Cellular Biology

Molecular preservation of the pigment melanin in fossil melanosomes.

by Engdahl Anders

Fossil feathers, hairs and eyes are regularly preserved as carbonized traces comprised of masses of micrometre-sized... more Fossil feathers, hairs and eyes are regularly preserved as carbonized traces comprised of masses of micrometre-sized bodies that are spherical, oblate or elongate in shape. For a long time, these minute structures were regarded as the remains of biofilms of keratinophilic bacteria, but recently they have been reinterpreted as melanosomes; that is, colour-bearing organelles. Resolving this fundamental difference in interpretation is crucial: if endogenous then the fossil microbodies would represent a significant advancement in the fields of palaeontology and evolutionary biology given, for example, the possibility to reconstruct integumentary colours and plumage colour patterns. It has previously been shown that certain trace elements occur in fossils as organometallic compounds, and hence may be used as biomarkers for melanin pigments. Here we expand this knowledge by demonstrating the presence of molecularly preserved melanin in intimate association with melanosome-like microbodies isolated from an argentinoid fish eye from the early Eocene of Denmark.

Celtic Beads from the British Isles

by heather smith

Draft Copy

Questioning what types of beads would have been in use during the Iron Age in Britain and drawing deeply from the work... more Questioning what types of beads would have been in use during the Iron Age in Britain and drawing deeply from the work of the late bead researcher Margaret Guido I’ve amassed a collocation of information which one can draw from not just for bead information concerning the Iron Age Celts in the Isles, but also for those interested in Celtic adornment and bead reproduction.  Please note, my citing is poor the majority of information and many of the pictures have come from Guido’s work ‘The Glass Beads of the Prehistoric and Roman Periods in Britain and Ireland’, (London:  The Society of Antiquaries of London, 1978).  I want to thank not just Guido for her amass of research, but also a wealth of museums and other sources for their invaluable photos, many of which I have to note are copyright protected. 

Cells compete for decapentaplegic survival factor to prevent apoptosis in Drosophila wing development

by Eduardo Moreno Lampaya

dMyc transforms cells into supercompetitors

by Eduardo Moreno Lampaya

Petrova et al 2012 DMM

by Eduardo Moreno Lampaya

Flower forms an extracellular code that reveals the fitness of a cell to its neighbors in Drosophila

by Eduardo Moreno Lampaya

ccm1 cell autonomously regulates endothelial cellular morphogenesis and vascular tubulogenesis in zebrafish

by Jeroen Bussmann

Cerebral cavernous malformations (CCMs) are a prevalent class of vascular anomalies characterized by thin-walled... more Cerebral cavernous malformations (CCMs) are a prevalent class of vascular anomalies characterized by thin-walled clusters of malformed blood vessels in the brain. Heritable forms are caused by mutations in CCM1, CCM2 and CCM3, but despite the importance of these factors in vascular biology, an understanding of their molecular and cellular functions remains elusive. Here we describe the characterization of a zebrafish embryonic model of CCM. Loss of ccm1 in zebrafish embryos leads to severe and progressive dilation of major vessels, despite normal endothelial cell fate and number. Vascular dilation in ccm1 mutants is accompanied by progressive spreading of endothelial cells and thinning of vessel walls despite ultrastructurally normal cell–cell contacts. Zebrafish ccm2 mutants display comparable vascular defects. Finally, we show that ccm1 function is cell autonomous, suggesting that it is endothelial cellular morphogenesis that is regulated by CCM proteins during development and pathogenesis.

Imaging of single light-responsive clock cells reveals fluctuating free-running periods

by Amanda-Jayne Carr

All-polymer microfluidic particle size sorter for biomedical applications

by Javier G. Fernandez

Co-authored with Christopher A. Mills and Josep Samitier, Published in "Physica Status Solidi"

The design and method for the production of an all-polymer microfluidic particle sorter, for use in biomedical... more The design and method for the production of an all-polymer microfluidic particle sorter, for use in biomedical applications, is described. The sorter is made from biocompatible materials with properties, such as high optical transparency, that make it useful in a biological laboratory. The method of sorting is designed to be gentle on biological species, using a method of guiding the particles towards the filter, and has been successfully used to separate latex beads depending on their diameters. Preliminary qualitative experiments have been able to separate beads of 45 and 90 μm in diameter from a mixture of the two. These dimensions are on the same scale as those of some eukaryotic cells

Directional alignment of MG63 cells on polymer surfaces containing point microstructures

by Javier G. Fernandez

Co-authored with Christopher A. Mills and Josep Samitier, Published in "Small"

MG63 cells cultured on regular arrays of point microstructures (posts and holes) are shown to preferentially align at... more MG63 cells cultured on regular arrays of point microstructures (posts and holes) are shown to preferentially align at certain angles to the pattern of the structures, at 0 degrees, 30 degrees, and 45 degrees in particular. The effect is found to be more pronounced for post rather than hole structures (although no significant difference is found for the angles the cells make to the holes or posts) and is thought to be due to the fact that the cells use the posts as anchorage points to hold themselves to the surface. It is also shown that cells preferentially align with the structures depending on the dimensions of the structures and the distance between neighboring structures. This is important when designing structured surfaces for cell-surface interaction studies for materials to be used in, for example, drug delivery or tissue engineering.

Caractérisation fonctionnelle de deux protéines à domaine Ypt/Rab GAP, Gyp5p et Gyl1p chez Saccharomyces cerevisiae

by Laurent Chesneau

Thèse de Laurent Chesneau

Thèse présentée pour obtenir le grade de
DOCTEUR EN SCIENCES DE L’UNIVERSITE PARIS-SUD 11
Spécialité Biologie Moléculaire de la Cellule

Thèse soutenue le 30 Janvier 2007 devant la Commission d’Examen composée de
M. Rosine HAGUENAUER-TSAPIS (Présidente)
M. Bruno GOUD (Rapporteur)
M. Robert ARKOWITZ (Rapporteur)
M. Barbara WINSOR (Examinatrice)
M. Michel JACQUET (Examinateur)
M. Marie-Hélène CUIF (Directrice de Thèse)

Les GTPases de la famille Ypt/Rab sont impliquées dans la régulation du trafic vésiculaire, et plus particulièrement... more Les GTPases de la famille Ypt/Rab sont impliquées dans la régulation du trafic vésiculaire, et plus particulièrement dans les étapes de transport, d’arrimage et de fusion des vésicules. La régulation de leur activité GTPase est importante pour la régulation de leurs fonctions. L’activité GTPase des protéines Ypt/Rab est stimulée par des protéines activatrices de GTPase. Chez la levure Saccharomyces cerevisiae, il existe 10 protéines portant un domaine catalytique des protéines activatrices des GTPases Ypt/Rab. Gyp5p et Gyl1p sont deux protéines paralogues qui font partie de cette famille de protéines. In vitro, Gyp5p stimule l’activité GTPase de Ypt1p, qui est impliquée dans le transport entre le réticulum endoplasmique et l’appareil de Golgi, et de Sec4p, impliquée dans l’exocytose. Gyl1p, qui possède un domaine catalytique partiellement dégénéré, n’a pas d’activité stimulatrice de GTPase connue.

L’objectif de mon travail de thèse était de rechercher les fonctions biologiques de Gyp5p et de Gyl1p.

Nous avons montré que Gyp5p et Gyl1p sont situées aux sites de croissance polarisée, où elles sont co-localisées avec Sec4p. Gyp5p est présente dans un complexe contenant Sec4p dans une fraction enrichie en vésicules post-golgiennes, et Gyp5p et Gyl1p sont présentes dans un complexe contenant Sec4p dans une fraction enrichie en membrane plasmique. SEC2, qui code pour le facteur d’échange de Sec4p, et GYP5 présentent un effet génétique antagoniste par rapport à la croissance cellulaire. Les cellules dépourvues de Gyp5p et Gyl1p présentent des défauts de sécrétion, et accumulent des vésicules uniquement chez les jeunes bourgeons à 13°C. Ces résultats montrent que Gyp5p et Gyl1p sont impliquées dans l’exocytose polarisée.
Gyp5p et Gyl1p présentent une localisation dynamique au cours du cycle cellulaire. Gyp5p et Gyl1p sont co-localisées aux étapes de croissance polarisée, mais sont dissociées au cours de la croissance isotropique. Nous avons montré que Gyp5p est délocalisée en l’absence de Gyl1p, et Gyl1p est délocalisée en l’absence de Gyp5p, ce qui montre que la localisation de Gyp5p et Gyl1p est interdépendante. Nous avons montré que Gyp5p et Gyl1p sont capables d’interagir directement in vitro. Nous avons observé que les sous-unités du polarisome Bni1p, Bud6p et Spa2p sont nécessaires à la localisation de Gyp5p et Gyl1p aux sites de croissance polarisée. Le polarisome est un complexe
dont une des fonctions est de réguler la formation de câbles d’actine au sommet du bourgeon par la formine Bni1p. Des défauts de localisation de Gyp5p et Gyl1p ont également été observés en l’absence de l’autre formine Bnr1p. Ces résultats suggèrent que la localisation de Gyp5p et Gyl1p serait dépendante des câbles d’actine.
Nous avons également montré qu’une partie de Gyp5p et de Gyl1p est présente dans un complexe avec Rvs167p. Rvs167p est une protéine connue pour être impliquée dans l’endocytose. Une partie de Rvs167p est co-localisée avec Gyp5p et Gyl1p aux sites de croissance polarisée. Mais en l’absence de Gyp5p et de Gyl1p, Rvs167p n’est plus présente au sommet des jeunes bourgeons et au cou du bourgeon lors de la cytocinèse. Gyp5p et Gyl1p sont donc nécessaire à la localisation de Rvs167p aux sites de croissance polarisée.

Gyp5p and Gyl1p are involved in the control of polarized exocytosis in budding yeast.

by Laurent Chesneau

Chesneau L, Dupré S, Burdina A, Roger J, Le Panse S, Jacquet M, Cuif MH. J Cell Sci. 2004 Sep 15;117(Pt 20):4757-67.

We report here elements for functional characterization of two members of the Saccharomyces cerevisiae Ypt/Rab GTPase... more We report here elements for functional characterization of two members of the Saccharomyces cerevisiae Ypt/Rab GTPase activating proteins family (GAP): Gyp5p, a potent GAP in vitro for Ypt1p and Sec4p, and the protein Ymr192wp/APP2 that we propose to rename Gyl1p (GYp like protein). Immunofluorescence experiments showed that Gyp5p and Gyl1p partly colocalize at the bud emergence site, at the bud tip and at the bud neck during cytokinesis. Subcellular fractionation and co-immunoprecipitation experiments showed that Gyp5p and Gyl1p co-fractionate with post-Golgi vesicles and plasma membrane, and belong to the same protein complexes in both localizations. We found by co-immunoprecipitation experiments that a fraction of Gyp5p interacts with Sec4p, a small GTPase involved in exocytosis, and that a fraction of Gyl1p associates at the plasma membrane with the Gyp5p/Sec4p complexes. We showed also that GYP5 genetically interacts with SEC2, which encodes the Sec4p exchange factor. Examination of the gyp5Deltagyl1Delta mutants grown at 13 degrees C revealed a slight growth defect, a secretion defect and an accumulation of secretory vesicles in the small-budded cells. These data suggest that Gyp5p and Gyl1p are involved in control of polarized exocytosis.

Interdependence of the Ypt/RabGAP Gyp5p and Gyl1p for recruitment to the sites of polarized growth.

by Laurent Chesneau

Chesneau L, Prigent M, Boy-Marcotte E, Daraspe J, Fortier G, Jacquet M, Verbavatz JM, Cuif MH.  Traffic. 2008 Apr;9(4):608-22.

Gyp5p and Gyl1p are two members of the Ypt/Rab guanosine triphosphatases-activating proteins involved in the control... more Gyp5p and Gyl1p are two members of the Ypt/Rab guanosine triphosphatases-activating proteins involved in the control of polarized exocytosis in Saccharomyces cerevisiae. We had previously shown that Gyp5p and Gyl1p colocalize at the sites of polarized growth and belong to the same complex in subcellular fractions enriched in plasma membrane or secretory vesicles. Here, we investigate the interaction between Gyp5p and Gyl1p as well as the mechanism of their localization to the sites of polarized growth. We show that purified recombinant Gyp5p and Gyl1p interact directly in vitro. In vivo, both Gyp5p and Gyl1p are mutually required to concentrate at the sites of polarized growth. Moreover, the localization of Gyp5p and Gyl1p to the sites of polarized growth requires the formins Bni1p and Bnr1p and depends on actin cables. We show that, in a sec6-4 mutant, blocking secretion leads to coaccumulation of Gyp5p and Gyl1p, together with Sec4p. Electron microscopy experiments demonstrate that Gyp5p is associated with secretory vesicles. Altogether, our results indicate that both Gyp5p and Gyl1p access the sites of polarized growth by transport on secretory vesicles. Two polarisome components, Spa2p and Bud6p, are involved in maintaining Gyp5p and Gyl1p colocalized at the sites of polarized growth.

The RabGAP Proteins Gyp5p and Gyl1p Recruit the BAR Domain Protein Rvs167p for Polarized Exocytosis.

by Laurent Chesneau

Prigent M, Boy-Marcotte E, Chesneau L, Gibson K, Dupré-Crochet S, Tisserand H, Verbavatz JM, Cuif MH.

Traffic. 2011 Aug;12(8):1084-97.

The Rab GTPase-activating proteins (GAP) Gyp5p and Gyl1p are involved in the control of polarized exocytosis at the... more The Rab GTPase-activating proteins (GAP) Gyp5p and Gyl1p are involved in the control of polarized exocytosis at the small-bud stage in Saccharomyces cerevisiae. Both Gyp5p and Gyl1p interact with the N-Bin1/Amphiphysin/Rvs167 (BAR) domain protein Rvs167p, but the biological function of this interaction is unclear. We show here that Gyp5p and Gyl1p recruit Rvs167p to the small-bud tip, where it plays a role in polarized exocytosis. In gyp5Δgyl1Δ cells, Rvs167p is not correctly localized to the small-bud tip. Both P473L mutation in the SH3 domain of Rvs167p and deletion of the proline-rich regions of Gyp5p and Gyl1p disrupt the interaction of Rvs167p with Gyp5p and Gyl1p and impair the localization of Rvs167p to the tips of small buds. We provide evidence for the accumulation of secretory vesicles in small buds of rvs167Δ cells and for defective Bgl2p secretion in rvs167Δ cultures enriched in small-budded cells at 13°C, implicating Rvs167p in polarized exocytosis. Moreover, both the accumulation of secretory vesicles in Rvs167p P473L cells cultured at 13°C and secretion defects in cells producing Gyp5p and Gyl1p without proline-rich regions strongly suggest that the function of Rvs167p in exocytosis depends on its ability to interact with Gyp5p and Gyl1p.

Rab35 GTPase and OCRL phosphatase remodel lipids and F-actin for successful cytokinesis.

by Laurent Chesneau

Dambournet D, Machicoane M, Chesneau L, Sachse M, Rocancourt M, El Marjou A, Formstecher E, Salomon R, Goud B, Echard A.
Nat Cell Biol. 2011 Jun 26;13(8):981-8.

Abscission is the least understood step of cytokinesis. It consists of the final cut of the intercellular bridge... more Abscission is the least understood step of cytokinesis. It consists of the final cut of the intercellular bridge connecting the sister cells at the end of mitosis, and is thought to involve membrane trafficking as well as lipid and cytoskeleton remodelling. We previously identified the Rab35 GTPase as a regulator of a fast recycling endocytic pathway that is essential for post-furrowing cytokinesis stages. Here, we report that the phosphatidylinositol-4,5-bisphosphate (PtdIns(4,5)P(2)) 5-phosphatase OCRL, which is mutated in Lowe syndrome patients, is an effector of the Rab35 GTPase in cytokinesis abscission. GTP-bound (active) Rab35 directly interacts with OCRL and controls its localization at the intercellular bridge. Depletion of Rab35 or OCRL inhibits cytokinesis abscission and is associated with local abnormal PtdIns(4,5)P(2) and F-actin accumulation in the intercellular bridge. These division defects are also found in cell lines derived from Lowe patients and can be corrected by the addition of low doses of F-actin depolymerization drugs. Our data demonstrate that PtdIns(4,5)P(2) hydrolysis is important for normal cytokinesis abscission to locally remodel the F-actin cytoskeleton in the intercellular bridge. They also reveal an unexpected role for the phosphatase OCRL in cell division and shed new light on the pleiotropic phenotypes associated with Lowe disease.

The benzoquinone ansamycin 17-allylamino-17-demethoxygeldanamycin binds to HSP90 and shares important biologic activities with geldanamycin

by Robert Bradley

The redoubtable cell

by Andrew Reynolds

Prepublication version. Published in Studies In History and Philosophy of Biological and Biomedical Sciences (2010) 41(3): 194-201

The cell theory – the thesis that all life is made up of one or more cells, the fundamental structural and... more The cell theory – the thesis that all life is made up of one or more cells, the fundamental structural and physiological unit – is one of the most celebrated achievements of modern biological science. And yet from its very inception in the nineteenth century it has faced repeated criticism from some biologists. Why do some continue to criticize the cell theory, and how has it managed nevertheless to keep burying its undertakers? The answers to these questions reveal the complex nature of the cell theory and the cell concept on which it is based. Like other scientific laws, the assertion that all living things are made of cells purchases its universality at the expense of abstraction. If, however, it is regarded as a mere widely applicable empirical generalization with notable exceptions, it still remains too important to discard. Debate about whether the cell or the organism standpoint provides the more correct account of anatomical, physiological, and developmental facts illustrates the tension between our attempts to express the truth about reality in conceptual terms conducive to a unified human understanding.

Ernst Haeckel and the Theory of the Cell State: Remarks on the History of a Bio-political Metaphor

by Andrew Reynolds

Pre-publication version. Published in History of Science xlvi (2008): 123-152

Amoebae as Exemplary Cells: The Protean Nature of an Elementary Organism

by Andrew Reynolds

Pre-publication version without figures. Published in Journal of the History of Biology 2008 41:307-337

The cell's journey: from metaphorical to literal factory

by Andrew Reynolds

The concept of the cell has been based on metaphor since its inception, and the history of cell theory has continued... more The concept of the cell has been based on metaphor since its inception, and the history of cell theory has continued to rely on metaphor and analogy. In the nineteenth century, cells were most popularly conceived either as building stones or elementary autonomous organisms from which larger organisms are composed. With advances in physiology and the rise of modern biochemistry in the early twentieth century, the chemical factory or laboratory became the dominant metaphor for this biological unit. Today in the twenty-first century, the metaphorical imagery has become a reality, with cells acting as chemical factories for the synthesis of commercially valuable bio-products. The history of the cell shows how metaphors act as conceptual tools, with particular strengths for facilitating different sorts of questions and experimental techniques.