Abstract

The focus of this study was to elucidate the molecular and cellular mechanisms whereby fibroblast growth factors (FGFs) mediate outgrowth of the limb. Specifically, we examined the epistatic relationship between FGF and Wnt/Planar cell polarity (PCP) signaling in establishing cell polarity as a mechanism for outgrowth. By implanting beads into embryonic limbs and lateral plate mesoderm, we established that FGF activates Wnt5a in a gradient fashion. Once it was established that Wnt5a was expressed at the right time and place to turn on PCP signaling, we investigated the ability of Wnt5a to influence cell migration and/or cell polarity. Our analysis revealed that there was no difference in cell migration when cells were exposed to an exogenous Wnt5a source. However, this did not rule out the possibility that cells were responding in a more mild fashion and polarizing toward a Wnt5a source. Live cell imaging was performed to observe the movement and morphology of limb mesenchyme cell cultures in the presence or absence of a Wnt5a expressing cell bolus. It appears as though the cells orient and move in a random fashion regardless of Wnt5a. However, this in vitro method may not truly recapitulate in vivo events. Future studies aim to develop better methods of observing cell polarization in vitro, including developing better methods to tract the movement of cells and observe “PCP” events. Due to the lack of information gathered from our in vitro studies, an in vivo study was conducted to test if FGF is necessary to polarize limb mesenchyme cells. If FGF is turning on Wnt5a and Wnt/PCP signaling is directing cell polarization, then FGF mutant clones will not migrate toward the AER. Therefore, it is expected that these mutant clones would be unable to undergo directed cell movement and/or cell divisions. Early clonal analysis indicates that a response to FGFs appears to be necessary to direct polarized outgrowth of limb mesenchyme.

Degree

College and Department

Life Sciences; Physiology and Developmental Biology

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