Abstract

Wnt signaling has been shown to have several roles in the development of sensory neurons, particularly in the ophthalmic portion of the trigeminal nerve. Many of these studies have relied on the conclusion that Wnt is necessary but not sufficient for the induction and maintenance of the neural precursor cells that develop in the ophthalmic placode. Wnt had been inhibited in the ophthalmic placode using a dominant negative t-cell factor (TCF) and resulted in the loss of Pax3 expression (indicative of undifferentiated placode cells) in all targeted cells, suggesting a loss of specification/commitment of these cells to the sensory neuron fate. This study aimed to build on that conclusion by identifying the source of Wnt signaling that allowed for the maintenance of these placode cells. To investigate this, chick embryo ex ovo cultures were used and treated with small molecule chemical Wnt inhibitors to globally knock out Wnt signaling. The embryos were then sectioned and stained for cell markers of undifferentiated placode and differentiated neural cells (Pax3 and Islet1, respectively). Also used was a conditional knockout of Porcn, a gene critical to post-transcriptional modification of the Wnt ligand, using Wnt1-cre as a driver; this allowed for the knockout of Wnt secretion from the dorsal neural tube as well as neural crest cells. The data showed a decrease in placode cell differentiation but did not indicate a necessity for Wnt in maintenance of the ophthalmic placode cells—there was no loss of Pax3 expressing cells in the ectoderm. This suggested that maintenance of the ophthalmic placode could be through alternate pathways. Data is also presented describing how loss of Porcn in Wnt1 expressing cells impacts craniofacial development, where the mouse mutant used in this study displayed the absence and underdevelopment of cranial neural crest structures.

Degree

College and Department

Life Sciences; Physiology and Developmental Biology

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