Neural tube-ectoderm interactions are required for trigeminal placode formation

Cranial sensory ganglia in vertebrates develop from the ectodermal placodes, the neural crest, or both. Although much is known about the neural crest contribution to cranial ganglia, relatively little is known about how placode cells form, invaginate and migrate to their targets. Here, we identify Pax-3 as a molecular marker for placode cells that contribute to the ophthalmic branch of the trigeminal ganglion and use it, in conjunction with DiI labeling of the surface ectoderm, to analyze some of the mechanisms underlying placode development. Pax-3 expression in the ophthalmic placode is observed as early as the 4-somite stage in a narrow band of ectoderm contiguous to the midbrain neural folds. Its expression broadens to a patch of ectoderm adjacent to the midbrain and the rostral hindbrain at the 8- to 10-somite stage. Invagination of the first Pax-3-positive cells begins at the 13-somite stage. Placodal invagination continues through the 35-somite stage, by which time condensation of the trigeminal ganglion has begun. To challenge the normal tissue interactions leading to placode formation, we ablated the cranial neural crest cells or implanted barriers between the neural tube and the ectoderm. Our results demonstrate that, although the presence of neural crest cells is not mandatory for Pax-3 expression in the forming placode, a diffusible signal from the neuroectoderm is required for induction and/or maintenance of the ophthalmic placode

Competence, specification and induction of Pax-3 in the trigeminal placode

Placodes are discrete regions of thickened ectoderm that contribute extensively to the peripheral nervous system in the vertebrate head. The paired-domain transcription factor Pax-3 is an early molecular marker for the avian ophthalmic trigeminal (opV) placode, which forms sensory neurons in the ophthalmic lobe of the trigeminal ganglion. Here, we use collagen gel cultures and heterotopic quail-chick grafts to examine the competence, specification and induction of Pax-3 in the opV placode. At the 3-somite stage, the whole head ectoderm rostral to the first somite is competent to express Pax-3 when grafted to the opV placode region, though competence is rapidly lost thereafter in otic-level ectoderm. Pax-3 specification in presumptive opV placode ectoderm occurs by the 8-somite stage, concomitant with robust Pax-3 expression. From the 8-somite stage onwards, significant numbers of cells are committed to express Pax-3. The entire length of the neural tube has the ability to induce Pax-3 expression in competent head ectoderm and the inductive interaction is direct. We propose a detailed model for Pax-3 induction in the opV placode

Astro2020 APC White Paper: The MegaMapper: a z > 2 spectroscopic instrument for the study of Inflation and Dark Energy

MegaMapper is a proposed ground-based experiment to measure Inflation parameters and Dark Energy from galaxy redshifts at

Diagnosis of lower limb pain in a diabetic patient

peer reviewedBy presenting this clinical case, we aim at discussing the diagnosis between arteriopathy, neuropathy and osteoarticular pathology in a patient with type 2 diabetes who complains of lower limb pain. We emphasize the role of a global medical approach based upon anamnesis and clinical exam, which should contribute to select the most helpful paraclinical investigations

Chick muscle development

Striated muscle is the most abundant tissue in the body of vertebrates and it forms, together with the skeleton, the locomotory system required both for movement and the creation of the specific body shape of a species. Research on the embryonic development of muscles has a long tradition both in classical embryology and in molecular developmental biology. While the gene networks regulating muscle development have been discovered mostly in the mouse through genetics, our knowledge on cell lineages, muscle morphogenesis and tissue interactions regulating their formation is to a large extent based on the use of the avian model. This review highlights present knowledge of the development of skeletal muscle in vertebrate embryos. Special focus will be placed on the contributions from chicken and quail embryo model systems

Etude de deux aspects de la myogenèse chez l'embryon de poulet (la transition epitheliomesenchymateuse et la fusion des myoblastes)

Chez les vertébrés, les somites, structures transitoires du mésoderme, sont à l'origine de tous les muscles squelettiques des membres et du corps. Les muscles embryonnaires se forment en deux phases séquentielles à partir du dermomyotome épithélial (partie dorsale du somite). 1ère phase : les cellules des quatre lèvres du dermomyotome délaminent pour former le myotome primaire, composé de fibres musculaires mononucléées et post mitotiques. 2nde phase : les cellules de la partie centrale du dermomyotome subissent une transition épithélio mésenchymateuse (EMT) qui permet l'entrée massive dans le myotome primaire de progéniteurs musculaires, capables de proliférer et de se différencier en fibres musculaires. La croissance du myotome est également assurée par un processus de fusion : les myoblastes mononucléés fusionnent pour former des fibres musculaires multinucléées. Au cours de ma thèse, je me suis intéressée aux mécanismes moléculaires qui régulent temporellement l'initiation de l'EMT. J'ai pu montrer que le signal FGF provenant du myotome déclenche la voie de signalisation MAPK/ERK dans le dermomyotome, permettant l'activation du facteur de transcription Snail à l'origine de l'EMT. J'ai également cherché à caractériser le processus de fusion chez les vertébrés. Une étude descriptive m'a permis de montrer que le processus de fusion des myoblastes était initié 36h après la formation du somite. Les évènements de fusion ont lieu entre les myocytes mononucléés du myotome primaire et les progéniteurs musculaires. Je me suis ensuite intéressée aux mécanismes moléculaires régulant les évènements de fusion. J'ai réalisé des pertes de fonction des gènes Tanc1, Arf6 et NCKAP1, orthologues des gènes Rols1, Arf6 et Kette de drosophile. Les résultats obtenus suggèrent que ces molécules sont nécessaires au processus de fusion, indiquant une conservation au cours de l'évolution de la cascade moléculaire impliquée dans la fusion des myoblastes chez la Drosophile.In vertebrates, sketetal muscles of the trunk and the limbs form in two stages, from the dermomyotome (DM) : 1) cells located at the four borders of the DM delaminate to generate the primary myotome (PM); 2) cells from the central part of the DM undergo an epitheliomesenchymal transition (EMT), characterrised by a massive entrey of muscle progenitors into the PM. A myoblast fusion process allows the myotome growth. I analysed the temporal regulation of the EMT initiation. We propose that this process is regulated by a FGF signal emanating from the PM, that riggers within the DM a MAPK/ERK pathway that leads to the activation of the transcription factor Snail 1, a regulator of EMT. Then, I showed that the fuion process is initiated between mononucleated myocytes and muscles progenitors, 36h after somite formation. The loss of function of Tanc1, Arf6 and NCKAP1 genes, orthologous of Rols1, Arf6 and Kette genes of drosophila, suggests that theses genes regulate the fusion processAIX-MARSEILLE2-BU Sci.Luminy (130552106) / SudocSudocFranceF