27874
The testis - specific serine / threonine kinases ( TSSKs ) comprise a family of post - meiotic kinases expressed in spermatids , are critical to spermiogenesis and are required for male fertility in mammals .
 serine, threonine
Please list all entity words in the text that fit the category. Output format is "word1, word2". 
Option: Chemical 
Text: {0} 
Answer:
 serine, threonine