The daughters of the C blastomere, Ca and Cp, have nearly identical lineage patterns. However, Ca produces two neurons and has high levels of the POP-1 protein, while Cp does not make any neurons and has low levels of POP-1. We wondered if
pop-1 plays a role in the Ca/Cp difference since
pop-1(+) is required to specify many other a/p differences in the early embryo. Using a neuronal GFP marker (provided by D. Pilgrim), we find that neither Ca nor Cp produces neurons in embryos lacking POP-1 ( pop-1RNAi ). In embryos with high levels of POP-1 (such as
mom-2(wingless);
apr-1(apc)RNAi double mutants), both Ca and Cp can produce neurons. Epistasis analysis indicates that
pop-1(+) activity is required for Cp to make neurons in the
mom-2;
apr-1 double. These results indicate that high levels of POP-1 are required for the ability of Ca to make neurons and that the asymmetry of POP-1 between Ca and Cp is important for making these sisters different. When Ca and Cp divide, they each produce an anterior daughter that has high levels of POP-1 and makes hypodermis, and a posterior daughter that has low levels of POP-1 and makes muscle. Does
pop-1(+) play a role in this a/p difference? When Caa or Cpa, the hypodermal precursors, are isolated in
pop-1(RNAi) embryos, they each make muscle and appear to lack hypodermis, suggesting that
pop-1(+) is required. We noticed that when we lineaged Cpa in an intact
pop-1(RNAi) embryo, it produced hypodermal cells. This surprising result suggests a possible cell-cell interaction influencing cell fate decisions in the
pop-1 mutant embryos. We currently are investigating the biological relevance of such an interaction. We are interested in identifying factors that may act with POP-1 to specify cell fates in the daughters and granddaughters of the C blastomere. We have isolated a mutant,
zu352 , that is defective in specifying the fate of Cp. In
zu352 mutant embryos, Cp makes intestine while Ca produces hypodermis and muscle. We are interested in how the cell fates of Ca and Cp in
zu352 are specified, and if
pop-1(+) plays a role in this Ca/Cp difference.