The role of fibronectin and atypical protein kinase C iota in the development of notochord and chondrocytes

Abstract

The notochord is a conserved structure in the phylum chordate, which includes all vertebrates and some closely related invertebrates. In mouse embryos, the notochord is a midline structure underneath the neural tube and it consists of a rod of cells constrained by a thick extracellular sheath, which is rich in fibronectin and other extracellular matrix molecule. During notochord formation, two key processes are involved: cell migration and convergent extension. Two molecules are essential for these processes: fibronectin and Protein Kinase C iota (prkci). For cell migration, fibronectin regulates this process by modulating cell protrusion via a signaling pathway in which atypical protein kinase C (aPKC) is an essential factor. For convergent extension, fibronectin has been shown to be important in this process by regulating both cell migration and cell adhesion. The role of aPKCin convergent extension is revealed as it is asymmetrically expressed in Ciona notochord during convergent extension, indicating possible function of aPKC in convergent extension process and in the morphogenesis of notochord. These studies raised the possibility that fibronectin and prkci are important in notochord formation, by regulating cell migration and convergent extension.

In this thesis, Cre/loxP system was used to study the function of fibronectin and prkci in the development of notochord. I provided evidence that conditional deletion of fibronectin by Foxa2-Crein the notochord resulted in a notochord of smaller volume and fewer notochordal cells. The nucleus pulposus was also smaller in are and less in cell number. Fibronectin in the notochord was not affected at E9.5, but diminished in the core of the notochord at E12.5 and in nucleus pulposus at E15.5. The phenotypes of smaller notochord and the nucleus pulposus might be the results of reduced notochordal cell proliferation and increased cell death. However, more samples are needed to analyze to confirm this and perform statistical analysis. In addition, convergent extension of notochord seemed less effective. These results are consistent with previous study about fibronectin and α5β1 integrin. The results suggest that fibronectin is required for notochordal cell proliferation, survival, migration and efficient convergent extension, but not for notochordal cell fate determination. The results also demonstrated that prkci seemed not to be important for notochord development.