Fig. 1. Localization and degradation of PAR proteins. (A) Schematic diagram of early stages of embryogenesis; sister cells are linked by short bars. Somatic precursors are indicated by bold outlines, germline precursors are indicated by a yellow asterisk. Germline precursors divide asymmetrically into a somatic precursor and a new germline precursor; the germline daughter has a high level of germline proteins, such as PIE-1, (dark red cells) and the somatic daughter contains a low level of PIE-1 (pink cells) that is degraded within one or two additional cell cycles (white cells). (B) PAR expression in early embryos. Embryos are oriented as in panel A; yellow asterisks mark germline precursors. (a,b) 1-cell embryos expressing either PAR-6^GFP (a) or PAR-6^ZF1-GFP (b); arrows point to the anterior cortex. (c,d) 4-cell embryos stained for endogenous PAR-3 (c) or PAR-3^ZF1-GFP (d); large arrow in c points to the apical cortex of ABp. (d) Large arrow in d indicates the apical cortex of ABp, arrowhead indicates the apical cortex of EMS, and small arrow points to the cortex of the germline precursor. (e,f) 8-cell embryos expressing either PAR-6^GFP (e) or PAR-6^ZF1-GFP (f); note that PAR-6^ZF1-GFP has disappeared from the oldest somatic cells (arrow) but is still detectable in the younger somatic cells (arrowheads). (g,h) 24-cell embryos showing PAR-3 (g) and PAR-3^ZF1-GFP (h). (i,j) PAR-3 expression in epithelia of an organogenesis-stage wild-type embryo (i) and a par-3(ZF1) embryo (j); arrowheads point to the apical surfaces of cells forming the digestive tract. (k) Chimeric embryo formed by combining a wild-type embryo with a par-3 mutant embryo; arrowheads indicate former apical surfaces of the wild-type cells that now contact the par-3 mutant cells (p). (l) PAR-3 expression in the chimeric embryo in k; note localization of PAR-3 to the contact-free surface of the wild-type cell (arrows). In all panels, exposures were adjusted to visualize the background fluorescence of cells; the level of fluorescence in the ABa and ABp cells in d was similar to that in par-3 mutant embryos lacking the transgene. Transgene expression was identical in wild-type and par-3 mutant backgrounds; embryos shown are wild-type in a-c,e-g,i and par-3 in d,h,j. Embryos in this and subsequent figures are 50 µm in length. Scale bar: 10 µm.