15641
Transcripts of GPx4 genes were more highly expressed in most tissues examined in vivo ( except blood , head kidney and spleen ) , whereas those of the GPx1 genes were more responsive to selenium exposure in vitro , especially to the organic form .
 Chemical: selenium
Please list all entity words in the text that fit the category.Output format is "type1: word1; type2: word2". 
Option: Chemical 
Text: {0} 
Answer:
 Chemical: selenium