sentence: There are five Polycomb ( CBX2 , CBX4 , CBX6 , CBX7 , and CBX8 ) , two Sex combs extra ( RING1 / RING1A and RING2 / RING1B ) , three Polyhomeiotic ( PHC1 , PHC2 , and PHC3 ) , and six Posterior sex combs ; the latter are collectively known as PcG ring fingers ( PCGFs ) , including BMI1 , NSPC1 , MEL18 , PCGF3 , PCGF5 , and MBLR ( Vandamme et al ., 2011 ; Gao et al ., 2012 ) .