Biomorphologie

Résumé

En biologie, la morphologie (du grec , « forme », avec le suffixe -logie, « discours ») est l'étude de la forme externe et de la structure des êtres vivants. Histoire La morphologie désigne initialement la étudiant la forme et l'aspect visuel de la structure externe d'un animal, d'une plante ou d'un organe. La morphologie se distingue ainsi à l'origine de l'anatomie, qui s'intéresse à la structure interne. Cette science prend parfois une définition plus large, comprenant l'étude des structures externes (l') mais aussi internes (l'anatomie). Le poète et naturaliste Goethe, qui poursuivit des études dans le prolongement de Linné et de Rousseau, nous offre dès 1807 une conceptualisation de la morphologie. Celle-ci s'inscrit dans son projet d'étude de la métamorphose des plantes : « Lorsque les objets naturels, et surtout les êtres vivants, nous apparaissent de façon telle que nous souhaitons comprendre leur nature et leur activité dans l'ensemble, nous croyons parvenir au

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https://fr.wikipedia.org/wiki/Biomorphologie

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La biologie (du grec bios « la vie » et logos, « discours ») est la science du vivant. Elle recouvre une partie des sciences de la nature et de l'histoire naturelle des êtres vivants. La vie se pré

vignette|Illustration du traité d'anatomie De humani corporis fabrica d'André Vésale. L’ (emprunté au bas latin anatomia « dissection », issu du grec ἀνατέμνω (ànatémno), de ἀνά – ana, « en remontant

thumb|Les bactéries Escherichia coli sont des organismes unicellulaires. Un organisme (du grec organon, « instrument »), ou organisme vivant, est, en biologie et en écologie, un système vivant comple

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Multivalued morphology and segmentation-based coding

EPFL1996

Chargement

Neuronal morphologies: the shapes of thoughts

Lida Kanari

The mammalian brain, one of the most fascinating systems in nature, is a complex biological structure that has kept scientists busy for over a century. Many of the brain's mysteries have been unraveled due to the enormous efforts of the scientific community, but yet many questions remain unsolved. The detailed drawings of Ramon y Cajal revealed the hidden structure of the brain, identifying the neurons as its fundamental structural and functional units. Although a significant amount of experimental reconstructions have been gathered over the past years, neuronal morphologies still remain one of the unsolved riddles of the brain. Why is neuronal diversity important for the functionality of the brain and how do neuronal morphologies ''shape'' our thoughts? To address these questions one needs to characterize the various shapes of neuronal morphologies. Traditionally, this task has been performed by using a set of morphological features, such as total length, branch orders and asymmetry. However, these features focus on a specific morphological aspect thereby causing a significant information loss from the original structure. Inspired by algebraic topology, I have conceived a topological descriptor of neuronal trees that couples the topology of a tree with the geometric features of its structure, retaining more details of the original morphology than traditional morphometrics. This descriptor has proved to be very powerful in discriminating several neuronal types into concrete groups based on morphological grounds, and has lead to the discovery of two distinct classes of pyramidal cells in the human cortex. In addition, the Topological Morphology Descriptor is important for the generation of artificial cells whose morphologies remain faithful to the biological ones. Neurons of the same morphological type have similar topological and geometric characteristics, therefore appearing to be highly structured. However, it is still unknown to what extent the complex neuronal morphology is shaped by the genetic information of an organism and to what extent it arises from stochastic processes. To study the impact of randomness and structure of neuronal morphologies on the connectivity of the network they form, I compared the properties of networks that arise from different artificially generated morphologies, ranging from random walks to constrained branching structures, against those of biological networks and computational reconstructions built from biological morphologies. Surprisingly, networks that are generated from almost random morphologies share a lot of common properties with biological networks, such as the spatial clustering of connections and the common neighbor effect, indicating that stochastic processes that take place during development, contribute significantly to the observed neuronal shapes. This thesis resolves a number of the mysteries of neuronal morphologies and questions our beliefs about the role of randomness in the formation of the brain. Thus, it brings us closer to understanding the fundamental differences among morphologies, and how randomness and structure are combined together to generate one of the most complex biological systems.

EPFL2018

Chargement

Bone fracture healing problems, because of the loss of tissue regeneration, can affect many old or multi-pathologic patients around the world. Among the therapeutic strategies, bone substitutes, such as poly-(L-lactitve acid) with 5% wt. % ß-tricalcium phosphate (PLA/5%ß-TCP) scaffolds, are promising as a clinical solution. One strategy to tune their osteoinductive properties is the addition of bone progenitor cells. Therefore, cell- free and cell-seeded PLA/5% ß-TCP scaffolds were implanted into femoral condyles of rats to promote bone regeneration. The in vivo study showed that the bone growth inside a cell-seeded scaffold with human bone progenitor cells was delayed compared to cell-free scaffold. What happened to the cells? Did they trigger an immune response, migrate or die? Therefore, the goals of this project are to evaluate the cell adhesion in vitro to the scaffold and to propose a reliable cell labeling method to track them in future in vivo studies. In the first aim, the adhesion of the cells was qualitatively assessed by the cell morphology and the presence of fibronectin using fluorescence imaging. To quantify their adherence, seeded scaffolds were washed up to 3 times with a 0.9 % NaCl solution. The luminescence of the scaffolds and the washing solutions was measured using a cell viability assay. These experiments demonstrated that after 72h of culture, the measured adherent bone progenitor cells on the scaffolds decreased after 3 washes down to 50 % while it stayed stable after 14 days of culture. In the second aim, we focused on methods to label the cells either once implanted or prior to implantation. The first method was to translate the in situ hybridization protocol with the human specific Alu sequence from paraffin embedded samples to resin embedded ones. The obtained results were so far inconclusive. Concerning the labeling of the cells before implantation, the transmembrane label PKH26 was investigated. Its staining efficacy was high just after labeling, while it decreased drastically over time due to cell division.

2015

Chargement

Neuronal morphologies: the shapes of thoughts

Lida Kanari

EPFL2018

2015