| dc.description.abstracteng | Lymphatic vessels are essential for the maintenance of tissue homeostasis. Their primary functions are the return of excessive tissue fluid into blood circulation, the transport of antigens both in soluble form and after ingestion by cells of the immune system, and finally the transport of dietary fats. Malformations of the lymphatic system, caused by primary lymphedema (hereditary or spontaneous genetic mutation), operative injury or radiotherapy in the context of cancer treatment, can significantly affect the health and quality of life of patients. The aim of the present study was to investigate morphological changes in the dermal lymphatic vasculature due to the lack of the signaling molecule Wnt5a in 18-day-old mouse embryos by light and electron microscopy. Thereby, homozygous Wnt5a-knock-out (ko) mice are not viable. They die immediately after birth.
I therefore examined embryos at embryonic days (ED) 17.5-18.5. The central method in this work is the generation of electron micrographs of initial lymphatic vessels from selected ultrathin sections of abdominal skin of mouse embryos of all genotypes (wild-type, homozygous and heterozygous Wnt5a-ko). Dermis of all genotypes (+/+, +/-, -/-) was fixed, embedded and stained according to standard procedures. All images were taken with the electron microscope (Zeiss Leo906) and saved as tif and jpg format. A higher number of lymph capillaries were found at defined intervals in the upper dermis in both wild-type and heterozygous Wnt5a-ko mice than in the homozygous Wnt5a-ko. The electron micrographs show that the lymphatic vessels consist of a single-layer of lymphatic endothelial cells (LECs). LECs overlap roof tile-like. The vessel lumen is smoothly limited. The nuclei of LECs are elongated and lie parallel to the longitudinal axis of the vessel. A basal membrane per se is not recognizable in lymphatic capillaries. Significantly less lymph capillaries can be detected in the homozygous Wnt5a-ko mice, which, however, are very voluminous and dilated. In addition, these lymph capillaries are filled with erythrocytes, which I confirmed by immunohistological staining with the LEC-marker Lyve-1. Electron microscopy reveals distinct morphological changes in the LECs. These do not possess roof tile-like overlapping junctions. The cell nuclei take many shapes (elongated, lobed, oval).
In this work I could show that the loss of Wnt5a protein, in addition to many dramatic effects in various tissues (face, skin, extremities, genitals), also massively restricts the morphology and function of the lymphatic vessels. Swelling of tissue by lymphedema can be the result of a developmental defect of the lymphatic system. | de |