavefront’ model variants that have been proposed to explain how the clock regulates segmentation. An understanding of the somitogenesis clock will require addressing experimentally the many questions that arise from the study of simple models.

Christopherson R.I., Cinquin O., Shojaei M., Kuehn D., Menz R.I., Nucleos. Nucleot. Nucl. 23(8-9), pp1459-1465 (2004)

Abstract

We have cloned genes encoding three enzymes of the de novo pyrimidine pathway using genomic DNA from Plasmodium falciparum and sequence information from the Malarial Genome Project. Genes encoding dihydroorotase (reaction 3), orotate phosphoribosyltransferase (reaction 5), and OMP decarboxylase (reaction 6) have been cloned into the plasmid pET 3a or 3d with a thrombin cleavable 9xHis tag at the C-terminus and the enzymes were expressed in Escherichia coli. To overcome the toxicity of malarial OMP decarboxylase when expressed in E. coli, and the unusual codon usage of the malarial gene, a hybrid plasmid, pMICO, was constructed which expresses low levels of T7 lysozyme to inhibit T7 RNA polymerase used for recombinant expression, and extra copies of rare tRNAs. Catalytically-active OMP decarboxylase has been purified in tens of milligrams by chromatography on Ni-NTA. The gene encoding orotate phosphoribosyltransferase includes an extension of 66 amino acids from the N-terminus when compared with sequences for this enzyme from other organisms. We have found that other pyrimidine enzymes also contain unusual protein inserts. Milligram quantities of pure recombinant malarial enzymes from the pyrimidine pathway will provide targets for development of novel antimalarial drugs.

Cinquin O., Demongeot J., C.R. Biol. 325(11), pp1085-1095 (2002)

Abstract

We discuss the influence of positive and negative feedback on the stability of a system, which is not clear-cut, and involves complex, mathematical problems. We show in particular that positive feedback can have a stabilising effect on some systems. We also point out the role that positive feedback plays in the digital treatment of signals required by cellular signalling, drawing on analogies from electronics, and the role that negative feedback plays in making a system robust against alteration of its parameters. Both positive and negative feedback can be seen as important enhancers of the properties of biological systems.