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Here , we show that Hh signaling in the postembryonic brain is temporally regulated ; excess ( earlier onset of ) Hh signaling causes premature neuroblast cell cycle exit and under - proliferation , whereas loss of Hh signaling causes delayed cell cycle exit and excess proliferation .
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Please list all entity words in the text that fit the category.Output format is "type1: word1; type2: word2". 
Option: Chemical 
Text: {0} 
Answer:
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