Cardiovascular Development

Comprised of the heart and blood vessels of the embryo-proper, the yolk sac vasculature and the placenta, the cardiovascular system is the first organ system to develop during embryogenesis. Proper blood vessel development is essential not only for embryo survival and development in the uterus, but also for normal tissue healing in the adult and for growth of abnormal tissue like tumors. Learning about how the cardiovascular system forms during development therefore has great potential to impact human health. We may begin to understand and potentially prevent early pregnancy loss, to develop therapies important for healing tissue following heart attack or stroke, and prevent growth of tumors by restricting new vessel growth. We have learned from mouse embryos deficient for a protein called YAP that this protein is critical for the earliest stages of both blood vessel and placental development. We combine the power of mouse embryonic stem cell in vivo and in vitro differentiation capacity and genetic malleability with cell and tissue culture-base assays and mouse genetics to study the role of YAP in development.

We are working on the following topics:

• Learning how YAP impacts cell number regulation during development
   
• Defining YAP structural requirements underlying the critical role in vasculogenesis
   
• Determining cell- and tissue- level requirements for YAP in chorioallantoic union
   
• Characterizing pathways and protein complex components critical to YAP function in development

Contributing Personnel –past and present:

• Brian Boone research assistant
   
• Zack Hawkins research assistant
   
• Jessica Folmar undergraduate student
   
• David Lorance undergraduate student
   
• Tim Alves undergraduate student
   
• Jim Ericksen continuing education student
   
• Robin Shah undergraduate student
   
• Stephen Gee graduate student, Milgram lab

Collaborators:

• Dr. Sharon L. Milgram NIH

Apoptosis and Cell Proliferation- How Does developmental regulation of cell number require YAP?
Mouse embryos in which the Yap gene has been disrupted die before birth (Figure 1) with several distinct developmental problems including defective yolk sac blood vessel development (see below), failure to initiate development of the placenta (see below), and a profound disruption in the growth and elongation of the embryo-proper. Possibly the defects observed in the mutant embryo can be explained in part by a failure of the embryo to produce the proper number of cells. We know that careful regulation of cell number is critical to proper embryogenesis in many ways. This control of cell number can include both removal of cells by programmed cell death (apoptosis) and increases or decreases in the rate at which cells are dividing (proliferation). We use molecular biology, cell culture, biochemical and embryological techniques to learn if YAP may be important to developmentally-regulated apoptosis and proliferation. These studies will help us better understand how YAP functions in cells and also may help us better understand how cell number is regulated under normal conditions like embryonic development and under disease conditions like cancer.


 

Defining YAP structural requirements underlying the critical role in vasculogenesis

Mice developing with YAP perturbation die in early stages of embryogenesis showing profound defects in the development of the yolk sac vasculature (Figure 2). We are using molecular biology, cell culture, immunohistochemical, and genetic techniques to learn more about the role of YAP in blood vessel development. We expect that our studies will help us better understand how this protein functions in cells and will significantly advance our understanding of some of the earliest events in development of the cardiovascular system. Learning more about blood vessel development can be important for both cancer biology- if we can prevent vascular input to tumours, they can’t grow- and for potential treatment of ischemic tissue as in heart attacks and strokes -if we can get blood vessels to develop there, we may minimize damage.


 

Determining cell- and tissue- level requirements for YAP in chorioallantoic union

Mammalian embryos are entirely dependent upon proper development and function of a maternal-fetal interface- the chorioallantoic placenta- for their survival and growth in the uterus. In fact, a large fraction of human pregnancies are lost in very early stages just as these essential developmental events unfold. Moreover, many later health problems for both mother and child, such as preeclampsia and intrauterine growth restriction, may trace back to deficits in placental development. Despite the critical dependence of mammalian embryogenesis on proper placental development, remarkably little is known about the cellular and molecular details of this process. We have learned that YAP is essential for a very early step in placental development: in mouse embryos in which the Yap gene is disrupted, we observe a complete failure of the allantois to fuse with the chorion. To begin to understand the role of YAP in chorioallantoic union (Figure 3), we are using molecular biology, cell culture, immunohistochemical, and embryological techniques. These studies will help us better understand functions of YAP itself and likely will make a significant advance in current understanding of early placental development and so potentially help us gain insight into early pregnancy loss as well.
 

Identifying pathways and protein complex components critical to YAP function in development

YAP isoforms and the closely related protein WWTR1 are highly and widely expressed multi-domain phospho-proteins with multiple roles identified by biochemical and cell culture-based assays. We employ cutting edge biochemical techniques to learn about binding partners and participants in mult-protein complexes that are critical to YAP function(s) in a developmental context-sensitive manner.