Intrinsically disordered protein PID-2 modulates Z granules and is required for heritable piRNA-induced silencing in the C. elegans embryo (2020)
Figure 1

Figure 1. PID-2 is a novel factor required for establishing de novo silencing mediated by maternally provided small RNAs.

A) Schematic representation of the Y48G1C.1 / pid-2 gene and its mutant alleles (xf23 and tm1614). The line plot displays the predicted disorder of the Y48G1C.1 / PID-2 protein, as obtained from PONDR, using the algorithms VL3 and VL-XT.

B) Expression of the 21U sensor (left) and DAPI staining (right) of gonad arms in the indicated genetic backgrounds. Gonads are outlined by a dashed line. The mCherry signal is represented in pseudo-colours [LUT fire (ImageJ)] to reflect differences in the intensity of the signal. Number of animals analysed and with indicated phenotype are given in the panel. Animals not showing the activation of the 21U sensor(+) were still silenced, and animals that did not show the silenced 21U sensor(RNAe) state were expressing weakly, comparable to the 21U sensor(+). Scale bar: 25 μm.

C) Tc1 reversion assay in different genetic backgrounds. All the strains tested carried the unc-22::Tc1(st136) allele. Tc1 excision can result in restoration of unc-22 function, which can be scored visually. Negative control = unc-22::Tc1(st136) in a wild type background; positive control = wago-1/-2/-3. Two independent experiments per strain are represented. See Materials and Methods for details.

D) Crossing scheme to address the re-initiation of silencing of the 21U sensor. A mut-7 mutant male expressing the 21U sensor is crossed with either a wild type (left), prg-1 (middle) or pid-2 (right) mutant hermaphrodite. Their F1 offspring was scored for expression of the 21U sensor by microscopy. Three states of expression were scored, and represented in a pie chart. The three expression states are exemplified by representative images at the bottom: OFF (left), FAINT (right) or ON (middle). DIC images are shown above the fluorescence panels. Gonads are outlined by a dashed line. Scale bar: 25 µm.

E) Crossing scheme to address if maternal 21U RNAs are sufficient to re-initiate the silencing of the 21U sensor. A pid-1 mutant male expressing the 21U sensor is crossed with a hermaphrodite, heterozygous for the same mutation. All their F1 offspring inherit a pool of 21U RNAs from the hermaphrodite, but in 50% of the F1, which is pid-1 homozygous mutant, no zygotic PID-1 is present, hence no zygotic 21U RNAs can be made. The silencing or expression of the 21U sensor in the pid-1 homozygous mutant F1 has been scored by microscopy, and depicted in a pie chart. At the bottom, a representative image of an animal carrying a silenced 21U sensor (lower: mCherry signal; upper: DAPI staining) in pid-1 mutant offspring. Gonads are outlined by a dashed line. Scale bar: 25 μm.

F) Crossing scheme to test the role of PID-2 in re-initiating the silencing of the 21U sensor, mediated by maternally provided 21U RNAs only. The expression of the 21U sensor in the F1 has been scored by microscopy, and depicted in a pie chart. White arrow heads indicate the many arrayed oocytes, typical of a feminized germline. DIC and fluorescence image of a representative animal are shown at the bottom. Gonads are outlined by a dashed line. Scale bar: 25 μm.