POP-1 ENCODES AN HMG BOX PROTEIN REQUIRED FOR THE SPECIFICATION OF A MESODERM PRECURSOR IN EARLY C-ELEGANS EMBRYOS

In C. elegans embryogenesis, the MS blastomere produces predominantly mesodermal cell types, while its sister E generates only endodermal ti ssue. We show that a maternal gene, pop-1, is essential for the specif ication of MS fate and that a mutation in pop-1 results in MS adopting an E fate. Previous studies have shown that the maternal gene skn-1 i s required for both MS and E development and that skn-1 encodes a tran scription factor. We show here that the pop-1 gene encodes a protein w ith an HMG box similar to the HMG boxes in the vertebrate lymphoid-spe cific transcriptional regulators TCF-1 and LEF-1. We propose that POP- 1 and SKN-1 function together in the early embryo to allow MS-specific differentiation.