4053
In vivo studies have suggested that gradients of CXCL12 ( aka stromal cell - derived factor 1 alpha ) may be critical for neural stem cell ( NSC ) migration during brain development and neural tissue regeneration .
 None
Given options, please tell me the categories of all the listed entity words.Output format is "type1: word1; type2: word2". 
Option: Chemical 
Text: {0} 
 Entities:  
Answer:
 None