RESUMO
BACKGROUND: The endocytosis of Gap junction plaques (GJP) requires cytoskeletal forces to internalize such large membranous structures. Actin, which partners the connexin proteins constituting Gap junctions and is located close to Annular Gap Junctions (AGJ), could be actively involved in this physiological process. RESULTS: Electron Microscopy and Light Microscopy images, associated with time-lapse analysis and 3D reconstruction, used at high resolution and enhanced using ImageJ based software analysis, revealed that: i) actin cables, originating from Donor cells, insert on the edge of GJP and contribute to their invagination, giving rise to AGJ, whereas actin cables on the Acceptor cell side of the plaque are not modified; ii) actin cables from the Donor cell are continuous with the actin network present over the entire GJP surface. These actin cables fuse at a single point distant from the plaque, which then detaches itself from the membrane, condensing to form an actin mass during the final internalization process; iii) the Acceptor cell participates in the last step of the endocytic invagination process by forming an annular actin structure known as an actin ring. CONCLUSIONS: Together, these data suggest that the endocytosis of GJP is an example of a unique cooperative mechanism between the Donor (the traction of its actin cables) and the Acceptor cells (forming the actin ring).
RéSUMé: CONTEXTE: L'endocytose des plaques de jonctions communicantes ou jonctions gap (GJP) nécessite les forces du cytosquelette pour internaliser ces grandes structures membranaires. L'actine, partenaire des connexines, proteins constitutives des jonctions gap (Gj), localisée proche des jonctions gap annulaires (GJA), pourrait être impliquée dans ce processus physiologique. RéSULTATS: L' imagerie par microscopie optique et électronique, associées avec des analyses vidéo et des reconstructions en relief/3D, examinées à haute résolution et améliorées après traitement par des logiciels développés sous ImageJ, montrent que: i) des câbles d'actine, originaires des cellules donneuses, s'insèrent sur le bord des plaques jonctionnelles et facilitent leur invagination pour former les GJA tandis que les câbles d'actine des cellules receveuses ne sont pas modifies; ii) les câbles d'actine des cellules donneuses sont en continuité avec le réseau d'actine qui couvre la totalité de la surface de la plaque. De plus, ces câbles fusionnent en un point unique, à distance de la plaque, qui se détache de la région membranaire pour former une masse d'actine à la fin du processus d'endocytose; iii) la cellule receveuse participe à l'étape ultime du processus d'endocytose de la plaque en formant un anneau d'actine. CONCLUSIONS: L'ensemble de nos résultats montrent que l'endocytose des plaques jonctionnelles est un exemple de coopération unique entre la cellule donneuse (grâce à la traction des câbles d'actine) et la cellule receveuse (anneau d'actine).
RESUMO
The thymus is a central lymphoid organ primarily responsible for the development of T cells. A small proportion of B cells, however, also reside in the thymus to assist negative selection of self-reactive T cells. Here we show that the thymus of human neonates contains a consistent contingent of CD138+ plasma cells, producing all classes and subclasses of immunoglobulins with the exception of IgD. These antibody-secreting cells are part of a larger subset of B cells that share the expression of signature genes defining mouse B1 cells, yet lack the expression of complement receptors CD21 and CD35. Data from single-cell transcriptomic, clonal correspondence and in vitro differentiation assays support the notion of intrathymic CD138+ plasma cell differentiation, alongside other B cell subsets with distinctive molecular phenotypes. Lastly, neonatal thymic plasma cells also include clones reactive to commensal and pathogenic bacteria that commonly infect children born with antibody deficiency. Thus, our findings point to the thymus as a source of innate humoral immunity in human neonates.
