La construction de routes et de logements à Nairobi par des entreprises chinoises.

Résultat d’une présence croissante de la Chine en Afrique, les projets chinois en matière de développement urbain se multiplient dans les villes du continent. À Nairobi, l’aide au développement et les entreprises d’État chinoises contribuent à la construction d’infrastructures routières. Les promoteurs immobiliers chinois, principalement privés, construisent et commercialisent des logements pour les classes moyennes. Les productions urbaines d’acteurs publics et privés chinois concourent au développement de la capitale kenyane et à l’exportation des pratiques d’urbanisme chinoises en Afrique. Ils constituent un vecteur du pouvoir d’attraction de la Chine. Cet article présente les résultats d’une enquête de terrain

La construction de routes et de logements à Nairobi par des entreprises chinoises.

Résultat d’une présence croissante de la Chine en Afrique, les projets chinois en matière de développement urbain se multiplient dans les villes du continent. À Nairobi, l’aide au développement et les entreprises d’État chinoises contribuent à la construction d’infrastructures routières. Les promoteurs immobiliers chinois, principalement privés, construisent et commercialisent des logements pour les classes moyennes. Les productions urbaines d’acteurs publics et privés chinois concourent au développement de la capitale kenyane et à l’exportation des pratiques d’urbanisme chinoises en Afrique. Ils constituent un vecteur du pouvoir d’attraction de la Chine. Cet article présente les résultats d’une enquête de terrain

Mechanical Coupling Coordinates the Co-elongation of Axial and Paraxial Tissues in Avian Embryos.

Tissues undergoing morphogenesis impose mechanical effects on one another. How developmental programs adapt to or take advantage of these effects remains poorly explored. Here, using a combination of live imaging, modeling, and microsurgical perturbations, we show that the axial and paraxial tissues in the forming avian embryonic body coordinate their rates of elongation through mechanical interactions. First, a cell motility gradient drives paraxial presomitic mesoderm (PSM) expansion, resulting in compression of the axial neural tube and notochord; second, elongation of axial tissues driven by PSM compression and polarized cell intercalation pushes the caudal progenitor domain posteriorly; finally, the axial push drives the lateral movement of midline PSM cells to maintain PSM growth and cell motility. These interactions form an engine-like positive feedback loop, which sustains a shared elongation rate for coupled tissues. Our results demonstrate a key role of inter-tissue forces in coordinating distinct body axis tissues during their co-elongation

Cell-to-cell heterogeneity in Sox2 and Bra expression guides progenitor motility and destiny.

Although cell-to-cell heterogeneity in gene and protein expression within cell populations has been widely documented, we know little about its biological functions. By studying progenitors of the posterior region of bird embryos, we found that expression levels of transcription factors Sox2 and Bra, respectively involved in neural tube (NT) and mesoderm specification, display a high degree of cell-to-cell heterogeneity. By combining forced expression and downregulation approaches with time-lapse imaging, we demonstrate that Sox2-to-Bra ratio guides progenitor's motility and their ability to stay in or exit the progenitor zone to integrate neural or mesodermal tissues. Indeed, high Bra levels confer high motility that pushes cells to join the paraxial mesoderm, while high levels of Sox2 tend to inhibit cell movement forcing cells to integrate the NT. Mathematical modeling captures the importance of cell motility regulation in this process and further suggests that randomness in Sox2/Bra cell-to-cell distribution favors cell rearrangements and tissue shape conservation

Modelling Oscillator synchronisation during vertebrate axis segmentation

he somitogenesis clock regulates the periodicity with which somites form in the posterior pre-somitic mesoderm. Whilst cell heterogeneity results in noisy oscillation rates amongst constituent cells, synchrony within the population is maintained as oscillators are entrained via juxtracine signalling mechanisms. Here we consider a population of phase-coupled oscillators and investigate how biologically motivated perturbations to the entrained state can perturb synchrony within the population. We find that the ratio of mitosis length to clock period can influence levels of desynchronisation. Moreover, we observe that random cell movement, and hence change of local neighbourhoods, increases synchronisation

A random cell motility gradient downstream of FGF controls elongation of amniote embryos

Vertebrate embryos are characterized by an elongated antero-posterior (AP) body axis, which forms by progressive cell deposition from a posterior growth zone in the embryo. Here, we used tissue ablation in the chicken embryo to demonstrate that the caudal presomitic mesoderm (PSM) has a key role in axis elongation. Using time-lapse microscopy, we analysed the movements of fluorescently labelled cells in the PSM during embryo elongation, which revealed a clear posterior-to-anterior gradient of cell motility and directionality in the PSM. We tracked the movement of the PSM extracellular matrix in parallel with the labelled cells and subtracted the extracellular matrix movement from the global motion of cells. After subtraction, cell motility remained graded but lacked directionality, indicating that the posterior cell movements associated with axis elongation in the PSM are not intrinsic but reflect tissue deformation. The gradient of cell motion along the PSM parallels the fibroblast growth factor (FGF)/mitogen-activated protein kinase (MAPK) gradient1, which has been implicated in the control of cell motility in this tissue2. Both FGF signalling gain- and loss-of-function experiments lead to disruption of the motility gradient and a slowing down of axis elongation. Furthermore, embryos treated with cell movement inhibitors (blebbistatin or RhoK inhibitor), but not cell cycle inhibitors, show a slower axis elongation rate. We propose that the gradient of random cell motility downstream of FGF signalling in the PSM controls posterior elongation in the amniote embryo. Our data indicate that tissue elongation is an emergent property that arises from the collective regulation of graded, random cell motion rather than by the regulation of directionality of individual cellular movements

Unus pro omnibus, omnes pro uno: A novel, evidence-based, unifying theory for the pathogenesis of endometriosis

The theory of retrograde menstruation as aetiopathogenesis of endometriosis formulated by John Sampson in 1927 shows clear shortcomings: this does not explain why retrograde menstruation is a physiological process that affects 90% of women, while endometriosis occurs in only 10% of cases; it also does not explain the endometriotic foci distant from the pelvis, nor explains the cases of endometriosis in male patients. The immunological alterations of the peritoneal fluid explains the effects of disease, such as the inhibition of the physiological processes of cytolysis, but does not explain the cause. There is evidence to support the hypothesis that ectopic müllerian remnants of the endometrium, endocervix and endosalpinx are items from the genital ridge leaked during organogenesis. It is known that tissues derived from coelomatic epithelial and mesenchymal cells have the potential to metaplastically differentiate into epithelium and stroma. In addition, the phenotype of the ectopic endometrial cells is significantly different from those ectopic. There is scientific evidence that, during organogenesis, the genes of the Homeobox and Wingless family play a fundamental role in the differentiation of the ducts of Muller and development of the anatomical structure of the urogenital tract. We present here a hypothesis that deregulation of genes and the Wnt signaling pathway Wnt/β-catenin leads to aberrations and deregulation within the mesoderm, thus, may cause aberrant placement of stem cells. In addition, immune cells, adhesion molecules, extracellular matrix metalloproteinase and pro-inflammatory cytokines activate/alter peritoneal microenvironment, creating the conditions for differentiation, adhesion, proliferation and survival of ectopic endometrial cells

China and the Making of African Cities : the impact of Chinese urban development practices on Africa’s path of urbanization

À travers des projets d’une échelle inégalée, les acteurs chinois contribuent à la transformation des villes africaines. Le développement urbain constitue un secteur émergent des relations sino-africaines.Combinant aide publique et capitaux privés, plusieurs catégories d’acteurs – instituts d’urbanisme, entreprises de construction, promoteurs privés – y conçoivent et construisent des projets de nature variée à différentes échelles : routes urbaines, résidences de logements, villes satellites,zones économiques spéciales conçues comme des villes nouvelles. Les productions urbaines chinoises en Afrique accélèrent la métropolisation des plus grandes villes du continent et densifient leurs espaces périurbains : elles contribuent à la formation d’une nouvelle strate urbaine. Les projets chinois accompagnent l’émergence des classes moyennes africaines en facilitant l’accession à un meilleur confort de vie. Parallèlement, l’exportation de pratiques chinoises d’urbanisme véhicule une image de réussite et participe au renforcement de la puissance chinoise.Urban development has become a growing sector within China-Africa relations. The Chinese contribute to the urbanization process in Africa. By combining development aid and business, a number of Chinese stakeholders – urban planning and design institutes, construction firms, and real estate developers – design and build there, on various scales, a great variety of projects such as urban roads, housing estates, satellite-towns, special economic zones planned as new cities. Chinese urban development projects in Africa have sped up the metropolization processin the largest African cities by making suburban areas denser and denser. This has contributed to the development of a new urban stratum in Africa. Chinese projects have been boosting the rise of the African urban middle class by facilitating access to better standards of living. At the same time, the export of Chinese urban development practices conveys an image of success andallows China to strengthen its soft power.中国对非洲城市发展的贡献: 中国城市规划式对非洲城市化的影响城市发展已成为中非合作越来越重要的行业。中国对非洲城市化进程作出了贡献。众多中国城市建设专业机构(城市规划设计研究院，施工企业，房地产开发商)在非洲设计和建造各类的城市发展项目: 城市道路、住宅区、卫星城市和经济特区。中国在非洲城市发展项目对加快特大城市的大都市化和密集化作出了贡献。这些项目已经推动一些非洲城市开始产生新的城市阶层。在非洲的中国项目推动非洲中产阶层的崛起，帮助他们方便获得更好的生活条件。同时，中国城市规划设计的走出去传达中国城市发展的成功形象，有利于中国加强自己的软实力。关键词：中非合作，城市发展，城市发展实践，大都市化，城市阶层，房地产，全球化，软实力，援助，新兴国家和发展中国家