The microenvironment of the embryonic neural stem cell: Lessons from adult niches?

A better understanding of the signals regulating embryonic neural stem cells is clearly an important goal. However, many studies on neural stem cell biology are conducted on the slowly-dividing cells found in the adult CNS, where specialized microenvironments or niches maintain the stem cells throughout life. By contrast, the embryonic VZ is a transient structure that does not fulfill the criteria conventionally used to define niches. In this review we will examine whether, despite these differences, the signals found in other adult stem cell niches are present in the VZ. Using the similarities and differences we observe, we will reconsider whether the location of embryonic stem cell populations such as the VZ can be thought of as niches. Finally, we will ask how these lessons from the niche inform our understanding of neurodevelopmental diseases and cancers of the CNS.