Fig. 6. FRK-1 is expressed ubiquitously in all cells during embryogenesis, and becomes nuclear excluded just before enclosure. FRK-1 is localized to the nucleus and at regions of cell-cell contacts in early embryos, as evident in 4-cell (A) and 40-cell (B) embryos. Immediately before enclosure, FRK-1 becomes nuclear-excluded, as seen in an embryo with approximately 550 cells (C). The protein remains nuclear-excluded throughout elongation (e.g. 1.25-fold stage; D), and cell surface localization is especially pronounced in the seam cells of elongated embryos (e.g. 3-fold embryo, E; overlay with MH27 apical junction antigen in F). Arrows point to apical junctions surrounding seam cells. Although both antibodies result in the same staining pattern, the images in this figure show localization using the antibody elicited to the FRK-1b peptide (see Materials and methods).