Table 1. Components of the piRNA pathway.

Mouse protein	Knockout phenotype	Role in the piRNA pathway	Fly homolog	References
PIWIL1 (MIWI)	Spermiogenic arrest	Primary biogenesis	PIWI	49, 51
PIWIL2 (MILI)	Meiotic arrest	Primary and secondary biogenesis	PIWI	16, 52
PIWIL4 (MIWI2)	Meiotic arrest	Secondary biogenesis	PIWI	50
MOV10L1	Meiotic arrest	Primary biogenesis	ARMITAGE	71, 115
DDX4 (MVH)	Meiotic arrest	Secondary biogenesis	VASA	98, 116
TDRD1	Meiotic arrest	Primary biogenesis	TUDOR	60, 105
TDRD9	Meiotic arrest	Secondary biogenesis	Spn-E	75
TDRD12	Meiotic arrest	Secondary biogenesis	Yb	92, 117
TDRKH	Meiotic arrest	Primary biogenesis	PAPI	82
MitoPLD	Meiotic arrest	Primary biogenesis	ZUCCHINI	97, 110
GASZ	Meiotic arrest	Primary biogenesis		73
MAEL	Meiotic arrest	Primary and secondary biogenesis	MAELSTROM	74, 100
GPAT2	N/A	Primary biogenesis		96
FKBP6	Meiotic arrest	Secondary biogenesis	SHUTDOWN	99
GTSF1	Meiotic arrest	Transcriptional transposon silencing	GTSF1	101–103
A-MYB	Meiotic arrest	Transcription of piRNA precursors		79