Final answer:
The factor that promotes early preneural progenitors to be competent to respond to TGFβ and Shh dorsoventral signals is Wnt ligands. These proteins are crucial in the development process, signaling ectodermal cells, and ensuring a proper response to future growth factor signals like TGFβ and Shh.
Step-by-step explanation:
The question pertains to the signals that promote early preneural progenitors to be competent to respond to TGFβ and Shh dorsoventral signals. Within the context of vertebrate development, specifically during the formation of the neural system, growth factors play a crucial role. They signal some ectodermal cells to transform into epidermal cells, while others become either neural plate or neural crest cells. For this specific question, the answer is d) Wnt ligands, as these proteins are involved in signaling ectodermal cells to form the epidermal cells and the neural plate, which is crucial for the cells to later respond properly to TGFβ and Sonic hedgehog (Shh) signals.
Summary of Wnt Signaling in Neural Development
In vertebrate development, Wnt signaling is a pivotal part of organogenesis, particularly in the formation of the neural system. It ensures that the proper cells become part of the neural plate versus becoming part of the epidermis through transcription factors and growth factors signaling. Increased expression of Wnt genes would affect the expression of downstream proteins, such as Bar-1, altering the developmental processes further.