pnm-6 was identified in screens for mutations that result in defects in embryonic cell division processes at the one-cell stage; the pnm-6 mutation results in several defects including aberrant pronuclear migration, absence of a functional mitotic spindle, occasional appearance of more than one female pronucleus, and large areas of the embryo that lack yolk granules; the molecular identity of pnm-6 is not yet known.