7871
The 1 . 1 - and 1 . 3 - kb mRNA species were found only in the heart , and the 2 . 6 - kb species was found in the heart , kidney and brain , but not in skeletal muscle or liver .
 None
Please list all entity words in the text that fit the category. Output format is "word1, word2". 
Option: GENE 
Text: {0} 
Answer:
 None