During embryonic development morphogenic signaling gradients inform cells of their relative positions so that they may take on specific fates. There has been controversy in many models whether these signaling gradients are generated spatially, temporally or a combination of these. We have used the neural ectoderm of the zebrafish as a model to study the interface between spatial and temporal morphogen gradient signaling and its effect on cell fate in anterior posterior (AP) neural patterning.
In vertebrates, all neural ectoderm cells initially have an anterior fate. Through morphogenic signals, including Wnt’s and Fgf’s, the cells within the neural ectoderm are informed of their spatial position and take on specific fates along the (AP) axis. The primary morphogen of early neural posteriorization, wnt8a, is expressed in the blastoderm margin during epiboly. wnt8a generates a signaling gradient and posteriorizes the neural ectoderm in a dose dependent manner, with high doses inducing a more posterior fate. This signaling event occurs over roughly 4 1/2-hour period that includes a large degree of dynamic cell movement as the cells of the blastoderm migrate towards the vegetal pole. How the timing and duration of the Wnt8a signal affects its ability to posteriorize the neural ectoderm is poorly understood. Of particular interest is how the different regions of the neural ectoderm change in response to the Wnt8a signaling gradient at different times during neural posteriorization.
To better understand the temporal aspect of Wnt8a’s signaling gradient we have used heat shock inducible lines to analyze the response of the neural ectoderm to Wnt8a signaling during early neural posteriorization. Through comprehensive analysis of the temporal response to Wnt signaling we will determine how spatial and temporal factors can integrate to establish a morphogenic signaling gradient in development.