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Table 1 A comparison of piRNA biogenesis among C. elegans, Drosophila, mice and humans

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

  C. elegans Drosophila Mouse Human Reference
Size 21 nt 23-29 nt 24-30 nt 26-32 nt [23,24,25,26]
Structure 5′ Uridine
3′ 2′-O-methylation
5′ Uridine
3′ 2′-O-methylation
5′ Uridine
3′ 2′-O-methylation
5′ Uridine [4, 25,26,27]
PIWI proteins PRG-1 Piwi
Aub
Ago3
MIWI (PIWIL1)
MILI (PIWIL2)
MIWI2 (PIWIL4)
HIWI (PIWIL1)
HILI (PIWIL2)
HIWI3 (PIWIL3)
HIWI2 (PIWIL4)
[19,20,21,22, 28]
Transcription loci Type I loci,
Type II loci,
mainly from chromosome IV
flamenco loci, 42AB loci, distributed across all chromosomes Distinct intergenic loci, distributed across all chromosomes Distributed across 22 autosomal chromosomes and X chromosome [24, 26, 29,30,31,32]
Amplification RdRp Ping-pong cycle Ping-pong cycle Ping-pong cycle [33,34,35,36]
Biogenesis factor FKH transcription factors,
TOFU genes, PRG-1,
EGO-1
RDC complex,
MitoPLD/Zuc,
TDRD proteins,
PIWI proteins
A-MYB transcription factor,
MitoPLD/Zuc,
TDRD proteins,
PIWI proteins
PIWI proteins [23, 33, 37]
Downstream effects RNA degradation,
histone modification,
22G-RNA biogenesis
RNA degradation,
histone modification
RNA degradation,
histone modification,
DNA methylation
RNA degradation,
histone modification,
DNA methylation
[23, 33, 37]
  1. Abbreviations: RdRp RNA-dependent RNA polymerases, RDC complex Rhino-Deadlock-Cutoff complex, FKH Fork head