Establishment of a functional circulatory system during development is crucial for delivery of nutrients and oxygen to the embryo. Defects in the development of blood vessels result in death before birth or in congenital cardiovascular abnormalities. Our main focus is to examine the molecular and genetic pathways that regulate the three principal processes of vascular development: endothelial cell lineage determination, vasculogenesis, and angiogenesis. We focus on the mouse model because of the ready availability of genetics and experimental tools and because of similarities between mice and humans. Using an expression-based "gene trap" screen in mouse embryonic stem (ES) cells and embryos, we previously identified two novel genes involved in vascular system development, Vezf1 and Egfl7.

VEZF1 IS AN EARLY TRANSCRIPTION FACTOR ESSENTIAL FOR NORMAL BLOOD VASCULAR AND LYMPHATIC DEVELOPMENT. Vezf1 (= vascular endothelial zinc finger 1) encodes a Zn finger transcription factor protein that is expressed in vascular endothelial cells. Vezf1 plays an essential and dosage-dependent role in the proliferation, remodeling, and integrity of the developing blood vasculature. Strikingly, mutant embryos also display lymphatic vessel abnormalities with a phenotype reminiscent of the human congenital malformation syndrome, cystic hygroma. A future focus will be to understand its role in normal and pathological processes of lymphangiogenesis. We are also examining the genetic pathways of Vezf1 during embryogenesis and in adults. In particular, we focus on the interaction of VEZF1 with specific Rho GTPases. Moreover, several genes were identified as potential downstream targets for Vezf1, including fibrinogen, claudin, and apolipoproteins. Using molecular genetic approaches, we wish to understand how these pathways modulate development and angiogenesis.

EGFL7 IS AN EARLY MARKER FOR ENDOTHELIAL CELLS AND THEIR PROGENITORS. A second endothelial gene identified in our screen, Egfl7 (= EGFF-like domain 7), is restricted to the vascular endothelium and its mesoderm-derived progenitors in the yolk sac. Egfl7 expression is highly up-regulated during physiological angiogenesis in the pregnant uterus and in the regenerating endothelium after vascular injury. EGFL7 protein is partially secreted and acts as a chemoattractant on endothelial cells. Our recent studies indicate that Egfl7 is involved in endothelial cell-signaling pathways through its interaction with Notch as well as extracellular matrix components. Our research is focused on dissecting these interactions on a molecular and biochemical level, and to understand their role in vascular development and angiogenesis by using gain- and loss-of-function approaches in endothelial cells and in mice.

DEVELOPMENT OF MULTIVALENT VIRAL NANOPARTICLES FOR IN VIVO VASCULAR TARGETING AND IMAGING. We have developed fluorescently labeled nanoparticles, based on the cowpea mosaic virus (CPMV), for non-invasive imaging and targeting of the mammalian cardiovascular system. These brightly fluorescent CPMV allow high-resolution intravital imaging of the vascular endothelium and blood flow deep inside mouse or chick embryos for extended periods of time. They provide a means to identify arterial versus venous vessels, and to monitor the neovascularization of the tumor microenvironment. We are extending these studies by conjugating peptides to the CPMV capsid to target the nanoparticles to the vasculature, both during development and in disease models.



Email: hes2011@med.cornell.edu