The circulatory system consists of endothelial cell-lined blood vessels that serve as a transport network for red blood cells, which carry oxygen, immune cells, and hormones of the endocrine system. In parallel, the lymphatic system comprises blind-ended vessels, which are similarly lined by endothelial cells and are closely associated with the blood vessels of the circulatory system. Lymphatic vessels collect and return interstitial fluid to the circulatory system, are a site of lymphoid cell development and transit, and are required for lipid absorption in the digestive system. In both systems, the primary cell type that initiates formation and mediates function is the endothelial cell. Interestingly, lymphatic endothelial cells derive from venous endothelial cells during embryonic development indicating a common origin for both vessel types. Not surprisingly, a number of signaling molecules are shared and required for the formation of the circulatory and lymphatic systems. Among these is Flt4, a receptor tyrosine kinase expressed on both vascular and lymphatic endothelial cells that binds the ligand vascular endothelial growth factor c (Vegfc). Loss of Flt4 function in mouse or zebrafish embryos leads to a range of defects in veins, angiogenic blood vessels, and lymphatic vessels. This diverse requirement for Flt4 is governed, in part, by its highly dynamic expression during embryonic development. However, little is known about upstream regulators responsible for dynamic expression. An additional aspect of the dynamic role of Flt4 is its ability to activate a wide range of downstream signaling effectors in endothelial cells. Studies in primary cell lines and in vivo suggest that distinct downstream effectors may play context dependent roles during embryonic vascular and lymphatic development. Given the importance of new blood and lymphatic vessel growth in both human development and pathological settings, a better understanding of how Flt4 signals is highly relevant. In this application we will rely on our expertise using the zebrafish as a model to address these issues.
In Aim 1, we will determine what controls dynamic expression of flt4. In particular, we will investigate the role of ERK and Ets transcription factors in directly activatin enhancers at the flt4 locus to induce tip cell expression. This will be achieved through application of transgenic and knockout zebrafish lines.
In Aim 2, we will determine which Flt4-proximal signaling outputs are essential for vascular and lymphatic development. This will be done through application of site-specific nucleases to generate zebrafish lines bearing targeted deletion of tyrosines in the Flt4 cytoplasmic domain. Analysis of these lines will allow us to determine the importance of different downstream effectors in mediating context-dependent roles of Flt4.

Public Health Relevance

The studies in this project will focus on signaling by the FLT4 receptor, which is mutated in forms of congenital lymphedema in humans. A better understanding of how FLT4 functions will provide insights into pathological mechanisms and possible treatments in these cases.

Agency
National Institute of Health (NIH)
Institute
National Heart, Lung, and Blood Institute (NHLBI)
Type
Research Project (R01)
Project #
5R01HL122599-02
Application #
8974787
Study Section
Cardiovascular Differentiation and Development Study Section (CDD)
Program Officer
Tolunay, Eser
Project Start
2014-11-24
Project End
2018-10-31
Budget Start
2015-11-01
Budget End
2016-10-31
Support Year
2
Fiscal Year
2016
Total Cost
$376,875
Indirect Cost
$151,875
Name
University of Massachusetts Medical School Worcester
Department
Genetics
Type
Schools of Medicine
DUNS #
603847393
City
Worcester
State
MA
Country
United States
Zip Code
01655
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Lawson, Nathan D (2017) A New Conserved Player in Lymphatic Morphogenesis. Circ Res 120:1216-1218
Shin, Masahiro; Male, Ira; Beane, Timothy J et al. (2016) Vegfc acts through ERK to induce sprouting and differentiation of trunk lymphatic progenitors. Development 143:3785-3795
Shin, Masahiro; Beane, Timothy J; Quillien, Aurelie et al. (2016) Vegfa signals through ERK to promote angiogenesis, but not artery differentiation. Development 143:3796-3805
Hen, Gideon; Nicenboim, Julian; Mayseless, Oded et al. (2015) Venous-derived angioblasts generate organ-specific vessels during zebrafish embryonic development. Development 142:4266-78
Nicenboim, J; Malkinson, G; Lupo, T et al. (2015) Lymphatic vessels arise from specialized angioblasts within a venous niche. Nature 522:56-61