Electronic Thesis and Dissertation Repository


Master of Science




Gregory M. Kelly


Mouse F9 cells differentiate into primitive endoderm (PrE) when treated with retinoic acid (RA). During PrE differentiation the canonical Wnt signaling pathway is known to play an integral role in the process. In addition to Wnt signaling, there have been implications that the Hedgehog (Hh) pathway may also be involved. Previous results show that the Indian Hedgehog (Ihh) gene is upregulated during RA-induced differentiation; however further details of Hh signaling during PrE differentiation have yet to be discovered. A Gli-luciferase construct indicated that Hh signaling increases during RA-induced differentiation, implicating that the pathway is involved in PrE formation. Inhibiting Hh signaling impeded the ability of RA to induce cells to differentiate to PrE, revealing that the Hh pathway is required for PrE differentiation. Despite being required, active Hh signaling alone was unable to facilitate differentiation. Overexpression of Gata6, a gene encoding a master regulator of extraembryonic endoderm pattering, was found to increase expression of Ihh as well as increasing Gli activity; further corroborating for the involvement of the Hh pathway during embryonic development. In addition to these findings, I found that there is signaling crosstalk between the Hh and Wnt pathways in F9 cells. For instance, while induced Wnt signaling was found to increase the activity of a Gli reporter, the inhibition of the Hh pathway impeded the ability of RA to increase Wnt signaling. Together, these results indicate that the Hh signaling pathway plays an important role in early embryogenesis, and this is obvious with its interactions with the Wnt signaling pathway in PrE differentiation.