Lack of embryonic homozygous or adult heterozygous lymphatic phenotypes for a Sos1 mutation and lack of lymphatic embryonic phenotypes for a homozygous Cx47 mutation in mice

We have studied the lymphatic phenotypes of 2 mutations, known to cause abnormalities of lymphatics in humans, in mice. The Cx47 R260C mutation (variably penetrant in humans heterozygous for it and causing limb lymphedema) had an adult mouse phenotype of hyperplasia and increased lymph nodes only in homozygous condition but we did not find any anatomical phenotype in day 16.5 homozygous embryos. Mice harboring the Sos1 mutation E846K (causing Noonan's in man which occasionally shows lymphatic dysplasia) had no adult heterozygous phenotype in lymphatic vessel appearance and drainage (homozygotes are early embryonic lethals) while day 16.5 heterozygous embryos also had no detectable anatomical phenotype.

Lymphatic vessel development: fluid flow and valve-forming cells

Hemodynamic forces regulate many aspects of blood vessel disease and development, including susceptibility to atherosclerosis and remodeling of primary blood vessels into a mature vascular network. Vessels of the lymphatic circulatory system are also subjected to fluid flow-associated forces, but the molecular and cellular mechanisms by which these forces regulate the formation and maintenance of lymphatic vessels remain largely uncharacterized. This issue of the JCI includes two articles that begin to address how fluid flow influences lymphatic vessel development and function. Sweet et al. demonstrate that lymph flow is essential for the remodeling of primary lymphatic vessels, for ensuring the proper distribution of smooth muscle cells (SMCs), and for the development and maturation of lymphatic valves. Kazenwadel et al. show that flow-induced lymphatic valve development is initiated by the upregulation of GATA2, which has been linked to lymphedema in patients with Emberger syndrome. Together, these observations and future studies inspired by these results have potential to lead to the development of strategies for the treatment of lymphatic disorders.

GATA2 is required for lymphatic vessel valve development and maintenance

Heterozygous germline mutations in the zinc finger transcription factor GATA2 have recently been shown to underlie a range of clinical phenotypes, including Emberger syndrome, a disorder characterized by lymphedema and predisposition to myelodysplastic syndrome/acute myeloid leukemia (MDS/AML). Despite well-defined roles in hematopoiesis, the functions of GATA2 in the lymphatic vasculature and the mechanisms by which GATA2 mutations result in lymphedema have not been characterized. Here, we have provided a molecular explanation for lymphedema predisposition in a subset of patients with germline GATA2 mutations. Specifically, we demonstrated that Emberger-associated GATA2 missense mutations result in complete loss of GATA2 function, with respect to the capacity to regulate the transcription of genes that are important for lymphatic vessel valve development. We identified a putative enhancer element upstream of the key lymphatic transcriptional regulator PROX1 that is bound by GATA2, and the transcription factors FOXC2 and NFATC1. Emberger GATA2 missense mutants had a profoundly reduced capacity to bind this element. Conditional Gata2 deletion in mice revealed that GATA2 is required for both development and maintenance of lymphovenous and lymphatic vessel valves. Together, our data unveil essential roles for GATA2 in the lymphatic vasculature and explain why a select catalogue of human GATA2 mutations results in lymphedema.

The pathogenesis of congenital hereditary lymphedema in the pig

The morphogenesis of congenital hereditary lymphedema was studied in pigs. The disorder, which is essentially a general underdevelopment or even total non-development of the lymphatic system proved to be present during the whole period of lymphatic development. It is suggested that a retardation in the differentiation of the lymphatic primordia from the primitive veins is the early event regulated by a chromosomal aberration. The longer this delay the more serious the lymphatic malformations.