22880
Together , these results underscore the requirement of neurofibromin and ERK1 / 2 for normal endochondral bone formation and support the notion that neurofibromin , by restraining RAS - ERK1 / 2 signaling , is a negative regulator of FGFR signaling in differentiating chondrocytes .
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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:
 None