Vie et mort des cellules dans les tissus L'épiderme et son renouvellement par les cellules souches Épithélium sensoriel Voies aériennes et intestin Vaisseaux sanguins et cellules endothéliales Renouvellement par des cellules souches multipotentes : la formation des cellules sanguines Genèse : modulation et régénération du muscle squelettique Les fibroblastes et leurs transformations : la famille des cellules du tissu conjonctif Ingénierie des cellules souches

Vie et mort des cellules dans les tissus Être unicellulaire : individu originel Être pluricellulaire : cellules au service du corps tout entier Plus de 200 types de cellules différents dans l’organisme p1259

Cells of the Adult Human Body : a Catalogue How many distinct cell types are there in an adult human being? In other words, how many normal adult ways are there of expressing the human genome? A large textbook of histology will mention about 200 cell types that qualify for individual names. These traditional names are not, like the names of colors, labels for parts of a continuum that has been subdivided arbitrarily: they represent, for the most part, discrete and distinctly different categories. Within a given category there is often some variation—the skeletal muscle fibers that move the eyeball are small, while those that move the leg are big; auditory hair cells in different parts of the ear may be tuned to different frequencies of sound; and so on. But there is no continuum of adult cell types intermediate in character between, say, the muscle cell and the auditory hair cell. The traditional histological classification is based on the shape and structure of the cell as seen in the microscope and on its chemical nature as assessed very crudely from its affinities for various stains. Subtler methods reveal new subdivisions within the traditional classification. Thus modern immunology has shown that the old category of “lymphocyte” includes more than 10 quite distinct cell types. Similarly, pharmacological and physiological tests reveal that there are many varieties of smooth muscle cell—those in the wall of the uterus, for example, are highly sensitive to estrogen, and in the later stages of pregnancy to oxytocin, while those in the wall of the gut are not. Another major type of diversity is revealed by embryological experiments of the sort discussed in Chapter 21. These show that, in many cases, apparently similar cells from different regions of the body are nonequivalent, that is, they are inherently different in their developmental capacities and in their effects on other cells. Thus, within categories such as “fibroblast” there are probably many distinct cell types, different chemically in ways that are not easy to perceive directly. For these reasons any classification of the cell types in the body must be somewhat arbitrary with respect to the fineness of its subdivisions. Here, we list only the adult human cell types that a histology text would recognize to be different, grouped into families roughly according to function. We have not attempted to subdivide the class of neurons of the central nervous system. Also, where a single cell type such as the keratinocyte is conventionally given a succession of different names as it matures, we give only two entries—one for the differentiating cell and one for the stem cell. With these serious provisos, the 210 varieties of cells in the catalogue represent a more or less exhaustive list of the distinctive ways in which a given mammalian genome can be expressed in the phenotype of a normal cell of the adult body. http://www.garlandscience.com/textbooks/0815332181/pdfs/appendix.pdf p1259

http://www. garlandscience. com/textbooks/0815332181/pdfs/appendix http://www.garlandscience.com/textbooks/0815332181/pdfs/appendix.pdfp://www.garlandscience.com/textbooks/0815332181/pdfs/appendix.pdf p1259

Tissu Association de ces types cellulaires qui collaborent entre elles Forment des organes p1259

Construction des tissus par la matrice extra cellulaire Conséquences du contrôle de l’expression des gènes et des mécanismes du développement animal Création de la diversification cellulaire dans l’embryon par des mécanismes génétiques moléculaires Maintien de la diversification des cellules grâce au dialogue et à la mémoire des cellules Construction des tissus par la matrice extra cellulaire Mode de vie des cellules spécialisées p1259

Questions posées Comment les cellules collaborent entre elles pour exécuter leur tâche ? Comment naissent vivent et meurent les nouvelles cellules spécialisées ? Comment est préservée l’architecture des nouveaux tissus malgré leur perpétuel remaniement ? p1259

Réponses diverses Exemples illustrant les principes généraux Intéressants par l’originalité de leurs moyens d’étude Nombreux problèmes non résolus p1259

Plan L'épiderme et son renouvellement par les cellules souches Épithélium sensoriel Voies aériennes et intestin Vaisseaux sanguins et cellules endothéliales Renouvellement par des cellules souches multipotentes : la formation des cellules sanguines Genèse : modulation et régénération du muscle squelettique Les fibroblastes et leurs transformations : la famille des cellules du tissu conjonctif Ingénierie des cellules souches p1272

Embryon 3 feuillets Ectoblaste : Mésoblaste Entoblaste I (épiderme) II (épithéliums sensoriels) Mésoblaste Entoblaste p1272

Ectoblaste Nombreuses variétés de tissus Spécialisations très différentes Modes de vie différents p1272

Entoblaste Couche interne de l’embryon  Tube digestif primitif Un véritable zoo de types cellulaires qui bordent le tube digestif et ses annexes p1272

Plan Respiratoire Tube digestif Foie

2 – Tube digestif Tous les vertébrés n’ont pas des poumons Mais tous (et les invertébrés aussi) ont un tube digestif Cellules spécialisées dans la digestion de nourriture et l’absorption des molécules nutritives Mais ne peuvent pas fonctionner en même temps : il ne faut pas digérer le tube digestif #3p1274

Organisation de la digestion Dans un lieu séparé : l’estomac Hydrolyse acide Actions enzymatiques Passage dans l’intestin grêle Absorption Poursuite de la digestion (à pH neutre)  #3p1274

Types cellulaires Estomac Glandes (comme le pancréas) Intestin Cellules qui sécrètent l’acide Cellules qui sécrètent les enzymes à pH acide Cellules à mucus Glandes (comme le pancréas) Cellules qui sécrètent bicarbonates pour neutraliser l’acide Cellules qui sécrètent des enzymes digestives Intestin Cellules absorbantes Cellules qui sécrètent le manteau de mucus #3p1274

Mesure supplémentaire de protection Renouvellement continu de l’épithélium Turnover d’une semaine ou moins #3p1274

Renouvellement dans l’intestin grêle Épithélium simple recouvrant Les villosités qui s’évaginent Les cryptes qui s’invaginent dans le tissu conjonctif sous-jacent #3p1274

Fig 22-19 A Renouvellement du revêtement de l’intestin grêle Mouvement général des cellules vers le sommet des villosités Toutefois quelques cellules (dont certaines cellules caliciformes et cellules entéro-endocrines) se différencient quand elles sont encore dans les cryptes Les cellules de Paneth Situées au fond des cryptes Durée de vie limitée Remplacées par la descendance des cellules souches Fig 22-19 A #3p1274

Fig 22-19 B Coupe d’intestin grêle Villosités Cryptes Cellules caliciformes en rouge Fig 22-19 B

Les cellules souches Localisation dans la profondeur des cryptes Donnent 4 types de cellules différenciées Cellules absorbantes Cellules caliciformes Cellules de Paneth Cellules endocrines #3p1274-1275

1 - Cellules absorbantes = cellules à bordure en brosse Nombreuses microvillosités Migrent de la région des cellules souches vers la surface des villosités #3p1275

2 - Cellules caliciformes Comme dans l’épithélium respiratoire Secrètent du mucus Migrent de la région des cellules souches vers la surface des villosités #3p1275

3 - Cellules de Paneth Système de défense Sécrètent des cryptdynes (famille des défensines) #3p1275

Cryptdynes Precursor to corticostatin/defensin-related peptide accumulates to high levels in mouse intestinal crypt epithelium during postnatal development 70-amino acid residues amino acid sequence given in first source #3p1275

4 - Cellules endocrines Plus de 15 sous-types Sécrètent sérotonine et hormones peptidiques (comme la cholécystokinine) Action sur les neurones et autres types cellulaires de l’intestin Régulation de la croissance, prolifération activités des cellules du tube digestif et autres tissus Action sur le système nerveux (comme des neuropeptides) Migrent de la région des cellules souches vers la surface des villosités #3p1275

Viennent des cellules souches multipotentes indifférenciées du fond des cryptes Cellules absorbantes microvillosités Absorption Ancrage des enzymes de digestion Cellules caliciformes Fig 22-20 A #3p1275

Cellules entéro-endocrines Cellules de Paneth Fig 22-20 B #3p1275

Renouvellement des 4 types de cellules Cellules absorbantes Cellules caliciformes Cellules endocrines Cellules de Paneth #3p1275

Cellules absorbantes Cellules caliciformes Cellules endocrines Migrent de la région des cellules souches vers la surface des villosités Étape d’amplification transitoire En sortant de la crypte les précurseurs déjà engagés dans la différenciation subissent 4 à 6 divisions rapides puis arrêtent leur divisions et terminent leur différenciation 2 à 5 jours entre les cryptes et la mort par apoptose au sommet des villosités #3p1275

Cellules de Paneth Produites en beaucoup plus petit nombre Restent au fond des cryptes Sont remplacées lentement Meurent par apoptose Phagocytées par les voisines #3p1275-1276

Mystère Origine des forces qui conduisent au mouvement de ces cellules Rôle de la lame basale ? Sous-unités de laminine 1 et 2  lame basale des cryptes Sous-unités de laminine 5 gradient dans les villosités avec un maximum au sommet #3p1276

Maintien de la population de cellules souches de l’intestin Deux questions Voie Notch Voie Wnt #4p1276

1 - Deux questions Qu’est ce qui contrôle le choix d’une cellule de garder ses caractères de cellules souche ou de s’engager dans une voie de différenciation ? Qu’est ce qui conduit à la diversification de la cellule souche en 4 types de cellules différenciées ? #4p1276

Deux éléments de réponse Notch Wnt #4p1276

2 - Receptors, Notch A family of conserved cell surface receptors that contain EPIDERMAL GROWTH FACTOR repeats in their extracellular domain and ANKYRIN repeats in their cytoplasmic domains. The cytoplasmic domain of notch receptors is released upon ligand binding and translocates to the CELL NUCLEUS where it acts as transcription factor. #4p1276

Pathway image captured from the dynamic graphical display of the information in the Connections Maps available 05 December 2006. For a key to the colors and symbols and to access the underlying data, please visit the pathway (http://stke.sciencemag.org/cgi/cm/stkecm;CMP_19043). Sci. STKE, 5 December 2006 Vol. 2006, Issue 364, p. cm7 Notch Signaling Pathway. Matthias Ehebauer, Penelope Hayward, and Alfonso Martinez-Arias Fig. 1. Pathway image captured from the dynamic graphical display of the information in the Connections Maps available 05 December 2006. For a key to the colors and symbols and to access the underlying data, please visit the pathway (http://stke.sciencemag.org/cgi/cm/stkecm;CMP_19043).

Notch Voie qui gouverne la production des cellules entéro-endocrines Comme la production des neurones dans le système nerveux central Mutations qui bloquent Notch  surproduction de cellules entéro-endocrines (au moins chez l’embryon) #4p1276

3 - Wnt Proteins Wnt proteins are a large family of secreted glycoproteins that play essential roles in EMBRYONIC AND FETAL DEVELOPMENT, and tissue maintenance. They bind to FRIZZLED RECEPTORS and act as PARACRINE PROTEIN FACTORS to initiate a variety of SIGNAL TRANSDUCTION PATHWAYS. The canonical Wnt signaling pathway stabilizes the transcriptional coactivator BETA CATENIN. #4p1276

Frizzled Receptors A family of seven-pass transmembrane cell-surface receptors. They contain an extracellular cysteine-rich domain and are receptors for WNT PROTEINS. Frizzled receptors often couple with HETEROTRIMERIC G PROTEINS and regulate multiple SIGNAL TRANSDUCTION PATHWAYS.

http://www.stanford.edu/~rnusse/pathways/cell2.html #4p1276

Nusse,R2005p747 Cell biology: relays at the membrane. Nature Figure 1 | Crucial kinases. a, In cells not activated by Wnt, a complex between -catenin, Axin, APC and GSK3 causes phosphorylation of -catenin and its consequent destruction. The Wnt receptors LRP6 and Frizzled are unoccupied. b, Without Axin, -catenin is stabilized and it enters the nucleus to control gene expression. Inset, binding of Wnt to cells results in phosphorylation (P) of LRP6 residues in its cytoplasmic tail. Zeng et al. and Davidson et al. show that this is catalysed by the GSK3 and CK1 protein kinases. CK1 is attached to the membrane by a lipid anchor domain. Several other sites on LRP6 that become phosphorylated are not shown here. The phosphorylated LRP6 recruits Axin, removing it from the -catenin destruction complex and stabilizing -catenin. Crucial kinases. a, In cells not activated by Wnt, a complex between -catenin, Axin, APC and GSK3 causes phosphorylation of -catenin and its consequent destruction. The Wnt receptors LRP6 and Frizzled are unoccupied. b, Without Axin, -catenin is stabilized and it enters the nucleus to control gene expression. Inset, binding of Wnt to cells results in phosphorylation (P) of LRP6 residues in its cytoplasmic tail. Zeng et al. and Davidson et al. show that this is catalysed by the GSK3 and CK1 protein kinases. CK1 is attached to the membrane by a lipid anchor domain. Several other sites on LRP6 that become phosphorylated are not shown here. The phosphorylated LRP6 recruits Axin, removing it from the -catenin destruction complex and stabilizing -catenin.

Voie Wnt LEF-1/TCF : famille de protéines régulatrices de gènes impliquées dans la voie Wnt Une souris déficiente dans une de ces protéines  Pas de cryptes  Pas de cellules souches  absence de renouvellement de l’épithélium formé pendant la vie fœtale  Mort précoce Hyperactivation de la voie Wnt chez l’adulte (par mutation du gène APC par exemple)  Hyperprolifération des cellules des cryptes  Souvent cancer #4p1276

Stefan Hoppler and Claire Louise Kavanagh Stefan Hoppler and Claire Louise Kavanagh. Wnt signalling: variety at the core Journal of Cell Science 120, 385-393 (2007) #4p1276 Fig. 4. TCF/LEF function in intestine and colorectal cancer. The stem cell population at the base of the crypt in the intestine produces a proliferating progenitor cell population that migrates up the side of the crypt. Upon reaching the crypt-villus junction, cells begin to differentiate and continue moving up the villus until mature cells are shed into the lumen at the tip of the villus. The levels of nuclear -catenin, and therefore active TCF/LEF, are highest at the base of the crypt in the stem cell and proliferating progenitor population. In this population it is proposed that full-length TCF-4 (activating, green) and NTCF-1 (repressing, red) are the main active TCF/LEFs. However, when mutated Wnt signalling leads to colorectal cancer, ectopic expression of full-length LEF-1 is readily detected. As a result the predominant TCF/LEF isoforms present in colorectal cancer are activating (green) as opposed to repressive (red) TCF/LEFs. The levels of nuclear -catenin in colorectal cancer are very high because Wnt signalling pathway mutations mean that -catenin cannot be degraded. Figure modified from Radtke and Clevers (Radtke and Clevers, 2005). TCF/LEF (T-cell factor/lymphoïd enhancer factor) function in intestine and colorectal cancer. The stem cell population at the base of the crypt in the intestine produces a proliferating progenitor cell population that migrates up the side of the crypt. Upon reaching the crypt-villus junction, cells begin to differentiate and continue moving up the villus until mature cells are shed into the lumen at the tip of the villus. The levels of nuclear -catenin, and therefore active TCF/LEF, are highest at the base of the crypt in the stem cell and proliferating progenitor population. In this population it is proposed that full-length TCF-4 (activating, green) and NTCF-1 (repressing, red) are the main active TCF/LEFs. However, when mutated Wnt signalling leads to colorectal cancer, ectopic expression of full-length LEF-1 is readily detected. As a result the predominant TCF/LEF isoforms present in colorectal cancer are activating (green) as opposed to repressive (red) TCF/LEFs. The levels of nuclear -catenin in colorectal cancer are very high because Wnt signalling pathway mutations mean that -catenin cannot be degraded.

Warren Strober Science 25 August 2006 Vol 313, Issue 5790, Pages 1016-1145 Unraveling Gut Inflammation #4p1276 Antibacterial factors in mucosal homeostasis. The secretion of Paneth cell factors (including RegIII ) into the intestinal crypts regulates the number and type of bacteria in the crypt space and gut lumen under normal conditions and during the introduction of a potential pathogen. Loss of Paneth cell function (including decreased -defensin production) results in bacterial overgrowth. Inflammatory bowel disease (Crohn's Disease) involves a dysregulated mucosal immune response

Warren Strober Science 25 August 2006 Vol 313, Issue 5790, Pages 1016-1145 Unraveling Gut Inflammation #4p1276 Antibacterial factors in mucosal homeostasis. The secretion of Paneth cell factors (including RegIII ) into the intestinal crypts regulates the number and type of bacteria in the crypt space and gut lumen under normal conditions and during the introduction of a potential pathogen. Loss of Paneth cell function (including decreased -defensin production) results in bacterial overgrowth. Inflammatory bowel disease (Crohn's Disease) involves a dysregulated mucosal immune response.