Final answer:
Increasing doses of Sonic Hedgehog (Shh) during neural development lead to the ventralization of the neural tube, influencing cell differentiation and positioning.
Step-by-step explanation:
When Sonic Hedgehog (Shh) is applied in increasing doses during the development of the vertebrate neural tube, it leads to the ventralization of the neural tube. Shh is a critical signaling molecule that dictates the patterning of the neural tube, with higher concentrations of Shh promoting ventral cell fates and lower concentrations allowing for dorsal cell types. This gradient of Shh thus determines the positioning of dorsal-ventral and lateral-medial sides and ensures proper differentiation of cell layers within the developing nervous system. Excessive doses of Shh can disrupt the balance of this signaling, causing disorders in the development of the nervous system, such as an increased potential for motor versus sensory neuron development.