title: A novel multistep mechanism for initial lymphangiogenesis in mouse embryos based on ultramicroscopy.
abstract: During mammalian development, a subpopulation of endothelial cells in the cardinal vein (CV) expresses lymphatic-specific genes and subsequently develops into the first lymphatic structures, collectively termed as lymph sacs. Budding, sprouting and ballooning of lymphatic endothelial cells (LECs) have been proposed to underlie the emergence of LECs from the CV, but the exact mechanisms of lymph vessel formation remain poorly understood. Applying selective plane illumination-based ultramicroscopy to entire wholemount-immunostained mouse embryos, we visualized the complete developing vascular system with cellular resolution. Here, we report emergence of the earliest detectable LECs as strings of loosely connected cells between the CV and superficial venous plexus. Subsequent aggregation of LECs resulted in formation of two distinct, previously unidentified lymphatic structures, the dorsal peripheral longitudinal lymphatic vessel (PLLV) and the ventral primordial thoracic duct (pTD), which at later stages formed a direct contact with the CV. Providing new insights into their function, we found vascular endothelial growth factor C (VEGF-C) and the matrix component CCBE1 indispensable for LEC budding and migration. Altogether, we present a significantly more detailed view and novel model of early lymphatic development.
authors.affiliation: Mammalian Cell Signaling Laboratory, Department of Vascular Cell Biology, Max Planck Institute for Molecular Biomedicine, Münster, Germany.
authors.forename: René
authors.initials: R
authors.lastname: Hägerling
authors.forename: Cathrin
authors.initials: C
authors.lastname: Pollmann
authors.forename: Martin
authors.initials: M
authors.lastname: Andreas
authors.forename: Christian
authors.initials: C
authors.lastname: Schmidt
authors.forename: Harri
authors.initials: H
authors.lastname: Nurmi
authors.forename: Ralf H
authors.initials: RH
authors.lastname: Adams
authors.forename: Kari
authors.initials: K
authors.lastname: Alitalo
authors.forename: Volker
authors.initials: V
authors.lastname: Andresen
authors.forename: Stefan
authors.initials: S
authors.lastname: Schulte-Merker
authors.forename: Friedemann
authors.initials: F
authors.lastname: Kiefer
mesh_terms: D000818:Animals; D002135:Calcium-Binding Proteins / Q000502:physiology*; D002465:Cell Movement; D049109:Cell Proliferation; D004622:Embryo, Mammalian / Q000166:cytology* / Q000378:metabolism / Q000648:ultrastructure; D004729:Endothelium, Lymphatic / Q000166:cytology* / Q000378:metabolism / Q000648:ultrastructure; D004730:Endothelium, Vascular / Q000166:cytology* / Q000378:metabolism / Q000648:ultrastructure; D005455:Fluorescent Antibody Technique; D007124:Immunoenzyme Techniques; D042583:Lymphangiogenesis; D042601:Lymphatic Vessels; D051379:Mice; D008810:Mice, Inbred C57BL; D018345:Mice, Knockout; D025521:Tumor Suppressor Proteins / Q000502:physiology*; D042582:Vascular Endothelial Growth Factor C / Q000502:physiology*; D040321:Vascular Endothelial Growth Factor Receptor-3 / Q000502:physiology*; D014680:Veins / Q000166:cytology* / Q000378:metabolism / Q000648:ultrastructure
chemical_list: D002135:Calcium-Binding Proteins; C572375:Ccbe1 protein, mouse; D025521:Tumor Suppressor Proteins; D042582:Vascular Endothelial Growth Factor C; C467483:vascular endothelial growth factor C, mouse; D040321:Vascular Endothelial Growth Factor Receptor-3