The CERV protein of Cer1, a C. elegans LTR retrotransposon, is required for nuclear export of viral genomic RNA and can form giant nuclear rods
Fig 5
A. Panel 1 is a 3-micron Z-projection of an A4 gonad, showing nuclei with CERV rods in addition to nuclei with CERV foci. Note that the apoptotic cell (x) does not have a CERV rod. Panel 2 compares the sizes of nuclear rods, seen in both longitudinal (left) and cross-sectional (right) profiles, with the sizes of cytoplasmic GAG particles (red). The arrowhead indicates one end of a rod that appears to protrude slightly from the nucleus; additional examples of protruding rods are shown in panel 4. Panel 3 illustrates that rods are associated with the periphery of the nucleolus (FIB-1, red). Panel 5 shows a rod-containing nucleus with perinuclear P granules, which are lost in early apoptosis. Panel 6 shows that the rods are highly phosphorylated, similar to CERV foci. Panel 7 shows CERV rods in an apoptosis-defective ced-3(n717) mutant, and panel 8 shows CERV rods in the wild strain MY16 with a Cer1 insertion on LGX [20]. B. Panel 1 shows serial optical sections of a single nucleus, demonstrating that the rings of CERV represent cross sections of CERV rods (see also S2 Video). Note that both ends of the CERV rod appear to fill the nuclear channel, but the middle of the rod (at z = -0.6 microns) shifts asymmetrically toward the nucleolus. Panels 2 and 3 indicate the paired LGIII homologs (dotted line) between the two nuclear foci of gRNA (asterisks), and show that the CERV rod localizes to only one of the two flanking nuclear channels (arrows). Increased exposures (+ exp) show gRNA in some rods (panels 3 and 4, arrowheads). C. The plot shows the total number of rod-containing germ nuclei per gonad (left vertical axis) and the percentage of gonads with at least one rod-containing nucleus (right vertical axis, grey bars). Mated animals in the wild-type and fog-2 mutant series were marked and mixed with wild-type males 24 hours before processing; mating was confirmed for each gonad by sperm in the spermatheca, but this experiment did not determine when mating occurred. P-values were calculated using nonparametric Mann-Whitney U test and graphing was performed using GraphPad Prism software version 9.5. **** P< 0.0001, ***P ≤ 0.01, ns = not significant. D. Gonad of a mated wild-type animal at A5 showing large numbers of CERV rods, all of which stained positively with α-pS/T-P. Scale bars in microns = (A,B) 1.0; (D) 5.0.