Date of Award


Document Type


Degree Name

Doctor of Philosophy (PhD)

Legacy Department

Biological Sciences


Chapman, Susan C.

Committee Member

Rice , Charles D.

Committee Member

Paul , Kimberly S.

Committee Member

McNealy , Tamara L.


This study investigates the role of pharyngeal endoderm in the specification of prechondrogenic identity and initiation of chondrogenesis in the proximal mesenchyme of the second pharyngeal arch. The results show that pharyngeal endoderm is sufficient but not necessary for specification of prechondrogenic identity in the cranial neural crest derived arch mesenchyme. A number of Fgf genes - Fgf3, 4, 8 and 19 are expressed in the pharyngeal endoderm. Further, FGF signaling is sufficient and required for the specification of prechondrogenic identity, marked by Sox9 expression. However, FGF signaling is unable to maintain the Sox9 expression and initiate the chondrogenic program. In contrast, BMP signaling can induce and maintain Sox9 expression in the arch mesenchyme. However, a combination of FGF and BMP signaling is required to initiate chondrogenesis, marked by Col2a1 expression.
Additionally, this study reports the cloning and gene expression patterns of previously uncharacterized Fgf genes - Fgf5, 6 and 7 during early development in chick. Fgf5 is expressed in the nascent otic placode, dorsal neural tube and the developing otic cup, which gives rise to the inner ear, suggesting the potential role of Fgf5 in the development of inner ear. Fgf6 expression is detected in the head, pharyngeal and visceral mesoderm. Fgf7 is expressed in the mesoderm but is excluded from the pharyngeal arches.