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

RNA interference is a widely conserved mechanism of gene regulation and silencing across eukaryotes. In , RNA silencing is coordinated through perinuclear nuage containing at least four granules: P granules, Z granules, 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 P 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.