Live imaging of blood vessel development

Blood vessels form an intricate network of interconnected tubes and ensure the proper distribution of oxygen, nutrients, immune cells and hormones throughout the body, while at the same time removing waste products. Furthermore, blood vessels play an important role during several disease settings, such as diabetes, stroke and cancer. Despite these important functions of the vasculature, we still lack an understanding of how this network forms. For instance, we do not understand how arteries and veins remodel and interconnect. Furthermore, it is often difficult to determine the origin of individual blood vessels. This stems in part from the previous inability to visualize the growth of blood vessels in vivo. The establishment of the zebrafish as a model system has recently shed light on these questions due to the transparency of the embryos in combination with transgenic fish lines that allow for the visualization of growing blood vessels. Using these tools, we have performed an analysis of the formation of the first brain blood vessels and found that the arterial components of these vessels are derived from veins (Bussmann et al., Development, 2011). We furthermore showed that the first forming brain capillaries require signaling via the chemokine receptor cxcr4a in order to properly connect arteries with veins. We are currently extending our time-lapse imaging approaches to other vascular beds and the regenerating zebrafish fin.

Angiogenesis during tissue regeneration

In the early embryo, blood vessels often form in a stereotyped manner, leading to an identical looking vasculature in different individuals. At later stages of development and during woundhealing or tissue regeneration, blood vessels form via a plexus intermediate. This plexus subsequently remodels into a hierarchical network of arteries and veins. Despite the importance of blood vessel plexus formation and remodeling, we lack an understanding of the morphogenetic processes that lead to the proper patterning of plexus blood vessels. Zebrafish, in contrast to mammals, possess the unique feature of regrowing amputated limbs, such as the fins. We could show that during fin regeneration, new blood vessels form via a plexus intermediate (Xu et al., Nature Communications, 2014; see also our press release). Importantly, we detected distinct migratory behaviors of arterially fated endothelial cells. These migration behaviors were dependent on the chemokine receptor Cxcr4a. We are currently investigating other signaling pathways controlling blood vessel formation during tissue regeneration. This work was in part funded by the Sonderforschungsbereich 629 of the Westphalian Wilhelms-University Münster.

Influence of blood flow on angiogenesis

Our work on the formation of the brain vasculature revealed that the expression of the chemokine receptor cxcr4a is negatively regulated by blood flow. Blood flow mediated shear stress influences many aspects of endothelial biology. It is important for proper vascular remodeling and can induce changes in gene transcription. In addition, several disease settings, such as atherosclerotic plaque formation, are influenced by alterations in shear stress. In order to better understand these changes, we aim at identifying the regulatory network of enhancer elements that controls shear stress mediated gene expression. This work is in part funded by the Cells in Motion Excellence Cluster (CiM Flex Fund Grant). See also our article in the MPG Yearbook 2014 (in German).

Using TALEN and CRISPR technologies to generate zebrafish mutants

The development of reverse genetic techniques that allow editing the endogenous open reading frames and promoter/enhancer regions of genes of interest has greatly impacted the zebrafish field. We have successfully used TALEN and CRISPR technologies to generate mutations in different zebrafish genes chosen because of their expression during different steps of the angiogenic program. We are currently analyzing the vascular phenotypes of these mutants.

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