6724
The large subfamily of receptor tyrosine kinases ( RTKs ) for which EPH is the prototype have likely roles in intercellular communication during normal mammalian development , but the biochemical signalling pathways utilised by this family are poorly characterised .
 receptor tyrosine kinases, RTKs, EPH
Please list all entity words in the text that fit the category. Output format is "word1, word2". 
Option: GENE 
Text: {0} 
Answer:
 receptor tyrosine kinases, RTKs, EPH