MATERNAL EFFECT OF LOW-TEMPERATURE ON HANDEDNESS DETERMINATION IN C-ELEGANS EMBRYOS

C. elegans embryos, larvae, and adults exhibit several left-right asym metries with an invariant dextral handedness, which first becomes evid ent in the embryo at the 6-cell stage. Reversed (sinistral) handedness was not observed among > 10,000 N2 adults reared at 16 degrees C or 2 0 degrees C under standard conditions. However, among the progeny of a dults reproducing at 10 degrees C, the frequency of animals with sinis tral handedness was increased to similar to 0.5%. Cold pulse experimen ts indicated that the critical period for this increase was in early o ogenesis, several hours before the first appearance of left-right asym metry in the embryo. Hermaphrodites reared at 10 degrees C and mated w ith males reared at 20 degrees C produced sinistral outcross as well a s sinistral self-progeny, indicating that the low temperature effect o n oocytes was sufficient to cause reversals. Increased frequency of re versal was also observed among animals developed from embryos lacking the egg shell. Possible mechanisms for the control of embryonic handed ness are discussed in the context of these results, including the hypo thesis that handedness could be dictated by the chirality of a gametic component. (C) 1996 Wiley-Liss, Inc.