During directed migration, cells decipher external guiding cues in order to properly reach their destination. Combining cellular simplicity and abundance of molecular tools, Ciona intestinalis is a unique chordate model to study the molecular basis of cell migration. In the embryo of Ciona, the cardiogenic progenitors (trunk ventral cells, TVCs) undergo a stereotyped migration away from the tail towards the ventral trunk. To determine which tissues are sending signals guiding TVC migration, I inhibited the secretory pathway through tissue specific expression of a dominant negative form of Sar1 (dnSar1) required for transport of proteins from the endoplasmic reticulum to the Golgi. I propose to identify candidate tissues involved in secreted guidance signals to the TVCs, and test their role via targeted expression of dnSar1 and assaying for TVC migration defects. My preliminary data indicate that expression of dnSar1 in either the notochord or the mesenchyme results in inhibition of TVC migration. Notably, the TVCs migrate away from the notochord and mesenchyme in wild-type embryos. This suggests that chemorepulsive signals derived from these two tissues are necessary for TVC migration. The secreted ligand Netrin is known for its conserved role in chemorepulsion through the activation of the receptor Unc5 (Lai Wing Sun et al., 2011). Published data along with my preliminary data shown that, in Ciona, netrin is expressed in the notochord while unc5 is expressed in the migrating TVCs (Woznica et al., 2012;Hotta et al., 2000). Eph-Ephrin signaling is also implicated in chemorepulsion. My in situ hybridization data show that the Eph1 receptor is expressed in the TVCs soon after their birth. The tail epidermis is in contact with the early TVCs and expresses the Eph ligand EphrinB, therefore posing as a good candidate tissue for polarizing the TVCs away from the tail towards the ventral trunk (Imai et al., 2004). My preliminary functional studies expressing truncated dominant negative forms of both the Unc5 and Eph1 receptor result in inhibition of TVC migration. I therefore hypothesize that Netrin-Unc5 and Eph-Ephrin signaling are involved in repelling the TVCs away from the tail towards the trunk. To test this hypothesis I will use gain and loss of function studies to perturb both Netrin-Unc5 and Eph-Ephrin signaling while assaying for additional TVC guidance cues and sources in parallel.
The goal of this project is to use Ciona cardiac progenitors as a model for understanding collective cell migration. I propose to determine the source and nature of guidance cues coordinating the spatio-temporal precision of migration of the Ciona cardiac progenitors. My finding on the regulation of collective cell migration in Ciona will be applicable to our understanding of migrations during development and disease in more complex systems.