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doi: 10.1242/10.1242/dev.00563

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Establishment of POP-1 asymmetry in early C. elegans embryos

Frederick D. Park and James R. Priess

Division of Basic Sciences, Howard Hughes Medical Institute, Fred Hutchinson Cancer Research Center, Seattle, WA 98109, USA



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  		Fig. 1. Early cleavages and POP-1 asymmetry. Schematic diagram of normal and devitellinized embryos from first cleavage to the AB8 stage; anterior is left in all drawings. Descendants of AB are shown in blue and descendants of EMS are shown in yellow. Sister cells are connected by short black lines. For some cells, the axis of the subsequent division is shown with either a double-headed arrow (division within the plane) or an asterisk (divisions into the plane). At the AB8 stage, levels of POP-1 are indicated as high (white nuclei) or low (black nuclei). Note that POP-1 polarity is reversed in the P2 daughters of devitellinized embryos. Red, blue and yellow arrows on devitellinized embryos indicate positions of graft cells described in the text.

 


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  		Fig. 2. POP-1 in wild-type and mom mutant embryos. Images are of AB32 stage embryos. (A,B) Wild-type. (C,D) mom-2(or42) mutant. (E,F) mom-2(or42);mom-5(RNAi) embryo. Left panels show embryos stained for POP-1; chevrons indicate examples of sister cells. Right panels show DAPI and PKL-2 images superimposed; small arrows indicate examples of midbodies between sister pairs. For each of the sister pairs indicated in D (small arrows), the anterior sister has low POP-1. POP-1 staining is cell cycle-dependent and not detected in prophase or anaphase nuclei (large arrows in B,D) (see also Lin et al., 1995Go). In all panels anterior is left; in B,D and F ventral is down (arrowhead indicates the P4 cell).

 


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  		Fig. 3. POP-1 in isolated AB descendants. (A,B) AB8 descendants of an isolated AB cell. (C,D) AB16 descendants of an isolated AB cell; the cell cluster has been flattened to visualize the majority of nuclei. (E,F) AB16 daughters of a sequentially isolated AB8 cell. (G,H) AB32 granddaughters of a sequentially isolated AB8 cell. POP-1 staining (left), corresponding DAPI-stained images (right); images of PKL-2 staining are superimposed on B,F and H with midbodies indicated by small arrows. Scale bars: 5 µm.

 


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  		Fig. 4. Generation of POP-1 polarity at the AB2 division. (A,B) Example of an a/p division of an AB2 cell in a goa-1(RNAi);gpa-16(RNAi) embryo; EMS also divided a/p. (C,D) Division of laser-fused AB2 cells in a wild-type embryo. (E,F) Division of an AB2 cell in a devitellinized wild-type embryo after grafting on a wild-type P2. (G,H) Division of an AB2 cell in a devitellinized wild-type embryo after grafting on a mom-2 mutant P2. Panels labeled as in Fig. 2; images of PKL-2 staining are superimposed on the DAPI images in F and H with midbodies indicated by arrows.

 


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  		Fig. 5. Signaling by P1 descendants. (A-D) Nomarski photomicrographs showing the division of ABpr in (A) wild-type and (B) mom-2(or42) embryos, and the division of ABpl in (C) wild-type and (D) mom-2(or42) embryos; the asterisk indicates a division into the focal plane. (E) GFP expression of an endoderm-specific transgene after combining isolated EMS and C cells; DAPI staining of the same cells is shown in F. At the time of fixation the EMS daughter distal to C had divided twice, whereas the proximal EMS daughter divided only once. (G) POP-1 expression after the division of combined AB4 and MS cells; DAPI staining is shown in H. (I) POP-1 expression after the division of the AB4 cells in a devitellinized embryo. Prior to cell division, a graft E cell was placed on one of the AB4 cells. Note that AB4 daughter proximal to E has low POP-1. J shows superimposed DAPI and PKL-2 images with arrows indicating midbodies.

 


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  		Fig. 6. POP-1 asymmetry in the P2 daughters. (A) mom-2(or42) mutant embryo at the AB4 to AB8 division. POP-1 is low in P3 and high in C, as in wild-type embryos; note that the EMS daughters show little if any POP-1 asymmetry. (C) POP-1 in a devitellinized embryo. Note reversal of POP-1 polarity in the P2 daughters. (E) POP-1 after the division of combined EMS and P2 cells. The EMS daughters are entering prophase and hence show low POP-1 levels (see legend to Fig. 2). (G) POP-1 in a devitellinized wild-type embryo after grafting AB2 cells from a mom-2(or42) mutant embryo onto P2. In all experiments the identity of P3 was confirmed by cell size and by immunostaining for P granules (data not shown). DAPI staining is shown in B,D,F and H.

 

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© The Company of Biologists Ltd 2003