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Table 2 Factors involved in piRNA biogenesis in C. elegans

From: An old weapon with a new function: PIWI-interacting RNAs in neurodegenerative diseases

Protein symbol Type Function Phenotype of  mutants Human orthologue Reference
FKH-3 ForKHead transcription factor Recognizing the Ruby motif; involved in type I 21 U-RNA biogenesis N/A N/A [24, 45]
FKH-4 ForKHead transcription factor Recognizing the Ruby motif; involved in type I 21 U-RNA biogenesis N/A N/A [24, 45]
FKH-5 ForKHead transcription factor Recognizing the Ruby motif; involved in type I 21 U-RNA biogenesis N/A N/A [24, 45]
UNC-130 UNCoordinated 130 Binding to 21 U-RNA upstream regulatory sequence; required for piRNA transcription N/A FOXD4 [59]
SNPC-4 Small nuclear RNA activating protein complex Binding to piRNA clusters; required for global piRNA expression Lethal or sterile SNAPC4 [59]
PRDE-1 Nuclear factor Required for production of piRNA precursors from the Ruby motif; recruiting RNA polymerase II to the FKH motif Mrt N/A [29, 60]
TOFU-3 Twenty-One-u Fouled Ups Required for the production or stability of 21 U-RNA precursors; a SUMO-related protease; interacting with HP1a and regulating its localization to pericentric heterochromatin Mrt N/A [29, 47]
TOFU-4 Twenty-One-u Fouled Ups Required for the production or stability of 21 U-RNA precursors Mrt N/A [29, 47]
TOFU-5 Twenty-One-u Fouled Ups Required for the production or stability of 21 U-RNA precursors; having a DNA-binding domain structurally related to that of Myb and found in various transcription regulatory factors Lethal or sterile N/A [29, 47]
TBP-1 TATA-box-binding protein An additional factor required for TOFU-5 binding to piRNA clusters N/A TBP
TBPL2
[46]
PID-1 piRNA-induced silencing-defective 1 A potential nuclear import and export factor Lethal N/A [56]
TOFU-1 Twenty-One-u Fouled Ups Required for precursor RNA processing after its production Mrt N/A [29, 47]
TOFU-2 Twenty-One-u Fouled Ups Required for precursor RNA processing after its production Mrt N/A [29, 47]
PARN-1 RNase Required for piRNA 3′ end trimming and having a 3′-to-5′ exo-RNase activity Mrt PARN PNLDC1 [48]
TOFU-6 Twenty-One-u Fouled Ups A component of PETISCO; required for 21 U biogenesis N/A N/A [29, 47]
TOFU-7 Twenty-One-u Fouled Ups Required for precursor RNA processing after its production N/A N/A [29, 47]
HENN-1 HEN methyltransferase 1 Required for precursor RNA processing after its production Sterile HENMT1 [61, 62]
PID-3
(PICS-1)
piRNA induced silencing defective A component of PETISCO; required for 21 U biogenesis; interacting with 21 U-RNA precursor Mes N/A [57]
ERH-2 Enhancer of rudimentary homolog A component of PETISCO; required for 21 U biogenesis; interacting with 21 U-RNA precursor Mes ERH [57]
IFE-3 Homologs of eIF4E A component of PETISCO; required for 21 U biogenesis; binding  to the 5′ cap of the 21 U precursor transcripts Mes EIF4E
EIF4E1B
[57]
EGO-1 Argonaute RNA-dependent RNA polymerase Sterile N/A [34, 63]
PRG-1 PIWI protein 21 U-RNA binding activity; combining  with piRNA to form RISC Mrt PIWIL1
PIWIL2
PIWIL3
PIWIL4
[19, 20]
CSR-1 Argonaute Self- and non-self-transcript discrimination Mrt N/A [54, 55]
TOST-1 Twenty-one U pathway antagonist Inhibiting  21 U-driven silencing Mes N/A [57]
EKL-1 Enhancer of ksr-1 Lethality Encoding a Tudor-domain protein required for RNAi; transgene silencing; transgene-mediated cosuppression in the germline N/A N/A [47, 64]
DRH-3 Dicer related helicase A core component of the RdRp complex and essential for 22G-siRNA biogenesis N/A DHX58 [65]
RRF-1 Argonaute RNA-dependent RNA polymerase N/A N/A [66]
RDE-2 RNAi defective Interacting with MUT-7; required for efficient RNAi N/A N/A [67]
MUT-7 Mutator Encoding a putative exoribonuclease; required for efficient RNAi N/A EXD3 [67]
RDE-8 RNAi defective Cleaving target mRNAs to mediate silencing; generating  mRNA fragments to serve as template for RdRp N/A N/A [68]
MUT-16 Mutator Required for the accumulation of 22G-siRNA N/A N/A [69]
SIMR-1 Tudor domain protein Mediating the production of secondary siRNAs by the mutator complex Mrt N/A [70]
HRDE-1 Nuclear Argonaute Germline nuclear RNAi Mrt N/A [71]
NRDE-3 Nuclear Argonaute Somatic nuclear RNAi Mrt N/A [71]
MET-2 H3K9me1/H3K9me2 methyltransferases Required for 22G-siRNA formation Mrt SETDB1
SETDB2
[72]
SET-25 H3K9me3 methyltransferase Heterochromatin maintenance, required for maintenance of piRNA-induced RNAi N/A N/A [72]
SET-32 H3K9me3 methyltransferase Silencing establishment; required for multigenerational inheritance of environmental RNAi and piRNA silencing Mrt N/A [73]
HPL-1 Heterochromatin protein 1 Binding with H3K9me2/H3K9me3; required for piRNA inducetion of heritable small RNAs Sterile CBX1
CBX3
CBX5
[74]
HPL-2 Heterochromatin protein 2 Binding with H3K9me2/H3K9me3; required for piRNA inducetion of heritable small RNAs Sterile CBX3 [75]
WAGO Argonaute Argonaute protein in C. elegans required for 22G-siRNA after RNA-dependent RNA polymerase activity N/A AGO1
AGO2
AGO3
AGO4
[76]
  1.  Abbreviations: Mrt mortal germline, Mes maternal-effect sterility, N/A not available