SIMR foci are found in the progenitor germ cells of C. elegans embryos

Abstract

RNA interference is a widely conserved mechanism of gene regulation and silencing across eukaryotes. In C. elegans, RNA silencing is coordinated through perinuclear nuage containing at least four granules: P granules, Z granules, Mutator foci, and SIMR foci. Embryonic localization of these granules is known for all except SIMR foci. Here we establish that SIMR foci first appear at the nuclear periphery in the P₄ germline blastomere and become numerous and bright in the Z2 and Z3 progenitor germ cells. This timing coincides with the appearance or de-mixing of other germline granules, providing further evidence for coordinated germ granule reorganization.

Figure 1. SIMR foci are numerous and bright in the Z2/Z3 progenitor germ cells

A-E: Representative live images of embryos expressing PGL-1::BFP (blue), MUT-16::GFP (green) and SIMR-1::mCherry (red) to visualize P granules, Mutator foci, and SIMR foci, respectively. Scale bars, 15 µm. For each stage at least 3 embryos were observed. A’-E’: Inset from boxed outline in A-E merge, highlighting the P lineage and progenitor germ cells. Scale bars, 1 µm. C’: Triangle arrowhead indicates early SIMR focus. D’-E’: Notched arrowheads indicate bright, numerous SIMR foci (red) interacting with Mutator foci (green) and P granules (blue).