Système de référence en anatomie

Un système de référence en anatomie désigne la terminologie utilisée pour se repérer de façon précise dans la structure anatomique d'un organisme, humain ou non. Un système de référence anatomique repose sur un ensemble de plans et d'axes définis par rapport à la position standard de l'organisme décrit. Par exemple, on utilise cette terminologie pour indiquer l'orientation des coupes histologiques ou des vues utilisées dans les schémas et images en ou en biologie humaine à partir de la position anatomique (dite de Poirier), c'est-à-dire lorsque le sujet est debout face à l'observateur. Plans de référence Plans sagittaux et plan médian Coupe sagittale Un plan sagittal est un plan vertical, orienté d'avant en arrière (du latin sagitta, « flèche », comme une flèche transperçant l'organisme). Parmi l'infinité de plans sagittaux, tous parallèles entre eux, un présente la particularité de séparer la moitié gauche de la moitié droite du corps : il s'agit du plan média

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Hunting for the wavefront: investigation of somite boundary positioning in zebrafish

Arianne Bercowsky Rama

Somitogenesis is the rhythmic and sequential formation of somites, which are tissue blocks that give rise to segmented adult body structures including the vertebrae and associated muscle. Somite formation is controlled by the segmentation clock, a population of genetic oscillators that are coordinated by an interplay of cell-intrinsic and -extrinsic spatiotemporal information. Disruption of the segmentation clock can lead to misplaced or defective somite boundaries, and consequently results in deformed adult structures (e.g., congenital scoliosis). Despite decades of research into how the segmentation clock pattern is established, and how it acts to position somite boundaries within the pre-segmental mesoderm(PSM), many open questions remain. The position where the somite boundary is set along the anteroposterior axis of the PSM has been named the "determination front". Question still remain as to the mechanism and location of the determination front, and what spatiotemporal information is instructive.Here I present three studies that tackle this question by advancing imaging and analysis tools such that questions that have persisted for decades can be directly addressed. My work contributed significantly to obtaining a better picture of how somite boundaries are precisely formed.

EPFL2022

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Aurora A depletion reveals centrosome-independent polarization mechanism in Caenorhabditis elegans

Coralie Busso, Christian Gentili, Pierre Gönczy, Sarah Herrman, Kerstin Klinkert Fabbri, Marie Juliette Ségolène Pierron, Lukas von Tobel

How living systems break symmetry in an organized manner is a fundamental question in biology. In wild-type Caenorhabditis elegans zygotes, symmetry breaking during anterior-posterior axis specification is guided by centrosomes, resulting in anterior-directed cortical flows and a single posterior PAR-2 domain. We uncover that C. elegans zygotes depleted of the Aurora A kinase AIR-1 or lacking centrosomes entirely usually establish two posterior PAR-2 domains, one at each pole. We demonstrate that AIR-1 prevents symmetry breaking early in the cell cycle, whereas centrosomal AIR-1 instructs polarity initiation thereafter. Using triangular microfabricated chambers, we establish that bipolarity of air-1(RNAi) embryos occurs effectively in a cell-shape and curvature-dependent manner. Furthermore, we develop an integrated physical description of symmetry breaking, wherein local PAR-2-dependent weakening of the actin cortex, together with mutual inhibition of anterior and posterior PAR proteins, provides a mechanism for spontaneous symmetry breaking without centrosomes.

2019

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Cripto promotes A-P axis specification independently of its stimulatory effect on Nodal autoinduction

Daniel Constam

The EGF-CFC gene cripto governs anterior-posterior (A-P) axis specification in the vertebrate embryo. Existing models suggest that Cripto facilitates binding of Nodal to an ActRII-activin-like kinase (ALK) 4 receptor complex. Cripto also has a crucial function in cellular transformation that is independent of Nodal and ALK4. However, how ALK4-independent Cripto pathways function in vivo has remained unclear. We have generated cripto mutants carrying the amino acid substitution F78A, which blocks the Nodal-ALK4-Smad2 signaling both in embryonic stem cells and cell-based assays. In cripto(F78A/F78A) mouse embryos, Nodal fails to expand its own expression domain and that of cripto, indicating that F78 is essential in vivo to stimulate Smad-dependent Nodal autoinduction. In sharp contrast to cripto-null mutants, cripto(F78A/F78A) embryos establish an A-P axis and initiate gastrulation movements. Our findings provide in vivo evidence that Cripto is required in the Nodal-Smad2 pathway to activate an autoinductive feedback loop, whereas it can promote A-P axis formation and initiate gastrulation movements independently of its stimulatory effect on the canonical Nodal-ALK4-Smad2 signaling pathway

Rockefeller University Press2008

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