Final answer:
When cell surface expression of delta is high, neighboring cells use notch receptors to downregulate their delta expression, leading them to differentiate into glial cells, such as astrocytes, rather than neurons.
Step-by-step explanation:
If cell surface expression of delta is high, neighboring cells, via their notch receptors, down regulate their own delta expression, do not become neurons, and move to a glial cell fate. This is a crucial part of how cells communicate their fate within a developing tissue, helping to ensure a balanced mix of cell types. Notch signaling is an example of lateral inhibition, where a cell adopting a particular fate inhibits its neighbors from doing the same.
It's a form of direct cell-to-cell communication. In the brain, neurogenesis and gliogenesis (the development of neurons and glial cells, respectively) are largely governed by cues from cell-to-cell signaling pathways like Notch-Delta. This pathway ensures that once a cell has committed to becoming a neuron, its neighbors are more likely to become glial cells by downregulating their own potential to become neurons.